Servlet

# Servlet

1.1Servlet简介

Servlet接口Sun公司有俩个默认实现类

  • Servlet就是sun公司开发动态web的一门技术

  • Sun在这些API中提供一个接口叫做：Servlet，如果你想开发一个Servlet程序，只需要完成以下俩步

    • 编写一个类，实现Servlet接口
    • 把开发好的Java类部署到web服务器中

把实现好的Servlet接口的Java程序叫做：Servlet

1.2 HelloServlet

(1)构建一个普通的Maven项目，删掉src目录，以后就在这个项目里建立Module；这个空的工程就是Maven主工程；

(2)关于Maven父子工程的理解

父项目pom.xml会有

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

子项目pom.xml会有

    <parent>
        <artifactId>javaweb-02-servlet</artifactId>
        <groupId>com.peng</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>

父项目中的jar包java子项目可以直接使用

(3)Maven环境优化

  • 修改web.xml为最新的

  • 将maven的结构搭建完整

(4)编写一个servlet程序

  • 编写一个普通类
  • 实现Servlet接口，这里我们直接继承HttpServlet
public class HelloServlet extends HttpServlet {
    //由于get或者post只是请求实现的不同方式，可以相互调用，业务逻辑都一样
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
       /*
        super.doGet(req, resp);
        */
        PrintWriter writer = resp.getWriter();
        writer.print("Hello,Servlet");
    }

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

(5)编写Servlet的映射

为什么需要映射：我们写的是Java程序，但是需要通过浏览器访问

，而浏览器需要连接web服务器，所以我们需要再web服务器中注册我们写的Servlet，还需要给他一个浏览器能够访问的路径

配置web.xml：

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

(6)配置Tomcat

image-20220114143523103

image-20220114143541125

(7)启动测试

image-20220114144535898

1.3.Servlet原理

Servlet是由Web服务器调用，web服务器在收到浏览器请求之后，会：

image-20220114145252471

1.4Maping问题

(1)一个Servlet可以指定一个映射路径

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

(2)一个Servlet可以指定多个映射路径

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

(3)一个Servlet可以指定通用映射路径

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

(4)默认请求路径

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

(5)指定一些后缀或者前缀等等...

<servlet-mapping>
  <servlet-name>hello</servlet-name>
  <!--*前不能加项目映射路径-->
  <url-pattern>*peng</url-pattern>
</servlet-mapping>

(5)优先级问题

指定了固有的隐射路径优先级最高，如果找不到就会走默认的处理请求

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

1.5 ServletContext

web容器在启动的时候，它会为每个web程序都创建一个对应的ServeletContext对象，它代表当前的web应用；

1.5.1共享数据

我们在这个Servlet保存的数据，可以在另外一个Servlet中拿到

HttpServlet

  public class GetServlet extends HttpServlet {
      @Override
      protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
          ServletContext context = this.getServletContext();
          String username = (String) context.getAttribute("username");
  
          resp.setContentType("text/html");
          resp.setCharacterEncoding("utf-8");
          resp.getWriter().print("名字：" + username);
      }
  
      @Override
      protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
          doGet(req, resp);
      }
  }

HttpServlet

public class HelloServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //System.out.println("Hello");
        ServletContext context = this.getServletContext();

        String username = "peng";
        context.setAttribute("username",username);
    }

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

web.xml

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

  <servlet>
    <servlet-name>getc</servlet-name>
    <servlet-class>com.peng.servlet.GetServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>getc</servlet-name>
    <url-pattern>/getc</url-pattern>
  </servlet-mapping>

结果

先访问hello，在访问getc

image-20220114154045443

1.5.2 获取初始化参数

web.xml

<context-param>
  <param-name>url</param-name>
  <param-value>jdbc:mysql://localhost:3306/mybaties</param-value>
</context-param>

<servlet>
  <servlet-name>gp</servlet-name>
  <servlet-class>com.peng.servlet.ServletDemo03</servlet-class>
</servlet>
<servlet-mapping>
  <servlet-name>gp</servlet-name>
  <url-pattern>/gp</url-pattern>
</servlet-mapping>

ServletDemo03

public class ServletDemo03  extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext context = this.getServletContext();
        String url = context.getInitParameter("url");
        resp.getWriter().print(url);
    }

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

1.5.3 请求转发

web.xml

<servlet>
  <servlet-name>sd4</servlet-name>
  <servlet-class>com.peng.servlet.ServletDemo04</servlet-class>
</servlet>
<servlet-mapping>
  <servlet-name>sd4</servlet-name>
  <url-pattern>/sd4</url-pattern>
</servlet-mapping>

ServletDemo04

public class ServletDemo04  extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext context = this.getServletContext();

        //转发的请求路径
        //RequestDispatcher requestDispatcher = context.getRequestDispatcher("/.gp");
        //调用forward实现请求转发
        //requestDispatcher.forward(req, resp);
        System.out.println("进入了ServletDemo04...");
        context.getRequestDispatcher("/gp").forward(req, resp);
    }

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

结果

image-20220114155834716

1.5.4读取资源文件

web.xml

<servlet>
  <servlet-name>sd5</servlet-name>
  <servlet-class>com.peng.servlet.ServletDemo05</servlet-class>
</servlet>
<servlet-mapping>
  <servlet-name>sd5</servlet-name>
  <url-pattern>/sd5</url-pattern>
</servlet-mapping>

ServletDemo05

public class ServletDemo05  extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext context = this.getServletContext();

        //InputStream is = this.getServletContext().getResourceAsStream("/WEB-INF/classes/db.properties");
        InputStream is = this.getServletContext().getResourceAsStream("/WEB-INF/classes/com/peng/servlet/aa.properties");
        Properties prop = new Properties();
        prop.load(is);
        String user = prop.getProperty("username");
        String pwd = prop.getProperty("password");

        resp.getWriter().print(user + ":" + pwd);

    }

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

结果

image-20220114161751072

1.6 HttpServletResponse

web服务器接收到客户端的http请求，针对这个请求，分别创建一个代表请求的HttpServletRequest对象，代表响应的HttpServletResponse；

  • 如果要获取客户端请求过来的参数：HttpServletRequest
  • 如果要给客户端响应一些信息：HttpServletResponse

1.6.1简单分类

负责向浏览器发送数据的方法

image-20220114170654725

负责向浏览器发送响应头的方法

image-20220114170904298

响应的状态码

int SC_CONTINUE = 100;
int SC_SWITCHING_PROTOCOLS = 101;
int SC_OK = 200;
int SC_CREATED = 201;
int SC_ACCEPTED = 202;
int SC_NON_AUTHORITATIVE_INFORMATION = 203;
int SC_NO_CONTENT = 204;
int SC_RESET_CONTENT = 205;
int SC_PARTIAL_CONTENT = 206;
int SC_MULTIPLE_CHOICES = 300;
int SC_MOVED_PERMANENTLY = 301;
int SC_MOVED_TEMPORARILY = 302;
int SC_FOUND = 302;
int SC_SEE_OTHER = 303;
int SC_NOT_MODIFIED = 304;
int SC_USE_PROXY = 305;
int SC_TEMPORARY_REDIRECT = 307;
int SC_BAD_REQUEST = 400;
int SC_UNAUTHORIZED = 401;
int SC_PAYMENT_REQUIRED = 402;
int SC_FORBIDDEN = 403;
int SC_NOT_FOUND = 404;
int SC_METHOD_NOT_ALLOWED = 405;
int SC_NOT_ACCEPTABLE = 406;
int SC_PROXY_AUTHENTICATION_REQUIRED = 407;
int SC_REQUEST_TIMEOUT = 408;
int SC_CONFLICT = 409;
int SC_GONE = 410;
int SC_LENGTH_REQUIRED = 411;
int SC_PRECONDITION_FAILED = 412;
int SC_REQUEST_ENTITY_TOO_LARGE = 413;
int SC_REQUEST_URI_TOO_LONG = 414;
int SC_UNSUPPORTED_MEDIA_TYPE = 415;
int SC_REQUESTED_RANGE_NOT_SATISFIABLE = 416;
int SC_EXPECTATION_FAILED = 417;
int SC_INTERNAL_SERVER_ERROR = 500;
int SC_NOT_IMPLEMENTED = 501;
int SC_BAD_GATEWAY = 502;
int SC_SERVICE_UNAVAILABLE = 503;
int SC_GATEWAY_TIMEOUT = 504;
int SC_HTTP_VERSION_NOT_SUPPORTED = 505;

1.6.2 常见应用

(1)向浏览器输出消息

(2)下载文件

  • 获取下载文件的路径
  • 下载的文件名
  • 设置浏览器可以下载我们需要的东西
  • 获取下载的文件流
  • 创建缓冲区
  • 获取OutputStream
  • 将FileOutputStream流写入到buffer缓冲区
  • 使用OutputStream将缓冲区中数据输出到客户端
public class FileServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //获取下载文件的路径
        //String realPath = this.getServletContext().getRealPath("/1.png");
        String realPath = "E:\\Data\\Java\\code\\javaweb-02-servlet\\response\\target\\classes\\1.png";
        System.out.println("下载的文件路径：" + realPath);
        //下载的文件名
        String fileName = realPath.substring(realPath.indexOf("\\") + 1);
        //设置浏览器可以下载我们需要的东西
        resp.setHeader("Content-Disposition", "attachment;filename=" + URLEncoder.encode(fileName,"UTF-8") );
        //获取下载的文件流
        FileInputStream in = new FileInputStream(realPath);
        //创建缓冲区
        int len = 0;
        byte[] buffer = new byte[1024];
        //获取OutputStream
        ServletOutputStream out = resp.getOutputStream();
        //将FileOutputStream流写入到buffer缓冲区
        //使用OutputStream将缓冲区中数据输出到客户端\
        while ((len = in.read(buffer)) > 0) {
            out.write(buffer, 0, len);
        }

        in.close();
        out.close();
    }

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

1.6.3 验证码下载

web.xml

<servlet>
  <servlet-name>ImageServlet</servlet-name>
  <servlet-class>com.peng.servlet.ImageServlet</servlet-class>
</servlet>
<servlet-mapping>
  <servlet-name>ImageServlet</servlet-name>
  <url-pattern>/ImageServlet</url-pattern>
</servlet-mapping>

ImageServlet

public class ImageServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //浏览器3s自动刷新一次
        resp.setHeader("refresh", "3");

        //在内存中创建一个图片
        BufferedImage image = new BufferedImage(80, 20, BufferedImage.TYPE_INT_RGB);
        //得到图片
        Graphics2D g = (Graphics2D) image.getGraphics();
        //设置图片背景色
        g.setColor(Color.white);
        g.fillRect(0, 0, 80, 20);
        //给图片写数据
        g.setColor(Color.BLUE);
        g.setFont(new Font(null, Font.BOLD, 20));
        g.drawString(makeNum(), 0, 20);

        //让浏览器请求以图片打开
        resp.setContentType("image/jpeg");
        //网站存在缓存，不让浏览器缓存
        resp.setDateHeader("expires", -1);
        resp.setHeader("Cache-Control", "no-cache");
        resp.setHeader("Pragma", "no-cache");

        ImageIO.write(image, "jpeg", resp.getOutputStream());
    }

    private String makeNum() {
        Random random = new Random();
        String num = random.nextInt(9999999) + "";
        StringBuffer sb = new StringBuffer();
        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);
    }
}

结果

image-20220114175955258

1.6.4实现重定向

一个web资源收到客户端请求，他会通知客户端去访问另外一个web资源，这个过程叫做重定向

常见场景：

  • 用户登录
void sendRedirect(String var1) throws IOException;

protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    /*
     resp.setHeader("Location","/r/img");
     resp.setStatus(302);
     */
    //重定向
    resp.sendRedirect("/r/img");
}

1.6.5重定向和转发的区别？

相同点：

  • 页面都会实现跳转

不同点

  • 请求转发的时候，url不会产生变化；307
  • 重定向的时候，url地址栏会发生变化；302

1.7HttpServletRequest

HttpServletRequest代表客户端的请求，用户通过Http协议访问服务器，HTTP请求中所有的信息会被封装到HttpServletRequest，通过HttpServletRequest方法，获得客户端的所以信息。

1.7.1获取前端传递的参数

index.jsp

<%--
  Created by IntelliJ IDEA.
  User: Peng
  Date: 2022/1/14
  Time: 20:48
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>登录</title>
</head>
<body>
<div>
<form action="/login" method="post">
     用户名：<input type="text" name="username"> <br>
     密  码：<input type="password" name="password"> <br>
     爱好：
    <input type="checkbox" name="hobbys" value="女孩">女孩
    <input type="checkbox" name="hobbys" value="代码">代码
    <input type="checkbox" name="hobbys" value="唱歌">唱歌
    <input type="checkbox" name="hobbys" value="电影">电影
    <br>
    <input type="submit">
</form>
</div>
</body>
</html>

HttpServlet

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

        req.setCharacterEncoding("utf-8");
        resp.setCharacterEncoding("utf-8");

        String username = req.getParameter("username");
        String password = req.getParameter("password");
        String[] hobbys = req.getParameterValues("hobbys");
        System.out.println("========================");
        System.out.println(username);
        System.out.println(password);
        System.out.println(Arrays.toString(hobbys));
        System.out.println("========================");

        //resp.sendRedirect("");
        //通过请求转发
        //这里的 / 代表当前应用
        req.getRequestDispatcher(req.getContextPath()+"/success.jsp").forward(req, resp);

    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}
posted @   peng_boke  阅读(35)  评论(0)  编辑  收藏  举报
相关博文：
· Asp.Net Core Middleware(中间件)
· Java Filter(过滤器)和Listener(监听器)
· Servlet
· Servlet详解
· Servlet
阅读排行：
· 阿里最新开源QwQ-32B，效果媲美deepseek-r1满血版，部署成本又又又降低了！
· AI编程工具终极对决：字节Trae VS Cursor，谁才是开发者新宠？
· 开源Multi-agent AI智能体框架aevatar.ai，欢迎大家贡献代码
· Manus重磅发布：全球首款通用AI代理技术深度解析与实战指南
· 被坑几百块钱后，我竟然真的恢复了删除的微信聊天记录！
点击右上角即可分享
微信分享提示
AI IDE Trae