java对象序列化知识

java对象序列化知识

1、java对象序列化不保存对象中的静态变量

serpublic class Test implements Serializable {

	private static final long serialVersionUID = 1L;

	public static int staticVar = 5;

	public static void main(String[] args) {
		try {
			//初始时staticVar为5
			ObjectOutputStream out = new ObjectOutputStream(
					new FileOutputStream("result.obj"));
			out.writeObject(new Test());
			out.close();

			//序列化后修改为10
			Test.staticVar = 10;

			ObjectInputStream oin = new ObjectInputStream(new FileInputStream(
					"result.obj"));
			Test t = (Test) oin.readObject();
			oin.close();
			
			//再读取，通过t.staticVar打印新的值
			System.out.println(t.staticVar);//10
			
		} catch (FileNotFoundException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		} catch (ClassNotFoundException e) {
			e.printStackTrace();
		}
	}
}

2、虚拟机是否允许反序列化，不仅取决于类路径和功能代码是否一致，一个非常重要的一点是两个类的序列化 ID 是否一致（就是 private static final long serialVersionUID = 1L）。

3、父类的序列化与transient关键字

只有子类和父类都实现了Serializable接口时，对子类反序列化时才会将父类也序列化。反序列化过程是先反序列过父类对象再反序列化子类。而如果不想序列化某一个变量，则可以在定义变量时使用transient关键字。

Parentimport java.io.Serializable;


public class Parent implements Serializable {
	
	private static final long serialVersionUID = 1L;
	
	public int pi = 2;
	
	public String pstr ="pstr";
	
	public  transient String ts  ; 
	
}

Son and mainimport java.io.File;
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;

public class Son extends Parent implements Serializable {

	private static final long serialVersionUID = 1L;

	public int si = 1;
	public String sstr = " sstr";

	public static void main(String[] args) throws FileNotFoundException, IOException, ClassNotFoundException {
		String path = "d:" + File.separator + "son.dll";
		Son s = new Son();
		s.si = 2;
		s.pi = 2;
		s.ts = "ts"; // ts在父类中的定义使用transient关键字

		ObjectOutputStream op = null;
		ObjectInputStream oi = null;

		op = new ObjectOutputStream(new FileOutputStream(new File(path)));
		op.writeObject(s);
		op.close();
		oi = new ObjectInputStream(new FileInputStream(path));
		Son s1 = (Son) oi.readObject();

		System.out.println("父类中的String pstr:" + s1.pstr);
		System.out.println("父类中的int pi:" + s1.pi);
		System.out.println("子类中的int si:" + s1.si);
		System.out.println("父类中的transient String ts :" + s1.ts);//

	}
}

4、Java 序列化机制为了节省磁盘空间，具有特定的存储规则，当写入文件的为同一对象时，并不会再将对象的内容进行存储，而只是再次存储一份引用。

 

从IBM DW 整理而来

http://www.ibm.com/developerworks/cn/java/j-lo-serial/index.html#icomments