Inet4Address.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.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package java.net;

import java.io.ObjectStreamException;

/**
 * This class represents an Internet Protocol version 4 (IPv4) address.
 * Defined by <a href="http://www.ietf.org/rfc/rfc790.txt">
 * <i>RFC&nbsp;790: Assigned Numbers</i></a>,
 * <a href="http://www.ietf.org/rfc/rfc1918.txt">
 * <i>RFC&nbsp;1918: Address Allocation for Private Internets</i></a>,
 * and <a href="http://www.ietf.org/rfc/rfc2365.txt"><i>RFC&nbsp;2365:
 * Administratively Scoped IP Multicast</i></a>
 *
 * <h3> <a id="format">Textual representation of IP addresses</a> </h3>
 *
 * Textual representation of IPv4 address used as input to methods
 * takes one of the following forms:
 *
 * <blockquote><ul style="list-style-type:none">
 * <li>{@code d.d.d.d}</li>
 * <li>{@code d.d.d}</li>
 * <li>{@code d.d}</li>
 * <li>{@code d}</li>
 * </ul></blockquote>
 *
 * <p> When four parts are specified, each is interpreted as a byte of
 * data and assigned, from left to right, to the four bytes of an IPv4
 * address.
 *
 * <p> When a three part address is specified, the last part is
 * interpreted as a 16-bit quantity and placed in the right most two
 * bytes of the network address. This makes the three part address
 * format convenient for specifying Class B net- work addresses as
 * 128.net.host.
 *
 * <p> When a two part address is supplied, the last part is
 * interpreted as a 24-bit quantity and placed in the right most three
 * bytes of the network address. This makes the two part address
 * format convenient for specifying Class A network addresses as
 * net.host.
 *
 * <p> When only one part is given, the value is stored directly in
 * the network address without any byte rearrangement.
 *
 * <p> For methods that return a textual representation as output
 * value, the first form, i.e. a dotted-quad string, is used.
 *
 * <h4> The Scope of a Multicast Address </h4>
 *
 * Historically the IPv4 TTL field in the IP header has doubled as a
 * multicast scope field: a TTL of 0 means node-local, 1 means
 * link-local, up through 32 means site-local, up through 64 means
 * region-local, up through 128 means continent-local, and up through
 * 255 are global. However, the administrative scoping is preferred.
 * Please refer to <a href="http://www.ietf.org/rfc/rfc2365.txt">
 * <i>RFC&nbsp;2365: Administratively Scoped IP Multicast</i></a>
 *
 * @since 1.4
 */
// IP4地址的实现类
public final class Inet4Address extends InetAddress {
    
    static final int INADDRSZ = 4;  // IP4地址包含的字节数
    
    /* Perform initializations */
    static {
        init();
    }
    
    
    
    /*▼ 构造器 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    Inet4Address() {
        super();
        holder().hostName = null;
        holder().address = 0;
        holder().family = IPv4;
    }
    
    Inet4Address(String hostName, byte[] addr) {
        holder().hostName = hostName;
        holder().family = IPv4;
        if(addr != null) {
            if(addr.length == INADDRSZ) {
                int address = addr[3] & 0xFF;
                address |= ((addr[2] << 8) & 0xFF00);
                address |= ((addr[1] << 16) & 0xFF0000);
                address |= ((addr[0] << 24) & 0xFF000000);
                holder().address = address;
            }
        }
        holder().originalHostName = hostName;
    }
    
    Inet4Address(String hostName, int address) {
        holder().hostName = hostName;
        holder().family = IPv4;
        holder().address = address;
        holder().originalHostName = hostName;
    }
    
    /*▲ 构造器 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 属性 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Returns the raw IP address of this {@code InetAddress}
     * object. The result is in network byte order: the highest order
     * byte of the address is in {@code getAddress()[0]}.
     *
     * @return the raw IP address of this object.
     */
    // 返回IP4地址的字节形式
    public byte[] getAddress() {
        int address = holder().getAddress();
        byte[] addr = new byte[INADDRSZ];
        
        addr[0] = (byte) ((address >>> 24) & 0xFF);
        addr[1] = (byte) ((address >>> 16) & 0xFF);
        addr[2] = (byte) ((address >>> 8) & 0xFF);
        addr[3] = (byte) (address & 0xFF);
        return addr;
    }
    
    /**
     * Returns the IP address string in textual presentation form.
     *
     * @return the raw IP address in a string format.
     */
    // 返回IP4地址的文本形式
    public String getHostAddress() {
        return numericToTextFormat(getAddress());
    }
    
    /*▲ 属性 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 特殊地址 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Utility routine to check if the InetAddress is a loopback address.
     *
     * @return a {@code boolean} indicating if the InetAddress is
     * a loopback address; or false otherwise.
     */
    // 判断当前地址是否为本地环回地址（特殊地址，如127.0.0.1）
    public boolean isLoopbackAddress() {
        /* 127.x.x.x */
        byte[] byteAddr = getAddress();
        return byteAddr[0] == 127;
    }
    
    /**
     * Utility routine to check if the InetAddress is a wildcard address.
     *
     * @return a {@code boolean} indicating if the Inetaddress is a wildcard address.
     */
    // 判断当前地址是否为通配地址（特殊地址，字节全为0）
    public boolean isAnyLocalAddress() {
        return holder().getAddress() == 0;
    }
    
    /**
     * Utility routine to check if the InetAddress is an link local address.
     *
     * @return a {@code boolean} indicating if the InetAddress is
     * a link local address; or false if address is not a link local unicast address.
     */
    /*
     * 判断当前地址是否为链路本地地址（特殊地址，169.254.0.0）
     *
     * 通常情况下，每台主机都通过DHCP服务器自动分配一个IP地址
     * 当DHCP分配失败或者没有DHCP服务器时，主机可以为自身分配169.254.0.0这个IP
     */
    public boolean isLinkLocalAddress() {
        // link-local unicast in IPv4 (169.254.0.0/16)
        // defined in "Documenting Special Use IPv4 Address Blocks
        // that have been Registered with IANA" by Bill Manning
        // draft-manning-dsua-06.txt
        int address = holder().getAddress();
        return (((address >>> 24) & 0xFF) == 169) && (((address >>> 16) & 0xFF) == 254);
    }
    
    /**
     * Utility routine to check if the InetAddress is a site local address.
     *
     * @return a {@code boolean} indicating if the InetAddress is
     * a site local address; or false if address is not a site local unicast address.
     */
    /*
     * 判断当前地址是否为站点本地地址（特殊地址10/8、172.16/12、192.168/16）
     * 该类地址被设计用于不会与互联网直接通信的设备，比如：打印机、内部网服务器、网络交换机等
     */
    public boolean isSiteLocalAddress() {
        // refer to RFC 1918
        // 10/8 prefix
        // 172.16/12 prefix
        // 192.168/16 prefix
        int address = holder().getAddress();
        return (((address >>> 24) & 0xFF) == 10) || ((((address >>> 24) & 0xFF) == 172) && (((address >>> 16) & 0xF0) == 16)) || ((((address >>> 24) & 0xFF) == 192) && (((address >>> 16) & 0xFF) == 168));
    }
    
    /**
     * Utility routine to check if the InetAddress is an
     * IP multicast address. IP multicast address is a Class D
     * address i.e first four bits of the address are 1110.
     *
     * @return a {@code boolean} indicating if the InetAddress is
     * an IP multicast address
     */
    // 判断当前地址是否为组播地址（D类地址，以1110开头）
    public boolean isMulticastAddress() {
        return ((holder().getAddress() & 0xf0000000) == 0xe0000000);
    }
    
    /**
     * Utility routine to check if the multicast address has node scope.
     *
     * @return a {@code boolean} indicating if the address has
     * is a multicast address of node-local scope, false if it is not
     * of node-local scope or it is not a multicast address
     */
    // 判断当前地址是否为节点（或接口）本地范围的组播地址
    public boolean isMCNodeLocal() {
        // unless ttl == 0
        return false;
    }
    
    /**
     * Utility routine to check if the multicast address has link scope.
     *
     * @return a {@code boolean} indicating if the address has
     * is a multicast address of link-local scope, false if it is not
     * of link-local scope or it is not a multicast address
     */
    // 判断当前地址是否为链路本地范围的组播地址（224.0.0/24）
    public boolean isMCLinkLocal() {
        // 224.0.0/24 prefix and ttl == 1
        int address = holder().getAddress();
        return (((address >>> 24) & 0xFF) == 224) && (((address >>> 16) & 0xFF) == 0) && (((address >>> 8) & 0xFF) == 0);
    }
    
    /**
     * Utility routine to check if the multicast address has site scope.
     *
     * @return a {@code boolean} indicating if the address has
     * is a multicast address of site-local scope, false if it is not
     * of site-local scope or it is not a multicast address
     */
    // 判断当前地址是否为站点本地范围的组播地址
    public boolean isMCSiteLocal() {
        // 239.255/16 prefix or ttl < 32
        int address = holder().getAddress();
        return (((address >>> 24) & 0xFF) == 239) && (((address >>> 16) & 0xFF) == 255);
    }
    
    /**
     * Utility routine to check if the multicast address has organization scope.
     *
     * @return a {@code boolean} indicating if the address has
     * is a multicast address of organization-local scope,
     * false if it is not of organization-local scope
     * or it is not a multicast address
     */
    // 判断当前地址是否为机构本地范围的组播地址
    public boolean isMCOrgLocal() {
        // 239.192 - 239.195
        int address = holder().getAddress();
        return (((address >>> 24) & 0xFF) == 239) && (((address >>> 16) & 0xFF) >= 192) && (((address >>> 16) & 0xFF)<=195);
    }
    
    /**
     * Utility routine to check if the multicast address has global scope.
     *
     * @return a {@code boolean} indicating if the address has
     * is a multicast address of global scope, false if it is not
     * of global scope or it is not a multicast address
     */
    // 判断当前地址是否为全局范围的组播地址（224.0.1.0到238.255.255.255）
    public boolean isMCGlobal() {
        // 224.0.1.0 to 238.255.255.255
        byte[] byteAddr = getAddress();
        return ((byteAddr[0] & 0xff) >= 224 && (byteAddr[0] & 0xff)<=238) && !((byteAddr[0] & 0xff) == 224 && byteAddr[1] == 0 && byteAddr[2] == 0);
    }
    
    /*▲ 特殊地址 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 序列化 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * use serialVersionUID from InetAddress, but Inet4Address instance
     * is always replaced by an InetAddress instance before being
     * serialized
     */
    private static final long serialVersionUID = 3286316764910316507L;
    
    /**
     * Replaces the object to be serialized with an InetAddress object.
     *
     * @return the alternate object to be serialized.
     *
     * @throws ObjectStreamException if a new object replacing this
     *                               object could not be created
     */
    private Object writeReplace() throws ObjectStreamException {
        // will replace the to be serialized 'this' object
        InetAddress inet = new InetAddress();
        inet.holder().hostName = holder().getHostName();
        inet.holder().address = holder().getAddress();
        
        /*
         * Prior to 1.4 an InetAddress was created with a family
         * based on the platform AF_INET value (usually 2).
         * For compatibility reasons we must therefore write
         * the InetAddress with this family.
         */
        inet.holder().family = 2;
        
        return inet;
    }
    
    /*▲ 序列化 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    /**
     * Converts IPv4 binary address into a string suitable for presentation.
     *
     * @param src a byte array representing an IPv4 numeric address
     *
     * @return a String representing the IPv4 address in
     * textual representation format
     */
    // 将二进制形式的IP4地址转换为文本形式的IP4地址
    static String numericToTextFormat(byte[] src) {
        return (src[0] & 0xff) + "." + (src[1] & 0xff) + "." + (src[2] & 0xff) + "." + (src[3] & 0xff);
    }
    
    /**
     * Perform class load-time initializations.
     */
    private static native void init();
    
    
    /**
     * Returns a hashcode for this IP address.
     *
     * @return a hash code value for this IP address.
     */
    public int hashCode() {
        return holder().getAddress();
    }
    
    /**
     * Compares this object against the specified object.
     * The result is {@code true} if and only if the argument is
     * not {@code null} and it represents the same IP address as
     * this object.
     * <p>
     * Two instances of {@code InetAddress} represent the same IP
     * address if the length of the byte arrays returned by
     * {@code getAddress} is the same for both, and each of the
     * array components is the same for the byte arrays.
     *
     * @param obj the object to compare against.
     *
     * @return {@code true} if the objects are the same;
     * {@code false} otherwise.
     *
     * @see java.net.InetAddress#getAddress()
     */
    public boolean equals(Object obj) {
        return (obj != null) && (obj instanceof Inet4Address) && (((InetAddress) obj).holder().getAddress() == holder().getAddress());
    }
    
}