As a Java integration developer, your job is to design and develop software for new and old systems using Java and customize any existing software to meet the changing needs of your employer. Each application you make may require connections to commerce platforms, access to external databases, and an interface that works well with the core platform. In many cases, companies ask you to continuously improve an existing code base or modify a program to address new issues. The complex programming needs of the Java integration developer position mean that many employers offer training, so you do not need to be fluent with every system they use.