LegStar Open Source Mainframe Integration LegStar is a set of development tools and execution runtimes aimed at integrating legacy COBOL applications with Java and SOA technologies. Here are some common use cases: Transform COBOL payloads to Java, XML or JSON LegStar generates COBOL Transformers. At runtime, mainframe data (containing EBCDIC, COMP, etc.) is transformed to Java, XML or JSON. The Le