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测试代码

//将172.16.12.171 替换为 xingyun25 打印结果一致Socket sock = new Socket("172.16.12.171",12331); InetAddress netAddress = sock.getInetAddress();System.out.println(netAddress.getHostName());System.out.println(netAddress.getHostAddress());sock.close();

打印结果

xingyun25172.16.12.171

查看 Socket 方法

public Socket(String host, int port) throws UnknownHostException, IOException    {
          //host != null 因此第一个参数为new InetSocketAddress(host, port)       this(host != null ? new InetSocketAddress(host, port) :             new InetSocketAddress(InetAddress.getByName(null),              //第二个参数 (SocketAddress) null              //第三个参数 true                             (SocketAddress) null, true);    }

查看 this 构造方法

private Socket(SocketAddress address, SocketAddress localAddr,                   boolean stream) throws IOException {
       setImpl();    // backward compatibility    if (address == null)        throw new NullPointerException();    try {
           createImpl(stream);        if (localAddr != null)            //localhost/127.0.0.1            bind(localAddr);        //建立连接        connect(address);    } catch (IOException | IllegalArgumentException | SecurityException e) {
           try {
               close();        } catch (IOException ce) {
               e.addSuppressed(ce);        }        throw e;    }}

对于 setImpl 方法

void setImpl() {    if (factory != null) {        impl = factory.createSocketImpl();        checkOldImpl();    } else {        // No need to do a checkOldImpl() here, we know it's an up to date        // SocketImpl!        impl = new SocksSocketImpl();    }    //Impl SET Socket     if (impl != null)        impl.setSocket(this);}

对于 createImpl 方法

// SocketImpl impl ：The implementation of this Socket. void createImpl(boolean stream) throws SocketException {
       if (impl == null)        setImpl();    try {
           impl.create(stream);        created = true;    } catch (IOException e) {
           throw new SocketException(e.getMessage());    }}

查看InetSocketAddress方法通过IP和域名创建有何不同

public InetSocketAddress(String hostname, int port) {        checkHost(hostname);        InetAddress addr = null;		String host = null;        try {            addr = InetAddress.getByName(hostname);        } catch(UnknownHostException e){           host = hostname;        }        //实际构造了 InetSocketAddressHolder         holder = new InetSocketAddressHolder(host, addr, checkPort(port));    }

connect 过程中实际使用的是 InetAddress

private InetSocketAddressHolder(String hostname, InetAddress addr, int port) {
               this.hostname = hostname;             this.addr = addr;            this.port = port;}

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