Java实现心跳机制的方法

一、心跳机制简介

在分布式系统中，分布在不同主机上的节点需要检测其他节点的状态，如服务器节点需要检测从节点是否失效。为了检测对方节点的有效性，每隔固定时间就发送一个固定信息给对方，对方回复一个固定信息，如果长时间没有收到对方的回复，则断开与对方的连接。

发包方既可以是服务端，也可以是客户端，这要看具体实现。因为是每隔固定时间发送一次，类似心跳，所以发送的固定信息称为心跳包。心跳包一般为比较小的包，可根据具体实现。心跳包主要应用于长连接的保持与短线链接。

一般而言，应该客户端主动向服务器发送心跳包，因为服务器向客户端发送心跳包会影响服务器的性能。

二、心跳机制实现方式

心跳机制有两种实现方式，一种基于TCP自带的心跳包，TCP的SO_KEEPALIVE选项可以，系统默认的默认跳帧频率为2小时，超过2小时后，本地的TCP 实现会发送一个数据包给远程的 Socket. 如果远程Socket 没有发回响应, TCP实现就会持续尝试 11 分钟, 直到接收到响应为止。否则就会自动断开Socket连接。但TCP自带的心跳包无法检测比较敏感地知道对方的状态，默认2小时的空闲时间，对于大多数的应用而言太长了。可以手工开启KeepAlive功能并设置合理的KeepAlive参数。

另一种在应用层自己进行实现，基本步骤如下：

Client使用定时器，不断发送心跳；
Server收到心跳后，回复一个包；
Server为每个Client启动超时定时器，如果在指定时间内没有收到Client的心跳包，则Client失效。

三、Java实现心跳机制

这里基于Java实现的简单RPC框架实现心跳机制。Java实现代码如下所示：

心跳客户端类：

public class HeartbeatClient implements Runnable {
 
 private String serverIP = "127.0.0.1";
 private int serverPort = 8089;
 private String nodeID = UUID.randomUUID().toString();
 private boolean isRunning = true;
 // 最近的心跳时间
 private long lastHeartbeat;
 // 心跳间隔时间
 private long heartBeatInterval = 10 * 1000;
 
 public void run() {
 try {
  while (isRunning) {
  HeartbeatHandler handler = RPClient.getRemoteProxyObj(HeartbeatHandler.class, new InetSocketAddress(serverIP, serverPort));
  long startTime = System.currentTimeMillis();
  // 是否达到发送心跳的周期时间
  if (startTime - lastHeartbeat > heartBeatInterval) {
   System.out.println("send a heart beat");
   lastHeartbeat = startTime;
 
   HeartbeatEntity entity = new HeartbeatEntity();
   entity.setTime(startTime);
   entity.setNodeID(nodeID);
 
   // 向服务器发送心跳，并返回需要执行的命令
   Cmder cmds = handler.sendHeartBeat(entity);
 
   if (!processCommand(cmds))
   continue;
  }
  }
 } catch (Exception e) {
  e.printStackTrace();
 }
 }
 
 private boolean processCommand(Cmder cmds) {
 // ...
 return true;
 }
 
}

心跳包实体类：

public class HeartbeatEntity implements Serializable {
 
 private long time;
 private String nodeID;
 private String error;
 private Map<String, Object> info = new HashMap<String, Object>();
 
 public String getNodeID() {
 return nodeID;
 }
 
 public void setNodeID(String nodeID) {
 this.nodeID = nodeID;
 }
 
 public String getError() {
 return error;
 }
 
 public void setError(String error) {
 this.error = error;
 }
 
 public Map<String, Object> getInfo() {
 return info;
 }
 
 public void setInfo(Map<String, Object> info) {
 this.info = info;
 }
 
 public long getTime() {
 return time;
 }
 
 public void setTime(long time) {
 this.time = time;
 }
}

　　服务器接受心跳包返回的命令对象类：

public class Cmder implements Serializable {
 
 private String nodeID;
 private String error;
 private Map<String, Object> info = new HashMap<String, Object>();
 
 public String getNodeID() {
 return nodeID;
 }
 
 public void setNodeID(String nodeID) {
 this.nodeID = nodeID;
 }
 
 public String getError() {
 return error;
 }
 
 public void setError(String error) {
 this.error = error;
 }
 
 public Map<String, Object> getInfo() {
 return info;
 }
 
 public void setInfo(Map<String, Object> info) {
 this.info = info;
 }
}

　　RPC服务注册中心：

public class ServiceCenter {
 
 private ExecutorService executor = Executors.newFixedThreadPool(20);
 
 private final ConcurrentHashMap<String, Class> serviceRegistry = new ConcurrentHashMap<String, Class>();
 
 private AtomicBoolean isRunning = new AtomicBoolean(true);
 
 // 服务器监听端口
 private int port = 8089;
 
 // 心跳监听器
 HeartbeatLinstener linstener;
 
 // 单例模式
 private static class SingleHolder {
 private static final ServiceCenter INSTANCE = new ServiceCenter();
 }
 
 private ServiceCenter() {
 }
 
 public static ServiceCenter getInstance() {
 return SingleHolder.INSTANCE;
 }
 
 public void register(Class serviceInterface, Class impl) {
 System.out.println("regeist service " + serviceInterface.getName());
 serviceRegistry.put(serviceInterface.getName(), impl);
 }
 
 public void start() throws IOException {
 ServerSocket server = new ServerSocket();
 server.bind(new InetSocketAddress(port));
 System.out.println("start server");
 linstener = HeartbeatLinstener.getInstance();
 System.out.println("start listen heart beat");
 try {
  while (true) {
  // 1.监听客户端的TCP连接，接到TCP连接后将其封装成task，由线程池执行
  executor.execute(new ServiceTask(server.accept()));
  }
 } finally {
  server.close();
 }
 }
 
 public void stop() {
 isRunning.set(false);
 executor.shutdown();
 }
 
 
 public boolean isRunning() {
 return isRunning.get();
 }
 
 public int getPort() {
 return port;
 }
 
 public void settPort(int port) {
 this.port = port;
 }
 
 public ConcurrentHashMap<String, Class> getServiceRegistry() {
 return serviceRegistry;
 }
 
 private class ServiceTask implements Runnable {
 Socket clent = null;
 
 public ServiceTask(Socket client) {
  this.clent = client;
 }
 
 public void run() {
  ObjectInputStream input = null;
  ObjectOutputStream output = null;
  try {
  // 2.将客户端发送的码流反序列化成对象，反射调用服务实现者，获取执行结果
  input = new ObjectInputStream(clent.getInputStream());
  String serviceName = input.readUTF();
  String methodName = input.readUTF();
  Class<?>[] parameterTypes = (Class<?>[]) input.readObject();
  Object[] arguments = (Object[]) input.readObject();
  Class serviceClass = serviceRegistry.get(serviceName);
  if (serviceClass == null) {
   throw new ClassNotFoundException(serviceName + " not found");
  }
  Method method = serviceClass.getMethod(methodName, parameterTypes);
  Object result = method.invoke(serviceClass.newInstance(), arguments);
 
  // 3.将执行结果反序列化，通过socket发送给客户端
  output = new ObjectOutputStream(clent.getOutputStream());
  output.writeObject(result);
  } catch (Exception e) {
  e.printStackTrace();
  } finally {
  if (output != null) {
   try {
   output.close();
   } catch (IOException e) {
   e.printStackTrace();
   }
  }
  if (input != null) {
   try {
   input.close();
   } catch (IOException e) {
   e.printStackTrace();
   }
  }
  if (clent != null) {
   try {
   clent.close();
   } catch (IOException e) {
   e.printStackTrace();
   }
  }
  }
 
 }
 }
}

　　心跳监听类：

package com.cang.heartbeat;
 
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.lang.reflect.Method;
import java.net.InetSocketAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.Iterator;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.atomic.AtomicBoolean;
 
/**
 * 心跳监听保存信息
 *
 * @author cang
 * @create_time 2016-09-28 11:40
 */
public class HeartbeatLinstener {
 
 private ExecutorService executor = Executors.newFixedThreadPool(20);
 
 private final ConcurrentHashMap<String, Object> nodes = new ConcurrentHashMap<String, Object>();
 private final ConcurrentHashMap<String, Long> nodeStatus = new ConcurrentHashMap<String, Long>();
 
 private long timeout = 10 * 1000;
 
 // 服务器监听端口
 private int port = 8089;
 
 // 单例模式
 private static class SingleHolder {
 private static final HeartbeatLinstener INSTANCE = new HeartbeatLinstener();
 }
 
 private HeartbeatLinstener() {
 }
 
 public static HeartbeatLinstener getInstance() {
 return SingleHolder.INSTANCE;
 }
 
 public ConcurrentHashMap<String, Object> getNodes() {
 return nodes;
 }
 
 public void registerNode(String nodeId, Object nodeInfo) {
 nodes.put(nodeId, nodeInfo);
 nodeStatus.put(nodeId, System.currentTimeMillis());
 }
 
 public void removeNode(String nodeID) {
 if (nodes.containsKey(nodeID)) {
  nodes.remove(nodeID);
 }
 }
 
 // 检测节点是否有效
 public boolean checkNodeValid(String key) {
 if (!nodes.containsKey(key) || !nodeStatus.containsKey(key)) return false;
 if ((System.currentTimeMillis() - nodeStatus.get(key)) > timeout) return false;
 return true;
 }
 
 // 删除所有失效节点
 public void removeInValidNode() {
 Iterator<Map.Entry<String, Long>> it = nodeStatus.entrySet().iterator();
 while (it.hasNext()) {
  Map.Entry<String, Long> e = it.next();
  if ((System.currentTimeMillis() - nodeStatus.get(e.getKey())) > timeout) {
  nodes.remove(e.getKey());
  }
 }
 }
 
}

　　心跳处理类接口：

public interface HeartbeatHandler {
 public Cmder sendHeartBeat(HeartbeatEntity info);
}

心跳处理实现类：

public class HeartbeatHandlerImpl implements HeartbeatHandler {
 public Cmder sendHeartBeat(HeartbeatEntity info) {
 HeartbeatLinstener linstener = HeartbeatLinstener.getInstance();
 
 // 添加节点
 if (!linstener.checkNodeValid(info.getNodeID())) {
  linstener.registerNode(info.getNodeID(), info);
 }
 
 // 其他操作
 Cmder cmder = new Cmder();
 cmder.setNodeID(info.getNodeID());
 // ...
 
 System.out.println("current all the nodes: ");
 Map<String, Object> nodes = linstener.getNodes();
 for (Map.Entry e : nodes.entrySet()) {
  System.out.println(e.getKey() + " : " + e.getValue());
 }
 System.out.println("hadle a heartbeat");
 return cmder;
 }
}

　　测试类：

public class HeartbeatTest {
 
 public static void main(String[] args) {
 new Thread(new Runnable() {
  public void run() {
  try {
   ServiceCenter serviceServer = ServiceCenter.getInstance();
   serviceServer.register(HeartbeatHandler.class, HeartbeatHandlerImpl.class);
   serviceServer.start();
  } catch (IOException e) {
   e.printStackTrace();
  }
  }
 }).start();
 Thread client1 = new Thread(new HeartbeatClient());
 client1.start();
 Thread client2 = new Thread(new HeartbeatClient());
 client2.start();
 }
}

四、总结

上面的代码还有很多不足的地方,希望有空能进行改善：

配置为硬编码；
命令类Cmder没有实际实现，返回的Cmder对象没有实际进行处理；

其他小问题就暂时不管了，希望以后能重写上面的代码。

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