java 获得网络资源

java在网络上请求地址，都会用到URL url = new URL(urlStr)来定位资源，
然后根据url获得输入流in = url.openStream();从而可以得到网络资源。

以下是一个完整的程序代码：

package com.zakisoft.tools;

import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.URL;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;

import javax.swing.JOptionPane;

public class GetGSInfo {

	private static String GOLD_PRICE_URL = "http://www.kitco.cn/cn/live_charts/goldcny.gif";
	private static String SILVER_PRICE_URL = "http://www.kitco.cn/cn/live_charts/silvercny.gif";

	private static String SAVE_PATH = "D://Glod_Silver//";

	private GetGSInfo() {		
		Date cd = new Date();
		DateFormat df = new SimpleDateFormat("yyyy-MM-dd");

		String cdstr = df.format(cd);
		String glodOutPath = SAVE_PATH + cdstr + "-Glod.gif";
		String silverOutPath = SAVE_PATH + cdstr + "-Silver.gif";

		getContext(GOLD_PRICE_URL, glodOutPath);
		getContext(SILVER_PRICE_URL, silverOutPath);

		JOptionPane.showMessageDialog(null, "价格保存完成...");
	}

	public void getContext(String urlStr, String outPath) {// 获得网络资源并写入指定文件
		InputStream in = null;
		OutputStream out = null;
		try {
			// 用streams，存储获得的资源
			URL url = new URL(urlStr);
			in = url.openStream();
			if (outPath == null) {
				out = System.out;
			} else {
				out = new FileOutputStream(outPath);
			}
			// 用输出流out，输出到指定位置
			byte[] buffer = new byte[1024];
			int bytes_read;
			while ((bytes_read = in.read(buffer)) != -1) {
				out.write(buffer, 0, bytes_read);
			}
		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			try {
				in.close();
				out.close();
			} catch (Exception e) {
			}
		}
	}

	public static void main(String[] args) {
		new GetGSInfo();
	}

}