17 January 2020
The JDT (Java Development Tools) is an important part of Eclipse IDE but it can also be used without Eclipse.
For example the Spring Tools 4, which is nowadays a cross-platform tool (Visual Studio Code, Eclipse IDE, …), is highly using the JDT behind the scene. If you would like to know more, I recommend you this podcast episode: Spring Tools lead Martin Lippert
A second known example is the Java Formatter that is also part of the JDT. Since a long time there are maven and gradle plugins that performs the same formatting as Eclipse IDE but as part of the build (often with the possibly to break the build when the code is wrongly formatted).
Reusing the JDT has been made easier since 2017 when it was decided to publish each release and its dependencies on maven central (with following groupId: org.eclipse.jdt, org.eclipse.platform). Stephan Herrmann did a lot of work to achieve this goal. I blogged about this: Use the Eclipse Java Development Tools in a Java SE application and I have pushed a simple example the Java Formatter is used in a simple main(String[]) method built by a classic minimal Maven project: java-formatter.
When using the JDT in an headless application, two cases needs to be distinguished:
Some features (the parser, the formatter…) can be used in a simple Java main method.
Other features (search index, AST rewriter…) require a workspace. This imply that the code run inside an OSGi runtime.
To illustrate this aspect, I took some of the examples provided by the site www.programcreek.com in the blog post series Eclipse JDT Tutorials and I adapted them so that each code snippet can be executed inside a JUnit test. This is the Programcreek examples project.
I have split the unit-tests into two projects:
programcreek-standalone for the one that do not require OSGi. The maven project is really simple (using the default convention everywhere)
programcreek-osgi for the one that must run inside an OSGi runtime. The bnd maven plugins are configured in the pom.xml to take care of the OSGi stuff.
If you run the test with Maven, it will work out-of-the box.
If you would like to run them inside an IDE, you should use one that starts OSGi when executing the tests (in the same way the maven build is doing it). To get a bnd aware IDE, you can use Eclipse IDE for Java Developers with the additional plugin Bndtools installed, but there are other possibilities.
Source code can be found on GitHub: programcreek-examples