接下来一段时间会对大家进行网络通信的魔鬼训练-理解socket

public void client() throws Exception {
    int i = 1;
    while (i <= 2) {
        Socket socket = new Socket("127.0.0.1", 520);
        //向服务器端第一次发送字符串
               OutputStream netOut = socket.getOutputStream();
        InputStream io = socket.getInputStream();
        String msg = i == 1 ? "客户端：我知道我是任性太任性，伤透了你的心。我是追梦的人，追一生的缘分。" :
                "客户端：我愿意嫁给你，你却不能答应我。";
        System.out.println(msg);
        netOut.write(msg.getBytes());
        netOut.flush();
        byte[] bytes = new byte[i == 1 ? 104 : 64];
        io.read(bytes);
        String response = new String(bytes);
        System.out.println(response);
        netOut.close();
        io.close();
        socket.close();
        i++;
    }
}

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)
            bind(localAddr);

} catch (IOException | IllegalArgumentException | SecurityException e) {
try {
            close();
        } catch (IOException ce) {
            e.addSuppressed(ce);
        }
        throw e;
    }
}

@Test
public void server() throws Exception {
    ServerSocket serverSocket = new ServerSocket(520);
    int i = 1;
    while (i <= 2) {
        String msg = i == 1 ? "服务端：我知道你是任性太任性，伤透了我的心。同是追梦的人，难舍难分。" :
                "服务端：你愿意嫁给你，我却不能向你承诺。";
        Socket socket = serverSocket.accept();
        InputStream io = socket.getInputStream();
        byte[] bytes = new byte[i == 1 ? 112 : 64];
        io.read(bytes);
        System.out.println(new String(bytes));
        OutputStream os = socket.getOutputStream();
        System.out.println(msg);
        byte[] outBytes = msg.getBytes();
        os.write(outBytes);
        os.flush();
        os.close();
        io.close();
        i++;
    }
}

/**
 * Create a server with the specified port, listen backlog, and
 * local IP address to bind to.  The <i>bindAddr</i> argument
 * can be used on a multi-homed host for a ServerSocket that
 * will only accept connect requests to one of its addresses.
 * If <i>bindAddr</i> is null, it will default accepting
 * connections on any/all local addresses.
 * The port must be between 0 and 65535, inclusive.
 * A port number of {@code 0} means that the port number is
 * automatically allocated, typically from an ephemeral port range.
 * This port number can then be retrieved by calling
 * {@link #getLocalPort getLocalPort}.
 *
 * <P>If there is a security manager, this method
 * calls its {@code checkListen} method
 * with the {@code port} argument
 * as its argument to ensure the operation is allowed.
 * This could result in a SecurityException.
 *
 * The {@code backlog} argument is the requested maximum number of
 * pending connections on the socket. Its exact semantics are implementation
 * specific. In particular, an implementation may impose a maximum length
 * or may choose to ignore the parameter altogther. The value provided
 * should be greater than {@code 0}. If it is less than or equal to
 * {@code 0}, then an implementation specific default will be used.
 * <P>
 * @param port  the port number, or {@code 0} to use a port
 *              number that is automatically allocated.
 * @param backlog requested maximum length of the queue of incoming
 *                connections.
 * @param bindAddr the local InetAddress the server will bind to
 *
 * @throws  SecurityException if a security manager exists and
 * its {@code checkListen} method doesn't allow the operation.
 *
 * @throws  IOException if an I/O error occurs when opening the socket.
 * @exception  IllegalArgumentException if the port parameter is outside
 *             the specified range of valid port values, which is between
 *             0 and 65535, inclusive.
 *
 * @see SocketOptions
 * @see SocketImpl
 * @see SecurityManager#checkListen
 * @since   JDK1.1
 */
public ServerSocket(int port, int backlog, InetAddress bindAddr) throws IOException {
    setImpl();
    if (port < 0 || port > 0xFFFF)
        throw new IllegalArgumentException(
                   "Port value out of range: " + port);
    if (backlog < 1)
      backlog = 50;
    try {
        bind(new InetSocketAddress(bindAddr, port), backlog);
    } catch(SecurityException e) {
        close();
        throw e;
    } catch(IOException e) {
        close();
        throw e;
    }
}