8 WebLogic Annotation for Web Components

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.

javax.servlet.Servlet

javax.servlet.Filter

javax.servlet.ServletContextListener
javax.servlet.ServletContextAttributeListener
javax.servlet.ServletRequestListener
javax.servlet.ServletRequestAttributeListener
javax.servlet.http.HttpSessionListener
javax.servlet.http.HttpSessionAttributeListener

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:

1. Annotation Processing—The Web container processes annotations during the Web application 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 at http://www.oracle.com/technetwork/java/javaee/servlet/index.html 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.

2. 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 run time.

   Note:

   In any Web application component, if one DI fails, 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.

The Web container makes 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.

WLServlet

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.

@WLServlet (
   name = "FOO",
   runAs = "SuperUser"
   initParams = { @WLInitParam (name="one", value="1") }
   mapping = {"/foo/*"}
)
. . .

<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>

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.

@WLFilter (
   name = "BAR",
   initParams = { @WLInitParam (name="one", value="1") } 
   Mapping = {"/bar/*"}
)
. . .

<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>

WLInitParam

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.

initParams = {@WLInitParam(name="one", value="1"),
               @WLInitParam(name="two", value="2")}

. . .
<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>
. . .