HttpClient使用之下载远程服务器中的文件(注意目录遍历漏洞)

参考文献：

http://bbs.csdn.net/topics/390952011

http://blog.csdn.net/ljj_9/article/details/53306468

1.下载地址

http://hc.apache.org/downloads.cgi

Apache-》Projects-》HttpComponents

2.DownloadServlet

 package com.servlet;

 import java.io.BufferedInputStream;
 import java.io.BufferedOutputStream;
 import java.io.File;
 import java.io.FileInputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
 import java.net.URLDecoder;
 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 {

     private static final long serialVersionUID = 1L;

     public void doGet(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {
         String filename = request.getParameter("id");
         String fileUrl = request.getServletContext().getRealPath("").replace("\\", "/");
         fileUrl = fileUrl + "/files/document/" + filename;
         System.out.println("fileUrl:"+fileUrl);
         String rname = new String(filename.getBytes("utf-8"));
         System.out.println("begin:"+rname);
         rname = URLEncoder.encode(rname);
         System.out.println("end:"+rname);
         response.addHeader("Content-Disposition", "attachment;filename="+rname);
         response.setContentType("application/octet-stream");

         File file = new File(fileUrl);
         InputStream is = new BufferedInputStream(new FileInputStream(file));
         byte[] buffer = new byte[is.available()];
         is.read(buffer);
         is.close();

         OutputStream os = new BufferedOutputStream(response.getOutputStream());
         os.write(buffer);
         os.flush();
         os.close();
     }

     public void doPost(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {

     }

     }

3.ClientA.java

package com.tool;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;

public class ClientA {

    /**
     *
     * @param args
     */

    public static void main(String[] args) {
        // TODO 自动生成的方法存根
        ClientA client = new ClientA();
        client.service();
    }

    public void service() {
        // TODO 自动生成的方法存根

        String url = "http://此处填写ip或网址/download.do";

        HttpClient client = new DefaultHttpClient();
        HttpGet get = new HttpGet(url);

        try {

            HttpResponse response = client.execute(get);

        } catch (ClientProtocolException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

}

4.注意服务器的编码方式和客户端的区别

统一为utf-8

5.注意目录遍历漏洞

目录遍历是通过操作URL强行访问web目录以外的文件，目录和命令，攻击者可以在目标机器的任何位置访问文件，执行命令。 
最基本的目录遍历攻击技术是在URL中使用"../"序列，改变访问资源的路径，访问到web目录以外的文件。 
例如： 
http://example.com/../../../../some/file 
http://example.com/..%255c..%255c/some/file 
正常请求为: 
http://example.com/test.cgi?look=intex.html 
如果存在目录遍历漏洞，攻击者可以访问 
http://example.com/test.cgi?look=test.cgi

解决办法：

过滤请求数据中"../"字符序列及其各种变形。 
验证用户请求中提交的需要访问的文件是否在限定的范围内。

java web使用fliter过滤url即可。