Producer<\/code> method to produce and inject both implementations in an application.<\/p>\nOur preferred development environment is Eclipse<\/a>. We are using Eclipse Juno (4.2) version, along with Maven<\/a> Integration plugin version 3.1.0. You can download Eclipse from here<\/a> and Maven Plugin for Eclipse from here<\/a>. The installation of Maven plugin for Eclipse is out of the scope of this tutorial and will not be discussed. Tomcat 7<\/a> is the application server used.<\/p>\nLet’s begin,<\/p>\n
1. Create a new Maven project<\/h2>\n
Go to File -> Project ->Maven -> Maven Project.<\/p>\n
![\"New-Maven-Project\"](\"https:\/\/examples.javacodegeeks.com\/wp-content\/uploads\/2013\/06\/New-Maven-Project.png\")
<\/a><\/p>\nIn the “Select project name and location” page of the wizard, make sure that “Create a simple project (skip archetype selection)” option is unchecked<\/strong>, hit “Next” to continue with default values.<\/p>\n![\"new](\"http:\/\/www.javacodegeeks.com\/wp-content\/uploads\/2013\/07\/new-project.png\")
<\/a><\/p>\nHere the maven archetype for creating a web application must be added. Click on “Add Archetype”<\/strong> and add the archetype. Set the “Archetype Group Id” variable to \"org.apache.maven.archetypes\"<\/code>, the “Archetype artifact Id” variable to \"maven-archetype-webapp\"<\/code> and the “Archetype Version” to \"1.0\"<\/code>. Click on “OK”<\/strong> to continue.<\/p>\n![\"maven-archetype-webapp\"](\"http:\/\/www.javacodegeeks.com\/wp-content\/uploads\/2013\/07\/maven-archetype-webapp.png\")
<\/a><\/p>\nIn the “Enter an artifact id” page of the wizard, you can define the name and main package of your project. Set the “Group Id” variable to \"com.javacodegeeks.snippets.enterprise\"<\/code> and the “Artifact Id” variable to \"cdibeans\"<\/code>. The aforementioned selections compose the main project package as \"com.javacodegeeks.snippets.enterprise.cdibeans\"<\/code> and the project name as \"cdibeans\"<\/code>. Set the “Package” variable to \"war\"<\/code>, so that a war file will be created to be deployed to tomcat server. Hit “Finish” to exit the wizard and to create your project.<\/p>\n![\"newcdiproject1\"](\"http:\/\/www.javacodegeeks.com\/wp-content\/uploads\/2013\/04\/newcdiproject1.png\")
<\/a><\/p>\nThe Maven project structure is shown below:<\/p>\n
![\"newcdiproject2\"](\"http:\/\/www.javacodegeeks.com\/wp-content\/uploads\/2013\/04\/newcdiproject2.png\")
<\/a><\/p>\nIt consists of the following folders:<\/p>\n- \/src\/main\/java folder, that contains source files for the dynamic content of the application,<\/li>\n
- \/src\/test\/java folder contains all source files for unit tests,<\/li>\n
- \/src\/main\/resources folder contains configurations files,<\/li>\n
- \/target folder contains the compiled and packaged deliverables,<\/li>\n
- \/src\/main\/resources\/webapp\/WEB-INF folder contains the deployment descriptors for the Web application ,<\/li>\n
- the pom.xml is the project object model (POM) file. The single file that contains all project related configuration.<\/li>\n<\/ul>\n
2. Add all the necessary dependencies<\/h2>\n
You can add the dependencies in Maven\u2019s pom.xml<\/code> file, by editing it at the “Pom.xml” page of the POM editor, as shown below:
\n
\npom.xml:<\/em><\/span> <\/div> <\/div><\/p>\n<project xmlns=\"http:\/\/maven.apache.org\/POM\/4.0.0\" xmlns:xsi=\"http:\/\/www.w3.org\/2001\/XMLSchema-instance\"\n\txsi:schemaLocation=\"http:\/\/maven.apache.org\/POM\/4.0.0 http:\/\/maven.apache.org\/maven-v4_0_0.xsd\">\n\t<modelVersion>4.0.0<\/modelVersion>\n\t<groupId>com.javacodegeeks.snippets.enterprise.cdi<\/groupId>\n\t<artifactId>cdibeans<\/artifactId>\n\t<packaging>war<\/packaging>\n\t<version>0.0.1-SNAPSHOT<\/version>\n\t<name>cdibeans Maven Webapp<\/name>\n\t<url>http:\/\/maven.apache.org<\/url>\n\t<dependencies>\n\t\t<dependency>\n\t\t\t<groupId>org.jboss.weld.servlet<\/groupId>\n\t\t\t<artifactId>weld-servlet<\/artifactId>\n\t\t\t<version>1.1.10.Final<\/version>\n\t\t<\/dependency>\n\t\t<dependency>\n\t\t\t<groupId>javax.servlet<\/groupId>\n\t\t\t<artifactId>jstl<\/artifactId>\n\t\t\t<version>1.2<\/version>\n\t\t<\/dependency>\n\t\t<dependency>\n\t\t\t<groupId>javax.servlet<\/groupId>\n\t\t\t<artifactId>javax.servlet-api<\/artifactId>\n\t\t\t<version>3.0.1<\/version>\n\t\t\t<scope>provided<\/scope>\n\t\t<\/dependency>\n\t\t<dependency>\n\t\t\t<groupId>org.glassfish<\/groupId>\n\t\t\t<artifactId>javax.faces<\/artifactId>\n\t\t\t<version>2.1.7<\/version>\n\t\t<\/dependency>\n\t<\/dependencies>\n\n\t<build>\n\t\t<finalName>cdibeans<\/finalName>\n\t<\/build>\n<\/project>\n<\/pre>\nAs you can see Maven manages library dependencies declaratively. A local repository is created (by default under {user_home}\/.m2 folder) and all required libraries are downloaded and placed there from public repositories. Furthermore intra \u2013 library dependencies are automatically resolved and manipulated.<\/p>\n
3. Create a simple Service<\/h2>\n
The service that will be used in the Producer<\/code> in this example is a simple service that creates a greeting message for the application that uses it. The GreetingCard.java<\/code> class is an interface with a method that produces the greeting message.<\/p>\nGreetingCard.java<\/em><\/span><\/p>\npackage com.javacodegeeks.snippets.enterprise.cdibeans;\n\npublic interface GreetingCard {\n\n\tvoid sayHello();\n}\n<\/pre>\nThe implementation of the service is shown below:<\/p>\n
GreetingCardImpl.java<\/em><\/span><\/p>\npackage com.javacodegeeks.snippets.enterprise.cdibeans.impl;\n\nimport com.javacodegeeks.snippets.enterprise.cdibeans.GreetingCard;\n\npublic class GreetingCardImpl implements GreetingCard {\n\n\tpublic void sayHello() {\n\t\tSystem.out.println(\"Hello!!!\");\n\t}\n\n}\n<\/pre>\nIn order to show how polymorphism works in CDI we will create another implementation of the service, as shown below:<\/p>\n
AnotherGreetingCardImpl.java<\/em><\/span><\/p>\npackage com.javacodegeeks.snippets.enterprise.cdibeans.impl;\n\nimport com.javacodegeeks.snippets.enterprise.cdibeans.GreetingCard;\n\n\npublic class AnotherGreetingCardImpl implements GreetingCard {\n\n\tpublic void sayHello() {\n\t\tSystem.out.println(\"Have a nice day!!!\");\n\t}\n\n}\n<\/pre>\n4. Use of the Producer in a Managed Bean<\/h2>\n
In the managed bean below, we are making use of the Producer<\/code> created above. In particular, in the GreetingCardFactory.java<\/code> class, we create a method, getGreetingCard()<\/code>, annotated with the @Produces<\/code> annotation. The method returns the correct implementation of the GreetingCard<\/code> according to the GreetingType<\/code> of the bean. In this way the polymorphism is supported.<\/p>\nGreetingCardFactory.java<\/em><\/span><\/p>\npackage com.javacodegeeks.snippets.enterprise.cdibeans;\n\nimport java.io.Serializable;\n\nimport javax.enterprise.context.SessionScoped;\nimport javax.enterprise.inject.Produces;\n\nimport com.javacodegeeks.snippets.enterprise.cdibeans.impl.AnotherGreetingCardImpl;\nimport com.javacodegeeks.snippets.enterprise.cdibeans.impl.GreetingCardImpl;\n\n@SessionScoped\npublic class GreetingCardFactory implements Serializable {\n\n\tprivate static final long serialVersionUID = -44416514616012281L;\n\n\tprivate GreetingType greetingType;\n\n\t@Produces\n\tpublic GreetingCard getGreetingCard() {\n\n\t\tswitch (greetingType) {\n\t\tcase HELLO:\n\t\t\treturn new GreetingCardImpl();\n\t\tcase ANOTHER_HI:\n\t\t\treturn new AnotherGreetingCardImpl();\n\t\tdefault:\n\t\t\treturn new GreetingCardImpl();\n\t\t}\n\t}\n}\n<\/pre>\nThe GreetingType.java<\/code> is an enumeration, as shown below:<\/p>\nGreetingType.java<\/em><\/span><\/p>\npackage com.javacodegeeks.snippets.enterprise.cdibeans;\n\npublic enum GreetingType {\n\n\tHELLO, HI;\n}\n<\/pre>\nAnother way to use polymorphism in CDI is through the @Qualifier<\/code>. We can create our own annotation in CDI, and then use it to in the Producer<\/code> method to get the correct implementation.<\/p>\nGreetings.java<\/em><\/span><\/p>\npackage com.javacodegeeks.snippets.enterprise.cdibeans;\n\nimport static java.lang.annotation.ElementType.FIELD;\nimport static java.lang.annotation.ElementType.TYPE;\nimport static java.lang.annotation.ElementType.METHOD;\nimport static java.lang.annotation.RetentionPolicy.RUNTIME;\nimport java.lang.annotation.Retention;\nimport java.lang.annotation.Target;\n\nimport javax.inject.Qualifier;\n\n@Qualifier\n@Retention(RUNTIME)\n@Target({ FIELD, TYPE, METHOD })\npublic @interface Greetings {\n\n\tGreetingType value();\n\n}\n<\/pre>\nNow, the GreetingCardFactory<\/code> can have a different Producer<\/code> method for every implementation. The annotation we created is used after the @Produces<\/code> annotation.<\/p>\nGreetingCardFactory.java<\/em><\/span><\/p>\npackage com.javacodegeeks.snippets.enterprise.cdibeans;\n\nimport java.io.Serializable;\n\nimport javax.enterprise.context.SessionScoped;\nimport javax.enterprise.inject.Produces;\n\nimport com.javacodegeeks.snippets.enterprise.cdibeans.impl.AnotherGreetingCardImpl;\nimport com.javacodegeeks.snippets.enterprise.cdibeans.impl.GreetingCardImpl;\n\n\n@SessionScoped\npublic class GreetingCardFactory implements Serializable {\n\n\tprivate static final long serialVersionUID = -44416514616012281L;\n\n\tprivate GreetingType greetingType;\n\n\t\n\t@Produces\n\t@Greetings(GreetingType.HELLO)\n\tpublic GreetingCard getGreetingCard() {\n\t\treturn new GreetingCardImpl();\n\t}\n\t\n\t@Produces\n\t@Greetings(GreetingType.HI)\n\tpublic GreetingCard getAnotherGreetingCard() {\n\t\treturn new AnotherGreetingCardImpl();\n\t}\n\t\n}\n<\/pre>\n5. Scope of Producer<\/h2>\n
An important thing to notice when creating a Producer<\/code> method is the scope of the Producer<\/code>. The scope of the Producer<\/code> is set to Dependent<\/code> by default. But a Producer<\/code> may also have any other scope according to its use. The problem is, what may happen if a Producer<\/code> produces a managed bean of a different scope. For example, we can create a @RequestScoped<\/code> bean and inject it to another bean, using a Producer<\/code> annotated as @SessionScoped<\/code>. In this case, the instance of the @RequestScoped<\/code> bean that the Producer<\/code> returns will be destroyed after the HTTP request finishes and the behaviour of the bean where it is injected might be unexpected. In order to avoid having reference to no longer existing beans, we can make use of the @New<\/code> annotation when using a Producer<\/code> method. In this way, a new Dependent<\/code> instance is injected via the Producer<\/code>, as shown in the code snippet below:<\/p>\nGreetingCardFactory.java<\/em><\/span><\/p>\npackage com.javacodegeeks.snippets.enterprise.cdibeans;\n\nimport java.io.Serializable;\n\nimport javax.enterprise.context.SessionScoped;\nimport javax.enterprise.inject.New;\nimport javax.enterprise.inject.Produces;\n\nimport com.javacodegeeks.snippets.enterprise.cdibeans.impl.GreetingCardImpl;\n\n\n@SessionScoped\npublic class GreetingCardFactory implements Serializable {\n\n\tprivate static final long serialVersionUID = -44416514616012281L;\n\t\n\tprivate GreetingCardImpl greetingCard;\n\t\n\t@Produces\n\tpublic GreetingCardImpl getGreetingCard(@New GreetingCardImpl greetingCard) {\n\t\treturn greetingCard;\n\t}\n\n\t\n}\n<\/pre>\n6. Run the application<\/h2>\n
In order to run the application, we have created a simple servlet, as shown below:<\/p>\n
GreetingServlet.java<\/em><\/span><\/p>\npackage com.javacodegeeks.snippets.enterprise.cdibeans.servlet;\n\nimport java.io.IOException;\nimport java.io.PrintWriter;\n\nimport javax.inject.Inject;\nimport javax.servlet.ServletException;\nimport javax.servlet.annotation.WebServlet;\nimport javax.servlet.http.HttpServlet;\nimport javax.servlet.http.HttpServletRequest;\nimport javax.servlet.http.HttpServletResponse;\n\nimport com.javacodegeeks.snippets.enterprise.cdibeans.GreetingCard;\nimport com.javacodegeeks.snippets.enterprise.cdibeans.GreetingType;\nimport com.javacodegeeks.snippets.enterprise.cdibeans.Greetings;\n\n@WebServlet(name = \"greetingServlet\", urlPatterns = {\"\/sayHello\"})\npublic class GreetingServlet extends HttpServlet {\n\n\tprivate static final long serialVersionUID = 2280890757609124481L;\n\t\n\t@Inject\n\t@Greetings(GreetingType.HELLO)\n\tprivate GreetingCard greetingCard;\n\n\t@Inject\n\t@Greetings(GreetingType.HI)\n\tprivate GreetingCard anotherGreetingCard;\n\n\t public void init() throws ServletException {\n\t }\n\n\t public void doGet(HttpServletRequest request, HttpServletResponse response)\n\t throws ServletException, IOException {\n\t response.setContentType(\"text\/html\");\n\t PrintWriter out = response.getWriter();\n\t out.println(\"<h1>\" + greetingCard.sayHello() + \"<\/h1>\");\n\t out.println(\"<h1>\" + anotherGreetingCard.sayHello() + \"<\/h1>\");\n\t }\n\t \n\t public void destroy(){\n\t }\n\n}\n<\/pre>\nIn the servlet above both implementations are injected. To run the example we must build the project with Maven, and then place the war<\/code> file produced in webbaps<\/code> folder of tomcat. Then, we can hit on :<\/p>\nhttp:\/\/localhost\/8080\/cdibeans\/sayHello<\/code><\/p>\nand the result is the one shown below:<\/p>\n
![\"prod\"](\"http:\/\/www.javacodegeeks.com\/wp-content\/uploads\/2013\/04\/prod.png\")
<\/a><\/p>\n