Java实现心跳机制

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：

1. Client使用定时器，不断发送心跳；
2. Server收到心跳后，回复一个包；
3. 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：

1. 配置为硬编码；
2. 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。