storedclasscatalog.java

嵌入式数据库Berkeley DB-4.5.20源代码

/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 2000-2006
 *      Oracle Corporation.  All rights reserved.
 *
 * $Id: StoredClassCatalog.java,v 12.4 2006/08/31 18:14:05 bostic Exp $
 */

package com.sleepycat.bind.serial;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.ObjectStreamClass;
import java.io.Serializable;
import java.math.BigInteger;
import java.util.HashMap;

import com.sleepycat.compat.DbCompat;
import com.sleepycat.db.Cursor;
import com.sleepycat.db.CursorConfig;
import com.sleepycat.db.Database;
import com.sleepycat.db.DatabaseConfig;
import com.sleepycat.db.DatabaseEntry;
import com.sleepycat.db.DatabaseException;
import com.sleepycat.db.EnvironmentConfig;
import com.sleepycat.db.LockMode;
import com.sleepycat.db.OperationStatus;
import com.sleepycat.db.Transaction;
import com.sleepycat.util.RuntimeExceptionWrapper;
import com.sleepycat.util.UtfOps;

/**
 * A <code>ClassCatalog</code> that is stored in a <code>Database</code>.
 *
 * <p>A single <code>StoredClassCatalog</code> object is normally used along
 * with a set of databases that stored serialized objects.</p>
 *
 * @author Mark Hayes
 */
public class StoredClassCatalog implements ClassCatalog {

    /*
     * Record types ([key] [data]):
     *
     * [0] [next class ID]
     * [1 / class ID] [ObjectStreamClass (class format)]
     * [2 / class name] [ClassInfo (has 8 byte class ID)]
     */
    private static final byte REC_LAST_CLASS_ID = (byte) 0;
    private static final byte REC_CLASS_FORMAT = (byte) 1;
    private static final byte REC_CLASS_INFO = (byte) 2;

    private static final byte[] LAST_CLASS_ID_KEY = {REC_LAST_CLASS_ID};

    private Database db;
    private HashMap classMap;
    private HashMap formatMap;
    private LockMode writeLockMode;
    private boolean cdbMode;
    private boolean txnMode;

    /**
     * Creates a catalog based on a given database. To save resources, only a
     * single catalog object should be used for each unique catalog database.
     *
     * @param database an open database to use as the class catalog.  It must
     * be a BTREE database and must not allow duplicates.
     *
     * @throws DatabaseException if an error occurs accessing the database.
     *
     * @throws IllegalArgumentException if the database is not a BTREE database
     * or if it configured to allow duplicates.
     */
    public StoredClassCatalog(Database database)
        throws DatabaseException, IllegalArgumentException {

        db = database;
        DatabaseConfig dbConfig = db.getConfig();
        EnvironmentConfig envConfig = db.getEnvironment().getConfig();

        writeLockMode = (DbCompat.getInitializeLocking(envConfig) ||
                         envConfig.getTransactional()) ? LockMode.RMW
                                                       : LockMode.DEFAULT;
        cdbMode = DbCompat.getInitializeCDB(envConfig);
        txnMode = dbConfig.getTransactional();

        if (!DbCompat.isTypeBtree(dbConfig)) {
            throw new IllegalArgumentException(
                    "The class catalog must be a BTREE database.");
        }
        if (DbCompat.getSortedDuplicates(dbConfig) ||
            DbCompat.getUnsortedDuplicates(dbConfig)) {
            throw new IllegalArgumentException(
                    "The class catalog database must not allow duplicates.");
        }

        /*
         * Create the class format and class info maps. Note that these are not
         * synchronized, and therefore the methods that use them are
         * synchronized.
         */
        classMap = new HashMap();
        formatMap = new HashMap();

        DatabaseEntry key = new DatabaseEntry(LAST_CLASS_ID_KEY);
        DatabaseEntry data = new DatabaseEntry();
        if (dbConfig.getReadOnly()) {
            /* Check that the class ID record exists. */
            OperationStatus status = db.get(null, key, data, null);
            if (status != OperationStatus.SUCCESS) {
                throw new IllegalStateException
                    ("A read-only catalog database may not be empty");
            }
        } else {
            /* Add the initial class ID record if it doesn't exist.  */
            data.setData(new byte[1]); // zero ID
            /* Use putNoOverwrite to avoid phantoms. */
            db.putNoOverwrite(null, key, data);
        }
    }

    // javadoc is inherited
    public synchronized void close()
        throws DatabaseException {

        if (db != null) {
            db.close();
        }
        db = null;
        formatMap = null;
        classMap = null;
    }

    // javadoc is inherited
    public synchronized byte[] getClassID(ObjectStreamClass classFormat)
        throws DatabaseException, ClassNotFoundException {

        ClassInfo classInfo = getClassInfo(classFormat);
        return classInfo.getClassID();
    }

    // javadoc is inherited
    public synchronized ObjectStreamClass getClassFormat(byte[] classID)
        throws DatabaseException, ClassNotFoundException {

        return getClassFormat(classID, new DatabaseEntry());
    }

    /**
     * Internal function for getting the class format.  Allows passing the
     * DatabaseEntry object for the data, so the bytes of the class format can
     * be examined afterwards.
     */
    private ObjectStreamClass getClassFormat(byte[] classID,
					     DatabaseEntry data)
        throws DatabaseException, ClassNotFoundException {

        /* First check the map and, if found, add class info to the map. */

        BigInteger classIDObj = new BigInteger(classID);
        ObjectStreamClass classFormat =
            (ObjectStreamClass) formatMap.get(classIDObj);
        if (classFormat == null) {

            /* Make the class format key. */

            byte[] keyBytes = new byte[classID.length + 1];
            keyBytes[0] = REC_CLASS_FORMAT;
            System.arraycopy(classID, 0, keyBytes, 1, classID.length);
            DatabaseEntry key = new DatabaseEntry(keyBytes);

            /* Read the class format. */

            OperationStatus status = db.get(null, key, data, LockMode.DEFAULT);
            if (status != OperationStatus.SUCCESS) {
                throw new ClassNotFoundException("Catalog class ID not found");
            }
            try {
                ObjectInputStream ois =
                    new ObjectInputStream(
                        new ByteArrayInputStream(data.getData(),
                                                 data.getOffset(),
                                                 data.getSize()));
                classFormat = (ObjectStreamClass) ois.readObject();
            } catch (IOException e) {
                throw new RuntimeExceptionWrapper(e);
            }

            /* Update the class format map. */

            formatMap.put(classIDObj, classFormat);
        }
        return classFormat;
    }

    /**
     * Get the ClassInfo for a given class name, adding it and its
     * ObjectStreamClass to the database if they are not already present, and
     * caching both of them using the class info and class format maps.  When a
     * class is first loaded from the database, the stored ObjectStreamClass is
     * compared to the current ObjectStreamClass loaded by the Java class
     * loader; if they are different, a new class ID is assigned for the
     * current format.
     */
    private ClassInfo getClassInfo(ObjectStreamClass classFormat)
        throws DatabaseException, ClassNotFoundException {

        /*
         * First check for a cached copy of the class info, which if
         * present always contains the class format object
         */
        String className = classFormat.getName();
        ClassInfo classInfo = (ClassInfo) classMap.get(className);
        if (classInfo != null) {
            return classInfo;
        } else {
            /* Make class info key.  */
            char[] nameChars = className.toCharArray();
            byte[] keyBytes = new byte[1 + UtfOps.getByteLength(nameChars)];
            keyBytes[0] = REC_CLASS_INFO;
            UtfOps.charsToBytes(nameChars, 0, keyBytes, 1, nameChars.length);
            DatabaseEntry key = new DatabaseEntry(keyBytes);

            /* Read class info.  */
            DatabaseEntry data = new DatabaseEntry();
            OperationStatus status = db.get(null, key, data, LockMode.DEFAULT);
            if (status != OperationStatus.SUCCESS) {
                /*