JavaWeb之Servlet（二）HttpServletResponse

一、HttpServletResponse概述

我们在创建Servlet时会覆盖service()方法，或doGet()/doPost(),这些方法都有两个参数，一个为代表请求的request和代表响应response。
service方法中的response的类型是ServletResponse，而doGet/doPost方法的response的类型是HttpServletResponse，HttpServletResponse是ServletResponse的子接口，功能和方法更加强大

二、response的运行流程

三、通过抓包工具抓取Http响应

因为response代表响应，所以我们可以通过该对象分别设置Http响应的响应行，响应头和响应体

四、通过response设置响应行中的状态码

设置响应行的状态码
setStatus(int sc)

package com.itheima.line;import java.io.IOException;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;public class StatusServlet extends HttpServlet {protected void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {//手动设置http响应行中的状态码response.setStatus(404);}protected void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}

五、通过response设置响应头

addHeader(String name, String value) 
addIntHeader(String name, int value) 
addDateHeader(String name, long date) 
setHeader(String name, String value) 
setDateHeader(String name, long date) 
setIntHeader(String name, int value)


其中，add表示添加，而set表示设置

package com.itheima.header;import java.io.IOException;import java.util.Date;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;public class HeaderServlet extends HttpServlet {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", 28);//response.addDateHeader("birthday", date.getTime());response.addHeader("name", "lisi");response.setHeader("age", "28");response.setHeader("age", "50");}protected void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}

重定向：

package com.itheima.header;import java.io.IOException;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;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到servlet2//1、设置状态码302//response.setStatus(302);//2、设置响应头Location//response.setHeader("Location", "/WEB14/servlet2");//封装成一个重定向的方法sendRedirect(url)response.sendRedirect("/WEB14/servlet2");}protected void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}

package com.itheima.header;import java.io.IOException;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;public class Servlet2 extends HttpServlet {protected void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {response.getWriter().write("hello haohao...");}protected void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}

设置定时刷新的头：

package com.itheima.header;import java.io.IOException;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;public class RefreshServlet extends HttpServlet {protected void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {//设置定时刷新的头response.setHeader("refresh", "5;url=http://www.baidu.com");}protected void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}

六、通过response设置响应体

(1)响应体设置文本
PrintWriter getWriter()
获得字符流，通过字符流的write(String s)方法可以将字符串设置到response 缓冲区中，随后Tomcat会将response缓冲区中的内容组装成Http响应返回给浏览 器端。


关于设置中文的乱码问题
原因：response缓冲区的默认编码是iso8859-1，此码表中没有中文，可以通过 response的setCharacterEncoding(String charset) 设置response的编码


但我们发现客户端还是不能正常显示文字
原因：我们将response缓冲区的编码设置成UTF-8，但浏览器的默认编码是本地系统的编码，因为我们都是中文系统，所以客户端浏览器的默认编码是GBK，我们可以手动修改浏览器的编码是UTF-8。


我们还可以在代码中指定浏览器解析页面的编码方式，
通过response的setContentType(String type)方法指定页面解析时的编码是UTF-8
response.setContentType("text/html;charset=UTF-8");


上面的代码不仅可以指定浏览器解析页面时的编码，同时也内含setCharacterEncoding的功能，所以在实际开发中只要编写response.setContentType("text/html;charset=UTF-8");就可以解决页面输出中文乱码问题。


(2)响应头设置字节
ServletOutputStream  getOutputStream()
获得字节流，通过该字节流的write(byte[] bytes)可以向response缓冲区中写入字节，在由Tomcat服务器将字节内容组成Http响应返回给浏览器。

七、案例-完成文件下载

<!DOCTYPE html><html><head><meta charset="UTF-8"><title>Insert title here</title></head><body><h1>使用a标签直接指向服务器上的资源</h1><a href="/web14_response/download/a.flv">a.flv</a><br><a href="/web14_response/download/a.jpg">a.jpg</a><br><a href="/web14_response/download/a.mp3">a.mp3</a><br><a href="/web14_response/download/a.mp4">a.mp4</a><br><a href="/web14_response/download/a.txt">a.txt</a><br><a href="/web14_response/download/a.zip">a.zip</a><br><h1>使用服务端编码的方式实现文件下载</h1><a href="/web14_response/DownloadServlet?filename=a.flv">a.flv</a><br><a href="/web14_response/DownloadServlet?filename=a.jpg">a.jpg</a><br><a href="/web14_response/DownloadServlet?filename=a.mp3">a.mp3</a><br><a href="/web14_response/DownloadServlet?filename=a.mp4">a.mp4</a><br><a href="/web14_response/DownloadServlet?filename=a.txt">a.txt</a><br><a href="/web14_response/DownloadServlet?filename=a.zip">a.zip</a><br></body></html>

package com.sh.content;import java.io.FileInputStream;import java.io.IOException;import java.io.InputStream;import javax.servlet.Servlet;import javax.servlet.ServletException;import javax.servlet.ServletOutputStream;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;public class DownloadServlet extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {//获得要下载文件按的名称String filename = request.getParameter("filename");//要下载这个文件的类型---------客户端通过文件的MIME类型去区分文件类型response.setContentType(this.getServletContext().getMimeType(filename));//告诉客户端该文件不是直接解析，而是以附件的形式打开（打开）response.setHeader("Content-Disposition", "attachment;filename="+filename);//获得文件的绝对路径String path = this.getServletContext().getRealPath("download/"+filename);//获得该文件的输入流InputStream is = new FileInputStream(path);//获得输出流----通过response获得输出流 用于向客户端写内容ServletOutputStream sos = response.getOutputStream();//文件拷贝的模板int len = 0;byte[] buf = new byte[1024];while((len=is.read(buf))!=-1) {sos.write(buf, 0, len);}is.close();sos.close();}public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {doGet(request, response);}}