理解Java序列化

向右看齐 2022-04-17 05:48 226阅读 0赞

# 序列化的理解 #

**序列化**：把对象转换为字节序列的过程称为对象的序列化。  
**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。

**序列化目的**：为了让不同JVM之间共享实例对象

**作用**：保存类对象某个时刻下的状态 (快照) ，让其可以多次复用或者是在其他JVM上恢复（还原）

**特点**：  
1.序列化将对象数据保存为一组字节数组，并且可以通过反序列化复原  
2. 仅保存某个时刻的成员变量，而并不关注静态变量  
3. 序列化对象的引用链的对象·

**应用**：保存对象快照，远程方法调用，网络传输对象

# 序列化的使用 #

## 1.Serializable 接口 ##

*  该接口会自动对成员变量进行序列化

public class Student implements Serializable{ 
    	private int id;
    	private String name;
        //通过transient关键字可以定义变量不被序列化
    	private transient char sex; 
    	
    	public Student(int id, String name, char sex) { 
    		super();
    		this.id = id;
    		this.name = name;
    		this.sex = sex;
    	}
    	
    	public int getId() { 
    		return id;
    	}
    	public String getName() { 
    		return name;
    	}
    	public char getSex() { 
    		return sex;
    	}
    	public String toString() { 
    		return "Student [id=" + id + ", name=" + name + ", sex=" + sex + "]";
    	}
    	
    }

public static void main(String[] args) throws FileNotFoundException, IOException { 
    		File file = new File("student");
    		ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream(file));
    		out.writeObject(new Student(20162590, "Reformat", 'M'));
    		System.out.println("输出成功");
        
        	ObjectInputStream in = new ObjectInputStream(new FileInputStream(file));
    		Student s =(Student) in.readObject();
    		System.out.println(s);
    		out.close();
    	}

输出成功
    反序列化：Student [id=20162590, name=Reformat, sex= ]

## 2.Externalizable接口 ##

*  这个接口需要自己实现`writeExternal` `readExternal` 里面的内容来确定哪些变量需要序列化

public class Student implements Externalizable{ 
    	private int id;
    	private String name;
    	private char sex;
    	
    	public Student(int id, String name, char sex) { 
    		super();
    		this.id = id;
    		this.name = name;
    		this.sex = sex;
    	}
    	
    	public int getId() { 
    		return id;
    	}
    	public void setId(int id) { 
    		this.id = id;
    	}
    	public String getName() { 
    		return name;
    	}
    	public char getSex() { 
    		return sex;
    	}
    	public void setSex(char sex) { 
    		this.sex = sex;
    	}
    	
    
    	public String toString() { 
    		return "Student [id=" + id + ", name=" + name + ", sex=" + sex + "]";
    	}
    
    	@Override
    	public void writeExternal(ObjectOutput out) throws IOException { 
    		out.writeInt(id);
    		out.writeObject(name);
    		out.writeObject(sex);
    	}
    
    	@Override
    	public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException { 
    		id = in.readInt();
    		name = (String) in.readObject();
    		sex = (char) in.readObject();
    	}
    	
    }

public static void main(String[] args) throws FileNotFoundException, IOException, ClassNotFoundException { 
    		Student s = new Student(20162590, "Reformat", 'M');
    		
    		File file = new File("student2");
    		ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream(file));
    		s.writeExternal(out);
    		System.out.println("输出为:"+s);
    		
    		s.setId(20162516);s.setSex('X');
    		System.out.println("更改为:"+s);
    		
    		ObjectInputStream in = new ObjectInputStream(new FileInputStream(file));
    		s.readExternal(in);
    		System.out.println("还原后:"+s);
    		out.close();
    	}

结果为：
    输出为:Student [id=20162590, name=Reformat, sex=M]
    更改为:Student [id=20162516, name=Reformat, sex=X]
    还原后:Student [id=20162590, name=Reformat, sex=M]