Externalizable接口继承了Serializable接口，用来在序列化时手动的把需要的对象信息进行序列化。
Externalizable接口提供了两个方法：writeExternal(ObjectOuput out) 和 readExternal(ObjectInput in)
在你需要被序列化的类中实现这两个方法，这样在此类序列化时这两个方法将被自动执行，用以可定制地序列化此类。举例如下：
假如你需要序列化一个类Test：
import java.io.*;
class Test implements Externalizable{ //Test类必须实现Externalizable接口
private String letterstates = "fanruijun";
private int num = 0;
public Test(){
}
public void writeExternal(ObjectOutput out) throws IOException {
out.writeObject(letterstates);
out.write(88); //在序列化的数据最后加个88
}
public void readExternal(ObjectInput in) throws IOException,
ClassNotFoundException {
letterstates = (String)in.readObject();
num = in.read(); //把数字88加进来
}
public void putOut(){ //测试
System.out.println(letterstates +num);
}
}
序列化上面的Test类：AppTest
import java.io.*;
public class AppTest {
private void saveGame(){
Test m = new Test();
if (m != null){
try{
FileOutputStream ostream = new FileOutputStream("t.txt");
ObjectOutputStream p = new ObjectOutputStream(ostream);
p.writeObject(m); //writeExternal()自动执行
p.flush();
ostream.close();
} catch (IOException ioe) {
System.out.println ("Error saving file:");
System.out.println (ioe.getMessage());
}
}
}
private void loadGame(){
try{
FileInputStream instream = new FileInputStream("t.txt");
ObjectInputStream p = new ObjectInputStream(instream);
Test m = (Test)p.readObject();//readExternal()自动执行
m.putOut();
instream.close();
} catch (Exception e) {
System.out.println ("Error loading file:");
System.out.println (e.getMessage());
}
}
public static void main(String[] args){
new AppTest().saveGame();
new AppTest().loadGame();
}
}
运行结果：
D:\test\basic>javac AppTest.java
D:\test\basic>javac Test.java
D:\test\basic>java AppTest
fanruijun88
