一、前言
web服务器接收到客户端的http请求,就会针对这个请求,分别创建一个代表请求的HttpServletRequest对象,代表响应的HttpServletResponse对象。
- 如果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
二、HttpServletResponse
1.首先我们通过查看该接口的源码,我们先将其中的方法简单分类:
- 负责想浏览器发送数据的方法:
ServletOutputStream getOutputStream() throws IOException;
PrintWriter getWriter() throws IOException;
- 负责向浏览器发送响应头的方法:
void setCharacterEncoding(String var1);
void setContentLength(int var1);
void setContentLengthLong(long var1);
void setContentType(String 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);
- 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;
2.常见应用:
- 向浏览器输出消息(通过响应对象调用方法得到流对象,向浏览器输出内容,不做过多解释很简单)
- 下载文件(重点)
步骤如下:
1.要获取下载文件的路径
2.下载的文件名字是什么
3.设置想办法让浏览器能够支持下载我们需要的东西
4.获取下载文件的输入流
5.创建缓冲区
6.获取OutputStream对象
7.将FileOutputStream流写入到缓冲区,使用OutputStream将缓冲区中的数据输出到客户端
注意:我们这次下载的对象是一张图片,图片名字为:1.png
这段代码的关键就是:resp.setHeader("Content-Disposition","attachment;filename=" + fileName);
代码展示如下:
package com.xu.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;
public class FileServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//1.要获取下载文件的路径
String realPath = "D:\\IdeaProjects\\untitled11\\untitled\\untitled11\\javaweb-servlet\\response\\target\\classes\\1.png";
System.out.println("下载文件的路径为:" + realPath);
//2.下载的文件名字是什么
String fileName = realPath.substring(realPath.lastIndexOf("//") + 1);
//3.设置想办法让浏览器能够支持(Content-Disposition)下载我们需要的东西
resp.setHeader("Content-Disposition","attachment;filename=" + fileName);
//4.获取下载文件的输入流
FileInputStream in = new FileInputStream(realPath);
//5.创建缓冲区
int len = 0;
byte[] buffer = new byte[1024];
//6.获取OutputStream对象
ServletOutputStream out = resp.getOutputStream();
//7.将FileOutputStream流写入到缓冲区,使用OutputStream将缓冲区中的数据输出到客户端
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);
}
}
我们在web.xml中配置url-pattern访问路径后访问该资源会得到下载页面: