Java中的关键字 transient

定义

java语言的关键字，变量修饰符，如果用transient声明一个实例变量，当对象存储时，它的值不需要维持。换句话来说就是，用transient关键字标记的成员变量不参与序列化过程。

作用

        Java的serialization提供了一种持久化对象实例的机制。当持久化对象时，可能有一个特殊的对象数据成员，我们不想用serialization机制来保存它。为了在一个特定对象的一个域上关闭serialization，可以在这个域前加上关键字transient。当一个对象被序列化的时候，transient型变量的值不包括在序列化的表示中，然而非transient型的变量是被包括进去的。

例子

新建一个User类，实现序列化接口

import java.io.Serializable;

public class User implements Serializable {
    private static final long serialVersionUID = -1897102804742639482L;

    private String userName;
    private transient String password;

    public User() {
    }

    public User(String userName, String password) {
        this.userName = userName;
        this.password = password;
    }

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    @Override
    public String toString() {
        return "User [userName=" + userName + ", password=" + password + "]";
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((userName == null) ? 0 : userName.hashCode());
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        User other = (User) obj;
        if (userName == null) {
            if (other.userName != null)
                return false;
        } else if (!userName.equals(other.userName))
            return false;
        return true;
    }

}

测试类

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

public class TestTransient {

    public static void main(String[] args) {
        User user = new User();
        
        user.setUserName("zhangsan");
        user.setPassword("123");

        String fileName = "user.out";
        ObjectOutputStream oos = null;
        try {
            oos = new ObjectOutputStream(new FileOutputStream(fileName));
            oos.writeObject(user);
            oos.flush();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                oos.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        
        
        User newUser = null;
        ObjectInputStream ois = null;
        try {
            ois = new ObjectInputStream(new FileInputStream(fileName));
            newUser = (User) ois.readObject();
            
            System.out.println(newUser.toString());
        } catch (IOException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } finally {
            try {
                ois.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

}

控制台打印：

User [userName=zhangsan, password=null]

注意：passsword为null