使用HttpClient將文件抓到內存byte數組內
然後進行文件的buff輸出
亦或者可以直接在內存中進行二次轉送
以達到各種目的
本例子只給出基本代碼
優化等其他操作請自行嘗試

import java.io.*;

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


public class downTest {
	private static final String GET_URL = "http://static-img1.cdn.aliyuncs.com/images/aliyun/404_ico.png";
	private static final String FILE_PATH = "/root/down.png";
	public static void main(String[] args) throws Exception {
		HttpClient hc = new DefaultHttpClient();
		HttpGet get = new HttpGet(GET_URL);
		HttpResponse response = hc.execute(get);
		if (response.getStatusLine().getStatusCode() == 200) {
			byte[] bytes = EntityUtils.toByteArray(response.getEntity());
			FileOutputStream outSTr = new FileOutputStream(new File(FILE_PATH));
			BufferedOutputStream Buff = new BufferedOutputStream(outSTr);
			Buff.write(bytes);
			Buff.flush();
			Buff.close();
			System.out.println("Done!");
		}
	}
}