序列化Serializable和Externalizable的区别 - c++编程基础

大家都知道Serializable是一个mark interface,告诉JVM这个对象可以被转换成二进制流来传输.
但是Serializable与Externalizable的转换二进制流的过程是不一样的.
Serializable 在我们实现这个接口的时候,我们可以使用4个私有方法来控制序列化的过程:
我们来看一个例子:
Java代码

public class FooImpl implements java.io.Serializable{
private String message;
public String getFoo() {
return message;
}
public void setMessage(String message) {
this.message = message;
}
private void writeObject(java.io.ObjectOutputStream out) throws IOException {
System.out.println("writeObject invoked");
out.writeObject(this.message == null ? "hohohahaha" : this.message);
}
private void readObject(java.io.ObjectInputStream in) throws IOException,
ClassNotFoundException {
System.out.println("readObject invoked");
this.message = (String) in.readObject();
System.out.println("got message:" + message);
}
private Object writeReplace() throws ObjectStreamException {
System.out.println("writeReplace invoked");
return this;
}
private Object readResolve() throws ObjectStreamException {
System.out.println("readResolve invoked");
return this;
}
public Object serialize() throws IOException, ClassNotFoundException {
ByteArrayOutputStream baos = new ByteArrayOutputStream();
ObjectOutputStream oos = new ObjectOutputStream(baos);
oos.writeObject(this);
ByteArrayInputStream bais = new ByteArrayInputStream(baos.toByteArray());
ObjectInputStream ois = new ObjectInputStream(bais);
return ois.readObject();
}
public static void main(String[] args) throws IOException,
ClassNotFoundException {
FooImpl fooimpl = new FooImpl();
fooimpl.serialize();
}
我们运行这段代码看到的debug信息:
writeReplace invoked
writeObject invoked
readObject invoked
readResolve invoked

当进行序列化的时候:

首先JVM会先调用writeReplace方法,在这个阶段,我们可以进行张冠李戴,将需要进行序列化的对象换成我们指定的对象.
跟着JVM将调用writeObject方法,来将对象中的属性一个个进行序列化,我们可以在这个方法中控制住哪些属性需要序列化.

当反序列化的时候:
JVM会调用readObject方法,将我们刚刚在writeObject方法序列化好的属性,反序列化回来.
然后在readResolve方法中,我们也可以指定JVM返回我们特定的对象(不是刚刚序列化回来的对象).

注意到在writeReplace和readResolve,我们可以严格控制singleton的对象,在同一个JVM中完完全全只有唯一的对象,控制不让singleton对象产生副本.

Externalizable 是一个有实际方法需要实现的interface,包括writeExternal和readExternal:
Java代码
1. public class FooImpl implements java.io.Externalizable {
2. private String message;
4. public String getFoo() {
5. return message;
6. }
8. public void setMessage(String message) {
9. this.message = message;
10. }
12. private Object writeReplace() throws ObjectStreamException {
13. System.out.println("writeReplace invoked");
14. return this;
15. }
17. private Object readResolve() throws ObjectStreamException {
18. System.out.println("readResolve invoked");
19. return this;
20. }
22. public Object serialize() throws IOException, ClassNotFoundException {
23. ByteArrayOutputStream baos = new ByteArrayOutputStream();
24. ObjectOutputStream oos = new ObjectOutputStream(baos);
25. oos.writeObject(this);
26. ByteArrayInputStream bais = new ByteArrayInputStream(baos.toByteArray());
27. ObjectInputStream ois = new ObjectInputStream(bais);
28. return ois.readObject();
29. }
31. public void readExternal(ObjectInput arg0) throws IOException,
32. ClassNotFoundException {
33. System.out.println("readExternal invoked");
34. Object obj = arg0.readObject();
35. }
37. public void writeExternal(ObjectOutput arg0) throws IOException {
38. System.out.println("writeExternal invoked");
39. arg0.writeObject("Hello world");
40. }
41. public static void main(S

序列化Serializable和Externalizable的区别(一)