Configuring CDI with Tomcat example

Tomcat is not a full-blown EE container so we must include some required libraries in order to enable CDI support. In this tutorial we will cover CDI configuration in Tomcat and also provide a working sample.

This tutorial considers the following software and environment:

1. Ubuntu 12.04
2. JDK 1.7.0.09
3. Weld 1.1.10
4. Tomcat 7.0.35

Tomcat is not a full-blown EE container so we must include some required libraries in order to enable CDI support. In this tutorial we will be using Weld - the CDI reference implementation. The required Maven dependencies used in this tutorial are the following:

<dependencies>
  <dependency>
    <groupId>org.jboss.weld.servlet</groupId>
    <artifactId>weld-servlet</artifactId>
    <version>1.1.10.Final</version>
  </dependency>
  <dependency>
    <groupId>javax.servlet</groupId>
    <artifactId>javax.servlet-api</artifactId>
    <version>3.0.1</version>
    <scope>provided</scope>
  </dependency>
</dependencies>

In order to enable CDI we must also place an empty beans.xml file in WEB-INF folder:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://java.sun.com/xml/ns/javaee" 
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
  http://java.sun.com/xml/ns/javaee/beans_1_0.xsd">
</beans>

The last configuration step is to configure our CDI listener. We do this in web.xml:

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xmlns="http://java.sun.com/xml/ns/javaee"
  xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
  xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
  http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
  id="WebApp_ID" version="3.0">

  <display-name>Tomcat CDI example</display-name>

  <listener>
    <listener-class>org.jboss.weld.environment.servlet.Listener</listener-class>
  </listener>

</web-app>

Now let's define the bean that will be injected by CDI in our test servlet. Following is the bean interface:

package com.byteslounge.cdi.bean;

public interface Service {

  int doWork(int a, int b);
	
}

Now the bean implementation:

package com.byteslounge.cdi.bean;

public class ServiceBean implements Service {
	
  @Override
  public int doWork(int a, int b) {
    return a + b;
  }

}

Now let's define a simple servlet where we will inject our bean:

package com.byteslounge.cdi.servlet;

import java.io.IOException;
import java.io.PrintWriter;

import javax.inject.Inject;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.byteslounge.cdi.bean.Service;

@WebServlet(name = "testServlet", urlPatterns = {"/testcdi"})
public class TestServlet extends HttpServlet {

  private static final long serialVersionUID = 2638127270022516617L;
  
  @Inject
  private Service service;
  
  protected void doGet(HttpServletRequest request,
    HttpServletResponse response)
    throws ServletException, IOException {
    
    int a = 2;
    int b = 3;
    
    PrintWriter out = response.getWriter();
    out.println("Hello World: " + service.doWork(a, b));
    out.close();
  }

}

Note that the private property service is annotated with @Inject. This means that when the container is initializing the servlet it will look for a Service implementation. It will find our implementation - ServiceBean - and inject it into the servlet.

When we deploy the application in Tomcat and access the servlet mapped URL we will get the following output:

The tutorial source code is available for download at the end of this page.

• Java EE CDI beans deployed in external library (WEB-INF/lib JAR file)
• Java EE CDI Extension example
• Java EE - Add CDI Interceptor programmatically
• Java EE 7 CDI bean scopes