JavaWeb-request和response

web服务器接收到客户端的http请求，分别创建一个代表请求的HttpServletRequest对象，代表响应的一个HttpServletResponse。

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

Response

向浏览器发送数据

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

设置响应头

void setCharacterEncoding(String var1);
void setContentLength(int var1);
void setContentLengthLong(long var1);
void setContentType(String var1);
void setBufferSize(int var1);
void setDateHeader(String var1, long var2);
void addDateHeader(String var1, long var2);
void setHeader(String var1, String var2);
void addHeader(String var1, String var2);
void setIntHeader(String var1, int var2);
void addIntHeader(String var1, int var2);

设置状态码

void setStatus(int var1);

文件下载

Demo1

package com.th0r.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 Demo1 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //获取文件信息和文件名
        String dir = "E:\\static\\img\\1.jpg";
        String fileName = dir.substring(dir.lastIndexOf("\\")+1);
        resp.setHeader("content-disposition", "attachment;filename=" + URLEncoder.encode(fileName, "UTF-8"));

        //将文件写入流
        FileInputStream fis = new FileInputStream(dir);
        ServletOutputStream os = resp.getOutputStream();
        int len;
        byte[] bys = new byte[1024];
        while ((len=fis.read(bys)) != -1){
            os.write(bys, 0, len);
        }

        //关闭流
        fis.close();
        os.close();
    }

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

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="4.0"
         xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
        	        http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         metadata-complete="true">
    
    <servlet>
        <servlet-name>download</servlet-name>
        <servlet-class>com.th0r.servlet.Demo1</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>download</servlet-name>
        <url-pattern>/download</url-pattern>
    </servlet-mapping>
</web-app>

访问 localhost:8080/test3_war/download

验证码生成

Demo2

package com.th0r.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 Demo2 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setHeader("refresh", "5");

        //创建图片
        BufferedImage img = new BufferedImage(80, 20, BufferedImage.TYPE_INT_RGB);
        Graphics2D g = img.createGraphics();
        g.setColor(Color.blue);
        g.fillRect(0,0,40,20);
        g.setColor(Color.gray);
        g.setFont(new Font(null, Font.BOLD, 18));
        g.drawString(getNum(), 0, 20);

        //设置响应头 刷新不缓存
        resp.setContentType("image/png");
        resp.setDateHeader("expires", -1);
        resp.setHeader("Cache-Control", "no-cache");
        resp.setHeader("pragma", "no-cache");

        ImageIO.write(img, "png", resp.getOutputStream());
    }

    //生成随机数
    private String getNum(){
        Random random1 = new Random();
        Random random2 = new Random();
        String num1 = random1.nextInt(9999)+"";
        String num2 = random2.nextInt(9)+"";
        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < 4-num1.length(); i++) {
            sb.append(num2);
        }
        num1 = num1 + sb.toString();
        return num1;
    }

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

web.xml

    <servlet>
        <servlet-name>img</servlet-name>
        <servlet-class>com.th0r.servlet.Demo2</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>img</servlet-name>
        <url-pattern>/img</url-pattern>
    </servlet-mapping>

重定向

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

package com.th0r.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 Demo3 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.sendRedirect("/test3_war/img");
        /**
        resp.setStatus(302);
        resp.setHeader("Location", "/test3_war/img");
         **/
    }

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

Request

HttpServletRequest代表客户端的请求，用户通过Http协议访问服务器，HTTP请求中的所有信息会被封装到HttpServletRequest，通过这个HttpServletRequest的方法，获得客户端的所有信息。

登录

index.jsp

<%@page pageEncoding="UTF-8" %>
<html>
<body>
<h2>Hello World!</h2>

<form action="${pageContext.request.contextPath}/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="hobbies" value="唱">唱
    <input type="checkbox" name="hobbies" value="跳">跳
    <input type="checkbox" name="hobbies" value="rap">rap
    <input type="checkbox" name="hobbies" value="篮球">篮球
    <br>
    <input type="submit">
</form>

</body>
</html>

Demo4.java

package com.th0r.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.util.Arrays;

public class Demo4 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("UTF-8");
        String username = req.getParameter("username");
        String password = req.getParameter("password");
        String[] hobbies = req.getParameterValues("hobbies");

        if(username.equals("root") && password.equals("123456")){
            System.out.println(username + "hobbies: " + Arrays.toString(hobbies));

            //请求转发
            req.getRequestDispatcher("/success.jsp").forward(req, resp);
        }
        else {
            resp.sendRedirect("/test3_war/index.jsp");
        }
    }

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