Serializable 和 Externalizable区别？

叁歲伎倆 2024-03-23 18:53 32阅读 0赞

### Serializable接口 ###

java.io.Serializable 接口没有方法或字段，仅用于标识可序列化的语义。

public interface Serializable {
        
    }

在进行序列化操作时，会判断要被序列化的类是否是`Enum`、`Array`和 `Serializable`类型，如果都不是则直接抛出`NotSerializableException`。

@Data
    public class A1_User implements Serializable {
        
        private String name;
        private int age;
    }

A1_User user = new A1_User();
    user.setName("xiaoming");
    user.setAge(18);
     
    序列化
    ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("tempFile"));
    oos.writeObject(user);
    
    反序列化
    ObjectInputStream ois = new ObjectInputStream(new FileInputStream(new File("tempFile")));
    A1_User newUser = (A1_User) ois.readObject();

--------------------

### Externalizable接口 ###

public interface Externalizable extends java.io.Serializable {
        
        void writeExternal(ObjectOutput out) throws IOException;
        void readExternal(ObjectInput in) throws IOException, ClassNotFoundException;
    }

需要重写writeExternal()与readExternal()方法。否则所有变量的值都会变成默认值。  
重写就会很灵活，可以随意加减属性

@Data
    public class B1_User implements Externalizable {
        
        private String name;
        private int age;
    
        public void writeExternal(ObjectOutput out) throws IOException {
        
            out.writeObject(name);
            out.writeInt(age);
        }
    
        public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
        
            name = (String) in.readObject();
            age = in.readInt();
        }
    }

B1_User user = new B1_User();
    user.setName("xiaoming");
    user.setAge(18);
    
    ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("tempFile"));
    oos.writeObject(user);
    
    ObjectInputStream ois = new ObjectInputStream(new FileInputStream(new File("tempFile")));
    B1_User newUser = (B1_User) ois.readObject();

--------------------

### 两种序列化的对比 ###

<table> 
 <thead> 
  <tr> 
   <th align="left">实现Serializable接口</th> 
   <th align="left">实现Externalizable接口</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td align="left">所有属性自动都会被序列化，简单但死板</td> 
   <td align="left">需要重写writeExternal()与readExternal()方法，啰嗦但灵活</td> 
  </tr> 
  <tr> 
   <td align="left">性能略差</td> 
   <td align="left">性能略好</td> 
  </tr> 
  <tr> 
   <td align="left"></td> 
   <td align="left">必须要提供一个public的无参的构造器</td> 
  </tr> 
 </tbody> 
</table>