### 服务器端
```java
package com.wang5;
import java.io.*;
import java.net.ServerSocket;
import java.net.Socket;
import java.nio.charset.StandardCharsets;
/**
* @ File : Server.java
* @ Author : Wangyuedong
* @ Time : 2021/9/13 16:56
*/
public class Server {
public static void main(String[] args) throws IOException {
ServerSocket ss = new ServerSocket(6666); //监听6666端口
System.out.println("Server is running...");
for(;;){
Socket sock = ss.accept();
System.out.println("connected from " + sock.getRemoteSocketAddress());
Thread t = new Handler(sock);
t.start();
}
}
}
class Handler extends Thread {
Socket sock;
public Handler(Socket sock) {
this.sock = sock;
}
@Override
public void run() {
try (InputStream input = this.sock.getInputStream()) {
try (OutputStream output = this.sock.getOutputStream()) {
handle(input, output);
}
} catch (Exception e) {
try {
this.sock.close();
} catch (IOException ioe) {
}
System.out.println("client disconnected.");
}
}
private void handle(InputStream input, OutputStream output) throws IOException {
BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(output, StandardCharsets.UTF_8));
BufferedReader reader = new BufferedReader(new InputStreamReader(input, StandardCharsets.UTF_8));
writer.write("hello\n");
writer.flush();
for (;;) {
String s = reader.readLine();
if (s.equals("bye")) {
writer.write("bye\n");
writer.flush();
break;
}
writer.write("ok: " + s + "\n");
writer.flush();
}
}
}
```
### 客户端
```java
package com.wang5;
import java.util.Scanner;
import java.io.*;
import java.net.Socket;
import java.nio.charset.StandardCharsets;
/**
* @ File : Client.java
* @ Author : Wangyuedong
* @ Time : 2021/9/13 17:08
*/
public class Client {
public static void main(String[] args) throws IOException {
Socket sock = new Socket("localhost", 6666); // 连接指定服务器和端口
try (InputStream input = sock.getInputStream()) {
try (OutputStream output = sock.getOutputStream()) {
handle(input, output);
}
}
sock.close();
System.out.println("disconnected.");
}
private static void handle(InputStream input, OutputStream output) throws IOException {
BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(output, StandardCharsets.UTF_8));
BufferedReader reader = new BufferedReader(new InputStreamReader(input, StandardCharsets.UTF_8));
Scanner scanner = new Scanner(System.in);
System.out.println("[server] " + reader.readLine());
for (;;) {
System.out.print(">>> "); // 打印提示
String s = scanner.nextLine(); // 读取一行输入
writer.write(s);
writer.newLine();
writer.flush();
String resp = reader.readLine();
System.out.println("<<< " + resp);
if (resp.equals("bye")) {
break;
}
}
}
}
```
### Socket流
当Socket连接创建成功后，无论是服务器端，还是客户端，我们都使用`Socket`实例进行网络通信。因为TCP是一种基于流的协议，因此，Java标准库使用`InputStream`和`OutputStream`来封装Socket的数据流，这样我们使用Socket的流，和普通IO流类似。
```java
// 用于读取网络数据:
InputStream in = sock.getInputStream();
// 用于写入网络数据:
OutputStream out = sock.getOutputStream();
```
如果不调用`flush()`，我们很可能会发现，客户端和服务器都收不到数据，这并不是Java标准库的设计问题，而是我们以流的形式写入数据的时候，并不是一写入就立刻发送到网络，而是先写入内存缓冲区，直到缓冲区满了以后，才会一次性真正发送到网络，这样设计的目的是为了提高传输效率。如果缓冲区的数据很少，而我们又想强制把这些数据发送到网络，就必须调用`flush()`强制把缓冲区数据发送出去。