javaweb——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;

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

    
    public static final int SC_CONTINUE = 100;

    
    public static final int SC_SWITCHING_PROTOCOLS = 101;

    
    public static final int SC_OK = 200;

    
    public static final int SC_CREATED = 201;

    
    public static final int SC_ACCEPTED = 202;

    
    public static final int SC_NON_AUTHORITATIVE_INFORMATION = 203;

    
    public static final int SC_NO_CONTENT = 204;

    
    public static final int SC_RESET_CONTENT = 205;

    
    public static final int SC_PARTIAL_CONTENT = 206;

    
    public static final int SC_MULTIPLE_CHOICES = 300;

    
    public static final int SC_MOVED_PERMANENTLY = 301;

    
    public static final int SC_MOVED_TEMPORARILY = 302;

    
    public static final int SC_FOUND = 302;

    
    public static final int SC_SEE_OTHER = 303;

    
    public static final int SC_NOT_MODIFIED = 304;

    
    public static final int SC_USE_PROXY = 305;

    
    public static final int SC_TEMPORARY_REDIRECT = 307;

    
    public static final int SC_BAD_REQUEST = 400;

    
    public static final int SC_UNAUTHORIZED = 401;

    
    public static final int SC_PAYMENT_REQUIRED = 402;

    
    public static final int SC_FORBIDDEN = 403;

    
    public static final int SC_NOT_FOUND = 404;

    
    public static final int SC_METHOD_NOT_ALLOWED = 405;

    
    public static final int SC_NOT_ACCEPTABLE = 406;

    
    public static final int SC_PROXY_AUTHENTICATION_REQUIRED = 407;

    
    public static final int SC_REQUEST_TIMEOUT = 408;

    
    public static final int SC_CONFLICT = 409;

    
    public static final int SC_GONE = 410;

    
    public static final int SC_LENGTH_REQUIRED = 411;

    
    public static final int SC_PRECONDITION_FAILED = 412;

    
    public static final int SC_REQUEST_ENTITY_TOO_LARGE = 413;

    
    public static final int SC_REQUEST_URI_TOO_LONG = 414;

    
    public static final int SC_UNSUPPORTED_MEDIA_TYPE = 415;

    
    public static final int SC_REQUESTED_RANGE_NOT_SATISFIABLE = 416;

    
    public static final int SC_EXPECTATION_FAILED = 417;

    
    public static final int SC_INTERNAL_SERVER_ERROR = 500;

    
    public static final int SC_NOT_IMPLEMENTED = 501;

    
    public static final int SC_BAD_GATEWAY = 502;

    
    public static final int SC_SERVICE_UNAVAILABLE = 503;

    
    public static final int SC_GATEWAY_TIMEOUT = 504;

    
    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  500
	502： 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

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 {

    @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);
    }
}

修改web.xml

 
        fileDown
        com.kuang.servlet.FileServlet
    
    
        fileDown
        /down

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 {

    @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);
    }
}

javaweb——Response下载文件

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