License3j is a Java library that can be used to create and check license files. This way Java programs can enforce the users to compensate their use of the software in the form of a payment. This is the usual way when closed source programs are distributed. License management alone does not guarantee that the program will not be stolen, pirated or used in any illegal way. However license management may increase the difficulty to use the program illegal and therefore may drive users to become customers. There is another effect of license management, which is legal. Using license management illegal users have less probability to successfully claim their use was based on the lack or false knowledge of license conditions. License3j is an open source license manager that you can use free of charge. The license terms covered by LGPL.