通过socket在本机上通信：

TCPClient.java

import java.io.BufferedReader;import java.io.DataOutputStream;import java.io.IOException;import java.io.InputStreamReader;import java.net.Socket;import java.net.UnknownHostException;public class TCPClient {    public static void main(String[] args) throws UnknownHostException, IOException {        String sentence;            //存储用户输入的字符串        String modifiedsentence;    //存储经过服务器修改的字符串        BufferedReader inFromUser=new BufferedReader(new InputStreamReader(System.in));//创建一个从标准输入流输入的对象        Socket clientSocket=new Socket("127.0.0.1",9999);//建立一个socket对象.127..0.0.1表示本机         DataOutputStream outToServer = new DataOutputStream(clientSocket.getOutputStream());//创建一个经由tcp的输出对象        BufferedReader inFromServer = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));//创建一个经由tcp的输入对象        sentence=inFromUser.readLine();//读取用户的输入        outToServer.writeBytes(sentence+'\n');//将用户数据传入到服务器        modifiedsentence=inFromServer.readLine();//将修改后的数据接收回来        System.out.println(modifiedsentence);//在标准输出上输出字符串        clientSocket.close();    }}

TCPServer.java

import java.io.BufferedReader;import java.io.DataOutputStream;import java.io.IOException;import java.io.InputStreamReader;import java.net.ServerSocket;import java.net.Socket;public class TCPServer {    public static void main(String[] args) throws IOException {    String clientSentence;    String capitalizedSentence;    @SuppressWarnings("resource")    ServerSocket welcomeSocket=new ServerSocket(9999);    while(true){        Socket connectionSocket=welcomeSocket.accept();        BufferedReader inFromClient=new BufferedReader(new InputStreamReader(connectionSocket.getInputStream()));        DataOutputStream outToClient=new DataOutputStream(connectionSocket.getOutputStream());        clientSentence=inFromClient.readLine();        capitalizedSentence=clientSentence.toUpperCase()+'\n';        outToClient.writeBytes(capitalizedSentence);              }    }}