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Twain has long allowed Win32 programmers to integrate imaging devices into their applications at no cost. Twain allows us to capture images from seemingly disparate devices like flatbed scanners, fingerprint readers, Web cams, and digital cameras. The standard allows Aunt Emma to take a picture at a wedding, acquire the images onto her PC that afternoon, and send the edited pictures to the entire family that night. Thus, when interfacing with image devices, application developers can free themselves from working with arcane and many times proprietary interfaces, and instead concentrate on one interface.
Twain functionality would greatly benefit the Win32 Java community, but, alas, these open-standards benefits have been available for years in the Win32 world, but, because of Java's platform independence, not the Java world. In this article I show how you too can talk Twain by introducing an architecture that integrates a Java 1.4 Swing application with a simple JNI (Java Native Interface)-based package.
Let's start by discussing the architectural layers involved in retrieving a JPEG file from your favorite Twain-enabled device. Twain natively acquires a Win32 DIB (Device-Independent Bitmap), but we will retrieve a Java readable JPEG file. Retrieving such a file involves five architectural layers:
org.scavino.jtwain source code shown later in this article.
Thankfully all these technologies are free.
Now that we have thought out the architectural layers, we now self impose a process. As an OOAD (object-oriented analysis and design) instructor, I insist on an inception phase and mission statement when developing new APIs. My mission is to build the smallest API possible that will satisfy the specified requirements. What requirements you may ask? Rather than enumerating countless never-to-be-read shall statements, I use the Rational Unified Process (RUP) for guidance. As RUP is a use-case-focused process, we start with our "Acquire a Twain Image" use-case, which has one primary flow consisting of several steps to accomplish our result.
You will find the entire use-case here. The document is intentionally human readable and devoid of code mumbo-jumbo. If we write our requirements in plain English, our stakeholders will take the time to understand our use-case. When analysts, management, and testers understand the use-cases, we receive software on time and on budget. Let me paraphrase the primary use-case as follows:
Acquire Twain image steps (Happy Day Scenario):