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What is singleton in Guice?

Following are the scopes that Guice supports: @Singleton Single instance for lifetime of the application. @Singleton object needs to be threadsafe. @SessionScoped Single instance for a particular session of the web application.

Is Guice inject singleton?

Guice provides an AbstractModule , used here, which provides some syntactic convenience. This Module simply defines the mapping of interfaces to implementations, e.g., binding injections requiring an OrderService to the DefaultOrderService implementation. For this application, singleton implementations are desired.

Is Guice singleton thread safe?

1 Answer. It’s not only that Guice will provide the same singleton across threads for the same injector, but Guice can only provide the same singleton across threads if you use toInstance . Modules are evaluated once per injector, and you gave Guice one instance and no way to produce a second one.

What is the point of Guice?

Google’s Guice is a Java-based dependency injection framework, which means approximately nothing to people who aren’t familiar with it. Google’s Guice is a way to build a graph of dependencies so you can instantiate complex objects made of simpler parts.

What problem does singleton solve?

The singleton design pattern solves problems by allowing it to: Ensure that a class only has one instance. Easily access the sole instance of a class. Control its instantiation.

When to use @ Singleton annotation in Google Guice?

Notice that class is annotated with @Singleton annotation. Since service objects will be created through injector classes, this annotation is provided to let them know that the service classes should be singleton objects. Google Guice 3.0 added the support for JSR-330 and we can use annotations from com.google.inject or javax.inject package.

How to create eager Singleton in Java Guice?

Now, let’s inject an eager singleton: The asEagerSingleton () call defines the singleton as eagerly instantiated. In addition to these two scopes, Guice supports custom scopes as well as the web-only @RequestScoped and @SessionScoped annotations, supplied by Jakarta EE (there are no Guice-supplied versions of those annotations).

How to inject a singleton into an application?

Let’s inject a singleton into our application: The in (Scopes.SINGLETON) specifies that any Communicator field with the @Named (“AnotherCommunicator”) will get a singleton injected. This singleton is lazily initiated by default.

Which is the basic entry point in Guice?

The basic entry point into Guice is the Injector: ? This main method retrieves an instance of our Communication class. It also introduces a fundamental concept of Guice: the Module (using BasicModule in this example). The Module is the basic unit of definition of bindings (or wiring, as it’s known in Spring).