什么是serialVersionUID，我为什么要使用它？ [英] What is a serialVersionUID and why should I use it?

问题描述

当缺少 serialVersionUID 时，Eclipse会发出警告。

Eclipse issues warnings when a serialVersionUID is missing.

可序列化类Foo没有声明类型为long的静态最终
serialVersionUID字段

The serializable class Foo does not declare a static final serialVersionUID field of type long

什么是 serialVersionUID ，为什么它很重要？请举例说明缺少 serialVersionUID 会导致问题。

What is serialVersionUID and why is it important? Please show an example where missing serialVersionUID will cause a problem.

推荐答案

<$的文档c $ c> java.io.Serializable 可能与你得到的解释一样好：

The docs for java.io.Serializable are probably about as good an explanation as you'll get:

序列化运行时将每个可序列化类与版本号相关联，称为 serialVersionUID ，在反序列化期间使用该版本号来验证序列化对象的发送方和接收方已经为该对象加载了与序列化兼容的类。如果接收者加载了一个类，该类的对象具有与相应发送者类不同的 serialVersionUID ，则反序列化将导致
InvalidClassException 。可序列化的类可以通过声明一个名为 serialVersionUID 的字段来显式声明它自己的 serialVersionUID ，该字段必须是静态的，最终的，并且是键入 long ：

The serialization runtime associates with each serializable class a version number, called a serialVersionUID, which is used during deserialization to verify that the sender and receiver of a serialized object have loaded classes for that object that are compatible with respect to serialization. If the receiver has loaded a class for the object that has a different serialVersionUID than that of the corresponding sender's class, then deserialization will result in an InvalidClassException. A serializable class can declare its own serialVersionUID explicitly by declaring a field named serialVersionUID that must be static, final, and of type long:

ANY-ACCESS-MODIFIER static final long serialVersionUID = 42L;

如果可序列化类没有明确声明 serialVersionUID ，然后序列化运行时将根据类的各个方面计算该类的默认 serialVersionUID 值，如Java（TM）对象序列化规范中所述。但是，强烈建议所有可序列化类都显式声明 serialVersionUID 值，因为默认 serialVersionUID 计算对类细节非常敏感，这些细节可能因编译器实现而异，因此在反序列化期间可能会导致意外的 InvalidClassExceptions 。因此，为了保证不同java编译器实现中的一致 serialVersionUID 值，可序列化类必须声明显式 serialVersionUID 值。强烈建议显式 serialVersionUID 声明尽可能使用private修饰符，因为此类声明仅适用于立即声明的类 serialVersionUID 字段作为继承成员无效。

If a serializable class does not explicitly declare a serialVersionUID, then the serialization runtime will calculate a default serialVersionUID value for that class based on various aspects of the class, as described in the Java(TM) Object Serialization Specification. However, it is strongly recommended that all serializable classes explicitly declare serialVersionUID values, since the default serialVersionUID computation is highly sensitive to class details that may vary depending on compiler implementations, and can thus result in unexpected InvalidClassExceptions during deserialization. Therefore, to guarantee a consistent serialVersionUID value across different java compiler implementations, a serializable class must declare an explicit serialVersionUID value. It is also strongly advised that explicit serialVersionUID declarations use the private modifier where possible, since such declarations apply only to the immediately declaring class serialVersionUID fields are not useful as inherited members.

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