怎么在JAVA中利用HttpURLConnection实现一个文件上传下载功能

package com.util;import java.io.BufferedInputStream;import java.io.BufferedReader;import java.io.DataOutputStream;import java.io.File;import java.io.FileInputStream;import java.io.FileOutputStream;import java.io.IOException;import java.io.InputStream;import java.io.InputStreamReader;import java.io.OutputStream;import java.io.OutputStreamWriter;import java.net.HttpURLConnection;import java.net.MalformedURLException;import java.net.URL;import java.net.URLConnection;import java.util.Iterator;import java.util.Map;public class HttpConnectionUtil {  @SuppressWarnings("finally") public static String uploadFile(String actionUrl, String[] uploadFilePaths) {  String end = "\r\n";  String twoHyphens = "--";  String boundary = "*****";  DataOutputStream ds = null;  InputStream inputStream = null;  InputStreamReader inputStreamReader = null;  BufferedReader reader = null;  StringBuffer resultBuffer = new StringBuffer();  String tempLine = null;  try {   // 统一资源   URL url = new URL(actionUrl);   // 连接类的父类，抽象类   URLConnection urlConnection = url.openConnection();   // http的连接类   HttpURLConnection httpURLConnection = (HttpURLConnection) urlConnection;   // 设置是否从httpUrlConnection读入，默认情况下是true;   httpURLConnection.setDoInput(true);   // 设置是否向httpUrlConnection输出   httpURLConnection.setDoOutput(true);   // Post 请求不能使用缓存   httpURLConnection.setUseCaches(false);   // 设定请求的方法，默认是GET   httpURLConnection.setRequestMethod("POST");   // 设置字符编码连接参数   httpURLConnection.setRequestProperty("Connection", "Keep-Alive");   // 设置字符编码   httpURLConnection.setRequestProperty("Charset", "UTF-8");   // 设置请求内容类型   httpURLConnection.setRequestProperty("Content-Type", "multipart/form-data;boundary=" + boundary);   // 设置DataOutputStream   ds = new DataOutputStream(httpURLConnection.getOutputStream());   for (int i = 0; i < uploadFilePaths.length; i++) {    String uploadFile = uploadFilePaths[i];    String filename = uploadFile.substring(uploadFile.lastIndexOf("//") + 1);    ds.writeBytes(twoHyphens + boundary + end);    ds.writeBytes("Content-Disposition: form-data; " + "name=\"file" + i + "\";filename=\"" + filename      + "\"" + end);    ds.writeBytes(end);    FileInputStream fStream = new FileInputStream(uploadFile);    int bufferSize = 1024;    byte[] buffer = new byte[bufferSize];    int length = -1;    while ((length = fStream.read(buffer)) != -1) {     ds.write(buffer, 0, length);    }    ds.writeBytes(end);        fStream.close();   }   ds.writeBytes(twoHyphens + boundary + twoHyphens + end);      ds.flush();   if (httpURLConnection.getResponseCode() >= 300) {    throw new Exception(      "HTTP Request is not success, Response code is " + httpURLConnection.getResponseCode());   }   if (httpURLConnection.getResponseCode() == HttpURLConnection.HTTP_OK) {    inputStream = httpURLConnection.getInputStream();    inputStreamReader = new InputStreamReader(inputStream);    reader = new BufferedReader(inputStreamReader);    tempLine = null;    resultBuffer = new StringBuffer();    while ((tempLine = reader.readLine()) != null) {     resultBuffer.append(tempLine);     resultBuffer.append("\n");    }   }  } catch (Exception e) {   // TODO Auto-generated catch block   e.printStackTrace();  } finally {   if (ds != null) {    try {     ds.close();    } catch (IOException e) {     // TODO Auto-generated catch block     e.printStackTrace();    }   }   if (reader != null) {    try {     reader.close();    } catch (IOException e) {     // TODO Auto-generated catch block     e.printStackTrace();    }   }   if (inputStreamReader != null) {    try {     inputStreamReader.close();    } catch (IOException e) {     // TODO Auto-generated catch block     e.printStackTrace();    }   }   if (inputStream != null) {    try {     inputStream.close();    } catch (IOException e) {     // TODO Auto-generated catch block     e.printStackTrace();    }   }   return resultBuffer.toString();  } } public static void main(String[] args) {  // 上传文件测试   String str = uploadFile("http://127.0.0.1:8080/image/image.do",new String[] { "/Users//H__D/Desktop//1.png","//Users/H__D/Desktop/2.png" });   System.out.println(str); }}