Tomcat and CDI

Running different technologies or products to work together can be sometimes challenging, especially for beginners. Therefore, in the next article, we will show how to easily configure Tomcat along with Weld, the reference CDI implementation.

Introduction

Before you start ensure Tomcat is successfully installed on your machine. The installation itself is not particularly difficult and indeed very well documented and already covered by many tutorials and videos. I will use Tomcat 8.5.11 (for supported versions of Tomcat, see the official Weld’s documentation).

Maven

At the beginning, we will create a blank maven project. For this purpose, use the command:

$ mvn archetype:generate -DgroupId=com.hradecek.cdi -DartifactId=tomcat-cdi -DinteractiveMode=false

By editing the pom.xml file, we add Apache Maven WAR Plugin:

<build>
  <plugins>
    <plugin>
      <groupId>org.apache.maven.plugins</groupId>
      <artifactId>maven-war-plugin</artifactId>
      <version>3.1.0</version>
    </plugin>
  </plugins>
</build>

This plugin will ensure that maven will not complain about the missing web.xml descriptor in time of compilation. Note that since version 3.0.0, you do not have to explicitly set failOnMissinWebXml property, which default value has change to false (see documentation for details).

Update: Moreover, starting with version 3.1.0, default value is set to false only if the project depends on the Servlet 3.0 API or newer.

Tomcat

Tomcat 8 has built-in support for Servlet API 3.1. (a.k.a. https://jcp.org/en/jsr/detail?id=340), which is part of Java EE 7 Web Profile, so we define it as a new dependency in our pom.xml:

<dependency>
  <groupId>javax</groupId>
  <artifactId>javaee-web-api</artifactId>
  <version>7.0</version>
  <scope>provided</scope>
</dependency>

The <scope>provided</scope> definition gives us the assurance that the libraries will not be included in the final web archive, because we want to use server-side libraries already included in Tomcat.

CDI

We use Weld for CDI support. Weld, as we already mentioned, is a reference implementation for CDI and has direct support for Tomcat.

Because we want to compile our project against the CDI specification, we need to add the CDI API dependency to the project:

<dependency>
  <groupId>javax.enterprise</groupId>
  <artifactId>cdi-api</artifactId>
  <version>2.0</version>
  <scope>provided</scope>
</dependency>

Dependency has defined </scope> as provided, because it will be used only at the time of the project compilation, just like the Servlet API above. During the runtime, Weld libraries will be used, which means that libraries are not necessary for compilation process itself, but for application run:

<dependency>
  <groupId>org.jboss.weld.servlet</groupId>
  <artifactId>weld-servlet</artifactId>
  <version>2.4.5.Final</version>
  <scope>runtime</scope>
</dependency>

For CDI support, we must add the beans.xml file (even if empty) as specification told us. In the WEB-INF folder, create a beans.xml file with the following content:

<beans xmlns="http://xmlns.jcp.org/xml/ns/javaee"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
                           http://xmlns.jcp.org/xml/ns/javaee/beans_2_0.xsd"
       version="2.0"
       bean-discovery-mode="all">
</beans>

Before version CDI 2.0, we would have have to define an appropriate resource factory either via Tomcat’s META-INF/context.xml file:

<Context>
  <Resource name="BeanManager"
            auth="Container"
            type="javax.enterprise.inject.spi.BeanManager"
            factory="org.jboss.weld.resources.ManagerObjectFactory"/>
</Context>

or standard WEB-INF/web.xml file:

<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
         http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.webxsd"
         version="3.1">
    <resource-env-ref>
        <resource-env-ref-name>BeanManager</resource-env-ref-name>
        <resource-env-ref-type>javax.enterprise.inject.spi.BeanManager</resource-env-ref-type>
    </resource-env-ref>
</web-app>

Now everything is set up and ready for use. When deploying application, notice Tomcat also confirms (in log messages) that CDI is available for us:

Tomcat 7+ detected, CDI injection will be available in Servlets, Filters and Listeners.

The fully working project is available at gitub.com/hradecek/tomcat-cdi.

Enjoy!