1.TCP通信：

TCP类似于打电话，需要服务器端开启才能进行信息传输
客户端/发送端：

package TCP;

import java.io.IOException;
import java.io.OutputStream;
import java.net.InetAddress;
import java.net.Socket;
import java.net.UnknownHostException;
import java.nio.charset.StandardCharsets;

public class Client {
    public static void main(String[] args) {
        //1.获取服务器地址和端口号
        InetAddress serverIp = null;
        int port =0;
        Socket socket =null;
        OutputStream out = null;
        try {
            serverIp = InetAddress.getByName("127.0.0.1");
            port=9999;
            //2.创建输出对象
            socket = new Socket(serverIp,port);
            //3.获取输出流
            out = socket.getOutputStream();
            //4.输出内容
            out.write("你好呀".getBytes(StandardCharsets.UTF_8));//通过字节传输
        } catch (Exception e) {
            e.printStackTrace();
        }
        finally {
            if (socket!=null){
                try {
                    socket.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (out != null){
                try {
                    out.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }

    }
}

服务器端/接收端：

package TCP;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.ServerSocket;
import java.net.Socket;

public class Server {
    public static void main(String[] args) {
        ServerSocket serverSocket = null;
        Socket socket = null;
        InputStream in = null;
        ByteArrayOutputStream baos = null;//管道输出流(有缓冲的作用)


        try {
             //1.创建一个端口
            serverSocket = new ServerSocket(9999);
            //2.等待用户连接
            socket = serverSocket.accept();
            //3.读取客户端消息
            in = socket.getInputStream();
            //使用管道流接收
            baos = new ByteArrayOutputStream();
            byte[] buffer = new byte[1024];
            int len ;
            while((len = in.read(buffer))!=-1) {
                baos.write(buffer,0,len);
            }
            System.out.println(baos.toString("utf-8"));
        } catch (IOException e) {
            e.printStackTrace();
        }
        finally {
            if (baos!=null){
                try {
                    baos.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (in != null) {
                try {
                    in.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (socket != null){
                try {
                    socket.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (serverSocket != null) {
                try {
                    serverSocket.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }

    }

    }

注意：服务器端和客户端是相对而言的，服务器端也可以是发送端
服务器端接收到信息并处理后就停止了，可以通过while+信号灯的方式一直开启，不过serverSocket.accept();方法会将开启的端口进行堵塞连接

2.TPC实现文件传输：

发送端：

package FileTransfer;

import java.io.*;
import java.net.InetAddress;
import java.net.Socket;

public class Send {
    public static void main(String[] args) {
        Socket socket = null;
        OutputStream out = null;
        FileInputStream fin = null;
        ByteArrayOutputStream baos = null;
        InputStream in = null;
        try {
            //获取连接
            socket = new Socket(InetAddress.getByName("127.0.0.1"),9999);
            out = socket.getOutputStream();
            //获取文件
            fin = new FileInputStream("src/en.jpg");//文件路径
            byte[] buffer = new byte[1024];
            int len =0;
            //写文件
            while((len = fin.read(buffer))!=-1){
                out.write(buffer,0,len);
            }
            //通知服务器我已经传输完了
            socket.shutdownOutput();

            //获取服务器的回复，确保服务器接收完成
            in = socket.getInputStream();
            //使用管道流
            baos = new ByteArrayOutputStream();
            byte[] buffer2 = new byte[1024];
            int len2 =0;
            while((len2 = in.read(buffer2))!= -1){
                baos.write(buffer2);
            }
            System.out.println(baos.toString("utf-8"));
        } catch (Exception e) {
            e.printStackTrace();
        }
        finally{
            //关闭连接
            if (baos!=null){
                try {
                    baos.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (in!=null){
                try {
                    in.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (out!=null){
                try {
                    out.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (fin!=null){
                try {
                    fin.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (socket!=null){
                try {
                    socket.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

接收端：

package FileTransfer;

import java.io.*;
import java.net.ServerSocket;
import java.net.Socket;
import java.nio.charset.StandardCharsets;

public class Receive {
    public static void main(String[] args) {

        ServerSocket serverSocket = null;
        Socket socket = null;
        InputStream in = null;
        FileOutputStream fos = null;
        OutputStream out = null;
        try {
            //创建服务
            serverSocket = new ServerSocket(9999);
            //创建监听客户端的连接，接收消息
            socket = serverSocket.accept();
            //获取输入流
            in = socket.getInputStream();
            //文件传输
            fos = new FileOutputStream("shoudaode.jpg");
            byte[] buffer = new byte[1024];
            int len = 0;
            while((len = in.read(buffer)) != -1){
                fos.write(buffer,0,len);
            }
            //告诉客户端我接收完毕
            out = socket.getOutputStream();
            out.write("我已经接收完成了，你可以关闭了".getBytes(StandardCharsets.UTF_8));


        } catch (IOException e) {
            e.printStackTrace();
        }finally{//关闭连接
            if (out != null){
                try {
                    out.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (fos != null){
                try {
                    fos.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (in != null){
                try {
                    in.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (socket != null){
                try {
                    socket.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (serverSocket != null){
                try {
                    serverSocket.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}