Skip to main content

Singleton class in java

What is Singleton class

Singleton is a design technique which gaurantees that there will be only instance of a class globally. Such classes are required when we need to create some objects which are memory/ resource extensive and we can't afford many such objects.

Using singleton We can maintain single object per JVM per classloader. Classloader could be different in different hierarchy and in such case we may have more than one instances of singleton but we can avoid it by loading it at appropriate classloader. For example in an ear application there could be multiple web modules and each one of them will have their own singleton instance. Sometimes it may be a need but sometimes it could be a flaw which can be resolved by loading it either at ear level or web module level as per requirement.

Implementing singleton class

There are two different ways to implement singleton in java.
  1. Using singleton design pattern

  2. In this pattern we can create singleton either using lazy loading or using eager loading.

    In lazy loading, we create the instance when we actually need it. But implementation is little tricky and we need to handle thread safety. Below is the example of lazy loading implementation.

      public class MySingleton{
          private static MySingleton instance = null;
          
          private MySingleton(){}
          
          public static MySingleton getInstance(){
              if(instance==null){
              	synchronised(MySingleton.class){
                	if(instance==null){
                  		instance=MySingleton();
                    }
                }
              }
              return instance;
          }
      }
      

    In eager loading, we create the instance as soon as class is loaded. Implementation is easy here and we don't need to worry about thread safety. But it creates the object whether we need it or notBelow is the example of lazy loading implementation.

      public class MySingleton{
          private static MySingleton instance = MySingleton();
          
          private MySingleton(){}
          
          public static MySingleton getInstance(){
    
               return instance;
          }
      
      }
      
  3. Using enum class

  4. Singleton creation is very easy using enums. Just create an enum class as given below. You can also create parameterized Enum instances by adding the relevant constructor.
      public enum MySingleton {
    	
    	instance;
    	
      }
      
    And then you can get the instance by just using below code.
    MySingleton i = MySingleton.instance;

Best approach to create singleton

You already saw here that you can create singleton either of the above approaches but there are some differences between them.

With singleton design pattern class creation need to handle synchronization. Also there is a chance that it can be serialized/ deserialized or class variables accessor can be modified using reflection which will destroy the singlton.

In my opinion using Enum for singleton will be the better option as it will automatically handle the above problems.

Comments

  1. Thanks for sharing a really needed post that i am looking for , if anyone looking for best java institute in delhi so join with us visit our website : https://www.htsindia.com/java-training-courses or contact us : +91-9311002620

    ReplyDelete

Post a Comment

Popular Posts

Asynchronous REST service implementation in Spring boot

In this tutorial we will see how to create an asynchronous REST service endpoint using Spring boot application. Asynchronous service works in a way that it will not block the client request and do the processing in separate thread. When work is complete the response returned to the client so our service will be able to handle more client requests at the same time, compare to synchronous processing model. Let's understand how it is working in synchronous mode. In such server/client application at server side it has a pool of threads which are serving the request. If a request received by a thread then it will be blocked until it send the response back to client. In this case if processing doesn't take much time it will be able to process it quickly and accept other client requests but there could be one situation when all threads are busy and not able to accept the new client requests. To overcome of such problems, asynchronous processing model introduced for REST service

SpringBoot - @ConditionalOnProperty example for conditional bean initialization

@ConditionalOnProperty annotation is used to check if specified property available in the environment or it matches some specific value so it can control the execution of some part of code like bean creation. It may be useful in many cases for example enable/disable service if specific property is available. Below are the attributes which can be used for property check. havingValue - Provide the value which need to check against specified property otherwise it will check that value should not be false. matchIfMissing - If true it will match the condition and execute the annotated code when property itself is not available in environment. name - Name of the property to be tested. If you want to test single property then you can directly put the property name as string like "property.name" and if you have multiple properties to test then you can put the names like {"prop.name1","prop.name2"} prefix - It can be use when you want to apply some prefix to

Setting up kerberos in Mac OS X

Kerberos in MAC OS X Kerberos authentication allows the computers in same domain network to authenticate certain services with prompting the user for credentials. MAC OS X comes with Heimdal Kerberos which is an alternate implementation of the kerberos and uses LDAP as identity management database. Here we are going to learn how to setup a kerberos on MAC OS X which we will configure latter in our application. Installing Kerberos In MAC we can use Homebrew for installing any software package. Homebrew makes it very easy to install the kerberos by just executing a simple command as given below. brew install krb5 Once installation is complete, we need to set the below export commands in user's profile which will make the kerberos utility commands and compiler available to execute from anywhere. Open user's bash profile: vi ~/.bash_profile Add below lines: export PATH=/usr/local/opt/krb5/bin:$PATH export PATH=/usr/local/opt/krb5/sbin:$PATH export LDFLAGS=&

Web scraper using JSoup and Spring Boot

What is webscraping Webscraping is a technique to extract or pull the data from a website to gather required information by parsing the HTML source of their websites, such as articles from news or books site, products information from online shopping sites or course information from education sites. There are many organisations who uses web scraper to provide the best experience to their customers, for example extract the price for a smartphone from multiple online websites and show their customers the best and cheap product URL. We will learn here how to code a web scraper by developing a simple new scraper service. News scraper News scraper is used to extract the news articles or other related contents from a news site. Here we are going to create a web scraper application to pull the articles from news site. Below are the operations provided by our news scraper service. List all the authors Search articles by author name Search articles by article title Search articles