Java：writeObject与writeExternal的效率 [英] Java: efficiency of writeObject vs writeExternal

问题描述

据说Java的默认序列化机制效率不高，因为a）它发现通过反射写入/读取的字段通常很慢b）它将额外的数据写入流。

It's said that Java's default serialization mechanism is not very efficient because a)it discovers which fields to write/read through reflection which is usually slow b) it writes extra data to stream.

提高效率的一种方法是实现Externalizable及其writeExternal / readExternal方法。

One way to make it more efficient is to implement Externalizable and its writeExternal/readExternal methods.

这是一个问题：如果我改为提供'writeObject / readObject '方法并且不要在其中调用deafiltWriteObject / defaultReadObject，那么这个机制不会使用反射来确定要写入/读取的字段，而且它不会将额外的数据写入流（或者它会不确定）。那么从效率的角度来看，实现上面提到的writeObject / readObject与实现Externalizable一样吗？或者后一个选项是否提供了一些更实际的好处，前者没有？

Here's the question: if I instead provide 'writeObject/readObject' methods and don't call deafiltWriteObject/defaultReadObject in them, then this mechanism won't use reflection to figure out which fields to write/read, plus it won't write extra data to stream (or will it? not sure). So from an efficiency perspective, is implementing writeObject/readObject mentioned above same as implementing Externalizable? Or does the latter option give some more practical benefits which the former doesn't?

编辑：当然，是一个实现readObject / writeObject的Serializable类被子类化的差异，如果子类有自己的readObject / writeObject，则不需要调用super的readObject / writeObject。如果超级/子类改为实现Externalizable，则不是这样。在这种情况下，需要显式调用super的writeExternal / readExternal。 然而，从效率的角度来看，这种差异是无关紧要的。

a difference, ofcourse, is when a Serializable class implementing readObject/writeObject is subclassed, and if the subclass has its own readObject/writeObject, they don't need to call super's readObject/writeObject. Not so if the super/subclass instead implement Externalizable. In this case, super's writeExternal/readExternal need to be explicitly called. However, this difference is irrelevant from an efficiency point of view.

推荐答案

还有一些结束首先选择要调用哪个类/ writeObject / readObject。但它显着减少了。

There is still some over head in choosing which class/writeObject/readObject to call next. but it is significantly reduced.

这可以与Externalizable相同，具体取决于你在做什么，以及你是否使用它给你的额外选项。例如readObject假定您每次都创建一个新对象，Externalizable具有readResolve，这意味着您可以重用对象。

This can perform the same as Externalizable depending on what you are doing and whether you use the extra options it gives you. e.g. readObject assumes you to create a new object each time, Externalizable has readResolve which means you can reuse objects.

http://docs.oracle.com/javase/1.5.0/docs/guide/serialization/spec/input .html

在许多情况下，回收对象是加速反序列化的下一步。 （假设这是你的选择）

In many cases, recycling objects is the "next" step in speeding up deserialization. (Assuming that's an option for you)

http://vanillajava.blogspot.co.uk/2011/10/recycling-objects-to-improve.html

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