servlet下载文件（五）

package com.learn;

import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

/**
 * Created by Administrator on 2017/09/24.
 */
public class DownLoadServlet extends HttpServlet {
    private String filePath;

    @Override
    public void init(ServletConfig config) throws ServletException {
        super.init(config);
        filePath = config.getInitParameter("filePath");
        //初始化路径
        //filePath = config.getServletContext().getRealPath(filePath);
        System.out.println("初始化文件路径："+filePath);
    }

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

    }

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

        OutputStream out; //输出流
        InputStream in; //输入流

        String fileName = req.getParameter("fileName");
        System.out.println("文件名称："+fileName);
        //如果把文件名为null则提示用户
        if(fileName == null){
            out = resp.getOutputStream();
            out.write("please input fileName".getBytes());
            out.close();
        }
        //获取文件流
        in = getServletContext().getResourceAsStream(filePath+ File.separator+fileName);
        System.out.println(in==null?true:false);
        int length = in.available();
        
        //设置返回消息头部信息
        resp.setContentType("application/force-download");
        resp.setHeader("Content-Length",String.valueOf(length));
        resp.setHeader("content-disposition","attachment;filename=\""+fileName+"\"");
        //输出文件到客户端
        out = resp.getOutputStream();
        int bytesend = 0 ;
        byte[] buff = new byte[512];
        while ((bytesend = in.read(buff))!= -1){
            out.write(buff,0,bytesend);
        }
        in.close();
        out.close();
    }
}

  <servlet>
    <servlet-name>download</servlet-name>
    <servlet-class>com.learn.DownLoadServlet</servlet-class>
    <init-param>
        <param-name>filePath</param-name>
        <param-value>file</param-value>
    </init-param>
 </servlet>
 <servlet-mapping>
    <servlet-name>download</servlet-name>
    <url-pattern>/download</url-pattern>
 </servlet-mapping>