Inet4AddressImpl.java

/*
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
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package java.net;

import java.io.IOException;
import java.util.Enumeration;

/**
 * Package private implementation of InetAddressImpl for IPv4.
 *
 * @since 1.4
 */
// Inet4Address类的补充
class Inet4AddressImpl implements InetAddressImpl {
    
    private InetAddress anyLocalAddress;    // 通配符地址
    private InetAddress loopbackAddress;    // 本地环回地址
    
    // 本地主机名称
    public native String getLocalHostName() throws UnknownHostException;
    
    // 本地环回地址
    public synchronized InetAddress loopbackAddress() {
        if(loopbackAddress == null) {
            byte[] loopback = {0x7f, 0x00, 0x00, 0x01};
            loopbackAddress = new Inet4Address("localhost", loopback);
        }
        return loopbackAddress;
    }
    
    // 通配符地址（特殊地址，字节全为0）
    public synchronized InetAddress anyLocalAddress() {
        if(anyLocalAddress == null) {
            anyLocalAddress = new Inet4Address(); // {0x00,0x00,0x00,0x00}
            anyLocalAddress.holder().hostName = "0.0.0.0";
        }
        return anyLocalAddress;
    }
    
    // 通过指定的网络接口判断给定的网络地址是否可用，ttl代表网络跳数
    public boolean isReachable(InetAddress addr, int timeout, NetworkInterface netif, int ttl) throws IOException {
        byte[] ifaddr = null;
        
        if(netif != null) {
            /* Let's make sure we use an address of the proper family */
            Enumeration<InetAddress> it = netif.getInetAddresses();
            InetAddress inetaddr = null;
            while(!(inetaddr instanceof Inet4Address) && it.hasMoreElements()) {
                inetaddr = it.nextElement();
            }
            
            if(inetaddr instanceof Inet4Address) {
                ifaddr = inetaddr.getAddress();
            }
        }
        
        return isReachable0(addr.getAddress(), timeout, ifaddr, ttl);
    }
    
    private native boolean isReachable0(byte[] addr, int timeout, byte[] ifaddr, int ttl) throws IOException;
    
    
    // 将主机名称或主机地址映射为InetAddress实例
    public native InetAddress[] lookupAllHostAddr(String hostname) throws UnknownHostException;
    
    // 根据主机地址查找映射的主机名称
    public native String getHostByAddr(byte[] addr) throws UnknownHostException;
    
}