Why is this an issue?

Java 7’s try-with-resources structure automatically handles closing the resources that the try itself opens. Thus, adding an explicit close() call is redundant and potentially confusing.

Noncompliant code example

try (PrintWriter writer = new PrintWriter(process.getOutputStream())) {
  String contents = file.contents();
  writer.write(new Gson().toJson(new MyObject(contents)));
  writer.flush();
  writer.close();  // Noncompliant
}

Compliant solution

try (PrintWriter writer = new PrintWriter(process.getOutputStream())) {
  String contents = file.contents();
  writer.write(new Gson().toJson(new MyObject(contents)));
  writer.flush();
}