资源下载:
 
 单纯地使用a标签时，只有浏览器不能解析的文件才会是下载，否则将被浏览器直接解析。
 a.mp3

 a.exe

 a.txt

 a.xlsx

 a.png

 
因此，使用a标签结合servlet的response指示浏览器不解析这些待下载文件
 a.mp3

 a.exe

 a.txt

 a.xlsx

 a.png

package com.download.servlet;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
 * Servlet implementation class Download
 */
public class Download extends HttpServlet {
 private static final long serialVersiOnUID= 1L;
 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
 //1.获取请求下载的文件名
 String filename = request.getParameter("filename");
 //2.获取文件的文件系统路径
 String filePath = request.getServletContext().getRealPath("resource/"+filename);
 //3.设置响应头，提示浏览器不要解析响应的文件数据，而是以附件(attachment)的形式解析，即下载功能
 response.setContentType(this.getServletContext().getMimeType(filename));
 response.setHeader("Content-Disposition", "attachment;filename="+filename);
 //4.读取文件的 输入流，以及响应的输出流，并将数据输出给客户端
 InputStream in = new FileInputStream(filePath);
 ServletOutputStream out = response.getOutputStream();
 int len = 0;
 byte[] buf = new byte[1024];
 while((len=in.read(buf))!=-1) {
  out.write(buf, 0, len);
 }
 in.close();
 }
 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
 doGet(request, response);
 }
}