基于servlet的文件下载

首先把服务器中的/download文件夹中可供下载的资源显示在带有下载链接的JSP页面中，后台servlet代码（该servlet带有转发到一个显示可供下载资源的JSP页面的操作）为：

import java.io.File;
import java.io.IOException;
import java.util.List;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet("/download")
public class downloadservlet extends HttpServlet {
@Override
protected void service(HttpServletRequest arg0, HttpServletResponse arg1) throws ServletException, IOException {
// TODO Auto-generated method stub
//reques里也有这个获取到项目名之前的路径方法 但是过时了这样获取
String path=getServletContext().getRealPath("/download");//获取到的结果是：D:\JEEeclipsework\.metadata\.plugins\org.eclipse.wst.server.core\tmp0\wtpwebapps\checkcode\download
//获取文件夹
File file=new File(path);
//
String []files=file.list();
arg0.setAttribute("filename", files);
System.out.println(files.length);
arg0.getRequestDispatcher("/download.jsp").forward(arg0, arg1);

}
}

带有下载链接的JSP页面代码为：

<%
for(String filename:(String[])request.getAttribute("filename")){
 out.println(filename);
 %><a href="do?filename=<%=filename%>">下载</a><br/>
 <%
}
%>

点击超链接后，发送请求，开始下载的servlet代码：

import java.io.FileInputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.net.URLEncoder;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
* Servlet implementation class dodownload
*/
@WebServlet("/do")
public class dodownload extends HttpServlet {
@Override
protected void service(HttpServletRequest arg0, HttpServletResponse arg1) throws ServletException, IOException {
// TODO Auto-generated method stub

//获取要下载的文件名
String filename=arg0.getParameter("filename");
filename=new String(filename.getBytes("ISO8859-1"),"UTF-8");//因为Tomcat是iso8859-1编码
System.out.println(filename);
//获取服务器的download路径
String basepath=getServletContext().getRealPath("/download");

//将要下载的文件写入输入流
FileInputStream fis=new FileInputStream(basepath+"/"+filename);
//通过response的outputstream向前台用户路径下写入  因为该内置对象是服务器响应客户端
//告诉浏览器以下载的方式打开
arg1.setHeader("content-disposition", "attachment;filename="+URLEncoder.encode(filename,"utf-8"));
OutputStream fos=arg1.getOutputStream();
byte[] buffer=new byte[1024];
int len=0;
while ((len=fis.read(buffer))!=-1) {
fos.write(buffer,0,len);
}
}
}