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HttpServletResponse对象，一个代表响应的HttpServletResponse对象；

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

1、简单分类

负责向浏览器发送数据的方法

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

负责向浏览器**发送响应头（encoding…）**的方法

void setCharacterEncoding(String charset);
void setContentLength(int len);
void setContentLengthLong(long length);
void setContentType(String type);
void setDateHeader(String name, long date);
void addDateHeader(String name, long date);
void setHeader(String name, String value);
void addHeader(String name, String value);
void setIntHeader(String name, int value);
void addIntHeader(String name, int value);

响应的状态码

/*** Status code (100) indicating the client can continue.*/public static final int SC_CONTINUE = 100;/*** Status code (101) indicating the server is switching protocols according* to Upgrade header.*/public static final int SC_SWITCHING_PROTOCOLS = 101;/*** Status code (200) indicating the request succeeded normally.*/public static final int SC_OK = 200;/*** Status code (201) indicating the request succeeded and created a new* resource on the server.*/public static final int SC_CREATED = 201;/*** Status code (202) indicating that a request was accepted for processing,* but was not completed.*/public static final int SC_ACCEPTED = 202;/*** Status code (203) indicating that the meta information presented by the* client did not originate from the server.*/public static final int SC_NON_AUTHORITATIVE_INFORMATION = 203;/*** Status code (204) indicating that the request succeeded but that there* was no new information to return.*/public static final int SC_NO_CONTENT = 204;/*** Status code (205) indicating that the agent <em>SHOULD</em> reset the* document view which caused the request to be sent.*/public static final int SC_RESET_CONTENT = 205;/*** Status code (206) indicating that the server has fulfilled the partial* GET request for the resource.*/public static final int SC_PARTIAL_CONTENT = 206;/*** Status code (300) indicating that the requested resource corresponds to* any one of a set of representations, each with its own specific location.*/public static final int SC_MULTIPLE_CHOICES = 300;/*** Status code (301) indicating that the resource has permanently moved to a* new location, and that future references should use a new URI with their* requests.*/public static final int SC_MOVED_PERMANENTLY = 301;/*** Status code (302) indicating that the resource has temporarily moved to* another location, but that future references should still use the* original URI to access the resource. This definition is being retained* for backwards compatibility. SC_FOUND is now the preferred definition.*/public static final int SC_MOVED_TEMPORARILY = 302;/*** Status code (302) indicating that the resource reside temporarily under a* different URI. Since the redirection might be altered on occasion, the* client should continue to use the Request-URI for future* requests.(HTTP/1.1) To represent the status code (302), it is recommended* to use this variable.*/public static final int SC_FOUND = 302;/*** Status code (303) indicating that the response to the request can be* found under a different URI.*/public static final int SC_SEE_OTHER = 303;/*** Status code (304) indicating that a conditional GET operation found that* the resource was available and not modified.*/public static final int SC_NOT_MODIFIED = 304;/*** Status code (305) indicating that the requested resource <em>MUST</em> be* accessed through the proxy given by the <code><em>Location</em></code>* field.*/public static final int SC_USE_PROXY = 305;/*** Status code (307) indicating that the requested resource resides* temporarily under a different URI. The temporary URI <em>SHOULD</em> be* given by the <code><em>Location</em></code> field in the response.*/public static final int SC_TEMPORARY_REDIRECT = 307;/*** Status code (400) indicating the request sent by the client was* syntactically incorrect.*/public static final int SC_BAD_REQUEST = 400;/*** Status code (401) indicating that the request requires HTTP* authentication.*/public static final int SC_UNAUTHORIZED = 401;/*** Status code (402) reserved for future use.*/public static final int SC_PAYMENT_REQUIRED = 402;/*** Status code (403) indicating the server understood the request but* refused to fulfill it.*/public static final int SC_FORBIDDEN = 403;/*** Status code (404) indicating that the requested resource is not* available.*/public static final int SC_NOT_FOUND = 404;/*** Status code (405) indicating that the method specified in the* <code><em>Request-Line</em></code> is not allowed for the resource* identified by the <code><em>Request-URI</em></code>.*/public static final int SC_METHOD_NOT_ALLOWED = 405;/*** Status code (406) indicating that the resource identified by the request* is only capable of generating response entities which have content* characteristics not acceptable according to the accept headers sent in* the request.*/public static final int SC_NOT_ACCEPTABLE = 406;/*** Status code (407) indicating that the client <em>MUST</em> first* authenticate itself with the proxy.*/public static final int SC_PROXY_AUTHENTICATION_REQUIRED = 407;/*** Status code (408) indicating that the client did not produce a request* within the time that the server was prepared to wait.*/public static final int SC_REQUEST_TIMEOUT = 408;/*** Status code (409) indicating that the request could not be completed due* to a conflict with the current state of the resource.*/public static final int SC_CONFLICT = 409;/*** Status code (410) indicating that the resource is no longer available at* the server and no forwarding address is known. This condition* <em>SHOULD</em> be considered permanent.*/public static final int SC_GONE = 410;/*** Status code (411) indicating that the request cannot be handled without a* defined <code><em>Content-Length</em></code>.*/public static final int SC_LENGTH_REQUIRED = 411;/*** Status code (412) indicating that the precondition given in one or more* of the request-header fields evaluated to false when it was tested on the* server.*/public static final int SC_PRECONDITION_FAILED = 412;/*** Status code (413) indicating that the server is refusing to process the* request because the request entity is larger than the server is willing* or able to process.*/public static final int SC_REQUEST_ENTITY_TOO_LARGE = 413;/*** Status code (414) indicating that the server is refusing to service the* request because the <code><em>Request-URI</em></code> is longer than the* server is willing to interpret.*/public static final int SC_REQUEST_URI_TOO_LONG = 414;/*** Status code (415) indicating that the server is refusing to service the* request because the entity of the request is in a format not supported by* the requested resource for the requested method.*/public static final int SC_UNSUPPORTED_MEDIA_TYPE = 415;/*** Status code (416) indicating that the server cannot serve the requested* byte range.*/public static final int SC_REQUESTED_RANGE_NOT_SATISFIABLE = 416;/*** Status code (417) indicating that the server could not meet the* expectation given in the Expect request header.*/public static final int SC_EXPECTATION_FAILED = 417;/*** Status code (500) indicating an error inside the HTTP server which* prevented it from fulfilling the request.*/public static final int SC_INTERNAL_SERVER_ERROR = 500;/*** Status code (501) indicating the HTTP server does not support the* functionality needed to fulfill the request.*/public static final int SC_NOT_IMPLEMENTED = 501;/*** Status code (502) indicating that the HTTP server received an invalid* response from a server it consulted when acting as a proxy or gateway.*/public static final int SC_BAD_GATEWAY = 502;/*** Status code (503) indicating that the HTTP server is temporarily* overloaded, and unable to handle the request.*/public static final int SC_SERVICE_UNAVAILABLE = 503;/*** Status code (504) indicating that the server did not receive a timely* response from the upstream server while acting as a gateway or proxy.*/public static final int SC_GATEWAY_TIMEOUT = 504;/*** Status code (505) indicating that the server does not support or refuses* to support the HTTP protocol version that was used in the request* message.*/public static final int SC_HTTP_VERSION_NOT_SUPPORTED = 505;

200：请求响应成功
3xx:请求重定向重定向：你重新到我给你新位置去；
4xx:找不到资源   404资源不存在
5xx：服务器代码错误  500502： 网关错误

2、常见应用

1.向浏览器输出消息
2.下载文件——
（1）要获取下载文件的路径
（2）下载的文件名是什么？
（3）设置想办法让浏览器能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buffer缓冲区
（8）将OutputStream将缓冲区中的数据输出到客户端

创建一个web项目

完善项目结构

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app 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"version="4.0"metadata-complete="true">
</web-app>

在resources下添加一个图片1.png

在com.kuang.servlet包下创建FileServlet文件

package com.kuang.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 FileServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {////  （1）要获取下载文件的 路径
//        String realPath = this.getServletContext().getRealPath("/1.png");String realPath = "D:\\学习笔记\\狂神说Java\\javaweb-02-servlet\\response\\target\\classes\\1.png";System.out.println("下载文件的路径："+realPath);//   （2）下载的文件名是什么？String fileName = realPath.substring(realPath.lastIndexOf("\\")+1);// （3）设置想办法让浏览器能支持(Content-Disposition)下载我们需要的东西.URLEncoder.encode(fileName,"UTF-8"))：用来处理中文编码,否则可能会乱码
//        resp.setHeader("Content-Disposition","attachment;filename="+ fileName);resp.setHeader("Content-Disposition","attachment;filename="+ URLEncoder.encode(fileName,"UTF-8"));// （4）获取下载文件的输入流;FileInputStream将文件变成流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buffer缓冲区，将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);}//（8）关闭流in.close();out.close();}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {super.doPost(req, resp);}
}

修改web.xml

 <servlet><servlet-name>fileDown</servlet-name><servlet-class>com.kuang.servlet.FileServlet</servlet-class></servlet><servlet-mapping><servlet-name>fileDown</servlet-name><url-pattern>/down</url-pattern></servlet-mapping>

HttpServletRequest

参考页面

web文件下载头信息

错误

文件下载只显示页面，不提示文件下载
错误显示

原因：

正确显示：

正确代码：

package com.kuang.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 FileServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {////  （1）要获取下载文件的 路径
//        String realPath = this.getServletContext().getRealPath("/1.png");String realPath = "D:\\学习笔记\\狂神说Java\\javaweb-02-servlet\\response\\target\\classes\\1.png";System.out.println("下载文件的路径："+realPath);//   （2）下载的文件名是什么？String fileName = realPath.substring(realPath.lastIndexOf("\\")+1);// （3）设置想办法让浏览器能支持(Content-Disposition)下载我们需要的东西.URLEncoder.encode(fileName,"UTF-8"))：用来处理中文编码
//        resp.setHeader("Content-Disposition","attachment;filename="+ fileName);
//        resp.setHeader("Content-Disposition","attachment:filename="+ URLEncoder.encode(fileName,"UTF-8"));resp.setHeader("Content-Disposition","attachment;filename="+ URLEncoder.encode(fileName,"UTF-8"));//    （4）获取下载文件的输入流;FileInputStream将文件变成流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buffer缓冲区，将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);}//（8）关闭流in.close();out.close();}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {super.doPost(req, resp);}
}

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