WebLogic Annotation for Web Components

Developing Web Applications, Servlets, and JSPs for Oracle WebLogic Server

WebLogic Annotation for Web Components

The following sections describe how to annotate web components.

Servlet Annotation and Dependency Injection
Annotating Servlets

Servlet Annotation and Dependency Injection

With Java EE metadata annotations, the standard web.xml deployment descriptor is now optional. The Servlet 2.5 specification, states annotations can be defined on certain web components, such as servlets, filters, listeners, and tag handlers. The annotations are used to declare dependencies on external resources. The container will detect annotations on such components and inject necessary dependencies before the component's life-cycle methods are invoked. Dependency Injection (DI) will only be done on certain components, as described in Web Component Classes That Support Annotations.
Annotation processing and DI will be performed on all Web applications that have the version set to 2.5. However, annotation processing is expensive and it can increase the deployment time for Web applications depending on the size of the included classes. Set the metadata-complete attribute to true in the web.xml descriptor if your Web application does not have any annotations and if you have the version set to 2.5 to avoid unnecessary scanning of the Web applications classes for annotations. Alternatively, you can turn off annotation processing and DI for all the Web applications by setting -Dweblogic.servlet.DIDisabled=true flag when starting WebLogic Server.
For more information about using Java EE annotations and dependency injection with WebLogic Server applications, see Using Annotations and Dependency Injection in Developing Applications With WebLogic Server. For detailed information about EJB-specific annotations for WebLogic Server Enterprise JavaBeans, see Programming WebLogic Enterprise JavaBeans, Version 3.0.

Web Component Classes That Support Annotations

This section describes the behavior of annotations and dependency injection (DI) of resources in a Java EE compliant web container.
The web container only processes annotations for the types of classes listed in Table 8-1.
Table 8-1 Web Components and Interfaces Supporting Annotations and Dependency Injection
Component Type Interfaces
Servlets javax.servlet.Servlet
Filters javax.servlet.Filter
Listeners javax.servlet.ServletContextListener javax.servlet.ServletContextAttributeListener javax.servlet.ServletRequestListener javax.servlet.ServletRequestAttributeListener javax.servlet.http.HttpSessionListener javax.servlet.http.HttpSessionAttributeListener
Tag handlers javax.servlet.jsp.tagext.SimpleTag javax.servlet.jsp.tagext.BodyTag

The web container will not process annotations on classes like Java Beans and other helper classes. The web container follows these steps to achieve DI:

Annotation Processing – The web container processes annotations during the WebApp deployment phase. As annotations are processed, the container figures out the relevant entries in the descriptor that get affected by the annotation and update the descriptor tree. The Servlet 2.5 specification indicates that all annotations can be declared in the descriptor by defining an injection target. The web container updates the descriptor tree with the injection targets so that as deployment continues the java:comp/env tree is updated with the necessary entries.
Dependency Injection (DI) – DI is done when instances are created (for the types listed in Table 8-1). For listeners and filters, this occurs during the deployment phase, and for servlets it can occur during the deployment or runtime.

In any WebApp component, if one DI fails, then it will cause all subsequent DIs upon the same component to be ignored.

Annotations Supported By a Web Container

Table 8-2 lists all the annotations that must be supported by the web container.
Table 8-2 List of Supported Annotations
@Annotation Specification Reference
DeclaresRoles 14.5.1
EJB 14.5.2
EJBs 14.5.3
PersistenceContext 14.5.5
PersistenceUnit 14.5.7
PersistenceUnits 14.5.8
PersistenceContexts 14.5.6
PostConstruct 14.5.9
PreDestroy 14.5.10
Resource 14.5.4
Resources 14.5.11
WebServiceRef 14.5.13
WebServiceRefs 14.5.14
RunAs 14.5.12

The web container make use of the Java EE container's annotation processing and dependency injection mechanisms to achieve this functionality.
The Servlet 2.5 specification states that the web container should not process annotations when metadata-complete attributes are set to true in the web.xml descriptor. If annotations are properly defined and annotation processing succeeds and dependencies are properly injected, the annotated fields are initialized properly and annotated methods are invoked at the proper phase in the life cycle. If DI fails, these annotated fields will be null.

Caution: If multiple methods in a web component class, such as a servlet, filter, etc., are annotated with PostConstruct or PreDestroy, then the web component will fail to deploy such an application. Similarly, if an EJB component class, such as a session bean, is annotated with PostConstruct or PreDestroy, or an EJB interceptor is annotated with PostConstruct, PreDestroy, PostActivate, or PrePassivate, then the EJB component will also fail to deploy such an application.

Fault Detection and Recovery

Any failure during annotation processing will yield a deployment exception that will prevent deployment of the web application. If a failure happens during DI, the container will log a warning message in the server logs indicating the reason for the failure. The annotated fields in the instance of the class will be null and any life-cycle annotated methods will not be invoked in case of DI failure.
Limitations

The WebLogic Servlet container supports annotations on web components that are declared in the web.xml descriptor. Any listeners, filters or servlets registered dynamically via the weblogic.servlet.WeblogicServletContext method will not have their annotations processed and no DI will be done for such components.

Annotating Servlets

The WebLogic Servlet container provides the @WLServlet annotation for servlets and the WLFilter annotation for filters that you to develop servlets and filters in a web application without having to declare them in a web.xml descriptor. The WebLogic Servlet container also provides the WLInitParam annotation to specify the initial parameters for servlets and filters declared using the WLServlet and WLFilter annotations.
All the required meta-data can be annotated in the servlet or filter and the container will detect them and update the descriptor tree so that the annotated servlet or filter is deployed.

WLServlet

Description

Target: Class
You can annotate a servlet class with WLServlet annotation (weblogic.servlet.annotation.WLServlet). This annotation defines various attributes for declaring parameters for the servlet. All attributes on this annotation are optional.
Attributes

Table 8-3 Attributes of WLServlet Annotation
Name Description Data Type Required?
displayName Display name for the Servlet after deployment String No
description Servlet description String No
icon Icon location String No
name Servlet name String No
initParams Initialization parameters for the Servlet WLInitParam[] No
loadOnStartup Whether the Servlet should load on startup int No
runAs The run-as user for the Servlet String No
mapping The url-pattern for the Servlet String[] No

Listing 8-1 illustrates the usage of the annotation in a Servlet class. Listing 8-1 WLServlet Annotation
@WLServlet (

   name = "FOO",

   runAs = "SuperUser"

   initParams = { @WLInitParam (name="one", value="1") }

   mapping = {"/foo/*"}

)

. . .
The WebLogic Servlet container detects the annotation and installs this servlet for deployment. During the annotation processing phase of the web applications deployment, the descriptor bean corresponding to web.xml descriptor is updated with the relevant entries corresponding to the annotation.
Listing 8-2 shows how the descriptor bean looks after being updated. Listing 8-2 Updated web.xml Descriptor
<web-app>
. . .

   <servlet>

      <servlet-name>FOO</servlet-name>

      <servlet-class>my.TestServlet</servlet-class>

      <init-param>

         <param-name>one</param-name>

         <param-value>1</param-value>

      </init-param>

   </servlet>
   <servlet-mapping>

      <servlet-name>FOO</servlet-name>

      <url-pattern>/foo/*</url-pattern>

   </servlet-mapping>

. . .

</web-app>
Fault Detection And Recovery

Any error during the processing of this annotation will result in a deployment error with a proper message in the server logs.

WLFilter

You can annotate a filter class with WLFilter annotation (weblogic.servlet.annotation.WLFilter). This annotation defines various attributes for declaring parameters for the filter. All attributes on this annotation are optional.
Attributes

Table 8-4 Attributes of WLFilter Annotation
Name Description Data Type Required?
displayName Display name for the Filter after deployment String No
description Filter description String No
icon Icon location String No
name Filter name String No
initParams Initialization parameters for the Filter WLInitParam[] No
mapping The url-pattern for the Filter String[] No

Listing 8-3 illustrates the usage of the annotation in a Filter class. Listing 8-3 WLFilter Annotation
@WLFilter (

   name = "BAR",

   initParams = { @WLInitParam (name="one", value="1") } 

   Mapping = {"/bar/*"}

)

. . .
The WebLogic Servlet container detects the annotation and installs this filter for deployment. During the annotation processing phase of the WebApp deployment, the descriptor bean corresponding to web.xml descriptor is updated with the relevant entries corresponding to the annotation.
Listing 8-4 shows how the descriptor bean looks after being updated. Listing 8-4 Updated web.xml Descriptor
<web-app>

. . .

   <filter>

      <filter-name>BAR</filter-name>

      <filter-class>my.TestFilter</filter-class>

      <init-param>

         <param-name>one</param-name>

         <param-value>1</param-value>

      </init-param>

   </filter>
   <filter-mapping>

      <filter-name>BAR</filter-name>

      <url-pattern>/bar/*</url-pattern>

   </filter-mapping>

. . .

</web-app>
Fault Detection and Recovery

Any error during the processing of this annotation will result in a deployment error with a proper message in the server logs.

WLInitParam

Description

You can use the @WLInitParam annotation (weblogic.servlet.annotation.WLInitParam) to specify the initial parameters for servlets and filters declared using the @WLServlet and @WLFilter annotations.
Attributes

Table 8-5 Attributes of WLFilter Annotation
Name Description Data Type Required?
name The initial parameter name. String No
value The initial parameter value. String No

Listing 8-5 provides an example of WLInitParam annotation. Listing 8-5 Example WLInitParam Annotation
  initParams = {@WLInitParam(name="one", value="1"),

                 @WLInitParam(name="two", value="2")}
Annotating a Servlet or Filter class with the above annotation is equivalent to declaring the init params in Listing 8-6 in the web.xml descriptor. Listing 8-6 Init Params In web.xml
  . . .
  <init-param>

    <param-name>one</param-name>

    <param-value>1</param-value>

  </init-param>

  <init-param>

    <param-name>two</param-name>

    <param-value>2</param-value>

  </init-param>

. . .

Component Type	Interfaces
Servlets	javax.servlet.Servlet
Filters	javax.servlet.Filter
Listeners	javax.servlet.ServletContextListener javax.servlet.ServletContextAttributeListener javax.servlet.ServletRequestListener javax.servlet.ServletRequestAttributeListener javax.servlet.http.HttpSessionListener javax.servlet.http.HttpSessionAttributeListener
Tag handlers	javax.servlet.jsp.tagext.SimpleTag javax.servlet.jsp.tagext.BodyTag

@Annotation	Specification Reference
DeclaresRoles	14.5.1
EJB	14.5.2
EJBs	14.5.3
PersistenceContext	14.5.5
PersistenceUnit	14.5.7
PersistenceUnits	14.5.8
PersistenceContexts	14.5.6
PostConstruct	14.5.9
PreDestroy	14.5.10
Resource	14.5.4
Resources	14.5.11
WebServiceRef	14.5.13
WebServiceRefs	14.5.14
RunAs	14.5.12

Name	Description	Data Type	Required?
displayName	Display name for the Servlet after deployment	String	No
description	Servlet description	String	No
icon	Icon location	String	No
name	Servlet name	String	No
initParams	Initialization parameters for the Servlet	WLInitParam[]	No
loadOnStartup	Whether the Servlet should load on startup	int	No
runAs	The run-as user for the Servlet	String	No
mapping	The url-pattern for the Servlet	String[]	No

Name	Description	Data Type	Required?
displayName	Display name for the Filter after deployment	String	No
description	Filter description	String	No
icon	Icon location	String	No
name	Filter name	String	No
initParams	Initialization parameters for the Filter	WLInitParam[]	No
mapping	The url-pattern for the Filter	String[]	No

Name	Description	Data Type	Required?
name	The initial parameter name.	String	No
value	The initial parameter value.	String	No