Java IoT Authors: Elizabeth White, Yeshim Deniz, Liz McMillan, Hollis Tibbetts, TJ Randall

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 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
Cloud based infrastructure deployment is becoming more and more appealing to customers, from Fortune 500 companies to SMEs due to its pay-as-you-go model. Enterprise storage vendors are able to reach out to these customers by integrating in cloud based deployments; this needs adaptability and interoperability of the products confirming to cloud standards such as OpenStack, CloudStack, or Azure. As compared to off the shelf commodity storage, enterprise storages by its reliability, high-availabil...
The security needs of IoT environments require a strong, proven approach to maintain security, trust and privacy in their ecosystem. Assurance and protection of device identity, secure data encryption and authentication are the key security challenges organizations are trying to address when integrating IoT devices. This holds true for IoT applications in a wide range of industries, for example, healthcare, consumer devices, and manufacturing. In his session at @ThingsExpo, Lancen LaChance, vic...
In the next forty months – just over three years – businesses will undergo extraordinary changes. The exponential growth of digitization and machine learning will see a step function change in how businesses create value, satisfy customers, and outperform their competition. In the next forty months companies will take the actions that will see them get to the next level of the game called Capitalism. Or they won’t – game over. The winners of today and tomorrow think differently, follow different...
The IoT industry is now at a crossroads, between the fast-paced innovation of technologies and the pending mass adoption by global enterprises. The complexity of combining rapidly evolving technologies and the need to establish practices for market acceleration pose a strong challenge to global enterprises as well as IoT vendors. In his session at @ThingsExpo, Clark Smith, senior product manager for Numerex, will discuss how Numerex, as an experienced, established IoT provider, has embraced a ...
SYS-CON Events announced today that Super Micro Computer, Inc., a global leader in Embedded and IoT solutions, will exhibit at SYS-CON's 20th International Cloud Expo®, which will take place on June 7-9, 2017, at the Javits Center in New York City, NY. Supermicro (NASDAQ: SMCI), the leading innovator in high-performance, high-efficiency server technology, is a premier provider of advanced server Building Block Solutions® for Data Center, Cloud Computing, Enterprise IT, Hadoop/Big Data, HPC and ...
The Internet of Things (IoT), in all its myriad manifestations, has great potential. Much of that potential comes from the evolving data management and analytic (DMA) technologies and processes that allow us to gain insight from all of the IoT data that can be generated and gathered. This potential may never be met as those data sets are tied to specific industry verticals and single markets, with no clear way to use IoT data and sensor analytics to fulfill the hype being given the IoT today.
Web Real-Time Communication APIs have quickly revolutionized what browsers are capable of. In addition to video and audio streams, we can now bi-directionally send arbitrary data over WebRTC's PeerConnection Data Channels. With the advent of Progressive Web Apps and new hardware APIs such as WebBluetooh and WebUSB, we can finally enable users to stitch together the Internet of Things directly from their browsers while communicating privately and securely in a decentralized way.
Donna Yasay, President of HomeGrid Forum, today discussed with a panel of technology peers how certification programs are at the forefront of interoperability, and the answer for vendors looking to keep up with today's growing industry for smart home innovation. "To ensure multi-vendor interoperability, accredited industry certification programs should be used for every product to provide credibility and quality assurance for retail and carrier based customers looking to add ever increasing num...
The Open Connectivity Foundation (OCF), sponsor of the IoTivity open source project, and AllSeen Alliance, which provides the AllJoyn® open source IoT framework, today announced that the two organizations’ boards have approved a merger under the OCF name and bylaws. This merger will advance interoperability between connected devices from both groups, enabling the full operating potential of IoT and representing a significant step towards a connected ecosystem.
Manufacturers are embracing the Industrial Internet the same way consumers are leveraging Fitbits – to improve overall health and wellness. Both can provide consistent measurement, visibility, and suggest performance improvements customized to help reach goals. Fitbit users can view real-time data and make adjustments to increase their activity. In his session at @ThingsExpo, Mark Bernardo Professional Services Leader, Americas, at GE Digital, discussed how leveraging the Industrial Internet a...
More and more brands have jumped on the IoT bandwagon. We have an excess of wearables – activity trackers, smartwatches, smart glasses and sneakers, and more that track seemingly endless datapoints. However, most consumers have no idea what “IoT” means. Creating more wearables that track data shouldn't be the aim of brands; delivering meaningful, tangible relevance to their users should be. We're in a period in which the IoT pendulum is still swinging. Initially, it swung toward "smart for smar...
SYS-CON Events announced today that LeaseWeb USA, a cloud Infrastructure-as-a-Service (IaaS) provider, will exhibit at the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. LeaseWeb is one of the world's largest hosting brands. The company helps customers define, develop and deploy IT infrastructure tailored to their exact business needs, by combining various kinds cloud solutions.
A completely new computing platform is on the horizon. They’re called Microservers by some, ARM Servers by others, and sometimes even ARM-based Servers. No matter what you call them, Microservers will have a huge impact on the data center and on server computing in general. Although few people are familiar with Microservers today, their impact will be felt very soon. This is a new category of computing platform that is available today and is predicted to have triple-digit growth rates for some ...
November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Penta Security is a leading vendor for data security solutions, including its encryption solution, D’Amo. By using FPE technology, D’Amo allows for the implementation of encryption technology to sensitive data fields without modification to schema in the database environment. With businesses having their data become increasingly more complicated in their mission-critical applications (such as ERP, CRM, HRM), continued ...
SYS-CON Events announced today that Cloudbric, a leading website security provider, will exhibit at the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Cloudbric is an elite full service website protection solution specifically designed for IT novices, entrepreneurs, and small and medium businesses. First launched in 2015, Cloudbric is based on the enterprise level Web Application Firewall by Penta Security Sys...
SYS-CON Events announced today that SoftNet Solutions will exhibit at the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. SoftNet Solutions specializes in Enterprise Solutions for Hadoop and Big Data. It offers customers the most open, robust, and value-conscious portfolio of solutions, services, and tools for the shortest route to success with Big Data. The unique differentiator is the ability to architect and ...
Most people haven’t heard the word, “gamification,” even though they probably, and perhaps unwittingly, participate in it every day. Gamification is “the process of adding games or game-like elements to something (as a task) so as to encourage participation.” Further, gamification is about bringing game mechanics – rules, constructs, processes, and methods – into the real world in an effort to engage people. In his session at @ThingsExpo, Robert Endo, owner and engagement manager of Intrepid D...
WebRTC adoption has generated a wave of creative uses of communications and collaboration through websites, sales apps, customer care and business applications. As WebRTC has become more mainstream it has evolved to use cases beyond the original peer-to-peer case, which has led to a repeating requirement for interoperability with existing infrastructures. In his session at @ThingsExpo, Graham Holt, Executive Vice President of Daitan Group, will cover implementation examples that have enabled ea...
SYS-CON Events announced today that Enzu will exhibit at the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Enzu’s mission is to be the leading provider of enterprise cloud solutions worldwide. Enzu enables online businesses to use its IT infrastructure to their competitive advantage. By offering a suite of proven hosting and management services, Enzu wants companies to focus on the core of their online busine...
SYS-CON Events announced today that Roundee / LinearHub will exhibit at the WebRTC Summit at @ThingsExpo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. LinearHub provides Roundee Service, a smart platform for enterprise video conferencing with enhanced features such as automatic recording and transcription service. Slack users can integrate Roundee to their team via Slack’s App Directory, and '/roundee' command lets your video conference ...