java 检测一个URL地址是否有效

import java.io.InputStream; import java.net.URL; public class Test { public static void main(String[] args) { URL url; try { url = new URL("http://www.baidu.com"); InputStream in = url.openStream(); System.out.println("连接可用"); } catch (Exception e1) { System.out.println("连接打不开!"); url = null; } } }
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import java.net.HttpURLConnection;import java.net.URL;/*** 文件名称为：URLAvailability.java* 文件功能简述： 描述一个URL地址是否有效* @author Jason* @time 2010-9-14 * */public class URLAvailability {private static URL url;private static HttpURLConnection con;private static int state = -1;/** * 功能：检测当前URL是否可连接或是否有效, * 描述：最多连接网络 5 次, 如果 5 次都不成功，视为该地址不可用 * @param urlStr 指定URL网络地址 * @return URL */public synchronized URL isConnect(String urlStr) { int counts = 0; if (urlStr == null || urlStr.length() <= 0) { return null; } while (counts < 5) { try { url = new URL(urlStr); con = (HttpURLConnection) url.openConnection(); state = con.getResponseCode(); System.out.println(counts +"= "+state); if (state == 200) { System.out.println("URL可用！"); } break; }catch (Exception ex) { counts++; System.out.println("URL不可用，连接第 "+counts+" 次"); urlStr = null; continue; } } return url;}public static void main(String[] args) { URLAvailability u=new URLAvailability(); u.isConnect("http://www.baidu.com");}}