TCP所提供服务的主要特点：
- 面向连接的传输；
- 端到端的通信；
- 高可靠性，确保传输数据的正确性，不出现丢失或乱序；
- 全双工方式传输；
- 采用字节流方式，即以字节为单位传输字节序列；
TCP传输需要建立客户端和服务器端，即Socket和Server Socket，建立连接后，通过Socket中的IO流进行数据的传输。传输结束后关闭Socket。
package com.demo.test;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.UnknownHostException;
import java.util.ArrayList;
import java.util.Scanner;
import java.util.Timer;
import java.util.TimerTask;
class TcpDemo {
private static String SERVER_ADDR = "127.0.0.1";
private static int PORT = 7777;
private static String EXIT = "exit";
static class TcpServerThread extends Thread {
static class TcpClient {
private Socket socket;
private BufferedReader br;
private BufferedWriter bw;
public TcpClient(Socket socket) throws IOException {
this.socket = socket;
br = new BufferedReader(new InputStreamReader(socket.getInputStream()));
bw = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
}
public String readLine() throws IOException {
if (br != null) {
return br.readLine();
}
return null;
}
public void write(String str) throws IOException {
if (bw != null) {
bw.write(str + "\n");
// 注意：刷新是关键，否则会等到缓冲区满才将数据实际地发送出去
bw.flush();
}
}
public void close() {
if (br != null) {
try {
br.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if (bw != null) {
try {
bw.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if (socket != null) {
try {
socket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
private ArrayList<TcpClient> clientList = new ArrayList<TcpClient>();
private ServerSocket serverSocket;
@Override
public void run() {
try {
// backlog=-1表示无限制，默认是50个最大等待队列，如果设置无限制，由于每一个TCP连接都会占用服务器的内存，当服务器无法处理那么多连接时，就会让服务器崩溃。
int backlog = -1;
serverSocket = new ServerSocket(PORT, backlog);
Socket socket = null;
while ((socket = serverSocket.accept()) != null) {
System.out.println("server accept");
final TcpClient tcpClient = new TcpClient(socket);
clientList.add(tcpClient);
new Thread(new Runnable() {
@Override
public void run() {
try {
String line;
while ((line = tcpClient.readLine()) != null) {
System.out.println("serverSocket received: " + line);
tcpClient.write(line);
if (EXIT.equals(line)) {
break;
}
}
} catch (IOException e) {
e.printStackTrace();
} finally {
close();
}
}
}).start();
}
} catch (IOException e) {
e.printStackTrace();
}
}
public void close() {
for (TcpClient client : clientList) {
client.close();
}
try {
if (serverSocket != null) {
serverSocket.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
static class TcpClientThread extends Thread {
private Socket socket;
private BufferedReader br;
private BufferedWriter bw;
private Scanner scanner;
@Override
public void run() {
try {
socket = new Socket(SERVER_ADDR, PORT);
br = new BufferedReader(new InputStreamReader(socket.getInputStream()));
bw = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
scanner = new Scanner(System.in);
new Thread(new Runnable() {
@Override
public void run() {
try {
String line;
while ((line = br.readLine()) != null) {
System.out.println("client received: " + line);
if (EXIT.equals(line)) {
break;
}
}
} catch (IOException e) {
e.printStackTrace();
} finally {
closeSocket();
}
}
}).start();
Timer timer = new Timer();
timer.schedule(new TimerTask() {
@Override
public void run() {
try {
bw.write("hello world\n");
// 注意：刷新是关键，否则会等到缓冲区满才将数据实际地发送出去
bw.flush();
System.out.println("client write");
} catch (IOException e) {
e.printStackTrace();
// 发生错误立刻取消定时器
this.cancel();
}
}
}, 0, 5000);
String line;
while (scanner.hasNext()) {
line = scanner.nextLine();
bw.write(line + "\n");
// 注意：刷新是关键，否则会等到缓冲区满才将数据实际地发送出去
bw.flush();
if (EXIT.equals(line)) {
break;
}
}
} catch (UnknownHostException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
closeSocket();
}
}
private void closeSocket() {
if (scanner != null) {
scanner.close();
}
if (br != null) {
try {
br.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if (bw != null) {
try {
bw.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if (socket != null) {
try {
socket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
public static void main(String[] args) {
new TcpServerThread().start();
new TcpClientThread().start();
}
}
这里需要格外注意一点：如果没有调用flush()，数据只会被写入输出缓冲区，并不会从输出缓冲区发送到输出流中，因此另一方也就不可能接收到数据