The TurboJPEG shared library can optionally be built with a Java Native Interface (JNI) wrapper, which allows the library to be loaded and used directly from Java applications. The Java front end for this (the TurboJPEG Java API) is defined in classes located under org/libjpegturbo/turbojpeg. The source code for these Java classes is licensed under a BSD-style license, so the files can be incorporated directly into both open source and proprietary projects without restriction. A Java archive (JAR) file containing these classes is also shipped with the “official” distribution packages of libjpeg-turbo.
TJComp.java, TJDecomp.java, and TJTran.java, which should be located in the same directory as this README file, demonstrate how to use the TurboJPEG Java API to compress, decompress, and transform JPEG images in memory.
The TurboJPEG Java API defines convenience methods that can allocate image buffers or instantiate classes to hold the result of compress, decompress, or transform operations. However, if you use these methods, then be mindful of the amount of new data you are creating on the heap. It may be necessary to manually invoke the garbage collector to prevent heap exhaustion or to prevent performance degradation. Background garbage collection can kill performance, particularly in a multi-threaded environment. (Java pauses all threads when the GC runs.)
The TurboJPEG Java API always gives you the option of pre-allocating your own source and destination buffers, which allows you to re-use those buffers for compressing/decompressing multiple images. If the image sequence you are compressing or decompressing consists of images of the same size, then pre-allocating the buffers is recommended.
The TurboJPEG Java classes will look for the TurboJPEG JNI library (libturbojpeg.so, libturbojpeg.dylib, or turbojpeg.dll) in the system library paths or in any paths specified in LD_LIBRARY_PATH (Un*x), DYLD_LIBRARY_PATH (Mac), PATH (Windows), or the java.library.path Java system property. Failing this, on Un*x and Mac systems, the classes will look for the JNI library under the library directory configured when libjpeg-turbo was built. If that library directory is /opt/libjpeg-turbo/lib32, then /opt/libjpeg-turbo/lib64 is also searched, and vice versa.