java - 为什么StringBuffer的readObject不同步？

Question

如果你查看StringBuffer的源代码，你会看到:

/**
 * readObject is called to restore the state of the StringBuffer from
 * a stream.
 */
private synchronized void writeObject(java.io.ObjectOutputStream s)
    throws java.io.IOException {
    java.io.ObjectOutputStream.PutField fields = s.putFields();
    fields.put("value", value);
    fields.put("count", count);
    fields.put("shared", false);
    s.writeFields();
}

/**
 * readObject is called to restore the state of the StringBuffer from
 * a stream.
 */
private void readObject(java.io.ObjectInputStream s)
    throws java.io.IOException, ClassNotFoundException {
    java.io.ObjectInputStream.GetField fields = s.readFields();
    value = (char[])fields.get("value", null);
    count = fields.get("count", 0);
}

为什么两个不同资源中的两个对象不会不同步？

为什么一个对象不会从两个不同的资源去同步反序列化？

请参阅我的示例:

    final ObjectInputStream objectInputABC=new ObjectInputStream(new FileInputStream("ABC"));
    final ObjectInputStream objectInputDE=new ObjectInputStream(new FileInputStream("DE"));

    final ObjectStreamClass osc = new ObjectStreamClass();
    final StringBuffer sb = (StringBuffer) objectInputABC.readObject();
    osc.invokeReadObject(sb,objectInputDE);

Answer 1

readObject() 仅在从序列化流构造新对象期间调用。两个线程没有范围在同一个对象上同时执行此方法。

相反，两个线程可能会尝试同时序列化同一个对象，因此 writeObject 是同步的。