SerialCallbackContext.java

/*
 * Copyright (c) 2006, 2012, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 */

package java.io;

/**
 * Context during upcalls from object stream to class-defined readObject/writeObject methods.
 * Holds object currently being deserialized and descriptor for current class.
 *
 * This context keeps track of the thread it was constructed on, and allows
 * only a single call of defaultReadObject, readFields, defaultWriteObject
 * or writeFields which must be invoked on the same thread before the class's
 * readObject/writeObject method has returned.
 *
 * If not set to the current thread, the getObj method throws NotActiveException.
 */
// (反)序列化上下文，存储了待序列化的对象(的序列化描述符)与该过程发生的线程
final class SerialCallbackContext {
    
    private final Object obj;               // 待序列化对象
    private final ObjectStreamClass desc;   // 待序列化对象的序列化描述符
    
    /**
     * Thread this context is in use by.
     * As this only works in one thread, we do not need to worry about thread-safety.
     */
    private Thread thread;  // 当前序列化/反序列化过程发生的线程
    
    public SerialCallbackContext(Object obj, ObjectStreamClass desc) {
        this.obj = obj;
        this.desc = desc;
        this.thread = Thread.currentThread();
    }
    
    public Object getObj() throws NotActiveException {
        checkAndSetUsed();
        return obj;
    }
    
    public ObjectStreamClass getDesc() {
        return desc;
    }
    
    public void check() throws NotActiveException {
        if(thread != null && thread != Thread.currentThread()) {
            throw new NotActiveException("expected thread: " + thread + ", but got: " + Thread.currentThread());
        }
    }
    
    public void setUsed() {
        thread = null;
    }
    
    public void checkAndSetUsed() throws NotActiveException {
        if(thread != Thread.currentThread()) {
            throw new NotActiveException("not in readObject invocation or fields already read");
        }
        thread = null;
    }
    
}