ZooKeeper源码(3)server包非核心类

这个是最主要的包，内容很多，可能会分好几次来写

admin包

JettyAdminServer和DummyAdminServer是AdminServer接口的实现类。其中DummyAdmin是空的实现，主要还是看JettyAdminServer的实现。AdminServerFactory是一个工厂方法，一般就是直接返回JettyAdminServer，也不用看了。其中要把ZooKeeperServer加入重点关注。

这个包是3.5新增的，用于监控状态的，不是核心组件，不看了。

auth包：各自验证授权，也不看，因为看不懂。。。

command包：

四字指令，AbstractFourLetterCommand是各种四字指令的基类，用到模板方法模式,并且在FourLetterCommands做一个集中管理 ,稍微看一下。

其实这种模式的最好读了，看一个等于看一堆

它告诉我要关注ServerCnxn，ServerCnxnFactory，ZooKeeperServer这3个类

public abstract class AbstractFourLetterCommand {
    private static final Logger LOG = LoggerFactory
        .getLogger(AbstractFourLetterCommand.class);
    protected static final String ZK_NOT_SERVING = "This ZooKeeper instance is not currently serving requests";
    protected PrintWriter pw;
    protected ServerCnxn serverCnxn;
    protected ZooKeeperServer zkServer;
    protected ServerCnxnFactory factory;

    public AbstractFourLetterCommand(PrintWriter pw, ServerCnxn serverCnxn) {
        this.pw = pw;
        this.serverCnxn = serverCnxn;
    }

    public void start() {
        run();
    }

    public void run() {
        try {
            //调用子类的commandRun()
            commandRun();
        } catch (IOException ie) {
            LOG.error("Error in running command ", ie);
        } finally {
            serverCnxn.cleanupWriterSocket(pw);
        }
    }

    public void setZkServer(ZooKeeperServer zkServer) {
        this.zkServer = zkServer;
    }

    /**
     * @return true if the server is running, false otherwise.
     */
    boolean isZKServerRunning() {
        return zkServer != null && zkServer.isRunning();
    }

    public void setFactory(ServerCnxnFactory factory) {
        this.factory = factory;
    }

    public abstract void commandRun() throws IOException;
}


//某一个子类
public class StatCommand extends AbstractFourLetterCommand {
    private static final Logger LOG = LoggerFactory
            .getLogger(AbstractFourLetterCommand.class);
    private int len;
    public StatCommand(PrintWriter pw, ServerCnxn serverCnxn, int len) {
        super(pw, serverCnxn);
        this.len = len;
    }

    @Override
    public void commandRun() {
        if (!isZKServerRunning()) {
            pw.println(ZK_NOT_SERVING);
        } else {
            pw.print("Zookeeper version: ");
            pw.println(Version.getFullVersion());
            if (zkServer instanceof ReadOnlyZooKeeperServer) {
                pw.println("READ-ONLY mode; serving only read-only clients");
            }
            if (len == FourLetterCommands.statCmd) {
                LOG.info("Stat command output");
                pw.println("Clients:");
                for(ServerCnxn c : factory.getConnections()){
                    c.dumpConnectionInfo(pw, true);
                    pw.println();
                }
                pw.println();
            }
            pw.print(zkServer.serverStats().toString());
            pw.print("Node count: ");
            pw.println(zkServer.getZKDatabase().getNodeCount());
        }
    }
}

persist包

看名字和内容是写文件的，有一个类的注释写的很好，来看一下。

 * The format of a Transactional log is as follows:
 * 
 * LogFile:
 *     FileHeader TxnList ZeroPad
 *
 * FileHeader: {
 *     magic 4bytes (ZKLG)
 *     version 4bytes
 *     dbid 8bytes
 *   }
 *
 * TxnList:
 *     Txn || Txn TxnList
 *
 * Txn:
 *     checksum Txnlen TxnHeader Record 0x42
 *
 * checksum: 8bytes Adler32 is currently used
 *   calculated across payload -- Txnlen, TxnHeader, Record and 0x42
 *
 * Txnlen:
 *     len 4bytes
 *
 * TxnHeader: {
 *     sessionid 8bytes
 *     cxid 4bytes
 *     zxid 8bytes
 *     time 8bytes
 *     type 4bytes
 *   }
 *
 * Record:
 *     See Jute definition file for details on the various record types
 *
 * ZeroPad:
 *     0 padded to EOF (filled during preallocation stage)
 * 

    protected void serialize(DataTree dt,Map<Long, Integer> sessions,
            OutputArchive oa, FileHeader header) throws IOException {
        // this is really a programmatic error and not something that can
        // happen at runtime
        if(header==null)
            throw new IllegalStateException(
                    "Snapshot's not open for writing: uninitialized header");
        header.serialize(oa, "fileheader");        
        SerializeUtils.serializeSnapshot(dt,oa,sessions);
    }

通过源码发现，完成工作的是SerializeUtils

Util类

ConfigUtil中有，创建服务器的，记录一下

QuorumPeer.QuorumServer qs;
             try {
               qs = new QuorumPeer.QuorumServer(-1, value);
             } catch (ConfigException e) {              
                    e.printStackTrace();
                    continue;
             }

SerializeUtils

    public static void deserializeSnapshot(DataTree dt,InputArchive ia,
            Map sessions) throws IOException {
        int count = ia.readInt("count");
        while (count > 0) {
            long id = ia.readLong("id");
            int to = ia.readInt("timeout");
            sessions.put(id, to);
            if (LOG.isTraceEnabled()) {
                ZooTrace.logTraceMessage(LOG, ZooTrace.SESSION_TRACE_MASK,
                        "loadData --- session in archive: " + id
                        + " with timeout: " + to);
            }
            count--;
        }
        dt.deserialize(ia, "tree");
    }

    public static void serializeSnapshot(DataTree dt,OutputArchive oa,
            Map sessions) throws IOException {
        HashMap sessSnap = new HashMap(sessions);
        oa.writeInt(sessSnap.size(), "count");
        for (Entry entry : sessSnap.entrySet()) {
            oa.writeLong(entry.getKey().longValue(), "id");
            oa.writeInt(entry.getValue().intValue(), "timeout");
        }
        dt.serialize(oa, "tree");
    }

可以看到，有dt.serialize(oa, “tree”);委派给了DataTree自己序列化。

其他类比较扯，不看了