如何实现java的socket对等通信，即既可以作为服务器端，也可以作为客户端?

Java的Socket通信可以通过建立客户端和服务器端之间的连接来实现对等通信。可以通过以下步骤来实现：

1. 创建一个ServerSocket对象来监听来自客户端的连接请求。

2. 创建一个Socket对象来与服务器进行连接。

3. 通过输入输出流来进行数据传输。

下面是一个简单的Java Socket对等通信的示例：

Server端

import java.net.*;
import java.io.*;

public class Server {
    public static void main(String[] args) throws IOException {
        ServerSocket serverSocket = null;
        try {
            serverSocket = new ServerSocket(8888);
        } catch (IOException e) {
            System.err.println("Could not listen on port: 8888.");
            System.exit(1);
        }
        Socket clientSocket = null;
        try {
            clientSocket = serverSocket.accept();
        } catch (IOException e) {
            System.err.println("Accept failed.");
            System.exit(1);
        }
        PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);
        BufferedReader in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
        String inputLine;
        while ((inputLine = in.readLine()) != null) {
            out.println(inputLine);
        }
        out.close();
        in.close();
        clientSocket.close();
        serverSocket.close();
    }
}

Client端

import java.io.*;
import java.net.*;

public class Client {
    public static void main(String[] args) throws IOException {
        Socket socket = null;
        PrintWriter out = null;
        BufferedReader in = null;
        try {
            socket = new Socket("localhost", 8888);
            out = new PrintWriter(socket.getOutputStream(), true);
            in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
        } catch (UnknownHostException e) {
            System.err.println("Don't know about host: localhost.");
            System.exit(1);
        } catch (IOException e) {
            System.err.println("Couldn't get I/O for the connection to: localhost.");
            System.exit(1);
        }
        BufferedReader stdIn = new BufferedReader(new InputStreamReader(System.in));
        String userInput;
        while ((userInput = stdIn.readLine()) != null) {
            out.println(userInput);
            System.out.println("echo: " + in.readLine());
        }
        out.close();
        in.close();
        stdIn.close();
        socket.close();
    }
}

以上是一个简单的Java Socket对等通信的示例，你可以根据实际需求进行修改。