This post demonstrates how Dependency Injection works with JavaEE CDI and Tomcat 8. We’ll display some text from a bean injected into our Servlet via CDI.

As we know, Tomcat is just a Servlet Container and does not have other JavaEE components available out-of-the-box. Tomee may be a better alternative but should we go all-out “Enterprise”, choose a JavaEE-compliant Application Server like JBoss WildFly or IBM Websphere.

Requirements

Stuff used in this post.

Eclipse Mars.2 Release (4.5.2)
Java 8
Windows 10 64bit
Tomcat 8.0.39
Maven 3.3.3 (Embedded in Eclipse)

Key Maven Dependencies

These are the key dependencies.

javaee-web-api

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This contains most API related to Web Applications.

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

<groupId>javax</groupId>

<artifactId>javaee-web-api</artifactId>

<scope>provided</scope>

</dependency>

cdi-api

This is the CDI API.

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

<groupId>javax.enterprise</groupId>

<scope>provided</scope>

</dependency>

weld-servlet

A reference implementation of CDI on a Servlet Container.

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<dependency>
    <groupId>org.jboss.weld.servlet</groupId>
    <artifactId>weld-servlet</artifactId>
    <version>2.4.4.Final</version>
</dependency>

<groupId>org.jboss.weld.servlet</groupId>

<artifactId>weld-servlet</artifactId>

<version>2.4.4.Final</version>

</dependency>

CDI Bean

This bean is created in the CDI “container” and injected into our Servlet. We used @ApplicationScoped and the bean is available until Tomcat/Web Application is shutdown.

package com.turreta.cdi.servlet.beans;

...

@Named
@ApplicationScoped
public class AppDetailBean implements Serializable {

	private String appName;
	private String version;

	@PostConstruct
	public void init() {
		appName = "Turreta.com Tomcat/CDI Demo";
		version = "1.0";
	}

	public String getAppName() {
		return appName;
	}

	public String getVersion() {
		return version;
	}
}

package com.turreta.cdi.servlet.beans;

...

@Named

@ApplicationScoped

public class AppDetailBean implements Serializable {

private String appName;

private String version;

@PostConstruct

public void init() {

appName = "Turreta.com Tomcat/CDI Demo";

version = "1.0";

}

public String getAppName() {

return appName;

}

public String getVersion() {

return version;

}

Our Servlet

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package com.turreta.cdi.servlet.demo;

...

import com.turreta.cdi.servlet.beans.AppDetailBean;

@WebServlet(urlPatterns = "/miservlet")
public class MyServlet extends HttpServlet {

	private static final long serialVersionUID = 1L;

	@Inject
	private AppDetailBean appDetailBean;

	@Override
	protected void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		/* I know it's old-school! Apologies :) */
		response.setContentType("text/html");
		PrintWriter out = response.getWriter();

		out.println("<html>");
		out.println("<head>");
		out.println("<title>App Detail</title>");
		out.println("</head>");
		out.println("<body>");
		out.println("<h1>App Name:" + appDetailBean.getAppName() + "</h1>");
		out.println("<h2>Version:" + appDetailBean.getVersion() + "</h2>");
		out.println("</body>");
		out.println("</html>");
	}

}

package com.turreta.cdi.servlet.demo;

...

import com.turreta.cdi.servlet.beans.AppDetailBean;

@WebServlet(urlPatterns = "/miservlet")

public class MyServlet extends HttpServlet {

private static final long serialVersionUID = 1L;

@Inject

private AppDetailBean appDetailBean;

@Override

protected void doGet(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

/* I know it's old-school! Apologies :) */

response.setContentType("text/html");

PrintWriter out = response.getWriter();

out.println("<html>");

out.println("<head>");

out.println("<title>App Detail</title>");

out.println("</head>");

out.println("<body>");

out.println("<h1>App Name:" + appDetailBean.getAppName() + "</h1>");

out.println("<h2>Version:" + appDetailBean.getVersion() + "</h2>");

out.println("</body>");

out.println("</html>");

}

Configuration and other XML files

There are other configurations that are needed before we could run and test our simple web application.

Define beans.xml

This file contains the following and should be placed in "Deployed Resources"/webapp/WEB-INF.

<?xml version="1.0" encoding="UTF-8"?>
<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_1_1.xsd"
  bean-discovery-mode="annotated"
  >
</beans>

<?xml version="1.0" encoding="UTF-8"?>

<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_1_1.xsd"

bean-discovery-mode="annotated"

</beans>

Define web.xml

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Same with beans.xml, this files should be placed "Deployed Resources"/webapp/WEB-INF.

<!DOCTYPE web-app PUBLIC
 "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
 "http://java.sun.com/dtd/web-app_2_3.dtd" >

<web-app>
  <display-name>Archetype Created Web Application</display-name>
    <resource-env-ref>
    <!-- Enable Weld CDI, also needs META-INF/context.xml entry -->
    <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>

<!DOCTYPE web-app PUBLIC

"-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"

"http://java.sun.com/dtd/web-app_2_3.dtd" >

<web-app>

<display-name>Archetype Created Web Application</display-name>

<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>

Define context.xml

This file should be placed under "Deployed Resources"/web-resources/META-INF.

<?xml version="1.0" encoding="UTF-8"?>
<Context antiJARLocking="true" path="/com-turreta-cdi-servlet-demo">
  <Resource
    name="BeanManager"
    auth="Container"
    type="javax.enterprise.inject.spi.BeanManager"
    factory="org.jboss.weld.resources.ManagerObjectFactory"
    />
</Context>