java序列化总结

1.Serializable接口

只是一个表识接口，仅仅是告诉jvm这是一个可以序列化的接口。

2.serialVersionUID

只要这个UID的值不变，在序列化的版本中增加属性或者减少属性就不会报错；否则当版本变更后，再反序列会报错；
如果自己不定义，每次在编译的时候，编译器会自动生成一个值，但是不能保证每次编译时的值都一样，所以务必自己定义！

 

3.readResolve、readObject、writeReplace、writeObject接口

 

public class FooImpl implements java.io.Serializable{    
    private String message;    
   
    public String getFoo() {            
        return message;    
    }    
   
    public void setMessage(String message) {    
        this.message = message;    
    }    
   
    private void writeObject(java.io.ObjectOutputStream out) throws IOException {    
        System.out.println("writeObject invoked");    
        out.writeObject(this.message == null ? "hohohahaha" : this.message);    
    }    
   
    private void readObject(java.io.ObjectInputStream in) throws IOException,    
            ClassNotFoundException {    
        System.out.println("readObject invoked");    
        this.message = (String) in.readObject();    
    }    
   
    private Object writeReplace() throws ObjectStreamException {    
        System.out.println("writeReplace invoked");    
        return this;    
    }    
   
    private Object readResolve() throws ObjectStreamException {    
        System.out.println("readResolve invoked");    
        return this;    
    }    
   
    public Object serialize() throws IOException, ClassNotFoundException {    
        ByteArrayOutputStream baos = new ByteArrayOutputStream();    
        ObjectOutputStream oos = new ObjectOutputStream(baos);    
        oos.writeObject(this);    
        ByteArrayInputStream bais = new ByteArrayInputStream(baos.toByteArray());    
        ObjectInputStream ois = new ObjectInputStream(bais);    
        return ois.readObject();    
    }    
         public static void main(String[] args) throws IOException,     
              ClassNotFoundException {    
                  FooImpl fooimpl = new FooImpl();    
                  fooimpl.serialize();    
    }    
}   

 

我们运行这段代码看到的debug信息:
writeReplace invoked (序列化时调用)
writeObject invoked (序列化时调用)
readObject invoked (反序列化时调用)
readResolve invoked(反序列化时调用)

4.Externalizable

Externalizable 是一个有实际方法需要实现的interface,包括writeExternal和readExternal,是Serializable接口的子接口:

   public class FooImpl implements java.io.Externalizable {
    private String message;

    public String getFoo() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }

    private Object writeReplace() throws ObjectStreamException {
        System.out.println("writeReplace invoked");
        return this;
    }

    private Object readResolve() throws ObjectStreamException {
        System.out.println("readResolve invoked");
        return this;
    }

    public Object serialize() throws IOException, ClassNotFoundException {
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream(baos);
        oos.writeObject(this);
        ByteArrayInputStream bais = new ByteArrayInputStream(baos.toByteArray());
        ObjectInputStream ois = new ObjectInputStream(bais);
        return ois.readObject();
    }

    public void readExternal(ObjectInput arg0) throws IOException,
            ClassNotFoundException {
        System.out.println("readExternal invoked");
        Object obj = arg0.readObject();
    }

    public void writeExternal(ObjectOutput arg0) throws IOException {
        System.out.println("writeExternal invoked");
        arg0.writeObject("Hello world");
    }
         public static void main(String[] args) throws IOException,
              ClassNotFoundException {
                  FooImpl fooimpl = new FooImpl();
                  fooimpl.serialize();
    }
}

我们运行这段代码看到的debug信息:
writeReplace invoked
writeExternal invoked
readExternal invoked
readResolve invoked
在此writeExternal 和readExternal 的作用与writeObject和readObject 一样.

最后,当我们同时实现了两个interface的时候,JVM只运行Externalizable 接口里面的writeExternal 和readExternal 方法对序列化内容进行处理.
需要注意的是:Serializable是一个真正的mark interface,
writeObject,readObject, writeReplace,readResolve是直接与JVM通信,告诉JVM序列化的内容.