Java序列化Serializable 接口

1、 java.io.Serializable 序列化 

Serializable里面没有抽象类以及实现的方法

package java.io;

/**
 * Serializability of a class is enabled by the class implementing the
 * java.io.Serializable interface. Classes that do not implement this
 * interface will not have any of their state serialized or
 * deserialized.  All subtypes of a serializable class are themselves
 * serializable.  The serialization interface has no methods or fields
 * and serves only to identify the semantics of being serializable. 

 *
 * To allow subtypes of non-serializable classes to be serialized, the
 * subtype may assume responsibility for saving and restoring the
 * state of the supertype's public, protected, and (if accessible)
 * package fields.  The subtype may assume this responsibility only if
 * the class it extends has an accessible no-arg constructor to
 * initialize the class's state.  It is an error to declare a class
 * Serializable if this is not the case.  The error will be detected at
 * runtime. 

 *
 * During deserialization, the fields of non-serializable classes will
 * be initialized using the public or protected no-arg constructor of
 * the class.  A no-arg constructor must be accessible to the subclass
 * that is serializable.  The fields of serializable subclasses will
 * be restored from the stream. 

 *
 * When traversing a graph, an object may be encountered that does not
 * support the Serializable interface. In this case the
 * NotSerializableException will be thrown and will identify the class
 * of the non-serializable object. 

 *
 * Classes that require special handling during the serialization and
 * deserialization process must implement special methods with these exact
 * signatures:
 *
 * 
 * private void writeObject(java.io.ObjectOutputStream out)
 *     throws IOException
 * private void readObject(java.io.ObjectInputStream in)
 *     throws IOException, ClassNotFoundException;
 * private void readObjectNoData()
 *     throws ObjectStreamException;
 * 
 *
 * 
The writeObject method is responsible for writing the state of the
 * object for its particular class so that the corresponding
 * readObject method can restore it.  The default mechanism for saving
 * the Object's fields can be invoked by calling
 * out.defaultWriteObject. The method does not need to concern
 * itself with the state belonging to its superclasses or subclasses.
 * State is saved by writing the individual fields to the
 * ObjectOutputStream using the writeObject method or by using the
 * methods for primitive data types supported by DataOutput.
 *
 * 
The readObject method is responsible for reading from the stream and
 * restoring the classes fields. It may call in.defaultReadObject to invoke
 * the default mechanism for restoring the object's non-static and
 * non-transient fields.  The defaultReadObject method uses information in
 * the stream to assign the fields of the object saved in the stream with the
 * correspondingly named fields in the current object.  This handles the case
 * when the class has evolved to add new fields. The method does not need to
 * concern itself with the state belonging to its superclasses or subclasses.
 * State is saved by writing the individual fields to the
 * ObjectOutputStream using the writeObject method or by using the
 * methods for primitive data types supported by DataOutput.
 *
 * 
The readObjectNoData method is responsible for initializing the state of
 * the object for its particular class in the event that the serialization
 * stream does not list the given class as a superclass of the object being
 * deserialized.  This may occur in cases where the receiving party uses a
 * different version of the deserialized instance's class than the sending
 * party, and the receiver's version extends classes that are not extended by
 * the sender's version.  This may also occur if the serialization stream has
 * been tampered; hence, readObjectNoData is useful for initializing
 * deserialized objects properly despite a "hostile" or incomplete source
 * stream.
 *
 * 
Serializable classes that need to designate an alternative object to be
 * used when writing an object to the stream should implement this
 * special method with the exact signature:
 *
 * 
 * ANY-ACCESS-MODIFIER Object writeReplace() throws ObjectStreamException;
 * 

 *
 * This writeReplace method is invoked by serialization if the method
 * exists and it would be accessible from a method defined within the
 * class of the object being serialized. Thus, the method can have private,
 * protected and package-private access. Subclass access to this method
 * follows java accessibility rules. 

 *
 * Classes that need to designate a replacement when an instance of it
 * is read from the stream should implement this special method with the
 * exact signature.
 *
 * 
 * ANY-ACCESS-MODIFIER Object readResolve() throws ObjectStreamException;
 * 

 *
 * This readResolve method follows the same invocation rules and
 * accessibility rules as writeReplace.

 *
 * 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 {@link 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. Array
 * classes cannot declare an explicit serialVersionUID, so they always have
 * the default computed value, but the requirement for matching
 * serialVersionUID values is waived for array classes.
 *
 * @author  unascribed
 * @see java.io.ObjectOutputStream
 * @see java.io.ObjectInputStream
 * @see java.io.ObjectOutput
 * @see java.io.ObjectInput
 * @see java.io.Externalizable
 * @since   JDK1.1
 */
public interface Serializable {
}

接口中存在一个serialVersionUID 用来标识

2、 序列化：把对象转换为字节序列的过程称为对象的序列化

就是为了在不同的时间或者不同的平台的JVM(Java的虚拟机)之间共享实例对象

反序列化：把字节序列恢复为对象的过程称为对象的反序列化。

通俗来说就是，给实体类进行标记

package com.systop.common.pojo;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

import java.io.Serializable;

@Data
@NoArgsConstructor
@AllArgsConstructor
public class Cource implements Serializable {

  private long c_id;
  private String c_name;


}

3、实体类中为什么要进行序列化

 序列化的作用：

        方便网络传输。

        可以持久化保存对象的状态。

        屏蔽了 *** 作系统的差异。

        {客户端开启某个会话功能时，web服务器就会创建一个与该客户端对应的HttpSession对象，这样会占用一定的内存空间，大量不活动但是未超时的HttpSession对象会对内存空间造成大量浪费，为了解决这种情况，我们可以将不活动但是未超时的这种HttpSession对象通过序列化转移到文件系统或数据库中保存，当服务器需要使用的时候在将他们反序列化恢复取出载入内存。}
 

 我个人的理解：为了让实体类实现持久化，方便网络传输。