Running the Basic Contexts and Dependency Injection Examples

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This chapter describes in detail how to build and run simple examples that use CDI.

Building and Running the CDI Samples

The examples are in the jakartaee-examples/tutorial/cdi/ directory.

To build and run the examples, you will do the following:

Use NetBeans IDE or the Maven tool to compile and package the example.
Use NetBeans IDE or the Maven tool to deploy the example.
Run the example in a web browser.

See Using the Tutorial Examples, for basic information on installing, building, and running the examples.

The simplegreeting CDI Example

The simplegreeting example illustrates some of the most basic features of CDI: scopes, qualifiers, bean injection, and accessing a managed bean in a Jakarta Faces application. When you run the example, you click a button that presents either a formal or an informal greeting, depending on how you edited one of the classes. The example includes four source files, a Facelets page and template, and configuration files.

The simplegreeting Source Files

The four source files for the simplegreeting example are:

The default Greeting class, shown in Beans as Injectable Objects
The @Informal qualifier interface definition and the InformalGreeting class that implements the interface, both shown in Using Qualifiers
The Printer managed bean class, which injects one of the two interfaces, shown in full in Adding Setter and Getter Methods

The source files are located in the jakartaee-examples/tutorial/cdi/simplegreeting/src/main/java/jakarta/tutorial/simplegreeting directory.

The Facelets Template and Page

To use the managed bean in a simple Facelets application:

Use a very simple template file and index.xhtml page.

The template page, /WEB-INF/templates/template.xhtml, looks like this:

<!DOCTYPE html>
<html lang="en"
      xmlns:h="jakarta.faces.html"
      xmlns:ui="jakarta.faces.facelets">
    <h:head>
        <title><ui:insert name="title">Default Title</ui:insert></title>
        <h:outputStylesheet name="css/default.css" />
    </h:head>
    <h:body>
        <main>
            <header>
                <h1>
                    <ui:insert name="head">
                        <ui:insert name="title">Default Header</ui:insert>
                    </ui:insert>
                </h1>
            </header>

            <article>
                <ui:insert name="content" />
            </article>
        </main>
    </h:body>
</html>

To create the Facelets page, redefine the title and head, then add a small form to the content:

<ui:composition template="/WEB-INF/templates/template.xhtml"
                xmlns:ui="jakarta.faces.facelets"
                xmlns:h="jakarta.faces.html">
    <ui:define name="title">Simple Greeting</ui:define>
    <ui:define name="content">
        <h:form id="simpleGreetingForm">
            <div class="input">
                <h:outputLabel for="name" value="Enter your name" />
                <h:inputText id="name" value="#{printer.name}"/>
            </div>
            <div class="actions">
                <h:commandButton id="createSalutation"
                                 value="Say Hello"
                                 action="#{printer.createSalutation}">
                    <f:ajax execute="@form" render="salutation" />
                </h:commandButton>
            </div>
            <div class="output">
                <p>
                    <h:outputText id="salutation"
                                  value="#{printer.salutation}" />
                </p>
            </div>
        </h:form>
    </ui:define>
</ui:composition>

The form asks the user to enter a name. The button is labeled Say Hello, and the action defined for it is to call the createSalutation method of the Printer managed bean. This method in turn calls the greet method of the defined Greeting class.

The output text for the form is the value of the greeting returned by the setter method. Depending on whether the default or the @Informal version of the greeting is injected, this is one of the following, where name is the name entered by the user:

Hello, name.

Hi, name!

The Facelets page and template are located in the jakartaee-examples/tutorial/cdi/simplegreeting/src/main/webapp/ directory.

The simple CSS file that is used by the Facelets page is in the following location:

jakartaee-examples/tutorial/cdi/simplegreeting/src/main/webapp/resources/css/default.css

Running the simplegreeting Example

You can use either NetBeans IDE or Maven to build, package, deploy, and run the simplegreeting application.

To Build, Package, and Run the simplegreeting Example Using NetBeans IDE

Make sure that GlassFish Server has been started (see Starting and Stopping GlassFish Server).
From the File menu, choose Open Project.
In the Open Project dialog box, navigate to:
```
jakartaee-examples/tutorial/cdi
```
Select the simplegreeting folder.
Click Open Project.
To modify the Printer.java file, perform these steps:
1. Expand the Source Packages node.
2. Expand the greetings node.
3. Double-click the Printer.java file.
4. In the editor, comment out the @Informal annotation:
  @Inject //@Informal Greeting greeting;
5. Save the file.
In the Projects tab, right-click the simplegreeting project and select Build.

This command builds and packages the application into a WAR file, simplegreeting.war, located in the target directory, and then deploys it to GlassFish Server.

To Build, Package, and Deploy the simplegreeting Example Using Maven

Make sure that GlassFish Server has been started (see Starting and Stopping GlassFish Server).

In a terminal window, go to:

jakartaee-examples/tutorial/cdi/simplegreeting/

Enter the following command to deploy the application:
```
mvn install
```
This command builds and packages the application into a WAR file, simplegreeting.war, located in the target directory, and then deploys it to GlassFish Server.

To Run the simplegreeting Example

In a web browser, enter the following URL:
```
http://localhost:8080/simplegreeting
```
The Simple Greeting page opens.
Enter a name in the field.

For example, suppose that you enter Duke.
Click Say Hello.

If you did not modify the Printer.java file, then the following text string appears below the button:
```
Hi, Duke!
```
If you commented out the @Informal annotation in the Printer.java file, then the following text string appears below the button:
```
Hello, Duke.
```

The guessnumber-cdi CDI Example

The guessnumber-cdi example, somewhat more complex than the simplegreeting example, illustrates the use of producer methods and of session and application scope. The example is a game in which you try to guess a number in fewer than ten attempts. It is similar to the guessnumber-faces example described in Introduction to Facelets, except that you can keep guessing until you get the right answer or until you use up your ten attempts.

The example includes four source files, a Facelets page and template, and configuration files. The configuration files and the template are the same as those used for the simplegreeting example.

The guessnumber-cdi Source Files

The four source files for the guessnumber-cdi example are:

The @MaxNumber qualifier interface
The @Random qualifier interface
The Generator managed bean, which defines producer methods
The UserNumberBean managed bean

The source files are located in the jakartaee-examples/tutorial/cdi/guessnumber-cdi/src/main/java/jakarta/tutorial/guessnumber directory.

The @MaxNumber and @Random Qualifier Interfaces

The @MaxNumber qualifier interface is defined as follows:

package guessnumber;

import java.lang.annotation.Documented;
import static java.lang.annotation.ElementType.FIELD;
import static java.lang.annotation.ElementType.METHOD;
import static java.lang.annotation.ElementType.PARAMETER;
import static java.lang.annotation.ElementType.TYPE;
import java.lang.annotation.Retention;
import static java.lang.annotation.RetentionPolicy.RUNTIME;
import java.lang.annotation.Target;
import jakarta.inject.Qualifier;

@Target({TYPE, METHOD, PARAMETER, FIELD})
@Retention(RUNTIME)
@Documented
@Qualifier
public @interface MaxNumber {
}

The @Random qualifier interface is defined as follows:

package guessnumber;

import java.lang.annotation.Documented;
import static java.lang.annotation.ElementType.FIELD;
import static java.lang.annotation.ElementType.METHOD;
import static java.lang.annotation.ElementType.PARAMETER;
import static java.lang.annotation.ElementType.TYPE;
import java.lang.annotation.Retention;
import static java.lang.annotation.RetentionPolicy.RUNTIME;
import java.lang.annotation.Target;
import jakarta.inject.Qualifier;

@Target({TYPE, METHOD, PARAMETER, FIELD})
@Retention(RUNTIME)
@Documented
@Qualifier
public @interface Random {
}

The Generator Managed Bean

The Generator managed bean contains the two producer methods for the application. The bean has the @ApplicationScoped annotation to specify that its context extends for the duration of the user’s interaction with the application:

package guessnumber;

import java.io.Serializable;
import jakarta.enterprise.context.ApplicationScoped;
import jakarta.enterprise.inject.Produces;

@ApplicationScoped
public class Generator implements Serializable {

    private static final long serialVersionUID = 1L;

    private final java.util.Random random =
        new java.util.Random( System.currentTimeMillis() );

    private final int maxNumber = 100;

    java.util.Random getRandom() {
        return random;
    }

    @Produces @Random int next() {
        return getRandom().nextInt(maxNumber + 1);
    }

    @Produces @MaxNumber int getMaxNumber() {
        return maxNumber;
    }

}

The UserNumberBean Managed Bean

The UserNumberBean managed bean, the managed bean for the Jakarta Faces application, provides the basic logic for the game. This bean does the following:

Implements setter and getter methods for the bean fields
Injects the two qualifier objects
Provides a reset method that allows you to begin a new game after you complete one
Provides a check method that determines whether the user has guessed the number
Provides a validateNumberRange method that determines whether the user’s input is correct

The bean is defined as follows:

package guessnumber;

import java.io.Serializable;
import jakarta.annotation.PostConstruct;
import jakarta.faces.view.ViewScoped;
import jakarta.enterprise.inject.Instance;
import jakarta.faces.application.FacesMessage;
import jakarta.faces.component.UIComponent;
import jakarta.faces.component.UIInput;
import jakarta.faces.context.FacesContext;
import jakarta.inject.Inject;
import jakarta.inject.Named;

@Named
@ViewScoped
public class UserNumberBean implements Serializable {

    private static final long serialVersionUID = 1L;

    private int number;
    private Integer userNumber;
    private int minimum;
    private int remainingGuesses;

    @MaxNumber
    @Inject
    private int maxNumber;

    private int maximum;

    @Random
    @Inject
    Instance<Integer> randomInt;

    @PostConstruct
    public void init() {
        minimum = 0;
        userNumber = 0;
        remainingGuesses = 10;
        maximum = maxNumber;
        number = randomInt.get();
    }

    public void check() {
        if (userNumber > number) {
            maximum = userNumber - 1;
        }
        if (userNumber < number) {
            minimum = userNumber + 1;
        }
        if (userNumber == number) {
            FacesContext.getCurrentInstance().addMessage(null,
                new FacesMessage("Correct!"));
        }
        remainingGuesses--;
    }

    public void reset() {
        init();
    }

    public void validateNumberRange(FacesContext context,
                                    UIComponent toValidate,
                                    Object value) {
        int input = (Integer) value;

        if (input < minimum || input > maximum) {
            throw new ValidatorException(new FacesMessage("Invalid guess"));
        }
    }

    public void setUserNumber(Integer userNumber) {
        this.userNumber = userNumber;
    }

    public Integer getUserNumber() {
        return userNumber;
    }

    public int getMaximum() {
        return maximum;
    }

    public int getMinimum() {
        return minimum;
    }

    public int getRemainingGuesses() {
        return remainingGuesses;
    }

}

The Facelets Page

This example uses the same template that the simplegreeting example uses. The index.xhtml file, however, is more complex.

<ui:composition template="/WEB-INF/templates/template.xhtml"
                xmlns:ui="jakarta.faces.facelets"
                xmlns:h="jakarta.faces.html">
    <ui:define name="title">Guess My Number</ui:define>
    <ui:define name="content">
        <h:form id="guessMyNumberForm">
            <p>
                I'm thinking of a number from #{userNumberBean.minimum}
                to #{userNumberBean.maximum}. You have
                <h:outputText id="remainingGuesses"
                              value="#{userNumberBean.remainingGuesses}" />
                guesses.
            </p>
            <div class="input">
                <h:outputLabel for="userNumber" value="Number" />
                <h:inputText id="userNumber"
                             value="#{userNumberBean.userNumber}"
                             required="true" size="3"
                             disabled="#{
                                userNumberBean.remainingGuesses le 0
                                    or
                                userNumberBean.number eq userNumberBean.userNumber
                             }"
                             validator="#{userNumberBean.validateNumberRange}" />
            </div>
            <div class="actions">
                <h:commandButton id="check" value="Guess"
                                 action="#{userNumberBean.check}"
                                 disabled="#{
                                    userNumberBean.remainingGuesses le 0
                                        or
                                    userNumberBean.number eq userNumberBean.userNumber
                                 }">
                    <f:ajax execute="@form"
                            render="@this remainingGuesses userNumber output messages" />
                </h:commandButton>
                <h:commandButton id="reset" value="Reset"
                                 action="#{userNumberBean.reset}">
                    <f:ajax execute="@this"
                            render="@this remainingGuesses userNumber output messages" />
                </h:commandButton>
            </div>
            <h:panelGroup id="output" layout="block">
                <h:outputText value="Higher!" rendered="#{
                    userNumberBean.userNumber ne 0
                        and
                    userNumberBean.number gt userNumberBean.userNumber
                }" />
                <h:outputText value="Lower!" rendered="#{
                    userNumberBean.userNumber ne 0
                        and
                    userNumberBean.number lt userNumberBean.userNumber
                }" />
            </h:panelGroup>
            <h:messages id="messages" />
        </h:form>
    </ui:define>
</ui:composition>

The Facelets page presents the user with the minimum and maximum values and the number of guesses remaining. The user’s interaction with the game takes place within the panelGrid table, which contains an input field, Guess and Reset buttons, and a field that appears if the guess is higher or lower than the correct number. Every time the user clicks Guess, the userNumberBean.check method is called to reset the maximum or minimum value or, if the guess is correct, to generate a FacesMessage to that effect. The method that determines whether each guess is valid is userNumberBean.validateNumberRange.

Running the guessnumber-cdi Example

You can use either NetBeans IDE or Maven to build, package, deploy, and run the guessnumber-cdi application.

To Build, Package, and Deploy the guessnumber-cdi Example Using NetBeans IDE

Make sure that GlassFish Server has been started (see Starting and Stopping GlassFish Server).
From the File menu, choose Open Project.
In the Open Project dialog box, navigate to:
```
jakartaee-examples/tutorial/cdi
```
Select the guessnumber-cdi folder.
Click Open Project.
In the Projects tab, right-click the guessnumber-cdi project and select Build.

This command builds and packages the application into a WAR file, guessnumber-cdi.war, located in the target directory, and then deploys it to GlassFish Server.

To Build, Package, and Deploy the guessnumber-cdi Example Using Maven

Make sure that GlassFish Server has been started (see Starting and Stopping GlassFish Server).
In a terminal window, change to the following directory:
```
jakartaee-examples/tutorial/cdi/guessnumber-cdi/
```
Enter the following command to deploy the application:
```
mvn install
```
This command builds and packages the application into a WAR file, guessnumber-cdi.war, located in the target directory, and then deploys it to GlassFish Server.

To Run the guessnumber Example

In a web browser, enter the following URL:
```
http://localhost:8080/guessnumber-cdi
```
The Guess My Number page opens.
On the Guess My Number page, enter a number in the Number field and click Guess.

The minimum and maximum values are modified, along with the remaining number of guesses.
Keep guessing numbers until you get the right answer or run out of guesses.

If you get the right answer or run out of guesses, the input field and Guess button are grayed out.
Click Reset to play the game again with a new random number.