Lifecycle of FacesContext?

Question

While going through the javadoc of `FacesContext`, I came across this sentence The instance remains active until its release() method is called, after which no further references to this instance are allowed. While a FacesContext instance is active, it must not be referenced from any thread other than the one upon which the servlet container executing this web application utilizes for the processing of this request Does this mean that `FacesContext` will never go for garbage collection, and the instance will be destroyed only when the current-webapplication stops (server is stopped)? Is `FacesContext` following singleton pattern? In that case, how will it behave when multiple request and coming for rendering response simultaneously as it serves only one request per time?

Accepted Answer

Does this mean that `FacesContext` will never go for garbage collection, and the instance will be destroyed only when the current-webapplication stops (server is stopped)?

No, you read it wrongly. The `FacesContext` lives as long as a single HTTP request. It will (actually, "can" is a better word) not immediately be GC'ed if you incorrectly reference it anywhere in your own code beyond its scope. E.g. as a property of a session scoped managed bean which lives longer than a single HTTP request:

```
@ManagedBean
@SessionScoped
public class BadSessionBean {

// Bad Example! Never do this! Not threadsafe and instance can't be GC'ed by end of request!
    private FacesContext context = FacesContext.getCurrentInstance();

}
```

If you aren't doing that anywhere in your code, and thus you're always obtaining the current instance in method local scope, then it will have the chance to be properly GC'ed.

```
@ManagedBean
@SessionScoped
public class GoodSessionBean {

public void someMethod() {
        // OK! Declared in method local scope and thus threadsafe.
        FacesContext context = FacesContext.getCurrentInstance();
    }

}
```

Please note that this GC behavior is not specific to JSF/`FacesContext`, it's just specific to basic Java in general.

Is `FacesContext` following singleton pattern? In that case, how will it behave when multiple request and coming for rendering response simultaneously as it serves only one request per time?

No, it's definitely not a singleton. It's a `ThreadLocal` instance which is created by `FacesServlet` right after the `service()` method is entered and destroyed by the `FacesServlet` right before the `service()` method is left. Thus, there's only one instance per request (and thus not per application). Note that one HTTP request counts as one separate thread. There can be multiple threads (read: requests) and thus there can be multiple instances of the `FacesContext` during application's lifetime. Its main pattern is the facade pattern, but that's further not related to it being a `ThreadLocal`.

Lifecycle of FacesContext?

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