JavaWeb 核心之 Response

简述：

HttpServletResponse是用于将Servlet处理好的内容发送给浏览器的类，服务器通过对HttpServletResponse对象中的内容进行截取、拼接就能获得一个完整的HTTP响应信息。

一、完成文件下载（文件拷贝）

二、生成验证码（了解其中原理，验证码图片生成的代码不用写）

1、设置 http 响应行的状态码

setStatus(int sc);

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

//1、手动设置 http 响应行的状态码

response.setStatus(404);

}

效果：

2、设置 http 响应头

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

Date date = new Date();

// 设置响应头

response.addHeader("name", "zhangsan");

response.addIntHeader("age", 20);

response.addDateHeader("birthday", date.getTime());

}

效果：

重定向：（状态码 302）

代码实现

Servlet1:

package com.ma.header;

import java.io.IOException;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

/**

* Servlet implementation class Servlet1

public class Servlet1 extends HttpServlet {

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

// 没有响应告知客户端去重定向 Servlet2

// 1、设置状态码

response.setStatus(302);

// 2、设置响应头 Location

response.setHeader("Location", "/WEB14/servlet2");

}

/**

* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

// TODO Auto-generated method stub

}

Servlet2:

package com.ma.header;

import java.io.IOException;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

/**

* Servlet implementation class Servlet2

public class Servlet2 extends HttpServlet {

private static final long serialVersionUID = 1L;

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

// 重定向的页面

response.getWriter().write("Servlet2 ! ! !");

}

/**

* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

// TODO Auto-generated method stub

}

重定向到 Servlet2:

封装的方法：

//封装成重定向方法

response.sendRedirect("/WEB14/servlet2");

页面跳转的方法：

// 设置定时刷新的头

response.setHeader("refresh", "5;url=http://baidu.com");

向客户端写内容：

package com.ma.header;

import java.io.FileInputStream;

import java.io.IOException;

import java.io.InputStream;

import javax.servlet.ServletException;

import javax.servlet.ServletOutputStream;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

/**

* Servlet implementation class ByteServlet

public class ByteServlet extends HttpServlet {

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

//使用 response 获得字节输出流

ServletOutputStream out = response.getOutputStream();

//获得服务器上的图片

String realpath = this.getServletContext().getRealPath("a.jpg");

InputStream in = new FileInputStream(realpath);

int len = 0;

byte[] buffer = new byte[1024];

while((len = in.read(buffer)) > 0){

out.write(buffer, 0, len);

}

in.close();

out.close();

}

/**

* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

// TODO Auto-generated method stub

}

案例一：完成文件下载

问题：1）什么时候会文件下载？

浏览器不能解析的文件就会下载

2）什么情况下需要在服务器端编写文件下载的代码？

1、使用 a 标签直接直接指向文件

代码一：

<!DOCTYPE html>

<html>

<head>

<title>Insert title here</title>

</head>

<body>

<h1>使用 a 标签直接服务器的资源</h1>

</body>

</html>

2、使用服务端编写代码

<!DOCTYPE html>

<html>

<head>

<title>Insert title here</title>

</head>

<body>

<h1>使用 a 标签直接服务器的资源</h1>

<h1>使用服务器端编码的方式实现文件的下载</h1>

</body>

</html>

代码二：

package com.ma.header;

import java.io.FileInputStream;

import java.io.IOException;

import java.io.InputStream;

import javax.servlet.ServletException;

import javax.servlet.ServletOutputStream;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

/**

* Servlet implementation class DownloadServlet

public class DownloadServlet extends HttpServlet {

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

//获得要下载的文件的名称

String filename = request.getParameter("filename");//a.flv

//获取文件的绝对路径

String path = this.getServletContext().getRealPath("download/"+filename);

//获得文件的输入流

InputStream in = new FileInputStream(path);

//获得输出流向客户端写内容

ServletOutputStream out = response.getOutputStream();

//文件拷贝的模板代码

int len = 0;

byte[] buffer = new byte[1024];

while((len = in.read(buffer)) > 0){

out.write(buffer, 0, len);

}

out.close();

in.close();

}

/**

* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

// TODO Auto-generated method stub

}

JavaWeb 核心之 Response

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