GlobalId.java

/**
 * Alipay.com Inc.
 * Copyright (c) 2004-2012 All Rights Reserved.
 */
package com.alipay.zdal.datasource.tm;

import java.io.IOException;

import javax.transaction.xa.Xid;

/**
 *  This object encapsulates the global transaction ID of a transaction.
 *  It is similar to an Xid, but holds only the GlobalId part.
 *  This implementation is immutable and always serializable at runtime.
 *
 * @author ����
 * @version $Id: GlobalId.java, v 0.1 2014-1-6 ����05:46:36 Exp $
 */
public class GlobalId implements java.io.Externalizable {
    static final long serialVersionUID = 6879509375433435464L;
    /**
     *  Format id of this instance.
     */
    private int       formatId;

    /**
     *  Global transaction id of this instance.
     *  The coding of this class depends on the fact that this variable is
     *  initialized in the constructor and never modified. References to
     *  this array are never given away, instead a clone is delivered.
     */
    private byte[]    globalId;

    /**
     *  Hash code of this instance. For a native GlobalId (one whose formatId
     *  is XidImpl.JBOSS_FORMAT_ID), this is really a sequence number.
     */
    private int       hash;

    // Constructors --------------------------------------------------

    public GlobalId() {
        // Used for Externalizable support
    }

    /**
     *  Create a new instance. This constructor is package-private, as it
     *  trusts the hash parameter to be good.
     */
    GlobalId(int formatId, byte[] globalId, int hash) {
        this.formatId = formatId;
        this.globalId = globalId;
        this.hash = hash;
    }

    /**
     *  Create a new instance. This constructor is public <em>only</em>
     *  to get around a class loader problem; it should be package-private.
     */
    public GlobalId(int formatId, byte[] globalId) {
        this.formatId = formatId;
        this.globalId = globalId;
        hash = computeHash();
    }

    public GlobalId(Xid xid) {
        formatId = xid.getFormatId();
        globalId = xid.getGlobalTransactionId();
        if (xid instanceof XidImpl && formatId == XidImpl.JBOSS_FORMAT_ID) {
            // native GlobalId: use its hash code (a sequence number)
            hash = xid.hashCode();
        } else {
            // foreign GlobalId: do the hash computation
            hash = computeHash();
        }
    }

    public GlobalId(int formatId, int bqual_length, byte[] tid) {
        this.formatId = formatId;
        if (bqual_length == 0)
            globalId = tid;
        else {
            int len = tid.length - bqual_length;
            globalId = new byte[len];
            System.arraycopy(tid, 0, globalId, 0, len);
        }
        hash = computeHash();
    }

    // Public --------------------------------------------------------

    /**
     *  Compare for equality.
     *
     *  Instances are considered equal if they both refer to the same
     *  global transaction id.
     */
    public boolean equals(Object obj) {
        if (obj instanceof GlobalId) {
            GlobalId other = (GlobalId) obj;

            if (formatId != other.formatId)
                return false;

            if (globalId == other.globalId)
                return true;

            if (globalId.length != other.globalId.length)
                return false;

            int len = globalId.length;
            for (int i = 0; i < len; ++i)
                if (globalId[i] != other.globalId[i])
                    return false;

            return true;
        }
        return false;
    }

    public int hashCode() {
        return hash;
    }

    public String toString() {
        return getClass().getName() + "[formatId=" + formatId + ", globalId="
               + new String(globalId).trim() + ", hash=" + hash + "]";
    }

    // Externalizable implementation ---------------------------------

    public void writeExternal(java.io.ObjectOutput out) throws IOException {
        out.writeInt(formatId);
        out.writeObject(globalId);
    }

    public void readExternal(java.io.ObjectInput in) throws IOException, ClassNotFoundException {
        formatId = in.readInt();
        globalId = (byte[]) in.readObject();
        hash = computeHash();
    }

    // Private -------------------------------------------------------

    private int computeHash() {
        if (formatId == XidImpl.JBOSS_FORMAT_ID) {
            return (int) TransactionImpl.xidFactory.extractLocalIdFrom(globalId);
        } else {
            int len = globalId.length;
            int hashval = 0;

            // TODO: use a better hash function
            for (int i = 0; i < len; ++i)
                hashval = 3 * globalId[i] + hashval;
            hashval += formatId;
            return hashval;
        }
    }

}