UDP(User Datagram Protocol)是一种无连接的协议,每个数据包都是一个独立的信息,包括完整的源地址或目的地址。由于UDP在网络上是以任何可能的路径传往目的地的,因此能否到达目的地、到达目的地的时间及内容的正确性都是不能被保证的。使用UDP时,每个数据包中都给出了完整的地址信息,无须再建立发送方和接收方的连接。但使用UDP传输数据是有大小限制的,每个被传输的数据包必须限定在64KB之内。UDP是一个不可靠的协议,发送方所发送的数据包不一定以相同的次序到达接收方。在java.net包中提供了两个类:DatagramSocket和DatagramPacket,用于支持数据包通信。DatagramSocket类用于在程序之间建立传送数据包的通信连接,DatagramPacket类用于表示一个数据包。
import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
public class HelloWorld {
public static void main(String[] args) throws InterruptedException {
Thread server = new Thread(new Server());
server.start();
Thread.sleep(1000);
Thread client = new Thread(new Client());
client.start();
}
}
class Server implements Runnable {
@Override
public void run() {
try {
DatagramSocket socket = new DatagramSocket(1090);
byte[] data = new byte[1024];
while (true) {
DatagramPacket dataPackage = new DatagramPacket(data, data.length);
socket.receive(dataPackage);
String dataString = new String(dataPackage.getData());
System.out.println(dataString);
if (dataString.substring(0, 4).equals("exit")) {
socket.close();
System.out.println("客户端退出，断开连接");
break;
}
dataPackage = new DatagramPacket("服务端已受到信息".getBytes(), "服务端已受到信息".getBytes().length,
dataPackage.getSocketAddress());
socket.send(dataPackage);
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
class Client implements Runnable {
@Override
public void run() {
byte[] data = new byte[1024];
// String sendString = "客户端信息";
String sendString = "exit";
try {
InetAddress address = InetAddress.getByName("127.0.0.1");
// DatagramPacket datagramPacket = new DatagramPacket(data, data.length,
// address, 1090);
DatagramPacket datagramPacket = new DatagramPacket(sendString.getBytes(),
sendString.getBytes().length, address, 1090);
DatagramSocket socket = new DatagramSocket();
socket.send(datagramPacket);
datagramPacket = new DatagramPacket(data, data.length);
socket.receive(datagramPacket);
System.out.println(new String(datagramPacket.getData()));
socket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
TCP(Tranfer Control Protocol)是一种面向连接的、保证可靠传输的协议。通过TCP协议传输,得到的是一个顺序的、无差错的数据流。发送方和接收方成对的两个套接字之间必须建立连接,一旦两个套接字连接起来,它们就可以进行双向数据传输,双方都可以进行发送或接收操作。与UDP不同,TCP对传输数据的大小没有限制。TCP是一个可靠的协议,其确保接收方完全正确地获取发送方所发送的全部数据。在java.net包中提供了两个类:Socket和ServerSocket,分别用于表示双向连接的客户端和服务器端。
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.net.ServerSocket;
import java.net.Socket;
public class HelloWorld {
public static void main(String[] args) throws InterruptedException {
Thread server = new Thread(new Server());
server.start();
Thread.sleep(1000);
Thread client = new Thread(new Client());
client.start();
}
}
class Server implements Runnable {
@Override
public void run() {
ServerSocket serverSocket = null;
try {
serverSocket = new ServerSocket(8090);
while (true) {
Socket socket = serverSocket.accept();
OutputStream out = socket.getOutputStream();
BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(out));
writer.write("服务端消息\n");
// writer.write("exit服务端消息\n");
writer.flush();
InputStream in = socket.getInputStream();
BufferedReader reader = new BufferedReader(new InputStreamReader(in));
String message = reader.readLine();
System.out.println(message);
reader.close();
in.close();
writer.close();
out.close();
socket.close();
if (message.substring(0, 4).equalsIgnoreCase("exit")) {
System.out.println("客户端退出，断开连接");
break;
}
}
serverSocket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
class Client implements Runnable {
@Override
public void run() {
Socket socket = null;
try {
while (true) {
socket = new Socket("127.0.0.1",8090);
InputStream in = socket.getInputStream();
BufferedReader reader = new BufferedReader(new InputStreamReader(in));
String message = reader.readLine();
System.out.println(message);
if (message.substring(0, 4).equalsIgnoreCase("exit")) {
reader.close();
in.close();
System.out.println("服务端退出，断开连接");
break;
}
OutputStream out = socket.getOutputStream();
BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(out));
writer.write("客户端消息\n");
writer.flush();
writer.close();
out.close();
reader.close();
in.close();
}
socket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
HTTP是一个属于应用层的面向对象的协议,适用于分布式超媒体信息系统。HTTP协议是基于请求/响应范式的。一个客户机与服务器建立连接后,发送一个请求给服务器,请求的格式为统一资源标识符、协议版本号,后面是MIME信息(包括请求修饰符、客户机信息和可能的内容)。服务器接收到请求后,给予相应的响应信息,其格式为信息的协议版本号、一个成功或错误的代码,后面是MIME信息(包括服务器信息、实体信息和可能的内容)。
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.URL;
import java.net.URLConnection;
import java.util.List;
import java.util.Map;
public class HelloWorld {
public static void main(String[] args) {
try {
URL url = new URL("https://dotcorejava.github.io/javaprograming");
URLConnection conn = url.openConnection();
System.out.printf("ConnectTimeout: %dms\n", conn.getConnectTimeout());
System.out.printf("ReadTimeout: %dms\n", conn.getReadTimeout());
Map<String, List<String>> headMap = conn.getHeaderFields();
for (Map.Entry<String, List<String>> entry : headMap.entrySet()) {
System.out.println(entry.getKey() + ":" + entry.getValue());
}
BufferedReader reader = new BufferedReader(
new InputStreamReader((InputStream) conn.getContent()));
String line = "";
while ((line = reader.readLine()) != null) {
System.out.println(line);
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
完成一个基于UDP或TCP协议的网络通信程序。