CDI Interceptors

Interceptor Class

• a class to intercept in (that occur in an associated target class)

  • method invocations, or

  • lifecycle events

• usage scope: on all managed objects of all kinds

• declare and invoke order:

  • annotate with both @Interceptor and the @interceptor-binding-type (see below)

  • Either (if @Priority used, no need to specify in beans.xml)

    • be specified in beans.xml <interceptors><class>....</class></interceptors> (classes in same archive) and interceptors are invoked in the order specified in beans.xml, or

    • @Priority(Interceptor.Priority.XXX) specifies globally (smaller priority value called first)

• intereptor method: can contain more than one, but no more than one of each type

• @AroundInvoke

  • parameter: javax.interceptor.InvocationContext

  • returns: java.lang.object

  • throws: Exception

  • usually calls InvocationContext.proceed() method to invoke the method

• @PostConstruct

• @PreDestroy

• @PrePassivate

• @PostActive

• @AroundTimeout - EJB timeout

Interceptor Binding Types

• annotations that associate interceptor with target beans or methods

• javax.interceptor.@InterceptorBinding - mark for interceptor binding types

• java.lang.annotation.@Inherited - subclasses inherit the annotation

Example interceptor binding type:

@Inherited

@InterceptorBinding

@Retention(RUNTIME)

@Target({METHOD, TYPE})

public @interface Logged {}

Applying Interceptor

Annotate the bean (then on all methods of the bean) and individual methods (on specific methods) with the binding type to specify the interceptor to be invoked.

Examples

Annotation

@Inherited @InterceptorBinding @Retention(RUNTIME) @Target({METHOD, TYPE}) public @interface Logged { }

Usage

@Logged @SessionScoped public class PaymentHandler implements Serializable {...}

@Logged public String pay() {...} @Logged public void reset() {...}

Interceptor class implementation

@Logged @Interceptor @Priority(Interceptor.Priority.APPLICATION) public class LoggedInterceptor implements Serializable { ... }

(if @Priority not used, must specify in beans.xml)

Interceptor method

@AroundInvoke public Object modifyGreeting(InvocationContext ctx) throws Exception { Object[] parameters = ctx.getParameters(); String param = (String) parameters[0]; param = param.toLowerCase(); parameters[0] = param; ctx.setParameters(parameters); try { return ctx.proceed(); } catch (Exception e) { logger.warning("Error calling ctx.proceed in modifyGreeting()"); return null; } }