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示例內容:基於Java Socket實現的客戶端與服務器非阻塞發送接收消息。代碼包含三個類,Client, Server都比較簡單,ChatThread implements Runnable類實現了接收與發送消息。
思路:從Socket中獲取的InputStream是阻塞的,可以用DataInputStream對inputStream進行封裝,然後用非阻塞的DataInputStream#available方法詢問流中是否有數據,有數據時才用阻塞的讀方法將數據讀出。發送消息時,從控制檯讀入,同樣的道理,可以用BufferedReader等類對System.in進行封裝,調用BufferedReader#ready方法判斷數據是否準備好。
其他:起初看網上有人用ReceiveThread和SendThread來實現這樣的非阻塞通信,我嘗試後發現有線程關閉、己方Socket關閉但對方Socket未關閉的問題,於是我寫了CallbackHandler來解決問題。但後來發現沒有必要將讀寫寫成兩個線程,因爲我們實現的是非阻塞通信。同步是指用戶線程發起IO請求後需要等待或者輪詢內核IO操作完成後才能繼續執行,所以示例代碼屬於同步非阻塞IO模型。
示例代碼的編譯命令:javac -d ./out .\noblocking\*.java
啓動Server的命令:java -cp ./out noblocking.Server
啓動Client的命令:java -cp ./out noblocking.Client
命令執行如下圖:
代碼如下,三個類加到一塊不到100行,比較容易閱讀。Client中寫的IP是我的局域網IP,端口使用的13579.
package noblocking;
import java.io.*;
import java.net.ServerSocket;
import java.net.Socket;
public class Server {
public static void main(String[] args) {
try (ServerSocket serverSocket = new ServerSocket(13579)) {
while (true) {
Socket socket = serverSocket.accept();
new Thread(()->{
System.out.println(socket.getInetAddress().getHostName() + " on line!");
new ChatThread(socket).run();
System.out.println(socket.getInetAddress().getHostName() + " off line!");
}).start();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
package noblocking;
import java.io.IOException;
import java.net.Socket;
public class Client {
public static void main(String[] args) {
try {
Socket socket = new Socket("192.168.2.141", 13579);
new Thread(new ChatThread(socket)).start();
} catch (IOException e) {
e.printStackTrace();
}
}
}
package noblocking;
import java.io.*;
import java.net.Socket;
public class ChatThread implements Runnable {
private Socket socket;
public ChatThread(Socket socket) {
this.socket = socket;
}
@Override
public void run() {
try (BufferedReader localReader = new BufferedReader(new InputStreamReader(System.in));
DataOutputStream writeToRemote = new DataOutputStream(socket.getOutputStream());
DataInputStream readFromRemote = new DataInputStream(socket.getInputStream());
) {
// localWrite: System.out
while(!socket.isClosed()) {
if (readFromRemote.available() > 0) {
String msg = readFromRemote.readUTF();
if (msg.equals("exit")) {
break; // passive Exit
}
System.out.println("receive: " + msg);
}
if (localReader.ready()) {
String msg = localReader.readLine();
writeToRemote.writeUTF(msg);
if (msg.equals("exit")) {
break; // Active exit
}
}
}
} catch (IOException e) {
e.printStackTrace();
} finally {
if (!socket.isClosed()) {
try {
socket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}
附非阻塞IO通信模型圖