原文：http://www.cnblogs.com/Csharpblogs/articles/2218156.html
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
/**
* 获取本机外网IP地址
* 思想是访问网站http://checkip.dyndns.org/，得到返回的文本后解析出本机在外网的IP地址
* @author Administrator
*
*/
public class ExternalIpAddressFetcher {
// 外网IP提供者的网址
private String externalIpProviderUrl;
// 本机外网IP地址
private String myExternalIpAddress;
public ExternalIpAddressFetcher(String externalIpProviderUrl) {
this.externalIpProviderUrl = externalIpProviderUrl;
String returnedhtml = fetchExternalIpProviderHTML(externalIpProviderUrl);
parse(returnedhtml);
}
/**
* 从外网提供者处获得包含本机外网地址的字符串
* 从http://checkip.dyndns.org返回的字符串如下
* <html><head><title>Current IP Check</title></head><body>Current IP Address: 123.147.226.222</body></html>
* @param externalIpProviderUrl
* @return
*/
private String fetchExternalIpProviderHTML(String externalIpProviderUrl) {
// 输入流
InputStream in = null;
// 到外网提供者的Http连接
HttpURLConnection httpConn = null;
try {
// 打开连接
URL url = new URL(externalIpProviderUrl);
httpConn = (HttpURLConnection) url.openConnection();
// 连接设置
HttpURLConnection.setFollowRedirects(true);
httpConn.setRequestMethod("GET");
httpConn.setRequestProperty("User-Agent",
"Mozilla/4.0 (compatible; MSIE 6.0; Windows 2000)");
// 获取连接的输入流
in = httpConn.getInputStream();
byte[] bytes=new byte[1024];// 此大小可根据实际情况调整
// 读取到数组中
int offset = 0;
int numRead = 0;
while (offset < bytes.length
&& (numRead=in.read(bytes, offset, bytes.length-offset)) >= 0) {
offset += numRead;
}
// 将字节转化为为UTF-8的字符串
String receivedString=new String(bytes,"UTF-8");
// 返回
return receivedString;
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
in.close();
httpConn.disconnect();
} catch (Exception ex) {
ex.printStackTrace();
}
}
// 出现异常则返回空
return null;
}
/**
* 使用正则表达式解析返回的HTML文本,得到本机外网地址
* @param html
*/
private void parse(String html){
Pattern pattern=Pattern.compile("(\\d{1,3})[.](\\d{1,3})[.](\\d{1,3})[.](\\d{1,3})", Pattern.CASE_INSENSITIVE);
Matcher matcher=pattern.matcher(html);
while(matcher.find()){
myExternalIpAddress=matcher.group(0);
}
}
/**
* 得到本机外网地址,得不到则为空
* @return
*/
public String getMyExternalIpAddress() {
return myExternalIpAddress;
}
public static void main(String[] args){
ExternalIpAddressFetcher fetcher=new ExternalIpAddressFetcher("http://checkip.dyndns.org/");
System.out.println(fetcher.getMyExternalIpAddress());
}
}
