Java 写入 readResolve方法解决 单例类序列化后破坏唯一实例规则的问题
- 单例类序列化后, 在反序列化会克隆出新的对象破坏了单例规则. 所以需要序列化的单例类需要含有 readResolve方法. 反序列化时会自动调用此方法返回对象, 来保证对象唯一性
public class EagerSingleton implements Serializable {
private static final long serialVersionUID = 7073777279565036708L;
private static volatile EagerSingleton instance = new EagerSingleton();
/**
* 为了防止通过反射机制实例化构造方法抛异常
* */
private EagerSingleton() {
if (instance != null) {
throw new RuntimeException("不允许被反射实例化");
}
}
public static EagerSingleton getInstance() {
return instance;
}
/**
* readResolve方法的作用为防止序列化单例时破坏唯一实例的规则
* */
private Object readResolve() throws ObjectStreamException {
return instance;
}
}
public class App {
public static void main(String[] args) {
EagerSingleton o = EagerSingleton.getInstance();
System.out.println("通过单例类实例化对象 " + EagerSingleton.getInstance());
try {
File file = new File("D:" + File.separator + "EagerSingleton");
ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream(file));
/** 对象写入到文件*/
oos.writeObject(o);
ObjectInputStream ois = new ObjectInputStream(new FileInputStream(file));
/** 从磁盘读取对象*/
System.out.println("从磁盘读取的对象 " + ois.readObject());
} catch (Exception e) {
e.printStackTrace();
}
}
}
- 输出 (单例类不包含 readResolve方法时
通过单例类实例化对象 com.test.web4.singleton.EagerSingleton@eed1f14
从磁盘读取的对象 com.test.web4.singleton.EagerSingleton@7a07c5b4
- 输出 (单例类包含 readResolve方法时
通过单例类实例化对象 com.test.web4.singleton.EagerSingleton@eed1f14
从磁盘读取的对象 com.test.web4.singleton.EagerSingleton@eed1f14
- 可以看出对象地址包含 readResolve方法和不包含是有区别的
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