一、目录结构：

二、servlet编写：Dowmn

package cn.xh.download.servlet;


import java.io.FileInputStream;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;


import org.apache.commons.io.IOUtils;


/**
 * Servlet implementation class Download
 */
public class Download extends HttpServlet {
private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public Download() {
        super();
        // TODO Auto-generated constructor stub
    }


/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {


String fname="F:/音乐/2.mp3";
//设置文件类型
String contentType=this.getServletContext().getMimeType(fname);
//设置下载时显示的名字
String contentDisposition="attachment;filename=yuuy.mp3";

//**一个文件流
FileInputStream fin=new FileInputStream(fname);

//**两个文件头  Cotent大写C也可
response.setHeader("content-Type", contentType);
response.setHeader("content-Disposition", contentDisposition);


ServletOutputStream fout=response.getOutputStream();
IOUtils.copy(fin, fout);
fout.close();

}


protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

doPost(request, response);
}
}

注意导包：commons-io.jar;  spring中有