gson.toJson() throws StackOverflowError

That problem is that you have a circular reference.

In the BomModule class you are referencing to:

private Collection<BomModule> parentModules;
private Collection<BomModule> subModules;

That self reference to BomModule, obviously, not liked by GSON at all.

A workaround is just set the modules to null to avoid the recursive looping. This way I can avoid the StackOverFlow-Exception.

item.setModules(null);

Or mark the fields you don't want to show up in the serialized json by using the transient keyword, eg:

private transient Collection<BomModule> parentModules;
private transient Collection<BomModule> subModules;

I had this problem when I had a Log4J logger as a class property, such as:

private Logger logger = Logger.getLogger(Foo.class);

This can be solved by either making the logger static or simply by moving it into the actual function(s).

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