- Data Structure
- Networking
- RDBMS
- Operating System
- Java
- MS Excel
- iOS
- HTML
- CSS
- Android
- Python
- C Programming
- C++
- C#
- MongoDB
- MySQL
- Javascript
- PHP
- Physics
- Chemistry
- Biology
- Mathematics
- English
- Economics
- Psychology
- Social Studies
- Fashion Studies
- Legal Studies
- Selected Reading
- UPSC IAS Exams Notes
- Developer's Best Practices
- Questions and Answers
- Effective Resume Writing
- HR Interview Questions
- Computer Glossary
- Who is Who
How to prevent Serialization to break a Singleton Class Pattern?
A Singleton pattern states that a class can have a single instance and multiple instances are not permitted to be created. For this purpose, we make the constructor of the class a private and return a instance via a static method. But using serialization, we can still create multiple instance of a class. See the example below −
Example - Breaking Singleton
import java.io.ByteArrayInputStream; import java.io.ByteArrayOutputStream; import java.io.IOException; import java.io.ObjectInputStream; import java.io.ObjectOutputStream; import java.io.Serializable; public class Tester{ public static void main(String[] args) throws ClassNotFoundException, IOException{ A a = A.getInstance(); A b = (A) getSerializedCopy(a); System.out.println(a.hashCode()); System.out.println(b.hashCode()); } public static Object getSerializedCopy(Object sourceObject) throws IOException, ClassNotFoundException { ObjectOutputStream objectOutputStream = null; ObjectInputStream objectInputStream = null; ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream(); objectOutputStream = new ObjectOutputStream(byteArrayOutputStream); objectOutputStream.writeObject(sourceObject); objectOutputStream.flush(); objectInputStream = new ObjectInputStream( new ByteArrayInputStream(byteArrayOutputStream.toByteArray())); return objectInputStream.readObject(); } } class A implements Serializable { private static A a; private A(){} public static A getInstance(){ if(a == null){ a = new A(); } return a; } }
Output
1550089733 865113938
Here you can see, we've created another object of a Singleton class. Let's see how to prevent such a situation −
Override readResolve() method in the singleton class.
Example - Protecting Singleton
// implement readResolve method protected Object readResolve() { return a; }
Output
1550089733 1550089733
Advertisements