public class FooImpl implements java.io.Externalizable {
private String message;
public String getFoo() {
return message;
}
public void setMessage(String message) {
this.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 void readExternal(ObjectInput arg0) throws IOException,
ClassNotFoundException {
System.out.println("readExternal invoked");
Object obj = arg0.readObject();
}
public void writeExternal(ObjectOutput arg0) throws IOException {
System.out.println("writeExternal invoked");
arg0.writeObject("Hello world");
}
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
writeExternal invoked
readExternal invoked
readResolve invoked
在此writeExternal 和readExternal 的作用与writeObject和readObject 一样.
最后,当我们同时实现了两个interface的时候,JVM只运行Externalizable 接口里面的writeExternal 和readExternal 方法对序列化内容进行处理.
需要注意的是:Serializable是一个真正的mark interface,
writeObject,readObject, writeReplace,readResolve是直接与JVM通信,告诉JVM序列化的内容.
责任编辑：小草
