Some methods and constructors require that the returned resource is closed. This includes user methods/constructors annotated with @MustBeClosed and some additional well-known APIs. (Some further well-known APIs are covered by a different check, StreamResourceLeak.)

This is enforced by checking that invocations occur within the resource variable initializer of a try-with-resources statement:

try (AutoCloseable resource = createTheResource()) {
  doSomething(resource);
}

or the return statement of another method annotated with @MustBeClosed:

@MustBeClosed
AutoCloseable createMyResource() {
  return createTheResource();
}

To support legacy code, the following pattern is also supported:

AutoCloseable resource = createTheResource();
try {
  doSomething(resource);
} finally {
  resource.close();
}