当有些属性不希望序列化时，transient关键字为我们提供了便利。
你只需要实现Serilizable接口，将不需要序列化的属性前添加关键字transient，序列化对象的时候，这个属性就不会序列化到指定的目的地中。

反序列化读取序列化对象的顺序要保持一致

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

/**
 * @description 使用transient关键字不序列化某个变量
 *        注意读取的时候，读取数据的顺序一定要和存放数据的顺序保持一致
 *        
 * @author Alexia
 * @date  2013-10-15
 */
public class TransientTest {
    
    public static void main(String[] args) {
        
        User user = new User();
        user.setUsername("Alexia");
        user.setPasswd("123456");
        
        System.out.println("read before Serializable: ");
        System.out.println("username: " + user.getUsername());
        System.err.println("password: " + user.getPasswd());
        
        try {
            ObjectOutputStream os = new ObjectOutputStream(
                    new FileOutputStream("C:/user.txt"));
            os.writeObject(user); // 将User对象写进文件
            os.flush();
            os.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        try {
            ObjectInputStream is = new ObjectInputStream(new FileInputStream(
                    "C:/user.txt"));
            user = (User) is.readObject(); // 从流中读取User的数据
            is.close();
            
            System.out.println("
read after Serializable: ");
            System.out.println("username: " + user.getUsername());
            System.err.println("password: " + user.getPasswd());
            
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
}

class User implements Serializable {
    private static final long serialVersionUID = 8294180014912103005L;  
    
    private String username;
    private transient String passwd;
    
    public String getUsername() {
        return username;
    }
    
    public void setUsername(String username) {
        this.username = username;
    }
    
    public String getPasswd() {
        return passwd;
    }
    
    public void setPasswd(String passwd) {
        this.passwd = passwd;
    }

}