Java Platform, Enterprise Edition (Java EE) 8 The Java EE Tutorial

## The encoder Example: Using Alternatives

The `encoder` example shows how to use alternatives to choose between two beans at deployment time, as described in Using Alternatives in CDI Applications. The example includes an interface and two implementations of it, a managed bean, a Facelets page, and configuration files.

The source files are located in the `tut-install/examples/cdi/encoder/src/main/java/javaeetutorial/encoder/` directory.

The following topics are addressed here:

- The Coder Interface and Implementations

- The encoder Facelets Page and Managed Bean

- Running the encoder Example

### The Coder Interface and Implementations

The `Coder` interface contains just one method, `codeString`, that takes two arguments: a string, and an integer value that specifies how the letters in the string should be transposed.

    public interface Coder {

        public String codeString(String s, int tval);
    }

The interface has two implementation classes, `CoderImpl` and `TestCoderImpl`. The implementation of `codeString` in `CoderImpl` shifts the string argument forward in the alphabet by the number of letters specified in the second argument; any characters that are not letters are left unchanged. (This simple shift code is known as a Caesar cipher because Julius Caesar reportedly used it to communicate with his generals.) The implementation in `TestCoderImpl` merely displays the values of the arguments. The `TestCoderImpl` implementation is annotated `@Alternative`:

    import javax.enterprise.inject.Alternative;

    @Alternative
    public class TestCoderImpl implements Coder {

        @Override
        public String codeString(String s, int tval) {
            return ("input string is " + s + ", shift value is " + tval);
        }
    }

The `beans.xml` file for the `encoder` example contains an `alternatives` element for the `TestCoderImpl` class, but by default the element is commented out:

    <beans ...>
        <!--<alternatives>
            <class>javaeetutorial.encoder.TestCoderImpl</class>
        </alternatives>-->
    </beans>

This means that by default, the `TestCoderImpl` class, annotated `@Alternative`, will not be used. Instead, the `CoderImpl` class will be used.

### The encoder Facelets Page and Managed Bean

The simple Facelets page for the `encoder` example, `index.xhtml`, asks the user to enter the string and integer values and passes them to the managed bean, `CoderBean`, as `coderBean.inputString` and `coderBean.transVal`:

    <html lang="en"
          xmlns="http://www.w3.org/1999/xhtml"
          xmlns:h="http://java.sun.com/jsf/html">
        <h:head>
            <h:outputStylesheet library="css" name="default.css"/>
            <title>String Encoder</title>
        </h:head>
        <h:body>
            <h2>String Encoder</h2>
            <p>Type a string and an integer, then click Encode.</p>
            <p>Depending on which alternative is enabled, the coder bean
                will either display the argument values or return a string that
                shifts the letters in the original string by the value you
                specify. The value must be between 0 and 26.</p>
            <h:form id="encodeit">
                <p><h:outputLabel value="Enter a string: " for="inputString"/>
                    <h:inputText id="inputString"
                                 value="#{coderBean.inputString}"/>
                    <h:outputLabel value="Enter the number of letters to shift by: "
                                   for="transVal"/>
                    <h:inputText id="transVal" value="#{coderBean.transVal}"/></p>
                <p><h:commandButton value="Encode"
                                    action="#{coderBean.encodeString()}"/></p>
                <p><h:outputLabel value="Result: " for="outputString"/>
                    <h:outputText id="outputString"
                                  value="#{coderBean.codedString}"
                                  style="color:blue"/></p>
                <p><h:commandButton value="Reset"
                                    action="#{coderBean.reset}"/></p>
            </h:form>
            ...
        </h:body>
    </html>

When the user clicks the Encode button, the page invokes the managed bean’s `encodeString` method and displays the result, `coderBean.codedString`, in blue. The page also has a Reset button that clears the fields.

The managed bean, `CoderBean`, is a `@RequestScoped` bean that declares its input and output properties. The `transVal` property has three Bean Validation constraints that enforce limits on the integer value, so that if the user enters an invalid value, a default error message appears on the Facelets page. The bean also injects an instance of the `Coder` interface:

    @Named
    @RequestScoped
    public class CoderBean {

        private String inputString;
        private String codedString;
        @Max(26)
        @Min(0)
        @NotNull
        private int transVal;

        @Inject
        Coder coder;
        ...

In addition to simple getter and setter methods for the three properties, the bean defines the `encodeString` action method called by the Facelets page. This method sets the `codedString` property to the value returned by a call to the `codeString` method of the `Coder` implementation:

        public void encodeString() {
            setCodedString(coder.codeString(inputString, transVal));
        }

Finally, the bean defines the `reset` method to empty the fields of the Facelets page:

        public void reset() {
            setInputString("");
            setTransVal(0);
        }

### Running the encoder Example

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

#### To Build, Package, and Deploy the encoder Example Using NetBeans IDE

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

2. From the File menu, choose Open Project.

3. In the Open Project dialog box, navigate to:

       tut-install/examples/cdi

4. Select the `encoder` folder.

5. Click Open Project.

6. In the Projects tab, right-click the `encoder` project and select Build.

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

#### To Run the encoder Example Using NetBeans IDE

1. In a web browser, enter the following URL:

       http://localhost:8080/encoder

2. On the String Encoder page, enter a string and the number of letters to shift by, and then click Encode.

   The encoded string appears in blue on the Result line. For example, if you enter `Java` and `4`, the result is `Neze`.

3. Now, edit the `beans.xml` file to enable the alternative implementation of `Coder`.

   1. In the Projects tab, under the `encoder` project, expand the Web Pages node, then expand the WEB-INF node.

   2. Double-click the `beans.xml` file to open it.

   3. Remove the comment characters that surround the `alternatives` element, so that it looks like this:

          <alternatives>
              <class>javaeetutorial.encoder.TestCoderImpl</class>
          </alternatives>

   4. Save the file.

4. Right-click the `encoder` project and select Clean and Build.

5. In the web browser, reenter the URL to show the String Encoder page for the redeployed project:

       http://localhost:8080/encoder/

6. Enter a string and the number of letters to shift by, and then click Encode.

   This time, the Result line displays your arguments. For example, if you enter `Java` and `4`, the result is:

       Result: input string is Java, shift value is 4

#### To Build, Package, and Deploy the encoder Example Using Maven

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

2. In a terminal window, go to:

       tut-install/examples/cdi/encoder/

3. Enter the following command to deploy the application:

       mvn install

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

#### To Run the encoder Example Using Maven

1. In a web browser, enter the following URL:

       http://localhost:8080/encoder/

   The String Encoder page opens.

2. Enter a string and the number of letters to shift by, and then click Encode.

   The encoded string appears in blue on the Result line. For example, if you enter `Java` and `4`, the result is `Neze`.

3. Now, edit the `beans.xml` file to enable the alternative implementation of `Coder`.

   1. In a text editor, open the following file:

          tut-install/examples/cdi/encoder/src/main/webapp/WEB-INF/beans.xml

   2. Remove the comment characters that surround the `alternatives` element, so that it looks like this:

          <alternatives>
              <class>javaeetutorial.encoder.TestCoderImpl</class>
          </alternatives>

   3. Save and close the file.

4. Enter the following command:

       mvn clean install

5. In the web browser, reenter the URL to show the String Encoder page for the redeployed project:

       http://localhost:8080/encoder

6. Enter a string and the number of letters to shift by, and then click Encode.

   This time, the Result line displays your arguments. For example, if you enter `Java` and `4`, the result is:

       Result: input string is Java, shift value is 4

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