1.zookeeper启动入口

在zkServer.sh的启动命令中，我们可以找到zookeeper启动的关键类org.apache.zookeeper.server.quorum.QuorumPeerMain

QuorumPeerMain#main

我们可以直接看org.apache.zookeeper.server.quorum.QuorumPeerMain中的main方法，从下面的main方法中，我们可以看到初始化了一个QuorumPeerMain对象，并进行调用initializeAndRun方法

public static void main(String[] args) {
        QuorumPeerMain main = new QuorumPeerMain();
        try {
            main.initializeAndRun(args);
        } catch (IllegalArgumentException e) {
            LOG.error("Invalid arguments, exiting abnormally", e);
            LOG.info(USAGE);
            System.err.println(USAGE);
            System.exit(2);
        } catch (ConfigException e) {
            LOG.error("Invalid config, exiting abnormally", e);
            System.err.println("Invalid config, exiting abnormally");
            System.exit(2);
        } catch (DatadirException e) {
            LOG.error("Unable to access datadir, exiting abnormally", e);
            System.err.println("Unable to access datadir, exiting abnormally");
            System.exit(3);
        } catch (AdminServerException e) {
            LOG.error("Unable to start AdminServer, exiting abnormally", e);
            System.err.println("Unable to start AdminServer, exiting abnormally");
            System.exit(4);
        } catch (Exception e) {
            LOG.error("Unexpected exception, exiting abnormally", e);
            System.exit(1);
        }
        LOG.info("Exiting normally");
        System.exit(0);
    }

QuorumPeerMain#initializeAndRun

我们紧接看这个initializeAndRun方法，方法里的代码如下：

protected void initializeAndRun(String[] args)
        throws ConfigException, IOException, AdminServerException
    {
        
        QuorumPeerConfig config = new QuorumPeerConfig();
        if (args.length == 1) {
            //解析参数信息
            config.parse(args[0]);
        }

        // Start and schedule the the purge task
        // 启动一个定时任务进行定时清理日志信息
        DatadirCleanupManager purgeMgr = new DatadirCleanupManager(config
                .getDataDir(), config.getDataLogDir(), config
                .getSnapRetainCount(), config.getPurgeInterval());
        purgeMgr.start();

        if (args.length == 1 && config.isDistributed()) {
            //作为集群启动
            runFromConfig(config);
        } else {
            LOG.warn("Either no config or no quorum defined in config, running "
                    + " in standalone mode");
            // there is only server in the quorum -- run as standalone
            // 如果没有配置文件的信息的话，就单机进行启动
            ZooKeeperServerMain.main(args);
        }
    }

QuorumPeerMain#runFromConfig

在上面的initializeAndRun方法中我们看到了zookeeper 根据配置文件进行判断是否是单机启动还是集群启动，这块我们就按照集群启动的方式进行启动。我们紧接看这个runFromConfig方法。

  public void runFromConfig(QuorumPeerConfig config)
            throws IOException, AdminServerException
    {
      /注册log4j的bean
      try {
          ManagedUtil.registerLog4jMBeans();
      } catch (JMException e) {
          LOG.warn("Unable to register log4j JMX control", e);
      }
      //从这块进行开始启动quorum peer 一个quorum peer就对应着一个zookeeper机器节点
      LOG.info("Starting quorum peer, myid=" + config.getServerId());
      try {
          //创建网络连接工厂
          ServerCnxnFactory cnxnFactory = null;
          ServerCnxnFactory secureCnxnFactory = null;

          if (config.getClientPortAddress() != null) {
              cnxnFactory = ServerCnxnFactory.createFactory();
              cnxnFactory.configure(config.getClientPortAddress(),
                      config.getMaxClientCnxns(),
                      false);
          }

          if (config.getSecureClientPortAddress() != null) {
              secureCnxnFactory = ServerCnxnFactory.createFactory();
              secureCnxnFactory.configure(config.getSecureClientPortAddress(),
                      config.getMaxClientCnxns(),
                      true);
          }

          //从这开始就是对quorumPeer的属性的设置
          //里面有很多属性暂时可以先不了解 

          // 一个Zookeeper主节点的启动
          quorumPeer = getQuorumPeer();
          //磁盘数据管理组件
          quorumPeer.setTxnFactory(new FileTxnSnapLog(
                      config.getDataLogDir(),
                      config.getDataDir()));
          quorumPeer.enableLocalSessions(config.areLocalSessionsEnabled());
          quorumPeer.enableLocalSessionsUpgrading(
              config.isLocalSessionsUpgradingEnabled());
          //quorumPeer.setQuorumPeers(config.getAllMembers());
          quorumPeer.setElectionType(config.getElectionAlg());
          quorumPeer.setMyid(config.getServerId());
          quorumPeer.setTickTime(config.getTickTime());
          quorumPeer.setMinSessionTimeout(config.getMinSessionTimeout());
          quorumPeer.setMaxSessionTimeout(config.getMaxSessionTimeout());
          quorumPeer.setInitLimit(config.getInitLimit());
          quorumPeer.setSyncLimit(config.getSyncLimit());
          quorumPeer.setConfigFileName(config.getConfigFilename());
          // zk的内存数据库
          quorumPeer.setZKDatabase(new ZKDatabase(quorumPeer.getTxnFactory()));
          quorumPeer.setQuorumVerifier(config.getQuorumVerifier(), false);
          if (config.getLastSeenQuorumVerifier()!=null) {
              quorumPeer.setLastSeenQuorumVerifier(config.getLastSeenQuorumVerifier(), false);
          }
          quorumPeer.initConfigInZKDatabase();
          quorumPeer.setCnxnFactory(cnxnFactory);
          quorumPeer.setSecureCnxnFactory(secureCnxnFactory);
          quorumPeer.setSslQuorum(config.isSslQuorum());
          quorumPeer.setUsePortUnification(config.sh