The Eclipse PDT V2.0 project was recently released. It includes many new usability features over the previous version, including the ability to add a build path, open types, and access improved code assistance.

This article demonstrates how to download and install WordPress, and how to use Eclipse PDT to build a plug-in. It also demonstrates how to export the plug-in from Eclipse so it can be shared.

To get the most out of this article, you need to have the following tools:

• PHP V4.3 or later
• MySQL V4.0 or later
• Eclipse V3.4 with PDT

An overview of WordPress

WordPress is a publishing platform written in PHP that allows you to quickly and easily publish content to the Web. It is highly extensible, allowing you to create plug-ins that provide nearly any functionality. Since 2005, millions of copies of it have been downloaded and used by large companies and individuals alike.

WordPress is easy to install and configure, and the requirements are few: only PHP and MySQL. To install WordPress, simply download the ZIP file from the Web site (see Resources) and extract the ZIP to a directory accessible from your Web server. In this article, I'm using a Web server configured to allow publication of the user directory (like the userdir module in Apache) to the Web server. Rename the directory, if you like: I changed mine from wordpress to blog.

After you finish extracting the files and renaming the directory, follow the "Famous 5-Minute Install" instructions (see Resources). If you have an Internet Service Provider (ISP) that supports WordPress's requirements, you can develop locally and FTP the entire directory to your site.

Back to top

Extending WordPress

Many people use WordPress for blogging, although it's good for publishing any content easily. I've worked on sites that use WordPress as the main engine to host informational sites about products that include forums, feedback forms, and Adobe® Flash® animation on the home page.

Many plug-ins are available for WordPress (see Resources). These plug-ins range from the ability to add custom fields that collect more information about the WordPress site's registered users to tag clouds, antispam utilities, and contact plug-ins that generate "Share this" links to popular sites like Facebook, MySpace, del.icio.us, and Technorati.

But even with all these plug-ins, there may be cases where you need to extend WordPress to fit your own needs. The rest of this article shows how you can use Eclipse and PDT to set up a development environment in which you can develop and test WordPress plug-ins.

Back to top

Setting up your workspace

Before setting up your workspace, make sure you have WordPress installed and running. You will need to have read and write access to the WordPress directory. The best scenario is to have user directories configured on the Web server on your machine so you can put the files in your own home directory. But a shared directory also works as long as you can read and write to it.

Before proceeding, create a directory inside the WordPress_home/wp-content/plugins directory (where WordPress_home is the full path to the directory into which you extracted WordPress) — for example, WordPress home/wp-content/plugins/myplugin. In just a few moments, that directory will be home to your new WordPress plug-in.

If you have WordPress up and running, and can read and write to the directory you just created for your plug-in, you are ready to create a new project for your WordPress plug-in:

1. Choose File > Project, then select PHP Project from the Wizards list, as Figure 1 shows.
   
   Figure 1. Creating your new PHP project
   
   
   
2. Click Next.
3. In the New PHP Project window, type the name of your plug-in in the Project name box.
4. Under Contents, select Create project from existing source. Then browse to or type the name of the directory that you just created (for example, my directory is /Users/ngood/Sites/blog/wp-content/plugins/myplugin) in the Directory box, as Figure 2 shows.
   
   Figure 2. Defining the project location
   
   
   
5. Click Finish when you've entered the directory information, as the rest of the information is left at the default values.

After creating the project, the directory listing of the your WordPress_home/wp-content/plugins/myplugin directory will look like Listing 1.

drwxr-xr-x  7 user  user    238 Feb  3 11:02 .
drwxr-xr-x@ 5 user  user    170 Feb  3 08:39 ..
-rw-r--r--  1 user  user    259 Feb  3 11:10 .buildpath
-rw-r--r--  1 user  user  30244 Feb  3 11:02 .pmd
-rw-r--r--  1 user  user    496 Feb  3 08:39 .project
drwxr-xr-x  3 user  user    102 Feb  3 08:39 .settings
-rw-r--r--  1 user  user    795 Feb  3 11:13 myplugin.php

Working in a team environment

If you're working in a team environment and sharing your code, the Eclipse tools will take care of checking the files in from the correct directory into the source-control repository. However, take note of the directory in which the files are being imported from your team sharing environment into your workspace. When you are importing files from a source-control repository into your workspace, you can define where you want the files to be stored (see Figure 3). For more information about using Eclipse with source-code repositories, see Resources.

Adding WordPress to your build path

The PDT project provides the ability to add folders to your build path, which also gives you the ability to have code-completion tools work with WordPress. To be able to see the add_filter and add_action functions in code completion, you can modify the build path to add the WordPress wp-includes directory.

To add the WordPress wp-includes directory to your build path, choose Project > Properties with your PHP project highlighted. On the Libraries tab, click Add External Source Folder, then browse to the wp-includes directory found where you installed WordPress. Click OK when you're finished. Now you can type add_ into the PHP editor, invoke code completion, and see a list that includes add_action and add_filter.

Back to top

Adding your first plug-in file

To add your first plug-in file, choose File > New > PHP File. The first file needs to be named the same as the directory in which the file resides. For example, if the plug-in directory is called myplugin, name the file myplugin.php. This will be the file WordPress reads to get information about your plug-in and to register your extension points.

For WordPress to identify your plug-in, you need to paste a comment block into your new plug-in file. If you're creating a lot of WordPress plug-ins, you may want to consider putting this code block in the code templates for PHP. See Listing 2 for an example of the completed code block.

/*
Plugin Name: My Plugin
Plugin URI: http://www.example.com/myplugin
Description: This is a really great plugin that extends WordPress.
Version: 1.0.0
Author: Nathan A. Good
Author URI: http://www.nathanagood.com
*/

Right now, your plug-in doesn't do anything. But with only the comment block, it will be displayed in WordPress's Plugins administrative area. To view your new plug-in, log in to your WordPress instance as an administrator, then click Plugins. You should see your new plug-in listed under the Inactive Plugins.

Back to top

Adding functionality

In this article, I add two pieces of functionality. The first is a simple one that makes the blog entry title uppercase. That is an example of adding a filter. The second is an extra field on the end of the registration form for a user. That is an example of adding an action.

I'm going to write the examples in functional code to keep them as brief as possible. Remember: If you're using PHP V5 or later, you can incorporate object-oriented concepts to make your code easier to read and maintain. For more information about writing more maintainable PHP by using object-oriented programming concepts and design patterns, see Resources.

The uppercase title

The code for the title filter is shown in Listing 3. In it, you can see that it uses the strtoupper() function in PHP to make the title of the blog post uppercase.

/**
 * Capitalizes the title given by $title.
 */
function capitalizeTitle($title) {
    return strtoupper($title);
}

When you have written the function, you need to call add_filter to register your function with WordPress as the specified filter extension point. A link to the full list of the available filters is provided in Resources. An example of adding the filter is shown below.

/* now add the filter */
add_filter('the_title', 'capitalizeTitle');

Adding the registration fields

The code to generate a new custom registration field is shown in Listing 5. I used the Firebug extension to view the Cascading Style Sheet (CSS) styles of the existing registration form fields to make sure my custom fields had the same CSS style class.

/**
 * Adds a custom field that prompts the user for their favorite
 * color.
 * @return void
 */
function drawCustomField() {
    echo '<p><label>Favorite Color:<br />';
    echo '<input autocomplete="off" class="input" name="fav_color" ';
    echo ' id="fav_color" size="25"';
    echo ' value="' . $_POST['fav_color'] . '" type="text" tabindex="32" />';
    echo '</label><br /></p>';
}

To add the custom action, use the code shown below.

/* now add the action */
add_action('register_form', 'drawCustomField');

This action simply draws the field on the form. It does not actually save the data when the user submits the form. To save the data, use the profile_update action. For a link to the full list of the available actions and what they do, see Resources.

Back to top

Testing the plug-in

With the code put into the project, you're ready to test the plug-in. Before testing it, you need to enable the plug-in in WordPress. Log in to WordPress as the administrator and click Plugins. Find your plug-in, then click Activate.

When you have activated the plug-in, go to the home page of your blog. You should notice that the "Hello World!" sample post title is now all in uppercase letters. If you deactivate your plug-in, it will revert to normal capitalization. You can use this functionality to do other things, such as turn URLs found in titles into hyperlinks. You can add more than one filter with the same name, so instead of creating one filter that does different things, consider making small, concentrated functions and chaining them together.

To test the registration field part of the plug-in, you must log in to WordPress as the administrative user and turn on the feature that allows users to register on the Settings page. After enabling this option, you will see the Favorite Color field when you go to the registration page.

Back to top

Other WordPress extension points

In addition to adding filters and actions, you can override functions in WordPress. The functions you can override are defined in the pluggable.php file in your WordPress home directory. One example is wp_mail, which gives you the opportunity to provide a different function for e-mailing your users. Many of the overridable functions deal with user authorization, such as logging in, setting cookies, and notification of different events. The ability to override authorization-based functionality allows you to build plug-ins that might provide alternative forms of authentication and authorization to WordPress, such as authentication against an enterprise user store.

Back to top

Exporting the plug-in

After you have written and thoroughly tested your plug-in, you will probably want to share it with others. WordPress plug-ins are packaged like WordPress itself: Most are simply a ZIP file that is expanded and copied into the WordPress plugins directory.

You can use Eclipse to export the plug-in files. By using Eclipse to export the project to a ZIP archive file, you can avoid sending along project-specific files and team sharing directories and files (like .svn or Concurrent Version Systems (CVS) directories).

To export your plug-in to an archive file, select your PHP project, then choose File > Export. In the Select window, choose Archive File from the destination list, then click Next.

In the Archive file window, shown in Figure 6, click Deselect All, then click the PHP files you want to include in your archive file (such as myplugin.php). When you're finished selecting the PHP files, choose the location of the archive file from To archive file, then click Finish to create the file. To maintain consistency, it's best to keep the name of the ZIP file the same as the plugin directory and the main plug-in file.

Now that you've created the archive file from Eclipse, you can publish it on a Web server or copy it to your ISP's location so you can use it.

To add information about your plug-in on the official WordPress site, see Resources and follow the directions.

Back to top

Conclusion

WordPress is an increasingly popular, extensible Web application that allows you to easily publish content to your users. You can extend WordPress to provide more functionality without having to modify any WordPress code.

The Eclipse IDE with PDT installed allows you to build a plug-in using PHP tools. You can test and run your plug-in with WordPress until it is complete. Then you can use the Eclipse export functionality to export the plug-in to an archive file suitable for distribution.

Resources

Learn

• Visit the official WordPress site to learn more about WordPress.
  
  
• To install WordPress quickly, check out the "Famous 5-Minute Install" tutorial.
  
  
• For a list of the available WordPress filters you can extend, see the Plugin API/Filter Reference.
  
  
• For a full list of the WordPress actions that you can extend, see the Plugin API/Action Reference.
  
  
• To learn how to have WordPress host your plug-in, visit http://wordpress.org/extend/plugins/about/.
  
  
• To learn how to set up debugging with PDT to debug your plug-in, read "Debugging PHP using Eclipse and PDT."
  
  
• To learn about good object-oriented coding habits in PHP, read "Build seven good object-oriented habits in PHP."
  
  
• Check out the "Recommended Eclipse reading list."
  
  
• Browse all the Eclipse content on developerWorks.
  
  
• Follow developerWorks on Twitter.
  
  
• New to Eclipse? Read the developerWorks article "Get started with the Eclipse Platform" to learn its origin and architecture, and how to extend Eclipse with plug-ins.
  
  
• Expand your Eclipse skills by checking out IBM developerWorks' Eclipse project resources.
  
  
• To listen to interesting interviews and discussions for software developers, check out check out developerWorks podcasts.
  
  
• Stay current with developerWorks' Technical events and webcasts.
  
  
• Watch and learn about IBM and open source technologies and product functions with the no-cost developerWorks On demand demos.
  
  
• Check out upcoming conferences, trade shows, webcasts, and other Events around the world that are of interest to IBM open source developers.
  
  
• Visit the developerWorks Open source zone for extensive how-to information, tools, and project updates to help you develop with open source technologies and use them with IBM's products.
  
  

Get products and technologies

• Check out the latest Eclipse technology downloads at IBM alphaWorks.
  
  
• Download Eclipse Platform and other projects from the Eclipse Foundation.
  
  
• Download IBM product evaluation versions, and get your hands on application development tools and middleware products from DB2®, Lotus®, Rational®, Tivoli®, and WebSphere®.
  
  
• Innovate your next open source development project with IBM trial software, available for download or on DVD.
  
  

Discuss

• The Eclipse Platform newsgroups should be your first stop to discuss questions regarding Eclipse. (Selecting this will launch your default Usenet news reader application and open eclipse.platform.)
  
  
• The Eclipse newsgroups has many resources for people interested in using and extending Eclipse.
  
  
• Participate in developerWorks blogs and get involved in the developerWorks community.
  
  

About the author

Rate this article

Comments

Back to top

Table of contents

• An overview of WordPress
• Extending WordPress
• Setting up your workspace
• Adding your first plug-in file
• Adding functionality
• Testing the plug-in
• Other WordPress extension points
• Exporting the plug-in
• Conclusion
• Resources
• About the author
• Comments

Next steps from IBM

With the no-charge DB2 Express-C, Zend Core PHP, and Java you can develop advanced Web 2.0 applications quickly that matter.

---

• Try: Download a free trial version of DB2 Express-C, which includes Zend Core PHP and pureXML technology that is ideally suited for managing both XML and relational data and powering a new breed of SOA and Web 2.0 solutions.
• Article: This IBM Redbook shows how to port PHP apps from MySQL to DB2, and includes code samples for creating Zend Core PHP applications.
• Tutorial: In this Mastering Facebook app development tutorial series, you will use Java and PHP in parallel to build a Facebook interface for an online stock trading J2EE application using the Spring framework.
• Buy: DB2 9 for Linux, UNIX and Windows

Dig deeper into Open source on developerWorks

IBM SmartCloud trial. No charge.

Unleash the power of hybrid cloud computing today!

---

Public and private solutions in one trial.

Special offers