WEB之文件下载

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

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

public class DownloadServlet extends HttpServlet {
    
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        
        String filename = request.getParameter("filename"); //1 获取要下载的文件名
        
        
        // 2 把文件所在的文件夹相对路径转成绝对路径
        String folderPath = this.getServletContext().getRealPath("download");
            
        // 3获得输入流用来将服务器上的文件读出
        InputStream is = new FileInputStream(folderPath+"/"+filename);
        
        // 4向相应的头部添加信息，作用是用来弹出保存文件的对话框
        //response.setHeader("Content-Disposition", "attachment;filename="+filename);
        // 中文文件名下载对话框中将是乱码。处理方式：IE浏览器和其他浏览器的处理方式不同
        
        //IE:
        //response.setHeader("Content-Disposition", "attachment;filename="+URLEncoder.encode(filename, "UTF-8"));
            
        //FireFox
        String newFilename = new String(filename.getBytes("UTF-8"),"iso-8859-1");
        response.setHeader("Content-Disposition", "attachment;filename="+newFilename);    
        
        // 5写到本地磁盘上
        OutputStream os = response.getOutputStream();
        
        int len=0;
        byte[] b = new byte[1024];
        
        while((len=is.read(b))!=-1){
            
            os.write(b,0, len);
        }    
        is.close();
        os.close();    
    }
}