Java对象序列化规范

体系架构

写出到对象流

writeObject 方法对特定 Java 对象进行序列化，并且递归序列化它引用的其他对象，构成完整的序列化数据流。在流中，对其他对象的第一次引用会使其序列化或外部化（externalized），并分配一个句柄（handle），后续对该对象的引用都会编码成该句柄，以此压缩流的大小

对于 arrays, enum constants, objects of type Class, ObjectStreamClass, String 这些类型的对象需要进行特殊处理，其他对象则需要实现 Serializable 或 Externalizable 接口

原始数据类型通过 DataOutput 接口的方法写出到流中，单字节和字节数组则通过 OutputStream 的方法写出。除非作为对象的可序列化属性，否则将原始数据写到流的 block-data 记录中，每个记录前面会表明该记录的字节长度

从对象流写入

使用 readObject 方法写入数据流，还原成完整的 Java 对象（包括引用对象）。

原始数据类型通过 DataInput 接口的方法读取，单字节和字节数组则通过 InputStream 的方法读取。block-data 记录中的原始数据也需要读取

序列化相关类和方法

反序列化相关类和方法

类描述符

ObjectStreamClass

ObjectStreamClass 用于存储序列化数据流中的类的信息，包括全限定类名和 UID

package java.io;
 
public class ObjectStreamClass
{
    public static ObjectStreamClass lookup(Class cl);
 
    public static ObjectStreamClass lookupAny(Class cl);
 
    public String getName();
 
    public Class forClass();
 
    public ObjectStreamField[] getFields();
 
    public long getSerialVersionUID();
 
    public String toString();
}

序列化对象版本

对象序列化流协议

以下数据在流中有特殊的表示方式：null objects, new objects, 类，数组，字符串，以及对已存在的对象的引用

每个写入到流中的对象都会分配一个 handle 用来引用该对象，handel 从 0x7E0000 开始递增

An ObjectStreamClass object for a Class that is not a dynamic proxy class is represented by the following:

The Stream Unique Identifier (SUID) of compatible classes.

A set of flags indicating various properties of the class, such as whether the class defines a writeObject method, and whether the class is serializable, externalizable, or an enum type

The number of serializable fields

The array of fields of the class that are serialized by the default mechanismFor arrays and object fields, the type of the field is included as a string which must be in “field descriptor” format (e.g., “Ljava/lang/Object;”) as specified in The Java Virtual Machine Specification.

Optional block-data records or objects written by the annotateClass method

The ObjectStreamClass of its supertype (null if the superclass is not serializable)

An ObjectStreamClass object for a dynamic proxy class is represented by the following:

The number of interfaces that the dynamic proxy class implements

The names of all of the interfaces implemented by the dynamic proxy class, listed in the order that they are returned by invoking the getInterfaces method on the Class object.

Optional block-data records or objects written by the annotateProxyClass method.

The ObjectStreamClass of its supertype, java.lang.reflect.Proxy.

java8: https://docs.oracle.com/javase/8/docs/platform/serialization/spec/protocol.html java17: https://docs.oracle.com/en/java/javase/17/docs/specs/serialization/protocol.html

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