eXo Platform 3.0

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## Chapter 4. Portlet development

## Portlet Primer

### JSR-168 and JSR-286 overview

The Java Community Process (`JCP`) uses Java Specification Requests (`JSR`s) to define proposed specifications and technologies designed for the Java platform.

The Portlet Specifications aim at defining portlets that can be used by any JSR-168 (Portlet 1.0) or JSR-286 (Portlet 2.0) portlet container.

Most Java EE (Enterprise Edition) portals include at least one compliant portlet container, and GateIn 3.1 is no exception. In fact, GateIn 3.1 includes a container that supports both versions.

This chapter gives a brief overview of the Portlet Specifications but portlet developers are strongly encouraged to read the JSR-286 Portlet Specification .

GateIn 3.1 is fully JSR-286 compliant. Any JSR-168 or JSR-286 portlet operates as it is mandated by the respective specifications inside the portal.

#### Portal Pages

A portal can be considered as a series of web pages with different areas within them. Those areas contain different windows and each window contains portlet:

The diagram below visually represents this nesting:

#### Rendering Modes

A portlet can have different view modes. Three modes are defined by the JSR-286 specification:

View

  Generates markup reflecting the current state of the portlet.

Edit

  Allows a user to customize the behavior of the portlet.

Help

  Provides information to the user as to how to use the portlet.

#### Window States

Window states are an indicator of how much page space a portlet consumes on any given page. The three states defined by the JSR-168 specification are:

Normal

  A portlet shares this page with other portlets.

Minimized

  A portlet may show very little information, or none at all.

Maximized

  A portlet may be the only portlet displayed on this page.

### Tutorials

The tutorials contained in this chapter are targeted toward portlet developers. It is also recommend that developers read and understand the JSR-286 Portlet Specification .

### Maven

This example is using Maven to compile and build the web archive. Maven versions can be downloaded from maven.apache.org

#### Deploying your first Portlet

This section describes how to deploy a portlet in GateIn 3.1. A sample portlet called `SimplestHelloWorld` is located in the `examples` directory at the root of your GateIn 3.1 binary package. This sample is used in the following examples.

##### Compiling

To compile and package the application:

1. Navigate to the `SimplestHelloWorld` directory and execute:

       mvn package

2. If the compile is successfully packaged the result will be available in: `SimplestHelloWorld/target/SimplestHelloWorld-0.0.1.war` .

3. Copy the package file into `JBOSS_HOME/server/default/deploy`.

4. Start JBoss Application Server (if it is not already running).

5. Create a new portal page and add the portlet to it.

##### Package Structure

Like other Java EE applications, GateIn 3.1 portlets are packaged in WAR files. A typical portlet WAR file can include servlets, resource bundles, images, HTML, JavaServer Pages (JSP), and other static or dynamic files.

The following is an example of the directory structure of the `SimplestHelloWorld` portlet:

    |-- SimplestHelloWorld-0.0.1.war
    |   `-- WEB-INF
    |       |-- classes
    |       |   `-- org
    |       |       `-- gatein
    |       |           `-- portal
    |       |               `-- examples
    |       |                   `-- portlets
    |       |                       `-- SimplestHelloWorldPortlet.class
    |       |-- portlet.xml
    |       `-- web.xml

| The compiled Java class implementing javax.portlet.Portlet (through javax.portlet.GenericPortlet )
| This is the mandatory descriptor files for portlets. It is used during deployment..
| This is the mandatory descriptor for web applications.

##### Portlet Class

Below is the `SimplestHelloWorldPortlet/src/main/java/org/gatein/portal/examples/portlets/SimplestHelloWorldPortlet.java` Java source:

    package org.gatein.portal.examples.portlets;

    import java.io.IOException;

    import java.io.PrintWriter;

    import javax.portlet.GenericPortlet;

    import javax.portlet.RenderRequest;

    import javax.portlet.RenderResponse;

    public class SimplestHelloWorldPortlet extends GenericPortlet

    {

       public void doView(RenderRequest request,

                           RenderResponse response) throws IOException

       {

          PrintWriter writer = response.getWriter();

          writer.write("Hello World !");

          writer.close();

       }

    }

| All portlets must implement the `javax.portlet.Portlet` interface. The portlet API provides a convenient implementation of this interface. The `javax.portlet.Portlet` interface uses the `javax.portlet.GenericPortlet` class which implements the `Portlet render` method to dispatch to abstract mode-specific methods. This makes it easier to support the standard portlet modes. `Portlet render` also provides a default implementation for the `processAction`, `init` and `destroy` methods. It is recommended to extend `GenericPortlet` for most cases.
| If only the `view` mode is required, then only the `doView` method needs to be implemented. The `GenericPortlet` `render` implementation calls our implementation when the `view` mode is requested.
| Use the RenderResponse to obtain a writer to be used to produce content.
| Write the markup to display.
| Closing the writer.

### Markup Fragments

Portlets are responsible for generating markup fragments, as they are included on a page and are surrounded by other portlets. This means that a portlet outputting HTML must not output any markup that cannot be found in a `<body>` element.

##### Application Descriptors

GateIn 3.1 requires certain descriptors to be included in a portlet WAR file. These descriptors are defined by the Jave EE (`web.xml`) and Portlet Specification (`portlet.xml`).

Below is an example of the `SimplestHelloWorldPortlet/WEB-INF/portlet.xml` file. This file must adhere to its definition in the JSR-286 Portlet Specification. More than one portlet application may be defined in this file:

    <portlet-app xmlns="http://java.sun.com/xml/ns/portlet/portlet-app_2_0.xsd"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://java.sun.com/xml/ns/portlet/portlet-app_2_0.xsd
                                             http://java.sun.com/xml/ns/portlet/portlet-app_2_0.xsd"
       version="2.0">
       <portlet>
          <portlet-name>SimplestHelloWorldPortlet</portlet-name>
          <portlet-class>
             org.gatein.portal.examples.portlets.SimplestHelloWorldPortlet
          </portlet-class>
          <supports>
            <mime-type>text/html</mime-type>
          </supports>
          <portlet-info>
              <title>Simplest Hello World Portlet</title>
          </portlet-info>
       </portlet>
    </portlet-app>

| Define the portlet name. It does not have to be the class name.
| The Fully Qualified Name (`FQN`) of your portlet class must be declared here.
| The `<supports>` element declares all of the markup types that a portlet supports in the `render` method. This is accomplished via the `<mime-type>` element, which is required for every portlet. The declared MIME types must match the capability of the portlet. It allows administrators to pair which modes and window states are supported for each markup type. This does not have to be declared as all portlets must support the `view` portlet mode. Use the `<mime-type>` element to define which markup type the portlet supports. In the example above this is `text/html`. This section tells the portal to only output HTML.
| When rendered, the portlet's title is displayed as the header in the portlet window, unless it is overridden programmatically. In the example above the title would be `Simplest Hello World Portlet` .

#### JavaServer Pages Portlet Example

This section discusses:

1. Adding more features to the previous example.

2. Using a JSP page to render the markup.

3. Using the portlet tag library to generate links to the portlet in different ways.

4. Using the other standard portlet modes.

1. The example used in this section can be found in the `JSPHelloUser` directory.

2. Execute mvn package in this directory.

3. Copy `JSPHelloUser/target/JSPHelloUser-0.0.1.war` to the `deploy` directory of JBoss Application Server.

4. Select the new `JSPHelloUser` tab in your portal.

### Note

The `EDIT` button only appears with logged-in users, which is not the case in the screenshot.

##### Package Structure

The package structure in this tutorial does not differ greatly from the previous example, with the exception of adding some JSP files detailed later.

The JSPHelloUser portlet contains the mandatory portlet application descriptors. The following is an example of the directory structure of the JSPHelloUser portlet:

    JSPHelloUser-0.0.1.war
        |-- META-INF
        |   |-- MANIFEST.MF
        |-- WEB-INF
        |   |-- classes
        |   |   `-- org
        |   |       `-- gatein
        |   |           `-- portal
        |   |               `-- examples
        |   |                   `-- portlets
        |   |                       `-- JSPHelloUserPortlet.class
        |   |-- portlet.xml
        |   `-- web.xml
        `-- jsp
            |-- edit.jsp
            |-- hello.jsp
            |-- help.jsp
            `-- welcome.jsp

##### Portlet Class

The code below is from the `JSPHelloUser/src/main/java/org/gatein/portal/examples/portlets/JSPHelloUserPortlet.java` Java source. It is split in different pieces.

    package org.gatein.portal.examples.portlets;

    import java.io.IOException;

    import javax.portlet.ActionRequest;

    import javax.portlet.ActionResponse;

    import javax.portlet.GenericPortlet;

    import javax.portlet.PortletException;

    import javax.portlet.PortletRequestDispatcher;

    import javax.portlet.RenderRequest;

    import javax.portlet.RenderResponse;

    import javax.portlet.UnavailableException;

    public class JSPHelloUserPortlet extends GenericPortlet

    {

       public void doView(RenderRequest request, RenderResponse response)

           throws PortletException, IOException

       {

          String sYourName = (String) request.getParameter("yourname");

          if (sYourName != null)

          {

             request.setAttribute("yourname", sYourName);

             PortletRequestDispatcher prd =

                getPortletContext().getRequestDispatcher("/jsp/hello.jsp");

             prd.include(request, response);

          }

          else

          {

             PortletRequestDispatcher prd = getPortletContext().getRequestDispatcher("/jsp/welcome.jsp");

             prd.include(request, response);

          }

       }

    ...

| Override the doView method (as in the first tutorial).
| This entry attempts to obtain the value of the render parameter named `yourname`. If defined it should redirect to the `hello.jsp` JSP page, otherwise to the `welcome.jsp` JSP page.
| Get a request dispatcher on a file located within the web archive.
| Perform the inclusion of the markup obtained from the JSP.

As well as the `VIEW` portlet mode, the specification defines two other modes; `EDIT` and `HELP`.

These modes need to be defined in the `portlet.xml` descriptor. This will enable the corresponding buttons on the portlet's window.

The generic portlet that is inherited dispatches the different views to the methods: `doView` , `doHelp` and `doEdit`.

    ...

       protected void doHelp(RenderRequest rRequest, RenderResponse rResponse) throws PortletException, IOException,

             UnavailableException

       {

          rResponse.setContentType("text/html");

          PortletRequestDispatcher prd = getPortletContext().getRequestDispatcher("/jsp/help.jsp");

          prd.include(rRequest, rResponse);

       }

       protected void doEdit(RenderRequest rRequest, RenderResponse rResponse) throws PortletException, IOException,

             UnavailableException

       {

          rResponse.setContentType("text/html");

          PortletRequestDispatcher prd = getPortletContext().getRequestDispatcher("/jsp/edit.jsp");

          prd.include(rRequest, rResponse);

       }

    ...

Portlet calls happen in one or two phases. One when the portlet is rendered and two when the portlet is actioned then rendered.

An action phase is a phase where some state changes. The render phase will have access to render parameters that will be passed each time the portlet is refreshed (with the exception of caching capabilities).

The code to be executed during an action has to be implemented in the processAction method of the portlet.

    ...

             public void processAction(ActionRequest aRequest, ActionResponse aResponse) throws PortletException, IOException,

             UnavailableException

       {

          String sYourname = (String) aRequest.getParameter("yourname");

          aResponse.setRenderParameter("yourname", sYourname);

       }

    ...

| `processAction` is the method from `GernericPorlet` to override for the action phase.
| Here the parameter is retrieved through an action URL .
| The value of `yourname` is kept to make it available in the rendering phase. The previous line simply copies an action parameters to a render parameter for this example.

##### JSP files and the Portlet Tag Library

The `help.jsp` and `edit.jsp` files are very simple. Note that CSS styles are used as defined in the portlet specification. This ensures that the portlet will render well within the theme and across portal vendors.

    <div class="portlet-section-header">Help mode</div>

    <div class="portlet-section-body">This is the help mode, a convenient place to give the user some help information.</div>

    <div class="portlet-section-header">Edit mode</div>

    <div class="portlet-section-body">This is the edit mode, a convenient place to let the user change his portlet preferences.</div>

The landing page contains the links and form to call our portlet:

    <%@ taglib uri="http://java.sun.com/portlet" prefix="portlet" %>

    <div class="portlet-section-header">Welcome !</div>

    <br/>

    <div class="portlet-font">Welcome on the JSP Hello User portlet,
    my name is GateIn Portal. What's yours ?</div>

    <br/>

    <div class="portlet-font">Method 1: We simply pass the parameter to the render phase:<br/>
    <a href="<portlet:renderURL><portlet:param name="yourname" value="John Doe"/>
                    </portlet:renderURL>">John Doe</a></div>

    <br/>

    <div class="portlet-font">Method 2: We pass the parameter to the render phase, using valid XML:
    Please check the source code to see the difference with Method 1.
    <portlet:renderURL var="myRenderURL">
        <portlet:param name="yourname" value='John Doe'/>
    </portlet:renderURL>
    <br/>
    <a href="<%= myRenderURL %>">John Doe</a></div>

    <br/>

    <div class="portlet-font">Method 3: We use a form:<br/>

    <portlet:actionURL var="myActionURL"/>
    <form action="<%= myActionURL %>" method="POST">
             <span class="portlet-form-field-label">Name:</span>
             <input class="portlet-form-input-field" type="text" name="yourname"/>
             <input class="portlet-form-button" type="Submit"/>
    </form>
    </div>

| The portlet taglib, needs to be declared.
| The first method showed here is the simplest one. `portlet:renderURL` will create a URL that calls the render phase of the current portlet and append the result at the place of the markup (within a tag). A parameter is also added directly to the URL.
| In this method the `var` attribute is used. This avoids having one XML tag within another. Instead of printing the url the `portlet:renderURL` tag will store the result in the referenced variable ( `myRenderURL`).
| The variable `myRenderURL` is used like any other JSP variable.
| The third method mixes form submission and action request. Again, a temporary variable is used to put the created URL into.
| The action URL is used in HTML form.

In the third method the action phase is triggered first then the render phase is triggered, which outputs some content back to the web browser based on the available render parameters.

##### JSF example using the JBoss Portlet Bridge

In order to write a portlet using JSF a 'bridge' is needed. This software allows developers to write a portlet application as if it was a JSF application. The bridge then negotiates the interactions between the two layers.

An example of the JBoss Portlet Bridge is available in `examples/JSFHelloUser`. The configuration is slightly different from a JSP application. This example can be used as a base to configure instead of creating a new application.

As in any JSF application, the file `faces-config.xml` is required. It must contain the following information:

    <faces-config>

    ...

        <application>

          <view-handler>org.jboss.portletbridge.application.PortletViewHandler</view-handler>

          <state-manager>org.jboss.portletbridge.application.PortletStateManager</state-manager>

       </application>

    ...

    </faces-config>

The portlet bridge libraries must be available and are usually bundled with the `WEB-INF/lib` directory of the web archive.

The other difference compare to a regular portlet application, can be found in the portlet descriptor. All details about it can be found in the JSR-301 specification that the JBoss Portlet Bridge implements.

    <?xml version="1.0" encoding="UTF-8"?>
    <portlet-app xmlns="http://java.sun.com/xml/ns/portlet/portlet-app_2_0.xsd"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://java.sun.com/xml/ns/portlet/portlet-app_2_0.xsd
                                             http://java.sun.com/xml/ns/portlet/portlet-app_2_0.xsd"
       version="2.0">
       <portlet>
          <portlet-name>JSFHelloUserPortlet</portlet-name>
          <portlet-class>javax.portlet.faces.GenericFacesPortlet</portlet-class>
          <supports>
             <mime-type>text/html</mime-type>
             <portlet-mode>view</portlet-mode>
             <portlet-mode>edit</portlet-mode>
             <portlet-mode>help</portlet-mode>
          </supports>
          <portlet-info>
             <title>JSF Hello User Portlet</title>
          </portlet-info>

          <init-param>
             <name>javax.portlet.faces.defaultViewId.view</name>
             <value>/jsf/welcome.jsp</value>
          </init-param>

          <init-param>
             <name>javax.portlet.faces.defaultViewId.edit</name>
             <value>/jsf/edit.jsp</value>
          </init-param>

          <init-param>
             <name>javax.portlet.faces.defaultViewId.help</name>
             <value>/jsf/help.jsp</value>
          </init-param>

       </portlet>
    </portlet-app>

| All JSF portlets define `javax.portlet.faces.GenericFacesPortlet` as portlet class. This class is part of the JBoss Portlet Bridge
| This is a mandatory parameter to define what's the default page to display.
| This parameter defines which page to display on the 'edit' mode.
| This parameter defines which page to display on the 'help' mode.

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