Contains annotations and interfaces for defining interceptor methods and interceptor classes, and for binding interceptor classes to target classes.

## Interceptor methods

An interceptor method is a method of an interceptor class or of a target class that is invoked to interpose on the invocation of a method of the target class, a constructor of the target class, a lifecycle event of the target class, or a timeout method of the target class.

An interceptor method for a target class may be declared in the target class, in an interceptor class associated with the target class, or in a superclass of the target class or interceptor class.

An {@link jakarta.interceptor.AroundConstruct} interceptor method may be defined only in an interceptor class or superclass of an interceptor class.

The Jakarta Interceptors specification defines the interceptor method types listed below. Extension specifications may define additional interceptor method types.

- {@link jakarta.interceptor.AroundInvoke} interceptor methods, which interpose on business methods of the target class.
- {@link jakarta.interceptor.AroundTimeout} interceptor methods, which interpose on the invocation of timeout methods, in response to timer events.
- {@link jakarta.annotation.PostConstruct} interceptor methods, which are invoked after dependency injection has been completed on the target instance.
- {@link jakarta.annotation.PreDestroy} interceptor methods, which are invoked before the target instance and all interceptor instances associated with it are destroyed.
- {@link jakarta.interceptor.AroundConstruct} interceptor methods, which interpose on the invocation of the constructor of the target instance.

{@link jakarta.annotation.PostConstruct}, {@link jakarta.annotation.PreDestroy}, and {@link AroundConstruct} interceptor methods are collectively referred to as lifecycle callback interceptor methods.

An interceptor method may be defined using annotations or, optionally, by means of a deployment descriptor. Interceptor methods may not be declared `abstract`, `static`, or `final`.

An interceptor class or target class may have multiple interceptor methods. However, an interceptor class or target class may have no more than one interceptor method of a given interceptor method type: {@link jakarta.interceptor.AroundInvoke}, {@link jakarta.interceptor.AroundTimeout}, {@link jakarta.annotation.PostConstruct}, {@link jakarta.annotation.PreDestroy}, {@link jakarta.interceptor.AroundConstruct}.

## Interceptor classes

An interceptor class is a class (distinct from the target class) whose methods are invoked in response to invocations and/or lifecycle events on the target class. Any number of interceptor classes may be associated with a target class.

An interceptor class must have a public constructor with no parameters.

Interceptor methods and interceptor classes may be defined for a class by means of metadata annotations or, optionally, by means of a deployment descriptor.

## Associating an interceptor class with the target class

An interceptor class may be associated with the target class or a method of the target class in several ways:

- By annotating both the interceptor class and the target class with an interceptor binding annotation. The set of interceptor bindings for the interceptor are specified by annotating the interceptor class with the binding types and the {@link jakarta.interceptor.Interceptor} annotation.
- By using the {@link jakarta.interceptor.Interceptors Interceptors} annotation to specify and associate one or more interceptor classes with a target class or method or constructor of a target class.
- If a deployment descriptor is supported, it can be used to associate interceptor classes with the target class and/or methods of the target class and specify the order of interceptor invocation or override metadata specified by annotations.

Any interceptor class may be defined to apply to a target class at the class level. In the case of around-invoke method interceptors, the interceptor applies to all business methods of the target class. In the case of timeout method interceptors, the interceptor applies to all timeout methods of the target class.

The {@link jakarta.interceptor.ExcludeClassInterceptors} annotation or, if supported, a deployment descriptor may be used to exclude the invocation of class level interceptors defined by the {@link jakarta.interceptor.Interceptors Interceptors} annotation for a method or constructor of a target class.

An around-invoke interceptor may be defined to apply only to a specific method of the target class. Likewise, an around-timeout interceptor may be defined to apply only to a specific timeout method of the target class. However, if an interceptor class that defines lifecycle callback interceptor methods is defined to apply to a target class at the method level, the lifecycle callback interceptor methods are not invoked.

## Default Interceptors

Default interceptors are interceptors that apply to a set of target classes. If a deployment descriptor is supported, it may be used to define default interceptors and their relative ordering.

The {@link jakarta.interceptor.ExcludeDefaultInterceptors} annotation may be used to exclude the invocation of default interceptors for a target class or method or constructor of a target class.

## Interceptor lifecycle

The lifecycle of an interceptor instance is the same as that of the target class instance with which it is associated. Except as noted below for {@link jakarta.interceptor.AroundConstruct} lifecycle callback interceptors, when the target instance is created, a corresponding interceptor instance is created for each associated interceptor class. These interceptor instances are destroyed when the target instance fails to be created or when it is removed.

An interceptor class shares the enterprise naming context of its associated target class. Annotations and/or XML deployment descriptor elements for dependency injection or for direct Naming and Directory Interface lookup refer to this shared naming context.

An interceptor instance may hold state. An interceptor instance may be the target of dependency injection. Dependency injection is performed when the interceptor instance is created, using the naming context of the associated target class.

With the exception of of {@link jakarta.interceptor.AroundConstruct} lifecycle callback interceptors, no interceptor methods are invoked until after dependency injection has been completed on both the interceptor instances and the target instance.

{@link jakarta.annotation.PostConstruct} interceptor methods, if any, are invoked after dependency injection has taken place on both the interceptor instances and the target instance.

{@link jakarta.annotation.PreDestroy} interceptor methods, if any, are invoked before the target instance and all interceptor instances associated with it are destroyed.

When a {@link jakarta.interceptor.AroundConstruct} lifecycle callback interceptor is used, the following rules apply:

- The {@link jakarta.interceptor.AroundConstruct} lifecycle callback is invoked after dependency injection has been completed on instances of all interceptor classes associated with the target class. Injection of the target component into interceptor instances that are invoked during the {@link jakarta.interceptor.AroundConstruct} lifecycle callback is not supported.
- The target instance is created and its constructor injection is performed, if applicable, after the last interceptor method in the {@link jakarta.interceptor.AroundConstruct} interceptor chain invokes the {@link jakarta.interceptor.InvocationContext#proceed InvocationContext.proceed()} method. If the {@link jakarta.interceptor.InvocationContext#proceed InvocationContext.proceed()} method is not invoked by an interceptor method, the target instance will not be created.
- The {@link jakarta.interceptor.AroundConstruct} interceptor method can access the constructed instance using the {@link jakarta.interceptor.InvocationContext#getTarget InvocationContext.getTarget()} method after the {@link jakarta.interceptor.InvocationContext#proceed InvocationContext.proceed()} completes.
- Dependency injection on the target instance is not completed until after invocations of all interceptor methods in the {@link jakarta.interceptor.AroundConstruct} interceptor chain complete successfully.
- The {@link jakarta.annotation.PostConstruct} lifecycle callback chain for the target instance, if any, will be invoked after dependency injection has been completed on the target instance.
- An {@link jakarta.interceptor.AroundConstruct} lifecycle callback interceptor method should exercise caution when invoking methods of the target instance since its dependency injection may not have been completed.

## Interceptors for lifecycle callbacks

A lifecycle callback interceptor method is a non-final, non-static method. A lifecycle callback interceptor method declared by the target class (or superclass) must have no parameters. A lifecycle callback interceptor method declared by an interceptor class must have a single parameter of type {@link jakarta.interceptor.InvocationContext}.

    @PostConstruct
    public void interceptPostConstruct(InvocationContext ctx) { ... }

A single lifecycle callback interceptor method may be used to interpose on multiple callback events.

    @PostConstruct @PreDestroy
    public void interceptLifecycle(InvocationContext ctx) { ... }

A class may not declare more than one lifecycle callback interceptor method for a particular lifecycle event.

Lifecycle callback interceptor methods are invoked in an unspecified security context. Lifecycle callback interceptor methods are invoked in a transaction context determined by their target class and/or method. The transaction context may be also changed by transactional interceptors in the invocation chain.

Lifecycle callback interceptor methods may throw runtime exceptions but not checked exceptions, except for {@link jakarta.interceptor.AroundConstruct} methods, which may throw may throw any exceptions that are allowed by the throws clause of the constructor on which they are interposing.

@see AroundConstruct @see AroundInvoke @see AroundTimeout @see Interceptors @see InvocationContext