java – 从文件中加载旧版本的对象

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如果我尝试从文件加载旧版本的对象会发生什么？

例如,如果我创建了一个对象,则使用FileOutputStream将该对象保存到文件中.然后,如果我添加了一个字段,并尝试重新加载此对象,Java将根本不识别该对象,还是将该字段设置为默认字段或……？

谢谢 ：)

解决方法:

当您尝试使用不同的类版本反序列化您的类时,您应该收到InvalidClassException.从javadocs：

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; 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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