PING和TELNET用法介绍
JAVA里的PING是在JDK 1.5后用了新的函数isreachable去实现,具体介绍如下:
InetAddress对象的常用方法
InetAddress类有很多get方法,用来获取主机名,主机地址等信息。主要有:
byte[] getAddress() 返回次InetAddress对象的原始IP地址,保存为一个byte数组
String getCanonicalHostName() 获取此IP地址的完全限定域名
String getHostAddress() 获取IP地址的字符串,返回为一个String
String getHostName() 获取此IP地址的主机名
下面一个简单的例子展示这些方法的使用:
package org.dakiler.javanet.chapter1;
import java.net.InetAddress;
public class Example3
{
public static void main(String args[])throws Exception
{
InetAddress address=InetAddress.getByName("www.microsoft.com");
System.out.println("ip: "+address.getHostAddress());
System.out.println("host: "+address.getHostName());
System.out.println("canonical host name: "+address.getCanonicalHostName());
byte[] bytes=address.getAddress();
for(byte b:bytes)
{
if(b>=0)System.out.print(b);
else System.out.print(256+b);
System.out.print(" ");
}
}
}
这个例子首先是获取www.microsoft.com的对应的InetAddress实例,然后分别打印address.getHostAddress() address.getHostName()以及address.getCanonicalHostName()。在这个例子中,需要注意的是IP地址中,每一个都是0-255之间的,是无符号的。但是java中的byte表示的区域是-128~127,所以中间需要做一个转换。
结果如下:
ip: 207.46.19.254 host: www.microsoft.com canonical host name: wwwbaytest2.microsoft.com 207 46 19 254
1.2. InetAddress对象的其他实用方法
isReachable(int timeout) 测试是否能达到特定IP地址
isReachable(NetworkInterface netif,int ttl,int timeout)测试是否能达到特定IP地址,并且制定特定的NetworkInterface,ttl表示路由过程中的最大跳数,timeout是超时时间。一个简单的例子如下:
package org.dakiler.javanet.chapter1;
import java.net.InetAddress;
public class Example4
{
public static void main(String args[])throws Exception
{
InetAddress address1=InetAddress.getLocalHost();
InetAddress address2=InetAddress.getByName("www.baidu.com");
System.out.println(address1.isReachable(5000));
System.out.println(address2.isReachable(5000));
}
}
分别测试本机是否可达以及www.baidu.com是否可达。运行的结果是:
true false
感觉奇怪么,前者是正常的,但是按理说www.baidu.com应该也是可达的,实际确实false,这个原因是因为isReachable的实现,通常是ICMP ECHO Request 或是尝试使用目标主机上的端口7进行连接,很有可能被防火墙拦截,所以会访问不到。
如果要TELNET的话,会比较准确,比如以下代码
// TODO Auto-generated method stub
Socket server = null;
try {
server = new Socket();
InetSocketAddress address = new InetSocketAddress("bbs.sysu.edu.cn",23);
server.connect(address, 5000);
System.out.println("ok!");
}
catch (UnknownHostException e) {
System.out.println("wrong!");
e.printStackTrace();
} catch (IOException e) {
System.out.println("wrong");
e.printStackTrace();
}





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