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: * <blockquote><pre> * 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) * </pre></blockquote>

    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<Long, Integer> 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<Long, Integer> sessions) throws IOException {        HashMap<Long, Integer> sessSnap = new HashMap<Long, Integer>(sessions);        oa.writeInt(sessSnap.size(), "count");        for (Entry<Long, Integer> 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