[java]代码库package cn.outofmemory.socket.example;

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;

public class App {

public static void main(String[] args) throws IOException {

int port = args.length > 0 ? Integer.parseInt(args[0]) : 19999;

ServerSocket server = new ServerSocket(port);

System.out.println("server waits client");

Socket client = server.accept();

System.out.println("client comes. please write to client");

BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(client.getOutputStream()));

BufferedReader consoleRdr = new BufferedReader(new InputStreamReader(System.in));

String line;

do {

line = consoleRdr.readLine();

if ("quit".equals(line)) {

break;

}

bw.write(line);

bw.write("\r\n");

bw.flush();

} while (true);

bw.close();

server.close();

System.out.println("bye");

}

}

//源代码片段来自云代码http://yuncode.net

package cn.outofmemory.socket.example;

import java.io.BufferedReader;

import java.io.IOException;

import java.io.InputStreamReader;

import java.net.Socket;

import java.net.UnknownHostException;

public class Client {

public static void main(String[] args) throws UnknownHostException, IOException {

final int PORT = 19999;

Socket client = new Socket("localhost", PORT);

BufferedReader rdr = new BufferedReader(new InputStreamReader(client.getInputStream()));

do {

String line = rdr.readLine();

System.out.print("server said:");

System.out.println(line);

} while (true);

}

}

//源代码片段来自云代码http://yuncode.net

最近项目涉及到与C的通讯，目的是转发一下信息，Java这边使用的时监听Socket的接口，只要给C提供IP和端口 就行了。

已知Socket的编程有 TCP和UDP协议，据说UDP更快一点 这里使用的UDP编程

1.创建一个服务类PushPrinterServer

import com.util.GetByteEncode;

import com.util.HttpClientUtil;

import org.slf4j.Logger;

import org.slf4j.LoggerFactory;

import java.net.DatagramPacket;

import java.net.DatagramSocket;

import java.nio.ByteBuffer;

import java.nio.CharBuffer;

import java.nio.charset.Charset;

import static com.constants.PrinterSocketConstants.PRINTER_URL;

public class PushPrinterServer extends Thread {

private static final int PORT=9002;//监听的端口号

private static final Logger LOGGER = LoggerFactory.getLogger(PushPrinterServer.class);

private DatagramSocket datagramSocket=null;

public PushPrinterServer(DatagramSocket datagramSocket) {

if (datagramSocket==null){

try {

LOGGER.info("开启推送打印服务器端口"+PORT);

this.datagramSocket = new DatagramSocket(PORT);

}catch (Exception e){

LOGGER.error("开启socket推送打印服务出错");

e.printStackTrace();

}

}

}

@Override

public void run() {

try {

while (!this.isInterrupted()) {

// // 一旦有堵塞, 则表示服务器与客户端获得了连接

byte[] receiveData= new byte[1024];

DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);

datagramSocket.receive(receivePacket);// 在接收到信息之前，一直保持阻塞状态

String encoding = GetByteEncode.getEncoding(receiveData);//编码判断

System.out.println("字符编码是："+encoding);

ByteBuffer byteBuffer = ByteBuffer.wrap(receiveData);

CharBuffer gb18030 = Charset.forName("GB18030").decode(byteBuffer);

ByteBuffer utf8 = Charset.forName("UTF8").encode(gb18030);

String data= new String(utf8.array());

LOGGER.info("客户端发送消息:"+data);

try {

if(receiveData!=null){

HttpClientUtil.requestHttpPost(data,PRINTER_URL);

LOGGER.info("已向管理平台发送请求...");

}

} catch (Exception e) {

e.printStackTrace();

LOGGER.info("向管理平台发送请求失败");

}

}

} catch (Exception e) {

LOGGER.error("推送打印异常: " + e.getMessage());

}

}

public void closeSocketServer(){

if(null!=datagramSocket && !datagramSocket.isClosed())

{

LOGGER.info("关闭推送打印服务器");

datagramSocket.close();

}

}

}

-----------------------------------------------------------------------------------------------

receiveData 是监听接口收到是字节组的源数据，由于发过来的中文乱码，但一直处理不了，所有这里先查出源数据的编码格式，再进行处理，data是处理

完的数据，然后转发一下就好了。

2.创建一个监听类PushPrinterSocketServiceLoader

网上许多写的多写在main方法里面，但是真实的项目怎么办呢，要让它项目已启动就开启线程监听，创建监听类

import com.service.PushPrinterServer;

import javax.servlet.ServletContextEvent;

import javax.servlet.ServletContextListener;

public class PushPrinterSocketServiceLoader implements ServletContextListener {

//socket server 线程

private PushPrinterServer pushPrinterServer;

@Override

public void contextInitialized(ServletContextEvent servletContextEvent) {

if(null==pushPrinterServer)

{

//新建线程类

pushPrinterServer=new PushPrinterServer(null);

//启动线程

pushPrinterServer.start();

}

}

@Override

public void contextDestroyed(ServletContextEvent servletContextEvent) {

if(null!=pushPrinterServer && !pushPrinterServer.isInterrupted())

{

System.out.println("推送打印服务器关闭");

pushPrinterServer.closeSocketServer();

pushPrinterServer.interrupt();

}

}

}

3.在web.xml添加配置

com.listener.PushPrinterSocketServiceLoader

一、业务场景

好多朋友在咨询如何得知(监测)MQTT客户端状态(在线、离线)，或者可以说是监测采集器状态。

其实这个在MQTT协议中已经给出系统主题，MQTT服务端可以知道客户端的任何情况，比如：什么时候上线和下线。

二、解决方案

$SYS/brokers/${node}/clients/${clientid}/connected：上线事件。当某客户端上线时，会向该主题(Topic)发布消息

$SYS/brokers/${node}/clients/${clientid}/disconnected：掉线事件。当某客户端掉线时，会向该主题(Topic)发布消息

当然在开发的时候我们订阅两个主题比较麻烦，在这里我们可以采用主题通配符模式直接订阅一个主题即可：

$SYS/brokers/+/clients/#

这样比较方便，只不过需要我们在回调函数中进行Topic主题的区分就可以了，例如：

/**

* subscribe后得到的消息会执行到这里面

*/

@Override

public void messageArrived(String topic, MqttMessage message) throws Exception {

String msg = new String(message.getPayload());

try {

JSONObject jsonObject = JSON.parseObject(msg);

String clientId = String.valueOf(jsonObject.get("clientid"));

if (topic.endsWith("disconnected")) {

log.info("客户端已掉线：{}",clientId);

} else {

log.info("客户端已上线：{}",clientId);

}

} catch (JSONException e) {

log.error("JSON Format Parsing Exception : {}", msg);

}

}