Maven系列第7篇：聚合、繼承、單繼承問題詳解，必備技能！

2019 年 11 月 25 日
筆記

maven系列目標：從入門開始開始掌握一個高級開發所需要的maven技能。

這是maven系列第7篇。

整個maven系列的內容前後是有依賴的，如果之前沒有接觸過maven，建議從第一篇看起，本文尾部有maven完整系列的連接。

本篇內容

maven中聚合詳解
maven中繼承詳解
pom.xml中parent元素的使用詳解
pom.xml中dependencyManagement元素使用詳解
pom.xml中pluginManagement元素使用詳解
單繼承存在的問題及解決方案詳解（springboot,springcloud中會常用）
解答上一篇遺留的2個問題

聚合

原始需求

我們需要使用java做一個電商網站，涉及到：pc端網站、h5微站、移動端接口部分，那麼我們可以使用maven創建3個項目用於這3塊業務的開發，3個項目名稱如下：

javacode2018-pc  javacode2018-h5  javacode2018-api

這3個項目的groupId都是com.javacode2018，artifactId取上面的，我們使用maven來搭建項目結構。

實現

創建第一個javacode2018-pc項目

打開idea，點擊File->New->Project，選擇Maven，如下：

點擊Next，輸入項目坐標信息，如下：

點擊Next，輸入Project name 為javacode2018-pc，如下：

點擊Finish，創建成功，如下：

配置一下idea的maven環境，點擊File->Settings，如下圖：

點擊上面的OK完成配置。

大家再按照上面一樣的操作，分別創建另外2個項目javacode2018-h5和javacode2018-api，創建完成之後，另外2個項目如下圖：

上面3個項目由整個項目組6個人共同開發，這幾個項目經常一起上線，上線過程，先由開發進行打包，然後將幾個包發給運行進行發佈。我們使用mvn package進行打包，需要在每個項目的pom.xml所在目錄都去執行一次這個命令，也就是說需要執行3次，這個電商項目還會涉及到後台系統、bi系統、監控系統等等，可能最後會多達10個小項目，那時候我們每次上線都需要執行10次打包操作，這個過程是相當繁瑣的。

那麼maven有沒有更好的辦法來解決這個事情呢？

這個用到的就是我們本次要說的maven中的聚合。

整個電商我們可以作為一個大的系統，上面的pc端、h5微站、api接口、後台系統、bi系統、監控系統都可以作為裏面的一個具體比較大一個模塊。

我們使用maven聚合功能來實現上面的需求，我們需要創建一個額外的maven項目javacode-aggregator來管理上面3個項目，然後只用在javacode-aggregator項目中執行mvn命令，就會自動為其他3個項目自動執行同樣的mvn命令。

Maven聚合

maven聚合需要創建一個新的maven項目，用來管理其他的maven構件模塊，新的maven項目中加入如下配置：

<modules>      <module>模塊1</module>      <module>模塊2</module>      <module>模塊n</module>  </modules>  <package>pom</package>

新的項目中執行任何mvn命令，都會modules中包含的所有模塊執行同樣的命令，而被包含的模塊不需要做任何特殊的配置，正常的maven項目就行。注意上面的module元素，這部分是被聚合的模塊pom.xml所在目錄的相對路徑。 package的值必須為pom，這個需要注意。下面看案例。

實操案例

下面過程仔細看了。

創建項目`javacode-aggregator`

打開idea，點擊File->New->Project，選擇Maven，如下：

點擊Next，輸入項目坐標信息，如下：

點擊Next，輸入Project name 為javacode-aggregator，如下：

點擊Finish，創建成功，如下：

配置一下idea的maven環境，點擊File->Settings，如下圖：

刪除下面無用的代碼：

項目變成了下面這樣：

pom.xml中加入下面配置：

<packaging>pom</packaging>

最後pom.xml內容如下：

<?xml version="1.0" encoding="UTF-8"?>  <project xmlns="http://maven.apache.org/POM/4.0.0"           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"           xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">      <modelVersion>4.0.0</modelVersion>        <groupId>com.javacode2018</groupId>      <artifactId>javacode-aggregator</artifactId>      <version>1.0-SNAPSHOT</version>      <packaging>pom</packaging>    </project>

創建`javacode2018-pc` 模塊

注意這裡說的是模塊，不再是創建項目，過程仔細看。

idea中選中javacode-aggregator

點擊File->New->Module，準備創建模塊，如下圖：

選擇Maven，如圖：

點擊Next，如下：

點擊下面的...按鈕，選擇None，如下：

輸入坐標信息，如下：

點擊Next，輸入Module name :javacode2018-pc，如下：

點擊Finish，完成javacode-2018模塊的創建，如下：

我們來看一下javacode-aggregator的pom.xml，多了一部分，如下：

注意上面的<packaging>pom</packaging>

創建javacode2018-h5模塊

創建步驟和上面javacode2018-pc步驟一樣。

創建javacode2018-api模塊

創建步驟和上面javacode2018-pc步驟一樣。

我們看一下項目最終結構，如下圖：

看一下上圖中的javacode-aggregator項目的pom.xml，modules元素中多出了3部分。

再來看看其他3個模塊的pom文件，和普通的pom.xml一樣，如下圖：

在javacode-aggregator/pom.xml目錄中執行mvn package感受一下效果：

D:codeIdeaProjectsjavacode-aggregator>mvn package  [INFO] Scanning for projects...  [INFO] ------------------------------------------------------------------------  [INFO] Reactor Build Order:  [INFO]  [INFO] javacode2018-pc                                                    [jar]  [INFO] javacode2018-h5                                                    [jar]  [INFO] javacode2018-api                                                   [jar]  [INFO] javacode-aggregator                                                [pom]  [INFO]  [INFO] ------------------< com.javacode2018:javacode2018-pc >------------------  [INFO] Building javacode2018-pc 1.0-SNAPSHOT                              [1/4]  [INFO] --------------------------------[ jar ]---------------------------------  [INFO]  [INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ javacode2018-pc ---  [WARNING] Using platform encoding (GBK actually) to copy filtered resources, i.e. build is platform dependent!  [INFO] Copying 0 resource  [INFO]  [INFO] --- maven-compiler-plugin:3.1:compile (default-compile) @ javacode2018-pc ---  [INFO] Nothing to compile - all classes are up to date  [INFO]  [INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ javacode2018-pc ---  [WARNING] Using platform encoding (GBK actually) to copy filtered resources, i.e. build is platform dependent!  [INFO] skip non existing resourceDirectory D:codeIdeaProjectsjavacode-aggregatorjavacode2018-pcsrctestresources  [INFO]  [INFO] --- maven-compiler-plugin:3.1:testCompile (default-testCompile) @ javacode2018-pc ---  [INFO] Nothing to compile - all classes are up to date  [INFO]  [INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ javacode2018-pc ---  [INFO] No tests to run.  [INFO]  [INFO] --- maven-jar-plugin:2.4:jar (default-jar) @ javacode2018-pc ---  [INFO] Building jar: D:codeIdeaProjectsjavacode-aggregatorjavacode2018-pctargetjavacode2018-pc-1.0-SNAPSHOT.jar  [INFO]  [INFO] ------------------< com.javacode2018:javacode2018-h5 >------------------  [INFO] Building javacode2018-h5 1.0-SNAPSHOT                              [2/4]  [INFO] --------------------------------[ jar ]---------------------------------  [INFO]  [INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ javacode2018-h5 ---  [WARNING] Using platform encoding (GBK actually) to copy filtered resources, i.e. build is platform dependent!  [INFO] Copying 0 resource  [INFO]  [INFO] --- maven-compiler-plugin:3.1:compile (default-compile) @ javacode2018-h5 ---  [INFO] Nothing to compile - all classes are up to date  [INFO]  [INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ javacode2018-h5 ---  [WARNING] Using platform encoding (GBK actually) to copy filtered resources, i.e. build is platform dependent!  [INFO] skip non existing resourceDirectory D:codeIdeaProjectsjavacode-aggregatorjavacode2018-h5srctestresources  [INFO]  [INFO] --- maven-compiler-plugin:3.1:testCompile (default-testCompile) @ javacode2018-h5 ---  [INFO] Nothing to compile - all classes are up to date  [INFO]  [INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ javacode2018-h5 ---  [INFO] No tests to run.  [INFO]  [INFO] --- maven-jar-plugin:2.4:jar (default-jar) @ javacode2018-h5 ---  [INFO] Building jar: D:codeIdeaProjectsjavacode-aggregatorjavacode2018-h5targetjavacode2018-h5-1.0-SNAPSHOT.jar  [INFO]  [INFO] -----------------< com.javacode2018:javacode2018-api >------------------  [INFO] Building javacode2018-api 1.0-SNAPSHOT                             [3/4]  [INFO] --------------------------------[ jar ]---------------------------------  [INFO]  [INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ javacode2018-api ---  [WARNING] Using platform encoding (GBK actually) to copy filtered resources, i.e. build is platform dependent!  [INFO] Copying 0 resource  [INFO]  [INFO] --- maven-compiler-plugin:3.1:compile (default-compile) @ javacode2018-api ---  [INFO] Nothing to compile - all classes are up to date  [INFO]  [INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ javacode2018-api ---  [WARNING] Using platform encoding (GBK actually) to copy filtered resources, i.e. build is platform dependent!  [INFO] skip non existing resourceDirectory D:codeIdeaProjectsjavacode-aggregatorjavacode2018-apisrctestresources  [INFO]  [INFO] --- maven-compiler-plugin:3.1:testCompile (default-testCompile) @ javacode2018-api ---  [INFO] Nothing to compile - all classes are up to date  [INFO]  [INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ javacode2018-api ---  [INFO] No tests to run.  [INFO]  [INFO] --- maven-jar-plugin:2.4:jar (default-jar) @ javacode2018-api ---  [INFO] Building jar: D:codeIdeaProjectsjavacode-aggregatorjavacode2018-apitargetjavacode2018-api-1.0-SNAPSHOT.jar  [INFO]  [INFO] ----------------< com.javacode2018:javacode-aggregator >----------------  [INFO] Building javacode-aggregator 1.0-SNAPSHOT                          [4/4]  [INFO] --------------------------------[ pom ]---------------------------------  [INFO] ------------------------------------------------------------------------  [INFO] Reactor Summary for javacode-aggregator 1.0-SNAPSHOT:  [INFO]  [INFO] javacode2018-pc .................................... SUCCESS [  2.542 s]  [INFO] javacode2018-h5 .................................... SUCCESS [  0.195 s]  [INFO] javacode2018-api ................................... SUCCESS [  0.218 s]  [INFO] javacode-aggregator ................................ SUCCESS [  0.024 s]  [INFO] ------------------------------------------------------------------------  [INFO] BUILD SUCCESS  [INFO] ------------------------------------------------------------------------  [INFO] Total time:  3.223 s  [INFO] Finished at: 2019-11-19T13:28:00+08:00  [INFO] ------------------------------------------------------------------------

我們分析一下上面的輸出：

[INFO] Reactor Build Order:  [INFO]  [INFO] javacode2018-pc                                                    [jar]  [INFO] javacode2018-h5                                                    [jar]  [INFO] javacode2018-api                                                   [jar]  [INFO] javacode-aggregator                                                [pom]

上面這個列出了需要構件的maven構件列表及順序，共有4個構件，3個jar包，1個pom類型的構件。

然後開始按照上面列出的順序，一個個開始執行mvn package命令，最後4個都執行成功了，我們來看一下最終產生的效果，如下圖：

從上圖中我們可以看到3個模塊都生成了jar包，說明我們執行了一次mvn package，分別在3個模塊中都運行了，我們在來執行一下mvn clean清理代碼，感受一下最終效果：

D:codeIdeaProjectsjavacode-aggregator>mvn clean  [INFO] Scanning for projects...  [INFO] ------------------------------------------------------------------------  [INFO] Reactor Build Order:  [INFO]  [INFO] javacode2018-pc                                                    [jar]  [INFO] javacode2018-h5                                                    [jar]  [INFO] javacode2018-api                                                   [jar]  [INFO] javacode-aggregator                                                [pom]  [INFO]  [INFO] ------------------< com.javacode2018:javacode2018-pc >------------------  [INFO] Building javacode2018-pc 1.0-SNAPSHOT                              [1/4]  [INFO] --------------------------------[ jar ]---------------------------------  [INFO]  [INFO] --- maven-clean-plugin:2.5:clean (default-clean) @ javacode2018-pc ---  [INFO] Deleting D:codeIdeaProjectsjavacode-aggregatorjavacode2018-pctarget  [INFO]  [INFO] ------------------< com.javacode2018:javacode2018-h5 >------------------  [INFO] Building javacode2018-h5 1.0-SNAPSHOT                              [2/4]  [INFO] --------------------------------[ jar ]---------------------------------  [INFO]  [INFO] --- maven-clean-plugin:2.5:clean (default-clean) @ javacode2018-h5 ---  [INFO] Deleting D:codeIdeaProjectsjavacode-aggregatorjavacode2018-h5target  [INFO]  [INFO] -----------------< com.javacode2018:javacode2018-api >------------------  [INFO] Building javacode2018-api 1.0-SNAPSHOT                             [3/4]  [INFO] --------------------------------[ jar ]---------------------------------  [INFO]  [INFO] --- maven-clean-plugin:2.5:clean (default-clean) @ javacode2018-api ---  [INFO] Deleting D:codeIdeaProjectsjavacode-aggregatorjavacode2018-apitarget  [INFO]  [INFO] ----------------< com.javacode2018:javacode-aggregator >----------------  [INFO] Building javacode-aggregator 1.0-SNAPSHOT                          [4/4]  [INFO] --------------------------------[ pom ]---------------------------------  [INFO]  [INFO] --- maven-clean-plugin:2.5:clean (default-clean) @ javacode-aggregator ---  [INFO] ------------------------------------------------------------------------  [INFO] Reactor Summary for javacode-aggregator 1.0-SNAPSHOT:  [INFO]  [INFO] javacode2018-pc .................................... SUCCESS [  0.250 s]  [INFO] javacode2018-h5 .................................... SUCCESS [  0.067 s]  [INFO] javacode2018-api ................................... SUCCESS [  0.068 s]  [INFO] javacode-aggregator ................................ SUCCESS [  0.034 s]  [INFO] ------------------------------------------------------------------------  [INFO] BUILD SUCCESS  [INFO] ------------------------------------------------------------------------  [INFO] Total time:  0.605 s  [INFO] Finished at: 2019-11-19T13:34:42+08:00  [INFO] ------------------------------------------------------------------------

項目結構如下圖：

3個項目中的target都被清理掉了，是不是感覺很爽。

上面介紹了pom.xml中的module元素的值為被聚合的模塊pom.xml所在的目錄路徑，可以是相對路徑，也可以是絕對路徑，上面演示的是相對路徑，大家可以自己去玩一下絕對路徑的情況。

聚合的功能中，聚合模塊的pom.xml中通過modules->module來引用被聚合的模塊，被聚合的模塊是不用感知自己被聚合了，所以被聚合的模塊中pom.xml中是不知道javacode-aggregator的存在的。

繼承

需求

細心的朋友已經發現了javacode2018-pc、javacode2018-h5、javacode2018-api3個項目的groupId、version都是一樣的。還有這幾個項目準備都是用springmvc、mybatis開發的，所以需要引入依賴如下：

<dependency>      <groupId>org.springframework</groupId>      <artifactId>spring-web</artifactId>      <version>5.2.1.RELEASE</version>  </dependency>  <dependency>      <groupId>org.mybatis</groupId>      <artifactId>mybatis-spring</artifactId>      <version>2.0.3</version>  </dependency>

3個項目中出現了同樣的配置，一個配置出現了多份，作為開發者，我想你們和我一樣，是無法接受的，必須要尋求一些方法來解決，需要將公共的部分提取出來共用。

maven也為我們考慮到了這種情況，maven中使用繼承來解決這個問題。

繼承的實現

操作分為3步驟：

創建一個父maven構件，將依賴信息放在pom.xml中 <dependencies> <dependency>依賴的構件的坐標信息</dependency> <dependency>依賴的構件的坐標信息</dependency> <dependency>依賴的構件的坐標信息</dependency> </dependencies>
將父構件的package元素的值置為pom <packaging>pom</packaging>
在子構件的pom.xml引入父構件的配置： <parent> <groupId>父構件groupId</groupId> <artifactId>父構件artifactId</artifactId> <version>父構件的版本號</version> <relativePath>父構件pom.xml路徑</relativePath> </parent>

relativePath表示父構件pom.xml相對路徑，默認是../pom.xml，所以一般情況下父子結構的maven構件在目錄結構上一般也採用父子關係。

實操案例

先創建一個父項目javacode-parent，坐標信息如下：

<groupId>com.javacode2018</groupId>  <artifactId>javacode2018-parent</artifactId>  <version>1.0-SNAPSHOT</version>

創建過程大家已經輕車熟路了，就不演示了，最終如下圖：

刪除無用的2目錄.idea和src

創建子模塊`javacode2018-pc` 模塊

注意這裡說的是模塊了，不在是創建項目了，過程仔細看。

idea中選中javacode-parent，如下圖：

點擊File->New->Module，準備創建模塊，如下圖：

選中Maven，如下圖：

點擊Next，這個頁面需要注意了，默認如下圖：

此時我們點擊第一個...按鈕，這個按鈕是設置聚合的，所以選中None，如下圖：

變成了下面這樣：

輸入構件信息，如下圖：

點擊Next，輸入Module-name的值為javacode2018-pc，如下圖：

點擊Finish完成創建操作，如下圖：

上圖中，看一下javacode2018-pc的pom.xml，多了個parent元素，並且這個pom.xml中構件的groupId、version都沒有了，這個pom.xml繼承了javacode2018-parent/pom.xml中的內容，他們的groupId、version都是一樣的，子構件可以從父pom.xml中繼承這些內容，所以如果是一樣的情況，可以不寫。

創建另外兩個子模塊javacode2018-h5、javacode2018-api

步驟參考javacode2018-pc模塊的創建過程。

最終項目如下圖：

下面我們來看一下4個pom.xml的內容。

javacode2018-parent/pom.xml的內容：

<?xml version="1.0" encoding="UTF-8"?>  <project xmlns="http://maven.apache.org/POM/4.0.0"           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"           xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">      <modelVersion>4.0.0</modelVersion>        <groupId>com.javacode2018</groupId>      <artifactId>javacode2018-parent</artifactId>      <version>1.0-SNAPSHOT</version>    </project>

javacode2018-pc/pom.xml的內容：

<?xml version="1.0" encoding="UTF-8"?>  <project xmlns="http://maven.apache.org/POM/4.0.0"           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"           xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">      <parent>          <artifactId>javacode2018-parent</artifactId>          <groupId>com.javacode2018</groupId>          <version>1.0-SNAPSHOT</version>      </parent>      <modelVersion>4.0.0</modelVersion>        <artifactId>javacode2018-pc</artifactId>    </project>

javacode2018-h5/pom.xml的內容：

<?xml version="1.0" encoding="UTF-8"?>  <project xmlns="http://maven.apache.org/POM/4.0.0"           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"           xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">      <parent>          <artifactId>javacode2018-parent</artifactId>          <groupId>com.javacode2018</groupId>          <version>1.0-SNAPSHOT</version>      </parent>      <modelVersion>4.0.0</modelVersion>        <artifactId>javacode2018-h5</artifactId>    </project>

javacode2018-api/pom.xml的內容：

<?xml version="1.0" encoding="UTF-8"?>  <project xmlns="http://maven.apache.org/POM/4.0.0"           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"           xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">      <parent>          <artifactId>javacode2018-parent</artifactId>          <groupId>com.javacode2018</groupId>          <version>1.0-SNAPSHOT</version>      </parent>      <modelVersion>4.0.0</modelVersion>        <artifactId>javacode2018-api</artifactId>    </project>

我們在父構件javacode2018-parent/pom.xml中加入下面配置：

<packaging>pom</packaging>  <dependencies>      <dependency>          <groupId>org.springframework</groupId>          <artifactId>spring-web</artifactId>          <version>5.2.1.RELEASE</version>      </dependency>      <dependency>          <groupId>org.mybatis</groupId>          <artifactId>mybatis-spring</artifactId>          <version>2.0.3</version>      </dependency>  </dependencies>

使用下面命令在javacode2018-parent/pom.xml所在目錄看一下javacode2018-parent構件依賴情況:

D:codeIdeaProjectsjavacode2018-parent>mvn dependency:tree  [INFO] Scanning for projects...  [INFO]  [INFO] ----------------< com.javacode2018:javacode2018-parent >-----------------  [INFO] Building javacode2018-parent 1.0-SNAPSHOT  [INFO] --------------------------------[ pom ]---------------------------------  [INFO]  [INFO] --- maven-dependency-plugin:2.8:tree (default-cli) @ javacode2018-parent ---  [INFO] com.javacode2018:javacode2018-parent:pom:1.0-SNAPSHOT  [INFO] +- org.springframework:spring-web:jar:5.2.1.RELEASE:compile  [INFO] |  +- org.springframework:spring-beans:jar:5.2.1.RELEASE:compile  [INFO] |  - org.springframework:spring-core:jar:5.2.1.RELEASE:compile  [INFO] |     - org.springframework:spring-jcl:jar:5.2.1.RELEASE:compile  [INFO] - org.mybatis:mybatis-spring:jar:2.0.3:compile  [INFO] ------------------------------------------------------------------------  [INFO] BUILD SUCCESS  [INFO] ------------------------------------------------------------------------  [INFO] Total time:  2.544 s  [INFO] Finished at: 2019-11-19T14:58:21+08:00  [INFO] ------------------------------------------------------------------------

mvn dependency:tree 這個插件可以根據pom.xml的配置，列出構件的依賴樹信息。

我們再來看看javacode2018-pc/pom.xml構件的依賴信息：

D:codeIdeaProjectsjavacode2018-parent>cd javacode2018-pc    D:codeIdeaProjectsjavacode2018-parentjavacode2018-pc>mvn dependency:tree  [INFO] Scanning for projects...  [INFO]  [INFO] ------------------< com.javacode2018:javacode2018-pc >-------------------  [INFO] Building javacode2018-pc 1.0-SNAPSHOT  [INFO] --------------------------------[ jar ]---------------------------------  [INFO]  [INFO] --- maven-dependency-plugin:2.8:tree (default-cli) @ javacode2018-pc ---  [INFO] com.javacode2018:javacode2018-pc:jar:1.0-SNAPSHOT  [INFO] +- org.springframework:spring-web:jar:5.2.1.RELEASE:compile  [INFO] |  +- org.springframework:spring-beans:jar:5.2.1.RELEASE:compile  [INFO] |  - org.springframework:spring-core:jar:5.2.1.RELEASE:compile  [INFO] |     - org.springframework:spring-jcl:jar:5.2.1.RELEASE:compile  [INFO] - org.mybatis:mybatis-spring:jar:2.0.3:compile  [INFO] ------------------------------------------------------------------------  [INFO] BUILD SUCCESS  [INFO] ------------------------------------------------------------------------  [INFO] Total time:  2.093 s  [INFO] Finished at: 2019-11-19T14:59:34+08:00  [INFO] ------------------------------------------------------------------------

從上圖中可以看到javacode2018-pc依賴的jar和父構件javacode2019-parent的一樣，說明從父類繼承了這些依賴。其他2個子構件，大家也可以去看一下，依賴關係都從父構件繼承過來了。

relativePath元素

上面演示的父構件和子構件的目錄結構剛好符合父子關係，如果父構件和子構件的目錄不是父子關係，比如都位於同等級別的目錄或者位於更複雜的目錄的時候，此時我們需要在子pom.xml的parent元素中使用relativePath元素來指定父pom.xml相對路徑位置，這個值我們上面沒有指定，默認是../pom.xml，表示父pom.xml位於子pom.xml的上一級目錄，我們的模塊剛好符合這種關係，所以這個值省略了。

正確的設置relativePath是非常重要的，這個需要注意，子模塊中執行mvn命令的時候，會去找父pom.xml的配置，會先通過relativePath指定的路徑去找，如果找不到，會嘗試通過坐標在本地倉庫進行查找，如果本地找不到，會去遠程倉庫找，如果遠程倉庫也沒有，會報錯。

可以通過繼承的元素有以下這些

上面我們看到了groupId、version、dependency中的依賴在子pom.xml中都沒有寫，這些都是從父pom.xml中繼承過來的，還有很多元素也可以被繼承過來，下面我們列個清單：

groupId：項目組ID，項目坐標的核心元素
version：項目版本，項目坐標的核心元素
description：項目的描述信息
organization：項目的組織信息
inceptionYear：項目的創始年份
url：項目的url地址
developers：項目的開發者信息
contributors：項目的貢獻者信息
distributionManagement：項目的部署配置信息
issueManagement：項目的缺陷跟蹤系統信息
ciManagement：項目的持續集成系統信息
scm：項目的版本控制系統信息
mailingLists：項目的郵件列表信息
properties：自定義的maven屬性配置信息
dependencyManagement：項目的依賴管理配置
repositories：項目的倉庫配置
build：包括項目的源碼目錄配置、輸出目錄配置、插件管理配置等信息
reporting：包括項目的報告輸出目錄配置、報告插件配置等信息

依賴管理(dependencyManagement)

大家是否發現了，上面的繼承存在的一個問題，如果我在新增一個子構件，都會默認從父構件中繼承依賴的一批構建，父pom.xml中配置的這些依賴的構建可能是其他項目不需要的，可能某個子項目只是想使用其中一個構件，但是上面的繼承關係卻把所有的依賴都給傳遞到子構件中了，這種顯然是不合適的。

maven中也考慮到了這種情況，可以使用dependencyManagement元素來解決這個問題。

maven提供的dependencyManagement元素既能讓子模塊繼承到父模塊的依賴配置，又能保證子模塊依賴使用的靈活性，在dependencyManagement元素下聲明的依賴不會引入實際的依賴，他只是聲明了這些依賴，不過它可以對dependencies中使用的依賴起到一些約束作用。

修改javacode2018-parent/pom.xml配置如下：

<?xml version="1.0" encoding="UTF-8"?>  <project xmlns="http://maven.apache.org/POM/4.0.0"           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"           xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">      <modelVersion>4.0.0</modelVersion>        <groupId>com.javacode2018</groupId>      <artifactId>javacode2018-parent</artifactId>      <version>1.0-SNAPSHOT</version>        <packaging>pom</packaging>        <dependencyManagement>          <dependencies>              <dependency>                  <groupId>org.springframework</groupId>                  <artifactId>spring-web</artifactId>                  <version>5.2.1.RELEASE</version>              </dependency>              <dependency>                  <groupId>org.mybatis</groupId>                  <artifactId>mybatis-spring</artifactId>                  <version>2.0.3</version>              </dependency>          </dependencies>      </dependencyManagement>    </project>

可以看到我們將dependencies配置移到dependencyManagement下面了。

我們使用下面命令看一下項目的依賴情況：

D:codeIdeaProjectsjavacode2018-parent>mvn dependency:tree  [INFO] Scanning for projects...  [INFO]  [INFO] ----------------< com.javacode2018:javacode2018-parent >-----------------  [INFO] Building javacode2018-parent 1.0-SNAPSHOT  [INFO] --------------------------------[ pom ]---------------------------------  [INFO]  [INFO] --- maven-dependency-plugin:2.8:tree (default-cli) @ javacode2018-parent ---  [INFO] com.javacode2018:javacode2018-parent:pom:1.0-SNAPSHOT  [INFO] ------------------------------------------------------------------------  [INFO] BUILD SUCCESS  [INFO] ------------------------------------------------------------------------  [INFO] Total time:  1.756 s  [INFO] Finished at: 2019-11-19T15:44:52+08:00  [INFO] ------------------------------------------------------------------------    D:codeIdeaProjectsjavacode2018-parent>cd javacode2018-pc    D:codeIdeaProjectsjavacode2018-parentjavacode2018-pc>mvn dependency:tree  [INFO] Scanning for projects...  [INFO]  [INFO] ------------------< com.javacode2018:javacode2018-pc >-------------------  [INFO] Building javacode2018-pc 1.0-SNAPSHOT  [INFO] --------------------------------[ jar ]---------------------------------  [INFO]  [INFO] --- maven-dependency-plugin:2.8:tree (default-cli) @ javacode2018-pc ---  [INFO] com.javacode2018:javacode2018-pc:jar:1.0-SNAPSHOT  [INFO] ------------------------------------------------------------------------  [INFO] BUILD SUCCESS  [INFO] ------------------------------------------------------------------------  [INFO] Total time:  1.676 s  [INFO] Finished at: 2019-11-19T15:45:08+08:00  [INFO] ------------------------------------------------------------------------

父子構件中都看不到依賴的jar包了，說明父pom.xml中dependencyManagement這些依賴的構建沒有被子模塊依賴進去。

子模塊如果想用到這些配置，可以dependencies進行引用，引用之後，依賴才會真正的起效。

在在3個子模塊的pom.xml中加入下面配置：

<dependencies>      <dependency>          <groupId>org.springframework</groupId>          <artifactId>spring-web</artifactId>      </dependency>      <dependency>          <groupId>org.mybatis</groupId>          <artifactId>mybatis-spring</artifactId>      </dependency>  </dependencies>

我們在運行一下上面的3個命令，看效果：

D:codeIdeaProjectsjavacode2018-parent>mvn dependency:tree  [INFO] Scanning for projects...  [INFO]  [INFO] ----------------< com.javacode2018:javacode2018-parent >-----------------  [INFO] Building javacode2018-parent 1.0-SNAPSHOT  [INFO] --------------------------------[ pom ]---------------------------------  [INFO]  [INFO] --- maven-dependency-plugin:2.8:tree (default-cli) @ javacode2018-parent ---  [INFO] com.javacode2018:javacode2018-parent:pom:1.0-SNAPSHOT  [INFO] ------------------------------------------------------------------------  [INFO] BUILD SUCCESS  [INFO] ------------------------------------------------------------------------  [INFO] Total time:  1.759 s  [INFO] Finished at: 2019-11-19T15:48:28+08:00  [INFO] ------------------------------------------------------------------------    D:codeIdeaProjectsjavacode2018-parent>cd javacode2018-pc    D:codeIdeaProjectsjavacode2018-parentjavacode2018-pc>mvn dependency:tree  [INFO] Scanning for projects...  [INFO]  [INFO] ------------------< com.javacode2018:javacode2018-pc >-------------------  [INFO] Building javacode2018-pc 1.0-SNAPSHOT  [INFO] --------------------------------[ jar ]---------------------------------  [INFO]  [INFO] --- maven-dependency-plugin:2.8:tree (default-cli) @ javacode2018-pc ---  [INFO] com.javacode2018:javacode2018-pc:jar:1.0-SNAPSHOT  [INFO] +- org.springframework:spring-web:jar:5.2.1.RELEASE:compile  [INFO] |  +- org.springframework:spring-beans:jar:5.2.1.RELEASE:compile  [INFO] |  - org.springframework:spring-core:jar:5.2.1.RELEASE:compile  [INFO] |     - org.springframework:spring-jcl:jar:5.2.1.RELEASE:compile  [INFO] - org.mybatis:mybatis-spring:jar:2.0.3:compile  [INFO] ------------------------------------------------------------------------  [INFO] BUILD SUCCESS  [INFO] ------------------------------------------------------------------------  [INFO] Total time:  1.875 s  [INFO] Finished at: 2019-11-19T15:48:38+08:00  [INFO] ------------------------------------------------------------------------

javacode2018-parent構件中沒有列出依賴信息，而javacode2018-pc列出了依賴信息。

大家看一下下面的截圖：

注意上面的紅框中依賴的構建沒有version，左邊2個紅圈中的2個向上的箭頭，表示這個是從父pom.xml中傳遞過來的，所以version可以省略。

再看一下父pom.xml截圖效果：

dependencyManagement中定義了依賴的構建，2個向下的箭頭表示被子模塊有繼承。

dependencyManagement不會引入實際的依賴，只有在子類中使用dependency來引入父dependencyManagement聲明的依賴之後，依賴的構建才會被真正的引入。

使用dependencyManagement來解決繼承的問題，子pom.xml中只用寫groupId,artifactId就可以了，其他信息都會從父dependencyManagement中聲明的依賴關係中傳遞過來，通常我們使用這種方式將所有依賴的構建在父pom.xml中定義好，子構件中只需要通過groupId,artifactId就可以引入依賴的構建，而不需要寫version，可以很好的確保多個子項目中依賴構件的版本的一致性，對應依賴構件版本的升級也非常方便，只需要在父pom.xml中修改一下就可以了。

單繼承問題

存在的問題及解決方案

上面講解了dependencyManagement的使用，但是有個問題，只有使用繼承的時候，dependencyManagement中聲明的依賴才可能被子pom.xml用到，如果我的項目本來就有父pom.xml了，但是我現在想使用另外一個項目dependencyManagement中聲明的依賴，此時我們怎麼辦？這就是單繼承的問題，這種情況在spring-boot、spring-cloud中會遇到，所以大家需要注意，這塊一定需要玩轉。

當我們想在項目中使用另外一個構件中dependencyManagement聲明的依賴，而又不想繼承這個項目的時候，可以在我們的項目中使用加入下面配置：

<dependencyManagement>      <dependencies>          <dependency>              <groupId>com.javacode2018</groupId>              <artifactId>javacode2018-parent</artifactId>              <version>1.0-SNAPSHOT</version>              <type>pom</type>              <scope>import</scope>          </dependency>          <dependency>構件2</dependency>          <dependency>構件3</dependency>          <dependency>構件n</dependency>      </dependencies>  </dependencyManagement>

上面這個配置會將javacode2018-parent構件中dependencyManagement元素中聲明的所有依賴導入到當前pom.xml的dependencyManagement中，相當於把下面部分的內容：

<dependency>      <groupId>com.javacode2018</groupId>      <artifactId>javacode2018-parent</artifactId>      <version>1.0-SNAPSHOT</version>      <type>pom</type>      <scope>import</scope>  </dependency>

替換成了javacode2018-parent/pom.xml中dependencyManagement元素內容，替換之後變成：

<dependencyManagement>      <dependencies>          <dependency>              <groupId>org.springframework</groupId>              <artifactId>spring-web</artifactId>              <version>5.2.1.RELEASE</version>          </dependency>          <dependency>              <groupId>org.mybatis</groupId>              <artifactId>mybatis-spring</artifactId>              <version>2.0.3</version>          </dependency>          <dependency>構件2</dependency>          <dependency>構件3</dependency>          <dependency>構件n</dependency>      </dependencies>  </dependencyManagement>

實操案例

創建項目javacode2018-pom-import，具體過程不演示了，坐標信息：

<groupId>com.javacode2018</groupId>  <artifactId>javacode2018-pom-import</artifactId>  <version>1.0-SNAPSHOT</version>

創建完畢之後，如下圖：

修改javacode2018-pom-import/pom.xml內容，如下：

<?xml version="1.0" encoding="UTF-8"?>  <project xmlns="http://maven.apache.org/POM/4.0.0"           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"           xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">      <modelVersion>4.0.0</modelVersion>        <groupId>com.javacode2018</groupId>      <artifactId>javacode2018-pom-import</artifactId>      <version>1.0-SNAPSHOT</version>        <dependencyManagement>          <dependencies>              <dependency>                  <groupId>com.alibaba</groupId>                  <artifactId>fastjson</artifactId>                  <version>1.2.62</version>              </dependency>              <dependency>                  <groupId>junit</groupId>                  <artifactId>junit</artifactId>                  <version>4.12</version>                  <scope>test</scope>              </dependency>          </dependencies>      </dependencyManagement>    </project>

上面我們在dependencyManagement中聲明了2個依賴：fastjson和junit。

在javacode2018-pom-import/pom.xml中執行mvn install將其安裝到本地倉庫

D:codeIdeaProjectsjavacode2018-pom-import>mvn install  [INFO] Scanning for projects...  [INFO]  [INFO] --------------< com.javacode2018:javacode2018-pom-import >--------------  [INFO] Building javacode2018-pom-import 1.0-SNAPSHOT  [INFO] --------------------------------[ jar ]---------------------------------  [INFO]  [INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ javacode2018-pom-import ---  [WARNING] Using platform encoding (GBK actually) to copy filtered resources, i.e. build is platform dependent!  [INFO] Copying 0 resource  [INFO]  [INFO] --- maven-compiler-plugin:3.1:compile (default-compile) @ javacode2018-pom-import ---  [INFO] Nothing to compile - all classes are up to date  [INFO]  [INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ javacode2018-pom-import ---  [WARNING] Using platform encoding (GBK actually) to copy filtered resources, i.e. build is platform dependent!  [INFO] skip non existing resourceDirectory D:codeIdeaProjectsjavacode2018-pom-importsrctestresources  [INFO]  [INFO] --- maven-compiler-plugin:3.1:testCompile (default-testCompile) @ javacode2018-pom-import ---  [INFO] Nothing to compile - all classes are up to date  [INFO]  [INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ javacode2018-pom-import ---  [INFO] No tests to run.  [INFO]  [INFO] --- maven-jar-plugin:2.4:jar (default-jar) @ javacode2018-pom-import ---  [INFO] Building jar: D:codeIdeaProjectsjavacode2018-pom-importtargetjavacode2018-pom-import-1.0-SNAPSHOT.jar  [INFO]  [INFO] --- maven-install-plugin:2.4:install (default-install) @ javacode2018-pom-import ---  [INFO] Installing D:codeIdeaProjectsjavacode2018-pom-importtargetjavacode2018-pom-import-1.0-SNAPSHOT.jar to C:UsersThink.m2repositorycomjavacode2018javacode2018-pom-import1.0-SNAPSHOTjavacode2018-pom-import-1.0-SNAPSHOT.jar  [INFO] Installing D:codeIdeaProjectsjavacode2018-pom-importpom.xml to C:UsersThink.m2repositorycomjavacode2018javacode2018-pom-import1.0-SNAPSHOTjavacode2018-pom-import-1.0-SNAPSHOT.pom  [INFO] ------------------------------------------------------------------------  [INFO] BUILD SUCCESS  [INFO] ------------------------------------------------------------------------  [INFO] Total time:  2.692 s  [INFO] Finished at: 2019-11-19T17:23:16+08:00  [INFO] ------------------------------------------------------------------------

現在我們想在javacode2018-pc/pom.xml中使用javacode2018-pom-import/pom.xml的dependencyManagement元素中定義的fastjson和junit的依賴，而我們的javacode2019-pc已經繼承了javacode-parent了，maven中只能單繼承，所以沒法通過繼承的方式來實現了，那麼我們可以在javacode2019-pc/pom.xml中加入下面配置：

<dependencyManagement>      <dependencies>          <dependency>              <groupId>com.javacode2018</groupId>              <artifactId>javacode2018-pom-import</artifactId>              <version>1.0-SNAPSHOT</version>              <type>pom</type>              <scope>import</scope>          </dependency>      </dependencies>  </dependencyManagement>

此時可以使用fastjson的依賴了，javacode2018-pc/pom.xml中project->dependencies元素中加入下面配置：

<dependency>      <groupId>com.alibaba</groupId>      <artifactId>fastjson</artifactId>  </dependency>

看一下效果：

上面的fastjson沒有指定版本號，直接可以使用，說明從javacode2018-pom-import傳遞過來了。

可以點擊一下上面紅圈中的箭頭，會跳到本地倉庫的javacode2018-pom-import-1.0-SNAPSHOT.pom文件，如下：

插件管理(pluginManagement)

maven中提供了dependencyManagement來解決繼承的問題，同樣也提供了解決插件繼承問題的pluginManagement元素，在父pom中可以在這個元素中聲明插件的配置信息，但是子pom.xml中不會引入此插件的配置信息，只有在子pom.xml中使用plugins->plugin元素正在引入這些聲明的插件的時候，插件才會起效，子插件中只需要寫groupId、artifactId，其他信息都可以從父構件中傳遞過來。

實操案例

在javacode2018-parent/pom.xml中加入下面配置：

<build>      <pluginManagement>          <plugins>              <plugin>                  <groupId>org.apache.maven.plugins</groupId>                  <artifactId>maven-source-plugin</artifactId>                  <version>3.2.0</version>                  <executions>                      <execution>                          <id>attach-source</id>                          <phase>verify</phase>                          <goals>                              <goal>jar-no-fork</goal>                          </goals>                      </execution>                  </executions>              </plugin>          </plugins>      </pluginManagement>  </build>

maven-source-plugin這個插件在上一章有介紹過，源碼打包的。上面是將插件maven-source-plugin的jar-no-fork目標綁定在default生命周期的verify階段，verify階段會在default生命周期的install周期前面執行。下面我們看效果。

在javacode2018-pc/pom.xml所在目錄運行下面命令

D:codeIdeaProjectsjavacode2018-parentjavacode2018-pc>mvn clean install  [INFO] Scanning for projects...  [INFO]  [INFO] ------------------< com.javacode2018:javacode2018-pc >-------------------  [INFO] Building javacode2018-pc 1.0-SNAPSHOT  [INFO] --------------------------------[ jar ]---------------------------------  [INFO]  [INFO] --- maven-clean-plugin:2.5:clean (default-clean) @ javacode2018-pc ---  [INFO] Deleting D:codeIdeaProjectsjavacode2018-parentjavacode2018-pctarget  [INFO]  [INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ javacode2018-pc ---  [WARNING] Using platform encoding (GBK actually) to copy filtered resources, i.e. build is platform dependent!  [INFO] Copying 0 resource  [INFO]  [INFO] --- maven-compiler-plugin:3.1:compile (default-compile) @ javacode2018-pc ---  [INFO] Nothing to compile - all classes are up to date  [INFO]  [INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ javacode2018-pc ---  [WARNING] Using platform encoding (GBK actually) to copy filtered resources, i.e. build is platform dependent!  [INFO] skip non existing resourceDirectory D:codeIdeaProjectsjavacode2018-parentjavacode2018-pcsrctestresources  [INFO]  [INFO] --- maven-compiler-plugin:3.1:testCompile (default-testCompile) @ javacode2018-pc ---  [INFO] Nothing to compile - all classes are up to date  [INFO]  [INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ javacode2018-pc ---  [INFO] No tests to run.  [INFO]  [INFO] --- maven-jar-plugin:2.4:jar (default-jar) @ javacode2018-pc ---  [INFO] Building jar: D:codeIdeaProjectsjavacode2018-parentjavacode2018-pctargetjavacode2018-pc-1.0-SNAPSHOT.jar  [INFO]  [INFO] --- maven-install-plugin:2.4:install (default-install) @ javacode2018-pc ---  [INFO] Installing D:codeIdeaProjectsjavacode2018-parentjavacode2018-pctargetjavacode2018-pc-1.0-SNAPSHOT.jar to C:UsersThink.m2repositorycomjavacode2018javacode2018-pc1.0-SNAPSHOTjavacode2018-pc-1.0-SNAPSHOT.jar  [INFO] Installing D:codeIdeaProjectsjavacode2018-parentjavacode2018-pcpom.xml to C:UsersThink.m2repositorycomjavacode2018javacode2018-pc1.0-SNAPSHOTjavacode2018-pc-1.0-SNAPSHOT.pom  [INFO] ------------------------------------------------------------------------  [INFO] BUILD SUCCESS  [INFO] ------------------------------------------------------------------------  [INFO] Total time:  2.254 s  [INFO] Finished at: 2019-11-19T16:24:39+08:00  [INFO] ------------------------------------------------------------------------

mvn clean install 會清理代碼，然後將打包構件，將構建安裝到本地倉庫，從輸入中可以看到javacode2018-pc-1.0-SNAPSHOT.jar被安裝到本地倉庫了。但是沒有看到打包源碼的插件的運行，說明了javacode2018-pc沒有從父pom.xml中繼承插件的配置信息，所以插件配置沒有起效，現在我們要讓插件起效，繼續看：

在javacode2018-pc/pom.xml中加入下面配置：

<build>      <plugins>          <plugin>              <groupId>org.apache.maven.plugins</groupId>              <artifactId>maven-source-plugin</artifactId>          </plugin>      </plugins>  </build>

截圖看效果：

又一個線上的箭頭，說明這個是從父pom.xml中傳遞過來了，大家仔細看一下上面的配置，插件只寫了groupId、artifactId，其他信息都沒有寫，其他信息都可以從父pom.xml中傳遞過來，下面我們看一下插件是否起效了，運行下面命令，見證奇蹟：

D:codeIdeaProjectsjavacode2018-parentjavacode2018-pc>mvn clean install  [INFO] Scanning for projects...  [INFO]  [INFO] ------------------< com.javacode2018:javacode2018-pc >-------------------  [INFO] Building javacode2018-pc 1.0-SNAPSHOT  [INFO] --------------------------------[ jar ]---------------------------------  [INFO]  [INFO] --- maven-clean-plugin:2.5:clean (default-clean) @ javacode2018-pc ---  [INFO] Deleting D:codeIdeaProjectsjavacode2018-parentjavacode2018-pctarget  [INFO]  [INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ javacode2018-pc ---  [WARNING] Using platform encoding (GBK actually) to copy filtered resources, i.e. build is platform dependent!  [INFO] Copying 0 resource  [INFO]  [INFO] --- maven-compiler-plugin:3.1:compile (default-compile) @ javacode2018-pc ---  [INFO] Nothing to compile - all classes are up to date  [INFO]  [INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ javacode2018-pc ---  [WARNING] Using platform encoding (GBK actually) to copy filtered resources, i.e. build is platform dependent!  [INFO] skip non existing resourceDirectory D:codeIdeaProjectsjavacode2018-parentjavacode2018-pcsrctestresources  [INFO]  [INFO] --- maven-compiler-plugin:3.1:testCompile (default-testCompile) @ javacode2018-pc ---  [INFO] Nothing to compile - all classes are up to date  [INFO]  [INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ javacode2018-pc ---  [INFO] No tests to run.  [INFO]  [INFO] --- maven-jar-plugin:2.4:jar (default-jar) @ javacode2018-pc ---  [INFO] Building jar: D:codeIdeaProjectsjavacode2018-parentjavacode2018-pctargetjavacode2018-pc-1.0-SNAPSHOT.jar  [INFO]  [INFO] --- maven-source-plugin:3.2.0:jar-no-fork (attach-source) @ javacode2018-pc ---  [INFO] Building jar: D:codeIdeaProjectsjavacode2018-parentjavacode2018-pctargetjavacode2018-pc-1.0-SNAPSHOT-sources.jar  [INFO]  [INFO] --- maven-install-plugin:2.4:install (default-install) @ javacode2018-pc ---  [INFO] Installing D:codeIdeaProjectsjavacode2018-parentjavacode2018-pctargetjavacode2018-pc-1.0-SNAPSHOT.jar to C:UsersThink.m2repositorycomjavacode2018javacode2018-pc1.0-SNAPSHOTjavacode2018-pc-1.0-SNAPSHOT.jar  [INFO] Installing D:codeIdeaProjectsjavacode2018-parentjavacode2018-pcpom.xml to C:UsersThink.m2repositorycomjavacode2018javacode2018-pc1.0-SNAPSHOTjavacode2018-pc-1.0-SNAPSHOT.pom  [INFO] Installing D:codeIdeaProjectsjavacode2018-parentjavacode2018-pctargetjavacode2018-pc-1.0-SNAPSHOT-sources.jar to C:UsersThink.m2repositorycomjavacode2018javacode2018-pc1.0-SNAPSHOTjavacode2018-pc-1.0-SNAPSHOT-sources.jar  [INFO] ------------------------------------------------------------------------  [INFO] BUILD SUCCESS  [INFO] ------------------------------------------------------------------------  [INFO] Total time:  2.477 s  [INFO] Finished at: 2019-11-19T16:28:18+08:00  [INFO] ------------------------------------------------------------------------

注意上面的輸出中有attach-source，這個就是上面我們插件任務的id，輸出中還有javacode2018-pc-1.0-SNAPSHOT-sources.jar信息，說明源碼也是打包成功了，最後也是上傳到了本地倉庫了。

上面演示了只用在子pom.xml中寫上插件的groupId、artifactId就可以了，其他信息會從父pom.xml中插件的定義中傳遞過來，而子pom.xml中也可以自定義插件的這些配置，修改javacode2018-pc/pom.xml配置，如下：

<build>      <plugins>          <plugin>              <groupId>org.apache.maven.plugins</groupId>              <artifactId>maven-source-plugin</artifactId>              <executions>                  <execution>                      <id>attach-source</id>                      <goals>                          <goal>help</goal>                      </goals>                  </execution>              </executions>          </plugin>      </plugins>  </build>

再看一下效果：

D:codeIdeaProjectsjavacode2018-parentjavacode2018-pc>mvn clean install  [INFO] Scanning for projects...  [INFO]  [INFO] ------------------< com.javacode2018:javacode2018-pc >-------------------  [INFO] Building javacode2018-pc 1.0-SNAPSHOT  [INFO] --------------------------------[ jar ]---------------------------------  [INFO]  [INFO] --- maven-clean-plugin:2.5:clean (default-clean) @ javacode2018-pc ---  [INFO] Deleting D:codeIdeaProjectsjavacode2018-parentjavacode2018-pctarget  [INFO]  [INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ javacode2018-pc ---  [WARNING] Using platform encoding (GBK actually) to copy filtered resources, i.e. build is platform dependent!  [INFO] Copying 0 resource  [INFO]  [INFO] --- maven-compiler-plugin:3.1:compile (default-compile) @ javacode2018-pc ---  [INFO] Nothing to compile - all classes are up to date  [INFO]  [INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ javacode2018-pc ---  [WARNING] Using platform encoding (GBK actually) to copy filtered resources, i.e. build is platform dependent!  [INFO] skip non existing resourceDirectory D:codeIdeaProjectsjavacode2018-parentjavacode2018-pcsrctestresources  [INFO]  [INFO] --- maven-compiler-plugin:3.1:testCompile (default-testCompile) @ javacode2018-pc ---  [INFO] Nothing to compile - all classes are up to date  [INFO]  [INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ javacode2018-pc ---  [INFO] No tests to run.  [INFO]  [INFO] --- maven-jar-plugin:2.4:jar (default-jar) @ javacode2018-pc ---  [INFO] Building jar: D:codeIdeaProjectsjavacode2018-parentjavacode2018-pctargetjavacode2018-pc-1.0-SNAPSHOT.jar  [INFO]  [INFO] --- maven-source-plugin:3.2.0:help (attach-source) @ javacode2018-pc ---  [INFO] Apache Maven Source Plugin 3.2.0    The Maven Source Plugin creates a JAR archive of the source files of the    current project.    This plugin has 7 goals:    source:aggregate    Aggregate sources for all modules in an aggregator project.    source:generated-test-jar    This plugin bundles all the test sources into a jar archive.    source:help    Display help information on maven-source-plugin.    Call mvn source:help -Ddetail=true -Dgoal=<goal-name> to display parameter    details.    source:jar    This plugin bundles all the sources into a jar archive.    source:jar-no-fork    This goal bundles all the sources into a jar archive. This goal functions the    same as the jar goal but does not fork the build and is suitable for attaching    to the build lifecycle.    source:test-jar    This plugin bundles all the test sources into a jar archive.    source:test-jar-no-fork    This goal bundles all the test sources into a jar archive. This goal functions    the same as the test-jar goal but does not fork the build, and is suitable for    attaching to the build lifecycle.      [INFO]  [INFO] --- maven-source-plugin:3.2.0:jar-no-fork (attach-source) @ javacode2018-pc ---  [INFO] Building jar: D:codeIdeaProjectsjavacode2018-parentjavacode2018-pctargetjavacode2018-pc-1.0-SNAPSHOT-sources.jar  [INFO]  [INFO] --- maven-install-plugin:2.4:install (default-install) @ javacode2018-pc ---  [INFO] Installing D:codeIdeaProjectsjavacode2018-parentjavacode2018-pctargetjavacode2018-pc-1.0-SNAPSHOT.jar to C:UsersThink.m2repositorycomjavacode2018javacode2018-pc1.0-SNAPSHOTjavacode2018-pc-1.0-SNAPSHOT.jar  [INFO] Installing D:codeIdeaProjectsjavacode2018-parentjavacode2018-pcpom.xml to C:UsersThink.m2repositorycomjavacode2018javacode2018-pc1.0-SNAPSHOTjavacode2018-pc-1.0-SNAPSHOT.pom  [INFO] Installing D:codeIdeaProjectsjavacode2018-parentjavacode2018-pctargetjavacode2018-pc-1.0-SNAPSHOT-sources.jar to C:UsersThink.m2repositorycomjavacode2018javacode2018-pc1.0-SNAPSHOTjavacode2018-pc-1.0-SNAPSHOT-sources.jar  [INFO] ------------------------------------------------------------------------  [INFO] BUILD SUCCESS  [INFO] ------------------------------------------------------------------------  [INFO] Total time:  2.752 s  [INFO] Finished at: 2019-11-19T16:41:21+08:00  [INFO] ------------------------------------------------------------------------

輸出中有下面2行：

[INFO] --- maven-source-plugin:3.2.0:help (attach-source) @ javacode2018-pc ---  [INFO] --- maven-source-plugin:3.2.0:jar-no-fork (attach-source) @ javacode2018-pc ---

說明maven-source-plugin插件執行了2個目標：help和jar-no-fork。此時父子pom.xml中插件配置信息合併了，所以出現了2個目標。具體最終javacode2018-pc/pom.xml中的內容是什麼樣的，可以通過下面這個命令看到：

mvn help:effective-pom

上面這個命令大家最好去看一下效果，當pom.xml中存在複雜的關係的時候，可以通過這個命令解析得到這個構件最終pom.xml的內容。

聚合與繼承的關係

前面已經詳解了聚合和繼承，想必大家對這塊也有了自己的理解。

聚合主要是為了方便多模塊快速構建。

而繼承主要是為了重用相同的配置。

對於聚合來說，聚合模塊是知道被聚合模塊的存在的，而被聚合模塊是感知不到聚合模塊的存在。

對於繼承來說，父構件是感知不到子構件的存在，而子構件需要使用parent來引用父構件。

兩者的共同點是，聚合模塊和繼承中的父模塊的package屬性都必須是pom類型的，同時，聚合模塊和父模塊中的除了pom.xml，一般都是沒有什麼內容的。

實際使用是，我們經常將聚合和繼承一起使用，能同時使用到兩者的優點。

下面我們在javacode2018-parent中加入聚合的配置：

<modules>      <module>javacode2018-pc</module>      <module>javacode2018-h5</module>      <module>javacode2018-api</module>  </modules>

javacode20180-parent/pom.xml目錄運行一下mvn install，看看效果：

D:codeIdeaProjectsjavacode2018-parent>mvn install  [INFO] Scanning for projects...  [INFO] ------------------------------------------------------------------------  [INFO] Reactor Build Order:  [INFO]  [INFO] javacode2018-parent                                                [pom]  [INFO] javacode2018-pc                                                    [jar]  [INFO] javacode2018-h5                                                    [jar]  [INFO] javacode2018-api                                                   [jar]  [INFO]  [INFO] ----------------< com.javacode2018:javacode2018-parent >----------------  [INFO] Building javacode2018-parent 1.0-SNAPSHOT                          [1/4]  [INFO] --------------------------------[ pom ]---------------------------------  [INFO]  [INFO] --- maven-install-plugin:2.4:install (default-install) @ javacode2018-parent ---  [INFO] Installing D:codeIdeaProjectsjavacode2018-parentpom.xml to C:UsersThink.m2repositorycomjavacode2018javacode2018-parent1.0-SNAPSHOTjavacode2018-parent-1.0-SNAPSHOT.pom  [INFO]  [INFO] ------------------< com.javacode2018:javacode2018-pc >------------------  [INFO] Building javacode2018-pc 1.0-SNAPSHOT                              [2/4]  [INFO] --------------------------------[ jar ]---------------------------------  [INFO]  [INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ javacode2018-pc ---  [WARNING] Using platform encoding (GBK actually) to copy filtered resources, i.e. build is platform dependent!  [INFO] Copying 0 resource  [INFO]  [INFO] --- maven-compiler-plugin:3.1:compile (default-compile) @ javacode2018-pc ---  [INFO] Nothing to compile - all classes are up to date  [INFO]  [INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ javacode2018-pc ---  [WARNING] Using platform encoding (GBK actually) to copy filtered resources, i.e. build is platform dependent!  [INFO] skip non existing resourceDirectory D:codeIdeaProjectsjavacode2018-parentjavacode2018-pcsrctestresources  [INFO]  [INFO] --- maven-compiler-plugin:3.1:testCompile (default-testCompile) @ javacode2018-pc ---  [INFO] Nothing to compile - all classes are up to date  [INFO]  [INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ javacode2018-pc ---  [INFO] No tests to run.  [INFO]  [INFO] --- maven-jar-plugin:2.4:jar (default-jar) @ javacode2018-pc ---  [INFO]  [INFO] --- maven-source-plugin:3.2.0:help (attach-source) @ javacode2018-pc ---  [INFO] Apache Maven Source Plugin 3.2.0    The Maven Source Plugin creates a JAR archive of the source files of the    current project.    This plugin has 7 goals:    source:aggregate    Aggregate sources for all modules in an aggregator project.    source:generated-test-jar    This plugin bundles all the test sources into a jar archive.    source:help    Display help information on maven-source-plugin.    Call mvn source:help -Ddetail=true -Dgoal=<goal-name> to display parameter    details.    source:jar    This plugin bundles all the sources into a jar archive.    source:jar-no-fork    This goal bundles all the sources into a jar archive. This goal functions the    same as the jar goal but does not fork the build and is suitable for attaching    to the build lifecycle.    source:test-jar    This plugin bundles all the test sources into a jar archive.    source:test-jar-no-fork    This goal bundles all the test sources into a jar archive. This goal functions    the same as the test-jar goal but does not fork the build, and is suitable for    attaching to the build lifecycle.      [INFO]  [INFO] --- maven-source-plugin:3.2.0:jar-no-fork (attach-source) @ javacode2018-pc ---  [INFO]  [INFO] --- maven-install-plugin:2.4:install (default-install) @ javacode2018-pc ---  [INFO] Installing D:codeIdeaProjectsjavacode2018-parentjavacode2018-pctargetjavacode2018-pc-1.0-SNAPSHOT.jar to C:UsersThink.m2repositorycomjavacode2018javacode2018-pc1.0-SNAPSHOTjavacode2018-pc-1.0-SNAPSHOT.jar  [INFO] Installing D:codeIdeaProjectsjavacode2018-parentjavacode2018-pcpom.xml to C:UsersThink.m2repositorycomjavacode2018javacode2018-pc1.0-SNAPSHOTjavacode2018-pc-1.0-SNAPSHOT.pom  [INFO] Installing D:codeIdeaProjectsjavacode2018-parentjavacode2018-pctargetjavacode2018-pc-1.0-SNAPSHOT-sources.jar to C:UsersThink.m2repositorycomjavacode2018javacode2018-pc1.0-SNAPSHOTjavacode2018-pc-1.0-SNAPSHOT-sources.jar  [INFO]  [INFO] ------------------< com.javacode2018:javacode2018-h5 >------------------  [INFO] Building javacode2018-h5 1.0-SNAPSHOT                              [3/4]  [INFO] --------------------------------[ jar ]---------------------------------  [INFO]  [INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ javacode2018-h5 ---  [WARNING] Using platform encoding (GBK actually) to copy filtered resources, i.e. build is platform dependent!  [INFO] Copying 0 resource  [INFO]  [INFO] --- maven-compiler-plugin:3.1:compile (default-compile) @ javacode2018-h5 ---  [INFO] Nothing to compile - all classes are up to date  [INFO]  [INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ javacode2018-h5 ---  [WARNING] Using platform encoding (GBK actually) to copy filtered resources, i.e. build is platform dependent!  [INFO] skip non existing resourceDirectory D:codeIdeaProjectsjavacode2018-parentjavacode2018-h5srctestresources  [INFO]  [INFO] --- maven-compiler-plugin:3.1:testCompile (default-testCompile) @ javacode2018-h5 ---  [INFO] Nothing to compile - all classes are up to date  [INFO]  [INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ javacode2018-h5 ---  [INFO] No tests to run.  [INFO]  [INFO] --- maven-jar-plugin:2.4:jar (default-jar) @ javacode2018-h5 ---  [INFO] Building jar: D:codeIdeaProjectsjavacode2018-parentjavacode2018-h5targetjavacode2018-h5-1.0-SNAPSHOT.jar  [INFO]  [INFO] --- maven-install-plugin:2.4:install (default-install) @ javacode2018-h5 ---  [INFO] Installing D:codeIdeaProjectsjavacode2018-parentjavacode2018-h5targetjavacode2018-h5-1.0-SNAPSHOT.jar to C:UsersThink.m2repositorycomjavacode2018javacode2018-h51.0-SNAPSHOTjavacode2018-h5-1.0-SNAPSHOT.jar  [INFO] Installing D:codeIdeaProjectsjavacode2018-parentjavacode2018-h5pom.xml to C:UsersThink.m2repositorycomjavacode2018javacode2018-h51.0-SNAPSHOTjavacode2018-h5-1.0-SNAPSHOT.pom  [INFO]  [INFO] -----------------< com.javacode2018:javacode2018-api >------------------  [INFO] Building javacode2018-api 1.0-SNAPSHOT                             [4/4]  [INFO] --------------------------------[ jar ]---------------------------------  [INFO]  [INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ javacode2018-api ---  [WARNING] Using platform encoding (GBK actually) to copy filtered resources, i.e. build is platform dependent!  [INFO] Copying 0 resource  [INFO]  [INFO] --- maven-compiler-plugin:3.1:compile (default-compile) @ javacode2018-api ---  [INFO] Nothing to compile - all classes are up to date  [INFO]  [INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ javacode2018-api ---  [WARNING] Using platform encoding (GBK actually) to copy filtered resources, i.e. build is platform dependent!  [INFO] skip non existing resourceDirectory D:codeIdeaProjectsjavacode2018-parentjavacode2018-apisrctestresources  [INFO]  [INFO] --- maven-compiler-plugin:3.1:testCompile (default-testCompile) @ javacode2018-api ---  [INFO] Nothing to compile - all classes are up to date  [INFO]  [INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ javacode2018-api ---  [INFO] No tests to run.  [INFO]  [INFO] --- maven-jar-plugin:2.4:jar (default-jar) @ javacode2018-api ---  [INFO] Building jar: D:codeIdeaProjectsjavacode2018-parentjavacode2018-apitargetjavacode2018-api-1.0-SNAPSHOT.jar  [INFO]  [INFO] --- maven-install-plugin:2.4:install (default-install) @ javacode2018-api ---  [INFO] Installing D:codeIdeaProjectsjavacode2018-parentjavacode2018-apitargetjavacode2018-api-1.0-SNAPSHOT.jar to C:UsersThink.m2repositorycomjavacode2018javacode2018-api1.0-SNAPSHOTjavacode2018-api-1.0-SNAPSHOT.jar  [INFO] Installing D:codeIdeaProjectsjavacode2018-parentjavacode2018-apipom.xml to C:UsersThink.m2repositorycomjavacode2018javacode2018-api1.0-SNAPSHOTjavacode2018-api-1.0-SNAPSHOT.pom  [INFO] ------------------------------------------------------------------------  [INFO] Reactor Summary for javacode2018-parent 1.0-SNAPSHOT:  [INFO]  [INFO] javacode2018-parent ................................ SUCCESS [  0.416 s]  [INFO] javacode2018-pc .................................... SUCCESS [  2.654 s]  [INFO] javacode2018-h5 .................................... SUCCESS [  0.262 s]  [INFO] javacode2018-api ................................... SUCCESS [  0.225 s]  [INFO] ------------------------------------------------------------------------  [INFO] BUILD SUCCESS  [INFO] ------------------------------------------------------------------------  [INFO] Total time:  3.827 s  [INFO] Finished at: 2019-11-19T17:51:42+08:00  [INFO] ------------------------------------------------------------------------

上篇文章中留下的2個問題

問題1

下面這個配置是幹什麼的？給哪個插件使用的？

<properties>      <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>  </properties>

編譯代碼的時候，涉及到資源文件和測試資源文件的拷貝，拷貝文件的時候涉及到文件的編碼，這個是設置文件的編碼為UTF-8格式的。

我們在上篇文章的maven-chat06項目的目錄中執行mvn compile命令，效果如下：

D:codeIdeaProjectsmaven-chat06>mvn compile  [INFO] Scanning for projects...  [INFO]  [INFO] -------------------< com.javacode2018:maven-chat06 >--------------------  [INFO] Building maven-chat06 1.0-SNAPSHOT  [INFO] --------------------------------[ jar ]---------------------------------  [INFO]  [INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ maven-chat06 ---  [INFO] Using 'UTF-8' encoding to copy filtered resources.  [INFO] Copying 0 resource  [INFO]  [INFO] --- maven-compiler-plugin:3.1:compile (default-compile) @ maven-chat06 ---  [INFO] Nothing to compile - all classes are up to date  [INFO] ------------------------------------------------------------------------  [INFO] BUILD SUCCESS  [INFO] ------------------------------------------------------------------------  [INFO] Total time:  1.179 s  [INFO] Finished at: 2019-11-19T17:57:27+08:00  [INFO] ------------------------------------------------------------------------

可以看到上面有這樣的輸出：

[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ maven-chat06 ---  [INFO] Using 'UTF-8' encoding to copy filtered resources.

從上面可以看出maven-resources-plugin插件的resources目標中會使用這個編碼的配置，我們來看一下這個目標具體參數配置，我們截取了部分輸出，如下：

D:codeIdeaProjectsmaven-chat06>mvn help:describe -Dplugin=resources -Dgoal=resources  -Ddetail  [INFO] Scanning for projects...  [INFO]  [INFO] -------------------< com.javacode2018:maven-chat06 >--------------------  [INFO] Building maven-chat06 1.0-SNAPSHOT  [INFO] --------------------------------[ jar ]---------------------------------  [INFO]  [INFO] --- maven-help-plugin:3.2.0:describe (default-cli) @ maven-chat06 ---  [INFO] Mojo: 'resources:resources'  resources:resources    Description: Copy resources for the main source code to the main output      directory. Always uses the project.build.resources element to specify the      resources to copy.    Implementation: org.apache.maven.plugin.resources.ResourcesMojo    Language: java    Bound to phase: process-resources      Available parameters:        delimiters        Set of delimiters for expressions to filter within the resources. These        delimiters are specified in the form 'beginToken*endToken'. If no '*' is        given, the delimiter is assumed to be the same for start and end.          So, the default filtering delimiters might be specified as:          <delimiters>         <delimiter>${*}</delimiter>         <delimiter>@</delimiter>        </delimiters>          Since the '@' delimiter is the same on both ends, we don't need to        specify '@*@' (though we can).        encoding (Default: ${project.build.sourceEncoding})        User property: encoding        The character encoding scheme to be applied when filtering resources.

注意上面輸出中最後的一部分，如下：

    encoding (Default: ${project.build.sourceEncoding})        User property: encoding        The character encoding scheme to be applied when filtering resources.

encoding這個參數用來指定編碼的，默認值是${project.build.sourceEncoding}，也可以通過encoding用戶屬性來設置。

所以這個設置編碼的還有下面3種寫法，共四種：

pom.xml中2種：  <encoding>UTF-8</encoding>  <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>    mvn命令中2種：  mvn compile -Dencoding=UTF-8  mvn compile -Dproject.build.sourceEncoding=UTF-8

問題2

mvn test運行測試用例的時候，測試用例類名的寫法默認是有規則的，這些規則有人知道么？從哪裡可以看到這些規則？如何自定義？

我們在上一篇中的maven-chat06項目中執行mvn test，看看效果：

D:codeIdeaProjectsmaven-chat06>mvn test  [INFO] Scanning for projects...  [INFO]  [INFO] -------------------< com.javacode2018:maven-chat06 >--------------------  [INFO] Building maven-chat06 1.0-SNAPSHOT  [INFO] --------------------------------[ jar ]---------------------------------  [INFO]  [INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ maven-chat06 ---  [INFO] Using 'UTF-8' encoding to copy filtered resources.  [INFO] Copying 0 resource  [INFO]  [INFO] --- maven-compiler-plugin:3.1:compile (default-compile) @ maven-chat06 ---  [INFO] Nothing to compile - all classes are up to date  [INFO]  [INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ maven-chat06 ---  [INFO] Using 'UTF-8' encoding to copy filtered resources.  [INFO] Copying 0 resource  [INFO]  [INFO] --- maven-compiler-plugin:3.1:testCompile (default-testCompile) @ maven-chat06 ---  [INFO] Nothing to compile - all classes are up to date  [INFO]  [INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ maven-chat06 ---  [INFO] ------------------------------------------------------------------------  [INFO] BUILD SUCCESS  [INFO] ------------------------------------------------------------------------  [INFO] Total time:  1.411 s  [INFO] Finished at: 2019-11-19T18:07:52+08:00  [INFO] ------------------------------------------------------------------------

可以看到下面這行：

[INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ maven-chat06 ---

表示運行測試使用的是插件maven-surefire-plugin的test目標。

我們看看這個目標詳細參數，只列出部分信息，如下：

D:codeIdeaProjectsmaven-chat06>mvn help:describe -Dplugin=surefire -Dgoal=test -Ddetail  [INFO] Scanning for projects...  [INFO]  [INFO] -------------------< com.javacode2018:maven-chat06 >--------------------  [INFO] Building maven-chat06 1.0-SNAPSHOT  [INFO] --------------------------------[ jar ]---------------------------------  [INFO]  [INFO] --- maven-help-plugin:3.2.0:describe (default-cli) @ maven-chat06 ---  [INFO] Mojo: 'surefire:test'  surefire:test    Description: Run tests using Surefire.    Implementation: org.apache.maven.plugin.surefire.SurefirePlugin    Language: java    Bound to phase: test      Available parameters:        includes        A list of <include> elements specifying the tests (by pattern) that        should be included in testing. When not specified and when the test        parameter is not specified, the default includes will be        <includes>         <include>**/IT*.java</include>         <include>**/*IT.java</include>         <include>**/*ITCase.java</include>        </includes>        Each include item may also contain a comma-separated sublist of items,        which will be treated as multiple  <include> entries.        This parameter is ignored if the TestNG suiteXmlFiles parameter is        specified.      [INFO] ------------------------------------------------------------------------  [INFO] BUILD SUCCESS  [INFO] ------------------------------------------------------------------------  [INFO] Total time:  4.458 s  [INFO] Finished at: 2019-11-19T18:10:09+08:00  [INFO] ------------------------------------------------------------------------

可以看到上面有個includes參數，可以用來配置需要運行的測試用例，可以配置通配符的方式。

上面還有一段信息：

 Implementation: org.apache.maven.plugin.surefire.SurefirePlugin

上面這部分列出了這個目標的具體實現類是SurefirePlugin。

那麼我們可以到本地倉庫中看一下這個構件的源碼，構件的坐標是：

<groupId>org.apache.maven.plugins</groupId>  <artifactId>maven-surefire-plugin</artifactId>  <version>2.12.4</version>

打開org.apache.maven.plugin.surefire.SurefirePlugin的源碼，會找到下面代碼：

protected String[] getDefaultIncludes()  {      return new String[]{ "**/Test*.java", "**/*Test.java", "**/*TestCase.java" };  }

這部分代碼就是我們測試用例默認需要滿足的格式，你創建的測試用例默認情況下必須滿足上面這3種格式，否則，測試用例不會被mvn test執行。

總結

需要掌握聚合的使用
掌握繼承的使用
掌握單繼承問題解決方案
掌握依賴管理和插件管理的使用

還是那句話，建議大家下去了多練練，都操作一遍，加深理解！