文件下载工具类DownLoadUtils及在Servlet中的使用

import sun.misc.BASE64Encoder;
import java.io.UnsupportedEncodingException;
import java.net.URLEncoder;


public class DownLoadUtils {

    public static String getFileName(String agent, String filename) throws UnsupportedEncodingException {
        if (agent.contains("MSIE")) {
            // IE浏览器
            filename = URLEncoder.encode(filename, "utf-8");
            filename = filename.replace("+", " ");
        } else if (agent.contains("Firefox")) {
            // 火狐浏览器
            BASE64Encoder base64Encoder = new BASE64Encoder();
            filename = "=?utf-8?B?" + base64Encoder.encode(filename.getBytes("utf-8")) + "?=";
        } else {
            // 其它浏览器
            filename = URLEncoder.encode(filename, "utf-8");
        }
        return filename;
    }
}

在Servlet中使用，将需要下载的文件放到WebContent目录下面的downloads子文件夹中

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

import javax.servlet.ServletContext;
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("/index1")
public class Index1Servlet extends HttpServlet {
    private static final long serialVersionUID = 1L;      
   
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String filename = request.getParameter("filename");
        ServletContext context = request.getServletContext();
        String path = context.getRealPath("downloads/"+filename);
        FileInputStream fis = new FileInputStream(path);    
        
        String agent = request.getHeader("User-agent");
        String filename1 = DownLoadUtils.getFileName(agent, filename);
        response.setHeader("content-disposition","attachment;filename="+filename1);
        OutputStream outputStream = response.getOutputStream();
        int len=0;
        byte[] b=new byte[1024];
        while((len=fis.read(b))!=-1) {
            outputStream.write(b, 0, len);
        }
        fis.close();
        outputStream.close();
    }

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

}

最后在地址栏输入：http://localhost:8080/项目名/index1?filename=文件名