storage.java

Java的面向对象数据库系统的源代码

// You can redistribute this software and/or modify it under the terms of
// the Ozone Core License version 1 published by ozone-db.org.
//
// The original code and portions created by SMB are
// Copyright (C) 1997-@year@, Leo Mekenkamp. All rights reserved.
//
// $Id: Storage.java,v 1.1 2004/01/02 09:24:38 leomekenkamp Exp $

package org.ozoneDB.core.storage.gammaStore;

import java.io.IOException;

/**
 * <p>A meganism for storing and retrieving data to a permament back-end.
 * While implementing classes are typically backed by file-based structures,
 * this is in no way a _must_. Inheriting classes must must simply support
 * read/write actions from a 'random' location.</p>
 * <p>As the <code>IndexManager</code> also uses instances of this type to
 * write index nodes as a whole (no seek needed) there are also implementations
 * that not support seek functionality.</p>
 *
 * @author <a href="mailto:ozoneATmekenkampD0Tcom">Leo Mekenkamp (mind the anti-sp@m)</a>
 */
public interface Storage {
    
    /**
     * <p>Introduced because some implementing classes (based on <code>FileOutputStream</code>
     * and <code>FileInputStream</code> for instance) might not support seek
     * operations. They may throw an <code>UnsupportedOperationException</code>
     * here, but still support writing and reading.</p>
     * <p>Implementations of this interface are used in 2 different ways: the
     * <code>IndexManager</code> does not perform any seek actions, and thus the
     * storage implementation it uses can include stream based ones; the 
     * <code>ClusterManager</code> however does perform seek actions and thus
     * cannot have a storage implementation with streams in it.</p>
     *
     * @throws UnsupportedOperationException
     */
    public void seek(long pos) throws IOException;
    
    /**
     * Write <code>lenght</code> bytes from <code>b</code>, starting at <code>
     * offset</code>.
     */
    public void write(byte[] b, int offset, int length) throws IOException;

    public void write(byte[] b) throws IOException;

    public void writeLong(long value) throws IOException;
    
    public void writeInt(int value) throws IOException;
    
    /**
     * Read <code>lenght</code> bytes from <code>b</code>, starting at <code>
     * offset</code>.
     */
    public void readFully(byte[] b, int offset, int length) throws IOException;

    public void readFully(byte[] b) throws IOException;
    
    public long readLong() throws IOException;

    public int readInt() throws IOException;

    /**
     * Sets the maximum length.
     */
    public void setLength(long length) throws IOException;
    
    public void close() throws IOException;
    
    public long length() throws IOException;

}