javaweb——Response下载文件_java response下载文件

作者：Monodyee | 2024-06-06 04:39:01

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java response下载文件

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;
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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);
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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;
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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  500
	502： 网关错误
	
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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

在这里插入图片描述

完善项目结构

在这里插入图片描述

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>
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在resources下添加一个图片1.png

在这里插入图片描述

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 {

    @Override
    protected 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();

    }

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

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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>
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在这里插入图片描述

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
在这里插入图片描述
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 {

    @Override
    protected 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();

    }

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


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