Over a million developers have joined DZone.

Singleton Pattern in Java EE

DZone's Guide to

Singleton Pattern in Java EE

· Java Zone ·
Free Resource

Distribute microservices between the private and public clusters, yet maintain bi-directional connectivity. Content provided by IBM Developer.

The singleton pattern is one of the most well known design patterns and is used extensively by frameworks such as Spring. Java EE offers an elegant and easy way to implement the singleton pattern. By adding the @Singleton annotation to a class you can turn it into a singleton bean as shown in the following code snippet.

public class SingletonBean {

  public String message(){
      return "Hello Singleton World!";

It is important to note that Java EE initialises singleton beans lazily unless annotated with @Startup.

We still have a potential problem with concurrency related method access. Java EE solves this issue rather simply with another set of annotations. By default the container manages concurrency, so an annotation is only required if you want to manage it yourself. This is called bean managed concurrency and is annotated on the class as in the following code snippet.

public class SingletonBean {

  public String getName(){
      return "Return name from Cache";

  public void addName(String){
      // code that adds name to cache

Further annotations are necessary when this option is chosen. We control access using the familiar read/write concept and annotate methods appropriately as can be seen in the above example.

If you are interested in learning more about how we can develop singletons in ways there were never possible before I suggest that you read chapter 4 of my book Professional Java EE Design Patterns.

Use this tool to look at the contents of GitHub and classify code based on the programming language used.  Content provided by IBM Developer.


Published at DZone with permission of

Opinions expressed by DZone contributors are their own.

{{ parent.title || parent.header.title}}

{{ parent.tldr }}

{{ parent.urlSource.name }}