java 下载图片流

  昨天在做日常时碰到了一个问题：根据图片的URL地址，返回该图片文件的byte数据。

  第一种方案：通过HttpURLConnection创建连接，然后，从该连接获取图片流。

public class ImageReaderUtil {
     /**
      * @param
      *     imageUrl
      * @return
      *    byte array of the file
      */
     public  static byte[] getBytesByURL(String imageUrl)throws IOException {
          ByteArrayOutputStream baos = new ByteArrayOutputStream();
          BufferedInputStream bis = null;
          HttpURLConnection urlconnection= null;
          URL url = null;
          byte[] buf = new byte[1024];
          try {
              url = new URL(imageUrl);
              urlconnection = (HttpURLConnection) url.openConnection();
              urlconnection.connect();
              bis = new BufferedInputStream(urlconnection.getInputStream());
              for (int len = 0; (len = bis.read(buf)) != -1;){
                   baos.write(buf,0,len);
              }
              return baos.toByteArray();
          } finally {
              try {
                   urlconnection.disconnect();
                   bis.close();
              } catch (IOException ignore) {
              }
          }
     }
}

第二种方案：通过httpClient下载

package com.ustc.java.io;

import java.io.IOException;

import org.apache.commons.httpclient.DefaultHttpMethodRetryHandler;
import org.apache.commons.httpclient.HttpClient;
import org.apache.commons.httpclient.HttpException;
import org.apache.commons.httpclient.HttpStatus;
import org.apache.commons.httpclient.methods.GetMethod;
import org.apache.commons.httpclient.params.HttpMethodParams;

public class DownLoadPicture {
    
    public DownLoadPicture() {
        super();
        // TODO Auto-generated constructor stub
    }

    public byte[] downLoad(String imgURL){
        // 构造HttpClient的实例
        HttpClient httpClient = new HttpClient();
        // 创建GET方法的实例
        GetMethod getMethod = new GetMethod(imgURL);
        // 使用系统提供的默认的恢复策略
        getMethod.getParams().setParameter(HttpMethodParams.RETRY_HANDLER,new DefaultHttpMethodRetryHandler());
        try {
            // 执行getMethod
            int statusCode = httpClient.executeMethod(getMethod);
            if (statusCode != HttpStatus.SC_OK) {
                System.err.println("Method failed: "+ getMethod.getStatusLine());
            }
            // 读取内容
            byte[] responseBody = getMethod.getResponseBody();
            return responseBody;
        } catch (HttpException e) {
            // 发生致命的异常，可能是协议不对或者返回的内容有问题
            System.out.println("Please check your provided http address!");
            e.printStackTrace();
        } catch (IOException e) {
            // 发生网络异常
            e.printStackTrace();
        } finally {
            // 释放连接
            getMethod.releaseConnection();
        }
        return null;
    }
    public static void main(String[] args) {
        String picture="http://upload3.mop.com/upload3/2009/06/27/02/1246083475154.jpg";
        new DownLoadPicture().downLoad(picture);
    }
}

需要注意的是，要是通过这种方法下载图片的byte流，则需要增加三个jar包：commons-logging,commons-httpclient,commons-codec

参考资料：http://www.ibm.com/developerworks/cn/opensource/os-httpclient/#ibm-pcon