050_Servlet詳解

2021 年 3 月 17 日
筆記
060_JavaWeb

Servlet

package com.qing.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

public class HelloServlet extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse response) throws ServletException, IOException {
        //響應的類型：html
        response.setContentType("text/html");
        //響應的編碼
        response.setCharacterEncoding("utf-8");
        //獲取響應的輸出流
        PrintWriter out = response.getWriter();
        out.println("<html>");
        out.println("<head>");
        out.println("<title>Hello World!</title>");
        out.println("</head>");
        out.println("<body>");
        out.println("<h1>Hello World!</h1>");
        out.println("</body>");
        out.println("</html>");
    }
}

<?xml version="1.0" encoding="UTF-8"?>

<web-app xmlns="//xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="//www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="//xmlns.jcp.org/xml/ns/javaee
                      //xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0"
         metadata-complete="true">

    <!--web.xml中配置web的核心應用-->
    <!--註冊Servlet-->
    <servlet>
        <!--名稱，可以隨意寫-->
        <servlet-name>helloServlet</servlet-name>
        <servlet-class>com.qing.servlet.HelloServlet</servlet-class>
    </servlet>
    <!--映射：一個Servlet對應一個mapping-->
    <servlet-mapping>
        <servlet-name>helloServlet</servlet-name>
        <!--請求路徑，可以隨意寫-->
        <url-pattern>/hello</url-pattern>
    </servlet-mapping>
</web-app>

Servlet簡介

Servlet是sun公司開發動態web的一門技術
sun公司在這些API中提供一個接口：Servlet，如果想開發一個Servlet程序，只需要完成兩個步驟
1. 編寫一個類，實現Servlet接口
2. 把開發好的java類部署到web服務器中
我們把實現了Servlet接口的java程序叫做Servlet
Servlet接口sun公司有兩個默認的實現類：HttpServlet和GenericServlet

HelloServlet

構建一個普通maven項目，刪掉src目錄，這個空的工程就是Maven主工程，可以在裏面建立Module；

配置pom.xml，添加依賴；

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

    <groupId>com.qing</groupId>
    <artifactId>javaweb-03-servlet</artifactId>
    <version>1.0-SNAPSHOT</version>

    <dependencies>
        <!-- //mvnrepository.com/artifact/javax.servlet/javax.servlet-api -->
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>4.0.1</version>
        </dependency>
    </dependencies>

</project>

在父工程中新建子模塊Module；

關於父子工程的理解：父項目中的jar包子項目可以直接使用；
1. 父項目中會有
2. 子項目中會有

    <modules>
        <module>servlet-01</module>
    </modules>

    <parent>
        <artifactId>javaweb-03-servlet</artifactId>
        <groupId>com.qing</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>

Maven環境優化：
1. 修改web.xml為最新版本：修改子工程web.xml中的版本；
2. 將maven的結構搭建完整：子工程添加java和resources目錄；

<?xml version="1.0" encoding="UTF-8"?>

<web-app xmlns="//xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="//www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="//xmlns.jcp.org/xml/ns/javaee
                      //xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0"
         metadata-complete="true">
</web-app>

編寫一個Servlet程序；
1. 編寫一個普通類
2. 實現Servlet接口，這裡繼承HttpServlet

package com.qing.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

public class HelloServlet extends HttpServlet {
    //由於get或者post只是請求實現的不同方式，可以相互調用，業務邏輯都一樣
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("進入doGet方法");
        PrintWriter writer = resp.getWriter();//響應流
        writer.print("hello,servlet");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

在web.xml中編寫Servlet的映射

為什麼需要映射？
我們寫的是Java程序，但是要通過瀏覽器訪問，而瀏覽器需要連接web服務器，所以我們需要在web服務中註冊我們寫的Servlet，還需要給他一個瀏覽器可以訪問的路徑

<?xml version="1.0" encoding="UTF-8"?>

<web-app xmlns="//xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="//www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="//xmlns.jcp.org/xml/ns/javaee
                      //xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0"
         metadata-complete="true">

    <!--註冊Servlet-->
    <servlet>
        <servlet-name>helloServlet</servlet-name>
        <servlet-class>com.qing.servlet.HelloServlet</servlet-class>
    </servlet>
    <!--Servlet的請求路徑-->
    <servlet-mapping>
        <servlet-name>helloServlet</servlet-name>
        <url-pattern>/hello</url-pattern>
    </servlet-mapping>
</web-app>

配置Tomcat

啟動測試

Servlet原理

Servlet是由web服務器調用，web服務器收到瀏覽器請求後，會：

servlet-mapping Servlet請求路徑

一個Servlet指定一個映射路徑

    <servlet-mapping>
        <servlet-name>helloServlet</servlet-name>
        <url-pattern>/hello</url-pattern>
    </servlet-mapping>

一個Servlet指定多個映射路徑

    <servlet-mapping>
        <servlet-name>helloServlet</servlet-name>
        <url-pattern>/hello</url-pattern>
    </servlet-mapping>
    <servlet-mapping>
        <servlet-name>helloServlet</servlet-name>
        <url-pattern>/hello1</url-pattern>
    </servlet-mapping>

一個Servlet指定通用映射路徑

    <servlet-mapping>
        <servlet-name>helloServlet</servlet-name>
        <url-pattern>/hello/*</url-pattern>
    </servlet-mapping>

默認請求路徑，會跳過index.jsp，直接進Servlet

    <servlet-mapping>
        <servlet-name>helloServlet</servlet-name>
        <url-pattern>/*</url-pattern>
    </servlet-mapping>

指定後綴

<!--可以自定義後綴實現請求映射，注意：*前面不能加任何字符，否則會報錯-->
<servlet-mapping>
  <servlet-name>helloServlet</servlet-name>
  <url-pattern>*.qing</url-pattern>
</servlet-mapping>

優先級問題：指定固定映射路徑優先級最高，如果找不到就會走默認請求路徑

<!--404-->
<servlet>
  <servlet-name>error</servlet-name>
  <servlet-class>com.qing.servlet.ErrorServlet</servlet-class>
</servlet>
<servlet-mapping>
  <servlet-name>error</servlet-name>
  <url-pattern>/*</url-pattern>
</servlet-mapping>

ServletContext Servlet上下文

web容器在啟動的時候，會為每個web程序都創建一個對應的ServletContext對象，它代表了當前web應用

ServletContext的應用

共享數據：在一個Servlet設置的數據，可以在另一個Servlet獲取到

package com.qing.servlet;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class HelloServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("hello");
        //Servlet上下文
        ServletContext context = this.getServletContext();
        //設置數據
        String username = "清風";
        context.setAttribute("username", username);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

package com.qing.servlet;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class GetServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("get");
        ServletContext context = this.getServletContext();
        String username = (String) context.getAttribute("username");
        System.out.println(username);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

<?xml version="1.0" encoding="UTF-8"?>

<web-app xmlns="//xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="//www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="//xmlns.jcp.org/xml/ns/javaee
                      //xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0"
         metadata-complete="true">

    <servlet>
        <servlet-name>hello</servlet-name>
        <servlet-class>com.qing.servlet.HelloServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>hello</servlet-name>
        <url-pattern>/hello</url-pattern>
    </servlet-mapping>

    <servlet>
        <servlet-name>get</servlet-name>
        <servlet-class>com.qing.servlet.GetServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>get</servlet-name>
        <url-pattern>/get</url-pattern>
    </servlet-mapping>
</web-app>

獲取初始化參數

<?xml version="1.0" encoding="UTF-8"?>

<web-app xmlns="//xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="//www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="//xmlns.jcp.org/xml/ns/javaee
                      //xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0"
         metadata-complete="true">

    <context-param>
        <param-name>url</param-name>
        <param-value>127.0.0.1</param-value>
    </context-param>

    <servlet>
        <servlet-name>get</servlet-name>
        <servlet-class>com.qing.servlet.GetServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>get</servlet-name>
        <url-pattern>/get</url-pattern>
    </servlet-mapping>
</web-app>

package com.qing.servlet;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class GetServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("get");
        ServletContext context = this.getServletContext();
        String url = context.getInitParameter("url");
        resp.getWriter().println(url);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

請求轉發

package com.qing.servlet;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class GetServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("get");
        ServletContext context = this.getServletContext();
        //轉發到/hello
        context.getRequestDispatcher("/hello").forward(req, resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

讀取Properties文件

username=root
password=123456

package com.qing.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;

public class PropertiesServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //獲取流，根路徑為打包後target下的項目名稱
        InputStream in = this.getServletContext().getResourceAsStream("/WEB-INF/classes/db.properties");
        Properties properties = new Properties();
        properties.load(in);
        String user = properties.getProperty("username");
        String pwd = properties.getProperty("password");
        resp.getWriter().print(user + ":" + pwd);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

<?xml version="1.0" encoding="UTF-8"?>

<web-app xmlns="//xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="//www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="//xmlns.jcp.org/xml/ns/javaee
                      //xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0"
         metadata-complete="true">

    <servlet>
        <servlet-name>prop</servlet-name>
        <servlet-class>com.qing.servlet.PropertiesServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>prop</servlet-name>
        <url-pattern>/prop</url-pattern>
    </servlet-mapping>
</web-app>

HttpServletResponse

web服務器接收到瀏覽器的http請求，針對這個請求，分別創建一個代表請求的HttpServletRequest對象和一個代表響應的HttpServletResponse對象
- 如果要獲取瀏覽器請求過來的參數：找HttpServletRequest
- 如果要給瀏覽器響應一下信息：找HttpServletResponse
簡單分類
- 負責向瀏覽器發送數據的方法

ServletOutputStream getOutputStream() throws IOException;
PrintWriter getWriter() throws IOException;

負責向瀏覽器發送響應頭的方法

void setCharacterEncoding(String var1);
void setContentLength(int var1);

響應的狀態碼

int SC_OK = 200;
int SC_CREATED = 201;

常見應用
- 向瀏覽器輸出消息

下載文件

  - 獲取下載文件的路徑
  - 獲取文件名
  - 設置瀏覽器支持下載
     - 文件下載的消息頭和編碼問題 [//www.cnblogs.com/hackxiyu/p/9046247.html](//www.cnblogs.com/hackxiyu/p/9046247.html)

response.setHeader("Content-Disposition", "attachment;filename="+new String(AREA_FILE.getBytes("gb2312"), "ISO-8859-1"));

  - 獲取下載文件的輸入流
  - 創建緩衝區
  - 獲取OutputStream對象
  - 將輸入流寫入buffer緩衝區，使用輸出流將緩衝區中的數據輸出到客戶端

package com.qing.servlet;

import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.FileInputStream;
import java.io.IOException;
import java.net.URLEncoder;

public class FileServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //獲取下載文件的路徑
        String realPath = this.getServletContext().getRealPath("/WEB-INF/classes/靜.jpg");
        System.out.println("下載文件的路徑為：" + realPath);
        //獲取文件名
        String fileName = realPath.substring(realPath.lastIndexOf("\\") + 1);
        System.out.println("文件名為：" + fileName);
        //設置瀏覽器支持下載
        resp.setHeader("Content-Disposition", "attachment;filename=" + URLEncoder.encode(fileName, "UTF-8"));
        //獲取下載文件的輸入流
        FileInputStream fileInputStream = new FileInputStream(realPath);
        //創建緩衝區
        int len = 0;
        byte[] buffer = new byte[1024];
        //獲取OutputStream對象
        ServletOutputStream outputStream = resp.getOutputStream();
        //將輸入流寫入buffer緩衝區，使用輸出流將緩衝區中的數據輸出到客戶端
        while ((len=fileInputStream.read(buffer)) != -1) {
            outputStream.write(buffer, 0, len);
        }
        fileInputStream.close();
        outputStream.close();
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

<?xml version="1.0" encoding="UTF-8"?>

<web-app xmlns="//xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="//www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="//xmlns.jcp.org/xml/ns/javaee
                      //xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0"
         metadata-complete="true">

    <servlet>
        <servlet-name>fileDown</servlet-name>
        <servlet-class>com.qing.servlet.FileServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>fileDown</servlet-name>
        <url-pattern>/fileDown</url-pattern>
    </servlet-mapping>
</web-app>

驗證碼功能

package com.qing.servlet;

import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;

public class ImageServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //設置瀏覽器3秒自動刷新一次
        resp.setHeader("refresh", "3");

        //在內存中創建一個圖片
        BufferedImage image = new BufferedImage(80, 20, BufferedImage.TYPE_INT_RGB);
        //得到畫筆
        Graphics2D g = (Graphics2D) image.getGraphics();
        //設置畫筆顏色，畫矩形背景
        g.setColor(Color.WHITE);
        g.fillRect(0,0,80,20);
        //設置畫筆顏色和字體，畫隨機數
        g.setColor(Color.BLUE);
        g.setFont(new Font(null,Font.BOLD,20));
        g.drawString(makeRandom(),0,20);

        //告訴瀏覽器，這個請求用圖片的方式打開
        resp.setContentType("image/jpeg");
        //網站存在緩存，不讓瀏覽器緩存
        resp.setDateHeader("expires",-1);
        resp.setHeader("Cache-Control","no-cache");
        resp.setHeader("Pragma","no-cache");

        //把圖片寫給瀏覽器
        ImageIO.write(image,"jpg",resp.getOutputStream());
    }

    //生產隨機數
    private String makeRandom() {
        Random random = new Random();
        String num = random.nextInt(9999999) + "";
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < 7 - num.length(); i++) {
            sb.append(0);
        }
        num = sb.toString() + num;
        return num;
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

<?xml version="1.0" encoding="UTF-8"?>

<web-app xmlns="//xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="//www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="//xmlns.jcp.org/xml/ns/javaee
                      //xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0"
         metadata-complete="true">

    <servlet>
        <servlet-name>imageServlet</servlet-name>
        <servlet-class>com.qing.servlet.ImageServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>imageServlet</servlet-name>
        <url-pattern>/image</url-pattern>
    </servlet-mapping>
</web-app>

重定向

一個web資源收到客戶端請求後，他會通知客戶端去訪問另外一個web資源，這個過程叫重定向。

常見場景：用戶登錄

package com.qing.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class RedirectServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        /*
        重定向相當於
        resp.setHeader("Location","/resp/image");
        resp.setStatus(302);
         */
        //重定向
        resp.sendRedirect("/resp/image");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

<?xml version="1.0" encoding="UTF-8"?>

<web-app xmlns="//xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="//www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="//xmlns.jcp.org/xml/ns/javaee
                      //xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0"
         metadata-complete="true">

    <servlet>
        <servlet-name>imageServlet</servlet-name>
        <servlet-class>com.qing.servlet.ImageServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>imageServlet</servlet-name>
        <url-pattern>/image</url-pattern>
    </servlet-mapping>

    <servlet>
        <servlet-name>redirectServlet</servlet-name>
        <servlet-class>com.qing.servlet.RedirectServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>redirectServlet</servlet-name>
        <url-pattern>/redirect</url-pattern>
    </servlet-mapping>
</web-app>

重定向和轉發的區別

相同點
- 頁面都會實現跳轉
不同點
- 請求轉發的時候，URL不會發生變化狀態碼：307
- 重定向的時候，URL會發生變化狀態碼：302

登錄demo

pom.xml添加jsp依賴：javax.servlet.jsp

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

    <groupId>com.qing</groupId>
    <artifactId>javaweb-03-servlet</artifactId>
    <packaging>pom</packaging>
    <version>1.0-SNAPSHOT</version>
    <modules>
        <module>servlet-01</module>
        <module>servlet-02</module>
        <module>response</module>
    </modules>

    <dependencies>
        <!-- //mvnrepository.com/artifact/javax.servlet/javax.servlet-api -->
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>4.0.1</version>
        </dependency>
        <!-- //mvnrepository.com/artifact/javax.servlet.jsp/javax.servlet.jsp-api -->
        <dependency>
            <groupId>javax.servlet.jsp</groupId>
            <artifactId>javax.servlet.jsp-api</artifactId>
            <version>2.3.3</version>
        </dependency>
    </dependencies>

</project>

編輯登錄頁，${pageContext.request.contextPath}代表當前項目

<html>
<body>
<h2>Hello World!</h2>
<%--這裡提交的路徑，需要尋找到項目的路徑--%>
<%--${pageContext.request.contextPath}代表當前項目--%>
<form action="${pageContext.request.contextPath}/login" method="get">
    用戶名：<input type="text" name="username">
    密碼：<input type="password" name="password">
    <input type="submit">
</form>
</body>
</html>

編輯登錄成功頁面

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Success</title>
</head>
<body>
<h1>Success</h1>
</body>
</html>

處理登錄請求，重定向到成功頁面

package com.qing.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class LoginServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("進入登錄請求");
        String username = req.getParameter("username");
        String password = req.getParameter("password");
        System.out.println(username + ":" + password);
        //重定向
        resp.sendRedirect("/resp/success.jsp");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

在web.xml中添加Servlet映射

<?xml version="1.0" encoding="UTF-8"?>

<web-app xmlns="//xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="//www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="//xmlns.jcp.org/xml/ns/javaee
                      //xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0"
         metadata-complete="true">

    <servlet>
        <servlet-name>loginServlet</servlet-name>
        <servlet-class>com.qing.servlet.LoginServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>loginServlet</servlet-name>
        <url-pattern>/login</url-pattern>
    </servlet-mapping>
</web-app>

HttpServletRequest

HttpServletRequest代表客戶端的請求，用戶通過http協議訪問服務器，http請求中的所有信息都會被封裝到HttpServletRequest，通過HttpServletRequest的方法，可以獲得客戶端的所有信息。

獲取瀏覽器傳遞的參數

String contextPath = req.getContextPath();//項目路徑
String servletPath = req.getServletPath();//Servlet路徑
String requestURI = req.getRequestURI();//請求路徑
String name = req.getParameter("name");
String[] names = req.getParameterValues("name");

請求轉發

//請求轉發
//這裡的/代表當前的web應用，即contextPath
req.getRequestDispatcher("/success.jsp").forward(req,resp);

Tags: 060_JavaWeb

050_Servlet詳解

Servlet

Servlet簡介

HelloServlet

Servlet原理

servlet-mapping Servlet請求路徑

ServletContext Servlet上下文

ServletContext的應用

共享數據：在一個Servlet設置的數據，可以在另一個Servlet獲取到

獲取初始化參數

請求轉發

讀取Properties文件

HttpServletResponse

下載文件

驗證碼功能

重定向

重定向和轉發的區別

登錄demo

HttpServletRequest

獲取瀏覽器傳遞的參數

請求轉發

VirMach 便宜 VPS

QNews

050_Servlet詳解

Servlet

Servlet簡介

HelloServlet

Servlet原理

servlet-mapping Servlet請求路徑

ServletContext Servlet上下文

ServletContext的應用

共享數據：在一個Servlet設置的數據，可以在另一個Servlet獲取到

獲取初始化參數

請求轉發

讀取Properties文件

HttpServletResponse

下載文件

驗證碼功能

重定向

重定向和轉發的區別

登錄demo

HttpServletRequest

獲取瀏覽器傳遞的參數

請求轉發

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