2. spring 應用之IOC

  • 2019 年 10 月 18 日
  • 筆記

 本文是作者原創,版權歸作者所有.若要轉載,請註明出處

 

我們知道Spring Framework 最重要的功能就是IoC (Inversion of Control ),也叫DI(dependency injection),這不是我說的,是官網這麼說的,截圖如下

spring官網說IoC,也叫DI,是同一個意思.

 

首先複習一下spring的應用

1.用xml方式將對象交給spring管理

首先是測試類

public class UserService  {        private String userName;        public String getUserName() {          return userName;      }        public void setUserName(String userName1) {          this.userName = userName1;      }    }

然後是applicationContext.xml

<?xml version="1.0" encoding="UTF-8"?>  <beans xmlns="http://www.springframework.org/schema/beans"         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"         xsi:schemaLocation="http://www.springframework.org/schema/beans          https://www.springframework.org/schema/beans/spring-beans.xsd"      default-autowire="no">          <bean class="com.lusaisai.service.UserService" id="userService" >          <!--此處name的值與set方法要一致-->          <property name="userName" value="lusai"></property>      </bean>    </beans>

最後是測試

public static void main(String[] args) {            ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");          UserService userService = (UserService) context.getBean("userService");
   
　　　　　　System.out.println(userService.getUserName());
 }

 

 可以看到注入成功

 

 2.依賴注入

首先是UserService依賴的對象UserDao

public interface UserDao {      void test();  }

然後是它的實現類

public class UserDaoImpl implements UserDao {      @Override      public void test() {          System.out.println("UserDaoImpl");      }  }

在UserService增加依賴的對象UserDao和set方法,注意,這裡需要UserService的空構造

public class UserService  {        private String userName;        private UserDao userDao;        public String getUserName() {          return userName;      }        public void setUserName(String userName1) {          this.userName = userName1;      }        public UserDao getUserDao() {          return userDao;      }        public void setUserDao(UserDao userDao) {          this.userDao = userDao;      }        public void serviceTest(){          userDao.test();      }    }

然後是xml配置

<!--必須有空構造-->      <bean class="com.lusaisai.service.UserService" id="userService" >          <property name="userName" value="lusai"></property>          <!--這裡的ref指定下方bean標籤配置對象的id-->          <!--此處name的值與UserService的屬性userDao的set方法名要一致-->          <property name="userDao" ref="userDao"></property>      </bean>        <bean class="com.lusaisai.dao.UserDaoImpl" id="userDao" ></bean>

然後是測試

ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");          UserService userService = (UserService) context.getBean("userService");          System.out.println(userService.getUserName());          userService.serviceTest();

看下結果

 

好了,注入成功

 

3.我們發現一個問題,我們已經在程式碼里寫了UserDao,還有它的set和get方法,為啥還要在xml里用配置告訴spring應該如何注入呢,其實spring提供了自動裝配的功能,如下圖

 我們可以看到default-autowire有5個可供選擇

 

 單獨的bean標籤里也有5個供選擇,這裡截個官網的圖

 

 

下面我們來測試一下,首先是byName,我們把手動裝配注釋掉,添加上default-autowire=”byName”

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xsi:schemaLocation="http://www.springframework.org/schema/beans
        https://www.springframework.org/schema/beans/spring-beans.xsd"
   default-autowire="byName" >

   <!--必須有空構造-->
   <bean class="com.lusaisai.service.UserService" id="userService" >
      <property name="userName" value="lusai"></property>
      <!--這裡的ref指定下方bean標籤配置對象的id-->
      <!--此處name的值與UserService的屬性userDao的set方法名要一致-->
      <!--<property name="userDao" ref="userDao"></property>-->
   </bean>

   <bean class="com.lusaisai.dao.UserDaoImpl" id="userDao" ></bean>

</beans>

UserService中的程式碼沒有改動,測試
ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");          UserService userService = (UserService) context.getBean("userService");          System.out.println(userService.getUserName());          UserDao userDao = userService.getUserDao();          System.out.println(userDao);

看下結果

 

 好的,成功了,我們改一下set方法的名字

public void setUserDao1(UserDao userDao) {          this.userDao = userDao;      }

重新運行一次

 

 

 可以看到,userDao沒有注入進來, 我們把方法名復原再次修改屬性名試一下

private String userName;        private UserDao userDao2;        public String getUserName() {          return userName;      }        public void setUserName(String userName1) {          this.userName = userName1;      }        public UserDao getUserDao() {          return userDao2;      }        public void setUserDao(UserDao userDao) {          this.userDao2 = userDao;      }

重新運行

 

 

 可以看到,注入成功,因此byName的set方法名要和依賴對象的bean標籤的id相同

 

接下來看下byType,我們將default-autowire=”byType” 再加上一個同一個類不同名的bean標籤

<?xml version="1.0" encoding="UTF-8"?>  <beans xmlns="http://www.springframework.org/schema/beans"         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"         xsi:schemaLocation="http://www.springframework.org/schema/beans          https://www.springframework.org/schema/beans/spring-beans.xsd"      default-autowire="byType" >        <!--必須有空構造-->      <bean class="com.lusaisai.service.UserService" id="userService" >          <property name="userName" value="lusai"></property>          <!--這裡的ref指定下方bean標籤配置對象的id-->          <!--此處name的值與UserService的屬性userDao的set方法名要一致-->          <!--<property name="userDao" ref="userDao"></property>-->      </bean>        <bean class="com.lusaisai.dao.UserDaoImpl" id="userDao" ></bean>        <bean class="com.lusaisai.dao.UserDaoImpl" id="userDao2" ></bean>    </beans>

userService程式碼

private String userName;        private UserDao userDao;        public String getUserName() {          return userName;      }        public void setUserName(String userName1) {          this.userName = userName1;      }        public UserDao getUserDao() {          return userDao;      }        public void setUserDao(UserDao userDao) {          this.userDao = userDao;      }

再運行一下結果

十月 17, 2019 11:53:15 下午 org.springframework.context.support.AbstractApplicationContext refresh  警告: Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'userService' defined in class path resource [applicationContext.xml]: Unsatisfied dependency expressed through bean property 'userDao'; nested exception is org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'com.lusaisai.dao.UserDao' available: expected single matching bean but found 2: userDao,userDao2  Exception in thread "main" org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'userService' defined in class path resource [applicationContext.xml]: Unsatisfied dependency expressed through bean property 'userDao'; nested exception is org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'com.lusaisai.dao.UserDao' available: expected single matching bean but found 2: userDao,userDao2      at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireByType(AbstractAutowireCapableBeanFactory.java:1499)      at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1379)      at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:592)      at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:515)      at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:320)      at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)      at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:318)      at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199)      at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:849)      at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:877)      at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:549)      at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:144)      at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:85)      at com.lusaisai.test.Test.main(Test.java:16)  Caused by: org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'com.lusaisai.dao.UserDao' available: expected single matching bean but found 2: userDao,userDao2      at org.springframework.beans.factory.config.DependencyDescriptor.resolveNotUnique(DependencyDescriptor.java:221)      at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1225)      at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1167)      at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireByType(AbstractAutowireCapableBeanFactory.java:1484)      ... 13 more

報錯資訊,顯示只要一個,但找到2個,我們注釋掉一個

<!--<bean class="com.lusaisai.dao.UserDaoImpl" id="userDao" ></bean>-->

重新運行,看下結果

 

 

 注入成功了,說明byType的自動個裝配方式中如果存在多個相同類型不同id的bean標籤，則拋出異常,如果沒有匹配的bean，則不自動裝配

 

最後看下構造方法注入

首先

default-autowire="constructor"

然後在UserService中注釋掉set方法,添加userDao的構造方法

private String userName;        private UserDao userDao;        public UserService(UserDao userDao) {          this.userDao = userDao;      }        public String getUserName() {          return userName;      }        public void setUserName(String userName1) {          this.userName = userName1;      }        public UserDao getUserDao() {          return userDao;      }

,運行,看結果

 

 注入成功了

我們把userDao的構造方法注釋了,再運行看下結果

 

 沒注入成功,但也不報錯

 

好,到此為止,我們的xml配置將對象交給spring管理就講完了總結一下

可以看出,no和Default是不自動裝配的,byName和byType是通過set方法自動裝配的,同時要確保有空構造存在,我猜底層是用newInstance()實現的具體源碼後面再看

byName是根據set方法名自動裝配的,set方法名要和bean標籤的id相對應,否則,注入不成功,但不會報錯

byType是根據類型裝配的,如果存在多個該屬性類型的bean標籤，則拋出異常,如果沒有匹配的bean，則不自動裝配

constructor是根據構造方法來裝配的,如果容器中沒有一個構造函數參數類型的bean，則不自動裝配

 

可以看到這種xml格式其實是非常麻煩的,實際項目中我們一般通過註解來將對象交給spring管理

只需要將spring的配置文件按以下配置即可,加入包掃描,就能將包下的所有對象通過註解方式來注入

<?xml version="1.0" encoding="UTF-8"?>  <beans xmlns="http://www.springframework.org/schema/beans"         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"         xmlns:context="http://www.springframework.org/schema/context"         xsi:schemaLocation="http://www.springframework.org/schema/beans          https://www.springframework.org/schema/beans/spring-beans.xsd          http://www.springframework.org/schema/context           http://www.springframework.org/schema/context/spring-context-3.0.xsd"        >        <context:component-scan base-package="com.lusaisai"></context:component-scan>    </beans>

我們來看例子,注意上面的spring配置文件中一個bean標籤都沒有了,加入了@Component註解,

這裡也可以用@Repository,@Service,@Controller,可以將對象注入到spring容器進行管理,效果是一樣的

@Component  public class UserDaoImpl implements UserDao {      @Override      public void test() {          System.out.println("UserDaoImpl");      }  }

這裡在依賴的對象上加入了@autowire註解,我猜底層是通過filed.set調用的，所以不需要set方法,這個以後看源碼了再講

@Component  public class UserService  {        private String userName="lusai";        @Autowired      private UserDao userDao;        public String getUserName() {          return userName;      }        public void setUserName(String userName1) {          this.userName = userName1;      }        public UserDao getUserDao() {          return userDao;      }    }

當然也可以將註解加在set方法上,如下

@Component
public class UserService  {

    private String userName="lusai";


    private UserDao userDao;

    @Autowired
    public void setUserDao(UserDao userDao) {
        this.userDao = userDao;
    }

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName1) {
        this.userName = userName1;
    }

    public UserDao getUserDao() {
        return userDao;
    }

測試一下

public static void main(String[] args) {            ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");          UserService userService = (UserService) context.getBean("userService");          System.out.println(userService.getUserName());          UserDao userDao = userService.getUserDao();          System.out.println(userDao);        }

看下結果

 

 可以看到,注入成功了

如果我們再給UserDao介面的另一個實現類也交給spring管理,會不會報錯呢?如下

@Component  public class UserDaoImpl2 implements UserDao{      @Override      public void test() {          System.out.println("UserDaoImpl2");      }  }

運行一下看結果

Caused by: org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'com.lusaisai.dao.UserDao' available: expected single matching bean but found 2: userDaoImpl,userDaoImpl2      at org.springframework.beans.factory.config.DependencyDescriptor.resolveNotUnique(DependencyDescriptor.java:221)      at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1225)      at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1167)      at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredMethodElement.inject(AutowiredAnnotationBeanPostProcessor.java:668)      ... 15 more

果然報錯了,說明同一個介面,最好不要寫多個實現類,那我非要寫多個實現類怎麼辦呢

我們可以用@Resource,並指定它的name屬性的別名為類名的首字母小寫,如下

@Component  public class UserService  {        private String userName="lusai";          @Resource(name = "userDaoImpl2")      private UserDao userDao;        public String getUserName() {          return userName;      }        public void setUserName(String userName1) {          this.userName = userName1;      }        public UserDao getUserDao() {          return userDao;      }    }

運行一下,看看結果

 

 成功了

 

總結:先來張網上的圖

 

 @Autowired與@Resource都可以用來裝配bean. 都可以寫在欄位上,或寫在setter方法上。兩者如果都寫在欄位上，那麼就不需要再寫setter方法

@Autowired默認按類型裝配（這個註解是屬業spring的）,需要導入包org.springframework.beans.factory.annotation.Autowired 默認按照類型來進行裝配

@Resource（這個註解屬於java的），需要導入包javax.annotation.Resource。默認按照名稱進行裝配，名稱可以通過name屬性進行指定

 

最後,現在流行用javaconfig而不是xml來配置spring,這裡貼一下javaconfig的程式碼

第一種:相當於寫bean標籤,如下,這裡使用@bean註解 將UserService 和UserDaoImpl對象交給spring管理

@Configuration  public class SpringConfig {        @Bean      public UserService userService(){          return new UserService();      }        @Bean      public UserDao userDao(){          return new UserDaoImpl();      }    }

這裡注入依賴

public class UserService  {        private String userName="lusai";        @Autowired      private UserDao userDao;        public String getUserName() {          return userName;      }        public void setUserName(String userName1) {          this.userName = userName1;      }        public UserDao getUserDao() {          return userDao;      }    }

這是測試demo

public static void main(String[] args) {            AnnotationConfigApplicationContext annotationContext = new AnnotationConfigApplicationContext(SpringConfig.class);          UserService userService = (UserService) annotationContext.getBean("userService");          System.out.println(userService.getUserName());          UserDao userDao = userService.getUserDao();          System.out.println(userDao);        }

看下結果

 

 

第二種:相當於掃描包,把上面的兩個@bean註解注釋了,開啟掃描

@Configuration  @ComponentScan("com.lusaisai")  public class SpringConfig {        /*@Bean      public UserService userService(){          return new UserService();      }        @Bean      public UserDao userDao(){          return new UserDaoImpl();      }*/    }

在UserService 和UserDaoImpl對象上加上@Component,將他們交給spring管理,如下

@Component  public class UserDaoImpl implements UserDao {      @Override      public void test() {          System.out.println("UserDaoImpl");      }  }

@Component  public class UserService  {        private String userName="lusai";        @Autowired      private UserDao userDao;        public String getUserName() {          return userName;      }        public void setUserName(String userName1) {          this.userName = userName1;      }        public UserDao getUserDao() {          return userDao;      }    }

重新測試

 

 可以看到,注入成功了.

最後 @Autowired與@Resource 和xml中的 default-autowire=”byName” 和byType是不是相同的原理的呢

先說結論:兩者不是同一套邏輯,這裡就後面看源碼的時候再來解釋吧

 

VirMach 便宜 VPS

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