storedclasscatalog.java

嵌入式数据库Berkeley DB-4.5.20源代码

                 * Not found in the database, write class info and class
                 * format.
                 */
                classInfo = putClassInfo(new ClassInfo(), className, key,
                                         classFormat);
            } else {
                /*
                 * Read class info to get the class format key, then read class
                 * format.
                 */
                classInfo = new ClassInfo(data);
                DatabaseEntry formatData = new DatabaseEntry();
                ObjectStreamClass storedClassFormat =
                    getClassFormat(classInfo.getClassID(), formatData);

                /*
                 * Compare the stored class format to the current class format,
                 * and if they are different then generate a new class ID.
                 */
                if (!areClassFormatsEqual(storedClassFormat,
                                          getBytes(formatData),
                                          classFormat)) {
                    classInfo = putClassInfo(classInfo, className, key,
                                             classFormat);
                }

                /* Update the class info map.  */
                classInfo.setClassFormat(classFormat);
                classMap.put(className, classInfo);
            }
        }
        return classInfo;
    }

    /**
     * Assign a new class ID (increment the current ID record), write the
     * ObjectStreamClass record for this new ID, and update the ClassInfo
     * record with the new ID also.  The ClassInfo passed as an argument is the
     * one to be updated.
     */
    private ClassInfo putClassInfo(ClassInfo classInfo,
				   String className,
				   DatabaseEntry classKey,
				   ObjectStreamClass classFormat)
        throws DatabaseException, ClassNotFoundException {

        /* An intent-to-write cursor is needed for CDB. */
        CursorConfig cursorConfig = null;
        if (cdbMode) {
            cursorConfig = new CursorConfig();
            DbCompat.setWriteCursor(cursorConfig, true);
        }
        Cursor cursor = null;
        Transaction txn = null;
        try {
            if (txnMode) {
                txn = db.getEnvironment().beginTransaction(null, null);
            }
            cursor = db.openCursor(txn, cursorConfig);

            /* Get the current class ID. */
            DatabaseEntry key = new DatabaseEntry(LAST_CLASS_ID_KEY);
            DatabaseEntry data = new DatabaseEntry();
            OperationStatus status = cursor.getSearchKey(key, data,
                                                         writeLockMode);
            if (status != OperationStatus.SUCCESS) {
                throw new IllegalStateException("Class ID not initialized");
            }
            byte[] idBytes = getBytes(data);

            /* Increment the ID by one and write the updated record.  */
            idBytes = incrementID(idBytes);
            data.setData(idBytes);
            cursor.put(key, data);

            /*
             * Write the new class format record whose key is the ID just
             * assigned.
             */
            byte[] keyBytes = new byte[1 + idBytes.length];
            keyBytes[0] = REC_CLASS_FORMAT;
            System.arraycopy(idBytes, 0, keyBytes, 1, idBytes.length);
            key.setData(keyBytes);

            ByteArrayOutputStream baos = new ByteArrayOutputStream();
            ObjectOutputStream oos;
            try {
                oos = new ObjectOutputStream(baos);
                oos.writeObject(classFormat);
            } catch (IOException e) {
                throw new RuntimeExceptionWrapper(e);
            }
            data.setData(baos.toByteArray());

            cursor.put(key, data);

            /*
             * Write the new class info record, using the key passed in; this
             * is done last so that a reader who gets the class info record
             * first will always find the corresponding class format record.
             */
            classInfo.setClassID(idBytes);
            classInfo.toDbt(data);

            cursor.put(classKey, data);

            /*
             * Update the maps before closing the cursor, so that the cursor
             * lock prevents other writers from duplicating this entry.
             */
            classInfo.setClassFormat(classFormat);
            classMap.put(className, classInfo);
            formatMap.put(new BigInteger(idBytes), classFormat);
            return classInfo;
        } finally {
            if (cursor != null) {
                cursor.close();
            }
            if (txn != null) {
                txn.commit();
            }
        }
    }

    private static byte[] incrementID(byte[] key) {

        BigInteger id = new BigInteger(key);
        id = id.add(BigInteger.valueOf(1));
        return id.toByteArray();
    }

    /**
     * Holds the class format key for a class, maintains a reference to the
     * ObjectStreamClass.  Other fields can be added when we need to store more
     * information per class.
     */
    private static class ClassInfo implements Serializable {

        private byte[] classID;
        private transient ObjectStreamClass classFormat;

        ClassInfo() {
        }

        ClassInfo(DatabaseEntry dbt) {

            byte[] data = dbt.getData();
            int len = data[0];
            classID = new byte[len];
            System.arraycopy(data, 1, classID, 0, len);
        }

        void toDbt(DatabaseEntry dbt) {

            byte[] data = new byte[1 + classID.length];
            data[0] = (byte) classID.length;
            System.arraycopy(classID, 0, data, 1, classID.length);
            dbt.setData(data);
        }

        void setClassID(byte[] classID) {

            this.classID = classID;
        }

        byte[] getClassID() {

            return classID;
        }

        ObjectStreamClass getClassFormat() {

            return classFormat;
        }

        void setClassFormat(ObjectStreamClass classFormat) {

            this.classFormat = classFormat;
        }
    }

    /**
     * Return whether two class formats are equal.  This determines whether a
     * new class format is needed for an object being serialized.  Formats must
     * be identical in all respects, or a new format is needed.
     */
    private static boolean areClassFormatsEqual(ObjectStreamClass format1,
                                                byte[] format1Bytes,
                                                ObjectStreamClass format2) {
        try {
            if (format1Bytes == null) { // using cached format1 object
                format1Bytes = getObjectBytes(format1);
            }
            byte[] format2Bytes = getObjectBytes(format2);
            return java.util.Arrays.equals(format2Bytes, format1Bytes);
        } catch (IOException e) { return false; }
    }

    /*
     * We can return the same byte[] for 0 length arrays.
     */
    private static byte[] ZERO_LENGTH_BYTE_ARRAY = new byte[0];

    private static byte[] getBytes(DatabaseEntry dbt) {
        byte[] b = dbt.getData();
        if (b == null) {
            return null;
        }
        if (dbt.getOffset() == 0 && b.length == dbt.getSize()) {
            return b;
        }
	int len = dbt.getSize();
	if (len == 0) {
	    return ZERO_LENGTH_BYTE_ARRAY;
	} else {
	    byte[] t = new byte[len];
	    System.arraycopy(b, dbt.getOffset(), t, 0, t.length);
	    return t;
	}
    }

    private static byte[] getObjectBytes(Object o)
        throws IOException {

        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream(baos);
        oos.writeObject(o);
        return baos.toByteArray();
    }
}