Welcome!

Java IoT Authors: Elizabeth White, Liz McMillan, Pat Romanski, Shelly Palmer, Karthick Viswanathan

Related Topics: Java IoT

Java IoT: Article

Making PDFs Portable: Integrating PDF and Java Technology

Making PDFs Portable: Integrating PDF and Java Technology

Since Adobe released the first public PDF Reference in 1993, a number of PDF utilities and libraries, supporting all kinds of languages and platforms, have been made available to users and developers alike. However, support for Adobe's technology has lagged in Java application development. And this is curious because PDF documents tend to be a popular way of storing and interchanging information when dealing with enterprise information systems - an application domain that Java technology is particularly well suited to. Yet it seems that, until recently, mature, capable PDF support wasn't readily available to Java applications developers.

PDFBox (an Open Source project released under the BSD license) is a pure Java library that lets developers read and create PDF documents. It has features such as:

  • Extracting text, including Unicode characters
  • Easy integration with text search engines like Jakarta Lucene
  • Encryption/Decryption of PDF documents
  • Importing/Exporting of form data in FDF and XFDF formats
  • Appending to existing PDF documents
  • Splitting a single PDF into multiple documents
  • Overlaying one PDF document on top of another
PDFBox API
PDFBox has been designed to represent PDF documents using familiar object-oriented paradigms. The data contained in a PDF document is a collection of basic object types: arrays, booleans, dictionaries, numbers, strings and binary streams. PDFBox captures these basic object types in the org.pdfbox.cos package (the COS Model). While it's possible to create any desired interactions with a PDF document using only these objects, it requires an intimate knowledge of the internals of PDF documents and the techniques used to represent higher-level concepts. For example, objects such as pages and fonts are represented as dictionaries with specialized attributes; deciphering all these various attributes and their types requires tedious consultation of the PDF Reference.

For this reason, the org.pdfbox.pdmodel package (the PD Model) sits on top the COS Model and provides a high-level API that accesses PDF document objects in a more familiar manner (see Figure 1). Objects such as PDPage and PDFont can be found in this package, which encapsulates their lower-level COS model counterparts.

A word of caution to developers: the PD Model offers many nice features but is still a work in progress. In some instances, use of the COS Model may be required to access a particular piece of PDF functionality. Consequently, all PD Model objects can retrieve the corresponding COS Model object that they represent, so it's always possible to start with the PD Model and drop down to the COS Model when the required piece of functionality is found to be missing.

Now that the general capabilities of PDFBox have been discussed a few examples of its use are appropriate. We will start by reading an existing PDF document:


PDDocument document =
PDDocument.load( "./test.pdf" );

This operation will cause the PDF file to be parsed and an in-memory representation of the document will be created. To facilitate the efficient handling of large documents, PDFBox only stores the document structure in memory; objects such as images, embedded fonts and page content are cached in a temporary file.

Note: When finished using a PDDocument object, care should be taken to invoke the close() method on the document object to release resources used during its creation.

Text Extraction and Lucene Integration
In an information retrieval age when applications are expected to have searching and indexing capabilities regardless of the medium, the ability to organize and catalog information into a searchable format is critical. This is simple for text and HTML documents, but PDF documents have more structure and meta-information that makes it difficult to extract the underlying text. The PDF language is similar to Postscript in that objects are drawn as vectors on the page at certain positions. For example:


/Helv 12 Tf
0 13.0847 Td
(Hello World) Tj

This set of instructions changes the font to Helvetica size 12, moves the caret to the next line and renders the string "Hello World." These command streams are usually compressed and the order in which the glyphs are displayed on the screen is not necessarily the order in which the characters appear in the file, so it isn't always possible to simply extract text strings directly from the raw PDF document. However, PDFBox has a sophisticated text-extraction algorithm that deals with this and other complexities, letting a developer get the text of the document as if reading off its rendered form.

Lucene, which is part of the Apache Jakarta project, is a popular Open Source search engine library. Lucene lets developers create an index and do complex searches on a large volume of textual content based on that index. Since Lucene has adopted text as the common denominator for content, it's the developer's responsibility to convert the data contained in other desired file formats to text to use Lucene. For example, file formats such as Microsoft Word and StarOffice documents have to be converted to text before they can be added to a Lucene index.

PDF files are no exception, but PDFBox makes it easy to include a PDF document in a Lucene index by supplying a special object that does the integration. A basic PDF document can be converted to a Lucene document with a single statement:


Document doc = LucenePDFDocument.getDocument( file );

This operation parses the PDF document, extracts the text and creates a Lucene document object that can then be added to the index. As mentioned above, PDF documents also contain metadata such as author information and keywords that are important to track when indexing PDF documents. Table 1 shows the fields that PDFBox will populate while creating the Lucene document.

This integration makes it easy for developers to support simple searching and indexing of PDF documents with Lucene. Of course, some applications require more sophisticated text-extraction methods. In that case, the PDFTextStripper class can be used directly, or extended to handle these complex requirements.

By extending this class and overriding the showCharacter() method, many aspects of text extraction can be controlled. For instance, an implementation of this method can use the x, y positioning information to limit the inclusion of certain blocks of text in the extraction. One use might exclude all of the text above a certain y-coordinate value effectively excluding an unwanted document header.

Another example: Oftentimes a group of PDF documents may have been created from forms and the source data are no longer available. In other words, the documents all have some interesting text at similar locations on the page, but the form data used to fill the document out are no longer available. For example, a collection of cover letters that have the name and address at the same location in the document. In this case, an extension of the PDFTextStripper class can be used as a sort of screen-scraping device to extract the desired fields.

More Stories By Ben Litchfield

Ben Litchfield is a business systems consultant within the development & integration practice at LPA Systems. He has been the lead developer of PDFBox for the past two years. Ben holds a BS in Software Engineering from the Rochester Institute of Technology. He has been providing solutions for enterprise applications for the past five years.

Comments (3) View Comments

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


Most Recent Comments
Lucious 03/23/05 02:27:55 PM EST

I can't believe I found this!! I was searching for tools to update pdf files in my java programs. All I could find was commercial tools that would charge for single/multiple CPU and development liscenses and then charge MORE for deployment!! I actually gave up and downloaded the pdf specs (over 1200 pages) to develop tools of my own. I can't wait to start using these tools!

Maulik 03/23/05 08:09:43 AM EST

Great easy-to-follow article for someone who knows next to nothing about integrating Java and PDF. Good job.

Richard Bouchard 03/12/05 09:15:57 PM EST

Excellent article and has great utility.

@ThingsExpo Stories
SYS-CON Events announced today that Suzuki Inc. will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Suzuki Inc. is a semiconductor-related business, including sales of consuming parts, parts repair, and maintenance for semiconductor manufacturing machines, etc. It is also a health care business providing experimental research for...
SYS-CON Events announced today that Ryobi Systems will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Ryobi Systems Co., Ltd., as an information service company, specialized in business support for local governments and medical industry. We are challenging to achive the precision farming with AI. For more information, visit http:...
SYS-CON Events announced today that Daiya Industry will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Daiya Industry specializes in orthotic support systems and assistive devices with pneumatic artificial muscles in order to contribute to an extended healthy life expectancy. For more information, please visit https://www.daiyak...
In his session at @ThingsExpo, Greg Gorman is the Director, IoT Developer Ecosystem, Watson IoT, will provide a short tutorial on Node-RED, a Node.js-based programming tool for wiring together hardware devices, APIs and online services in new and interesting ways. It provides a browser-based editor that makes it easy to wire together flows using a wide range of nodes in the palette that can be deployed to its runtime in a single-click. There is a large library of contributed nodes that help so...
SYS-CON Events announced today that mruby Forum will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. mruby is the lightweight implementation of the Ruby language. We introduce mruby and the mruby IoT framework that enhances development productivity. For more information, visit http://forum.mruby.org/.
SYS-CON Events announced today that N3N will exhibit at SYS-CON's @ThingsExpo, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. N3N’s solutions increase the effectiveness of operations and control centers, increase the value of IoT investments, and facilitate real-time operational decision making. N3N enables operations teams with a four dimensional digital “big board” that consolidates real-time live video feeds alongside IoT sensor data a...
Internet of @ThingsExpo, taking place October 31 - November 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with 21st Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. The Internet of Things (IoT) is the most profound change in personal and enterprise IT since the creation of the Worldwide Web more than 20 years ago. All major researchers estimate there will be tens of billions devic...
Mobile device usage has increased exponentially during the past several years, as consumers rely on handhelds for everything from news and weather to banking and purchases. What can we expect in the next few years? The way in which we interact with our devices will fundamentally change, as businesses leverage Artificial Intelligence. We already see this taking shape as businesses leverage AI for cost savings and customer responsiveness. This trend will continue, as AI is used for more sophistica...
SYS-CON Events announced today that SourceForge has been named “Media Sponsor” of SYS-CON's 21st International Cloud Expo, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. SourceForge is the largest, most trusted destination for Open Source Software development, collaboration, discovery and download on the web serving over 32 million viewers, 150 million downloads and over 460,000 active development projects each and every month.
SYS-CON Events announced today that Nihon Micron will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Nihon Micron Co., Ltd. strives for technological innovation to establish high-density, high-precision processing technology for providing printed circuit board and metal mount RFID tags used for communication devices. For more inf...
SYS-CON Events announced today that Massive Networks, that helps your business operate seamlessly with fast, reliable, and secure internet and network solutions, has been named "Exhibitor" of SYS-CON's 21st International Cloud Expo ®, which will take place on Oct 31 - Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. As a premier telecommunications provider, Massive Networks is headquartered out of Louisville, Colorado. With years of experience under their belt, their team of...
Elon Musk is among the notable industry figures who worries about the power of AI to destroy rather than help society. Mark Zuckerberg, on the other hand, embraces all that is going on. AI is most powerful when deployed across the vast networks being built for Internets of Things in the manufacturing, transportation and logistics, retail, healthcare, government and other sectors. Is AI transforming IoT for the good or the bad? Do we need to worry about its potential destructive power? Or will we...
SYS-CON Events announced today that B2Cloud will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. B2Cloud specializes in IoT devices for preventive and predictive maintenance in any kind of equipment retrieving data like Energy consumption, working time, temperature, humidity, pressure, etc.
What is the best strategy for selecting the right offshore company for your business? In his session at 21st Cloud Expo, Alan Winters, U.S. Head of Business Development at MobiDev, will discuss the things to look for - positive and negative - in evaluating your options. He will also discuss how to maximize productivity with your offshore developers. Before you start your search, clearly understand your business needs and how that impacts software choices.
SYS-CON Events announced today that NetApp has been named “Bronze Sponsor” of SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. NetApp is the data authority for hybrid cloud. NetApp provides a full range of hybrid cloud data services that simplify management of applications and data across cloud and on-premises environments to accelerate digital transformation. Together with their partners, NetApp em...
SYS-CON Events announced today that SIGMA Corporation will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. uLaser flow inspection device from the Japanese top share to Global Standard! Then, make the best use of data to flip to next page. For more information, visit http://www.sigma-k.co.jp/en/.
Agile has finally jumped the technology shark, expanding outside the software world. Enterprises are now increasingly adopting Agile practices across their organizations in order to successfully navigate the disruptive waters that threaten to drown them. In our quest for establishing change as a core competency in our organizations, this business-centric notion of Agile is an essential component of Agile Digital Transformation. In the years since the publication of the Agile Manifesto, the conn...
Real IoT production deployments running at scale are collecting sensor data from hundreds / thousands / millions of devices. The goal is to take business-critical actions on the real-time data and find insights from stored datasets. In his session at @ThingsExpo, John Walicki, Watson IoT Developer Advocate at IBM Cloud, will provide a fast-paced developer journey that follows the IoT sensor data from generation, to edge gateway, to edge analytics, to encryption, to the IBM Bluemix cloud, to Wa...
SYS-CON Events announced today that MIRAI Inc. will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. MIRAI Inc. are IT consultants from the public sector whose mission is to solve social issues by technology and innovation and to create a meaningful future for people.
There is huge complexity in implementing a successful digital business that requires efficient on-premise and cloud back-end infrastructure, IT and Internet of Things (IoT) data, analytics, Machine Learning, Artificial Intelligence (AI) and Digital Applications. In the data center alone, there are physical and virtual infrastructures, multiple operating systems, multiple applications and new and emerging business and technological paradigms such as cloud computing and XaaS. And then there are pe...