Home > Articles > Programming > Java

Like this article? We recommend

PCX Reader Plug-in Workshop

This section shows you how to build and test the PCX reader plug-in. You learn how to organize this plug-in’s directories and files, how to compile the source code, how to package the resulting classfiles into a special JAR file, and how to deploy this JAR file. You also discover an application for testing this plug-in. This application enables you to configure the plug-in and read/display PCX images according to this configuration.

Build the Reader Plug-in

Prior to compiling the plug-in’s source code, you must establish an appropriate directory and file structure. Assuming that Windows is your operating system, and assuming that c:\pcx is your project’s home directory, the following directory and file structure is required:


The PCXImageReaderSpi.java and PCXImageReader.java files contain the plug-in’s Java source code. Because of their package ca.mb.javajeff.pcx; statements, they must be stored in the ca\mb\javajeff\pcx directory.

The javax.imageio.spi.ImageReaderSpi file contains a single line of text: ca.mb.javajeff.pcx.PCXImageReaderSpi. This text identifies the PCX reader plug-in to the JVM. The jar command requires that this file be stored in the META-INF\services directory.

Assuming that c:\pcx is the current directory, the following commands compile the source files, create a JAR file, and deploy this JAR file to the JRE’s extensions directory: c:\Program Files\Java\jdk1.5.0\jre\lib\ext on my platforms:

  1. javac ca/mb/javajeff/pcx/*.java
  2. jar cf pcx.jar -C META-INF/ services ca/mb/javajeff/pcx/*.class
  3. copy pcx.jar \progra~1\java\jdk1.5.0\jre\lib\ext

The next time you launch Java, pcx.jar will be examined and detected as a reader plug-in. An instance of its SPI will be created and stored in a run-time registry class, waiting to be accessed from Java programs needing to read PCX images.

Test the Reader Plug-in

Now that you’ve built the plug-in, you’ll want to make sure that it works correctly. You could use JUnit to create unit tests that exercise the plug-in by invoking Image I/O methods. Or you could work with PCX Reader Plug-in Tester (PCXRPT).

PCXRPT is a Swing-based application for testing the PCX reader plug-in. This application displays a PCX image in its scrollable main window. It also reports the image’s width and height, and the path and name of the originating PCX file via a status bar. Check out Figure 1.

Figure 01

Figure 1 PCXRPT’s GUI lets you read and display PCX images.

The File menu presents a Configure menu item that launches a dialog box for configuring the plug-in prior to reading an image. As shown in Figure 2, this dialog box initially presents default configuration settings.

Figure 2

Figure 2 The configuration dialog box lets you configure the PCX reader plug-in.

The configuration dialog box organizes configuration information into four sections:

  • Method: Determines how PCXRPT obtains the PCX reader. It calls javax.imageio.ImageIO’s public static Iterator getImageReadersByFormatName(String formatName) method by default, but can also call public static Iterator getImageReaders(Object input), public static Iterator getImageReadersByMIMEType(String MIMEType), or public static Iterator getImageReadersBySuffix(String fileSuffix). Of these four methods, only getImageReaders() calls PCXImageReaderSpi’s canDecodeInput() method.
  • Destination Offset: Identifies the location of the displayed image’s upper-left corner. By default, this location is (0, 0). For any other location, PCXRPT invokes javax.imageio.ImageReadParam’s inherited public void setDestinationOffset(Point destinationOffset) method. PCXRPT displays black pixels in columns to the left of and rows above the upper-left corner.
  • Source Region: Identifies the region of the image that is to be displayed. By default, this region’s upper-left corner is (0, 0), its width is 0, and its height is 1. Setting the width to 0 causes PCXRPT to use the entire image as the source region. Otherwise, PCXRPT invokes ImageReadParam’s inherited public void setSourceRegion(Rectangle sourceRegion) method to set a smaller region.
  • Source Subsampling: Identifies the image columns and rows that will be displayed (in a periodic fashion), resulting in an image scaled smaller than the original. By default, the X and Y subsampling factors are 1. Setting either or both factors to values greater than 1 causes PCXRPT to invoke ImageReadParam’s inherited public void setSourceSubsampling(int sourceXSubsampling, int sourceYSubsampling, int subsamplingXOffset, int subsamplingYOffset) method. The first two parameters specify the subsampling period; the last two parameters specify an offset (I chose 0) from the source region origin to the first subsampled pixel.

Let’s assume that the destination offset is set to (50, 50), the source region’s upper-left corner is set to (100, 100), the source region’s width and height are each set to 400, and the subsampling factors are set to 2. Figure 3 reveals the displayed image.

Figure 3

Figure 3 The width and height apply to the original image.

Figure 3 shows that the PCX reader plug-has passed several tests. However, additional tests are needed to be certain that the plug-in is 100 percent correct. For example, you could base a test on ImageReadParam’s inherited public void setSourceBands(int[] sourceBands) and non-inherited public void setDestinationBands(int[] destinationBands) methods.

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020