package org.effectivejava.examples.chapter11.item77;
import java.io.ObjectStreamException;
import java.io.Serializable;
import java.util.Arrays;
// Broken singleton - has nontransient object reference field!
public class Elvis implements Serializable {
public static final Elvis INSTANCE = new Elvis();
private Elvis() {
}
private String[] favoriteSongs = { "Hound Dog", "Heartbreak Hotel" };
public void printFavorites() {
System.out.println(Arrays.toString(favoriteSongs));
}
private Object readResolve() throws ObjectStreamException {
return INSTANCE;
}
}
package org.effectivejava.examples.chapter11.item77;
import java.io.Serializable;
public class ElvisStealer implements Serializable {
static Elvis impersonator;
private Elvis payload;
private Object readResolve() {
// Save a reference to the "unresolved" Elvis instance
impersonator = payload;
// Return an object of correct type for favorites field
return new String[] { "A Fool Such as I" };
}
private static final long serialVersionUID = 0;
}
package org.effectivejava.examples.chapter11.item77;
import java.io.ByteArrayInputStream;
import java.io.InputStream;
import java.io.ObjectInputStream;
public class ElvisImpersonator {
// Byte stream could not have come from real Elvis instance!
private static final byte[] serializedForm = new byte[] { (byte) 0xac,
(byte) 0xed, 0x00, 0x05, 0x73, 0x72, 0x00, 0x05, 0x45, 0x6c, 0x76,
0x69, 0x73, (byte) 0x84, (byte) 0xe6, (byte) 0x93, 0x33,
(byte) 0xc3, (byte) 0xf4, (byte) 0x8b, 0x32, 0x02, 0x00, 0x01,
0x4c, 0x00, 0x0d, 0x66, 0x61, 0x76, 0x6f, 0x72, 0x69, 0x74, 0x65,
0x53, 0x6f, 0x6e, 0x67, 0x73, 0x74, 0x00, 0x12, 0x4c, 0x6a, 0x61,
0x76, 0x61, 0x2f, 0x6c, 0x61, 0x6e, 0x67, 0x2f, 0x4f, 0x62, 0x6a,
0x65, 0x63, 0x74, 0x3b, 0x78, 0x70, 0x73, 0x72, 0x00, 0x0c, 0x45,
0x6c, 0x76, 0x69, 0x73, 0x53, 0x74, 0x65, 0x61, 0x6c, 0x65, 0x72,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02, 0x00, 0x01,
0x4c, 0x00, 0x07, 0x70, 0x61, 0x79, 0x6c, 0x6f, 0x61, 0x64, 0x74,
0x00, 0x07, 0x4c, 0x45, 0x6c, 0x76, 0x69, 0x73, 0x3b, 0x78, 0x70,
0x71, 0x00, 0x7e, 0x00, 0x02 };
public static void main(String[] args) {
// Initializes ElvisStealer.impersonator and returns
// the real Elvis (which is Elvis.INSTANCE)
Elvis elvis = (Elvis) deserialize(serializedForm);
Elvis impersonator = ElvisStealer.impersonator;
elvis.printFavorites();
impersonator.printFavorites();
}
// Returns the object with the specified serialized form
private static Object deserialize(byte[] sf) {
Object result=null;
try {
InputStream is = new ByteArrayInputStream(sf);
ObjectInputStream ois = new ObjectInputStream(is);
result= ois.readObject();
} catch (Exception e) {
throw new IllegalArgumentException(e);
}
return result;
}
}
这代码根本跑不起来，会报错。而ElvisStealer类的readResolve方法居然return new String[] { "A Fool Such as I" };更是让人摸不着头脑，如果返回的是ElvisStealer那还好，但是这里却返回字符数组，那不必错无疑么。求帮忙纠正下这段代码，然后讲一下ElvisStealer类的readResolve方法的return
首先，我测试了你的代码，是能够运行的，我的环境是jdk1.8+Eclipse4.5，运行结果是：
[Hound Dog, Heartbreak Hotel]
[A Fool Such as I]
其次，这个readResolve方法的作用是让程序员定制反序列化操作返回的对象，反序列化调用readObject()时，底层是调用了readResolve()方法的。
最后，再分析你的main方法测试，给出的序列化字节serializedForm 是一个ElvisStealer类的对象的字节数组，它的两个属性payload都是有引用值的。所以你对这个字节数据反序列化时调用readObject时，先调用了ElvisStealer类的readResolve，然后又调用Elvis类的readResolve，得到了Elvis的实例，同时impersonator属性指向payload。
补充一下，而ElvisStealer类的readResolve方法，这里用return new String[] { "A Fool Such as I" }，其实是为了定制序列化操作的返回值，通常默认的就是返回原来序列话的值，不会破坏原有的对象信息的。这里可能是为了显示定制，而返回特定的值。它与writeReplace序列化时写入的信息是一致的。我们在定制序列化时应该保证writeReplace和readResolve信息的一致。
楼上答得很好，我也将代码运行了一下，也报错。我用的是 jdk1.7 + Kepler Service Release 2。我查了一下，readResolve()方法与writeReplace()方法是对应的，readResolve()方法可以实现保护性复制整个对象，并且它会紧接着readObject()方法运行，该方法的返回值将会代替原来反序列化的对象
(即也就是readObject()的返回值，这个值将被丢弃)。常用于序列化单例类、枚举类。所以正如楼上所说，readResolve()和writeReplace()方法的作用是让程序员定制反序列化和序列化操作返回的对象