transient关键字的使用

概述

transient的使用

public class TransientTest {

    public static void main(String[] args) {

        User user = new User();
        user.setUsername("Github");
        user.setPassword("123456");

        System.out.println("read before Serializable: ");
        System.out.println("username: " + user.getUsername());
        System.err.println("password: " + user.getPassword());

        try {
            ObjectOutputStream os = new ObjectOutputStream(new FileOutputStream("user.txt"));
            os.writeObject(user); // 将User对象写进文件
            os.flush();
            os.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
        try {
            ObjectInputStream is = new ObjectInputStream(new FileInputStream("user.txt"));
            user = (User) is.readObject(); // 从流中读取User的数据
            is.close();

            System.out.println("\nread after Serializable: ");
            System.out.println("username: " + user.getUsername());
            System.err.println("password: " + user.getPassword());

        } catch (IOException | ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
}

public class User implements Serializable {
    private static final long serialVersionUID = 1234567890L;

    private String username;
    private transient String 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;
    }
}

运行结果：

transient修饰静态变量

public class TransientTest {

    public static void main(String[] args) {

        User user = new User();
        user.setUsername("Github");
        user.setPassword("123456");

        System.out.println("read before Serializable: ");
        System.out.println("username: " + user.getUsername());
        System.err.println("password: " + user.getPassword());

        try {
            ObjectOutputStream os = new ObjectOutputStream(new FileOutputStream("user.txt"));
            os.writeObject(user); // 将User对象写进文件
            os.flush();
            os.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
        try {
            // 在反序列化前盖板username的值
            user.setUsername("Tom");

            ObjectInputStream is = new ObjectInputStream(new FileInputStream("user.txt"));
            user = (User) is.readObject(); // 从流中读取User的数据
            is.close();

            System.out.println("\nread after Serializable: ");
            System.out.println("username: " + user.getUsername());
            System.err.println("password: " + user.getPassword());

        } catch (IOException | ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
}

public class User implements Serializable {
    private static final long serialVersionUID = 1234567890L;

    private static String username;
    private transient String 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;
    }
}

运行结果：

总结

1. 一旦变量被transient修饰，变量将不再是对象持久化的一部分，该变量内容在序列化后无法获得访问。
2. transient关键字只能修饰变量，而不能修饰方法和类。本地变量是不能被transient关键字修饰的。变量如果是用户自定义类变量，则该类需要实现Serializable接口。
3. 一个静态变量不管是否被transient修饰，均不能被序列化。