System.out.println（）消息在客户端GWT模块中调用时会在哪里发生？

Question

When I write messages to log (ie com.allen_sauer.gwt.log.client.Log#debug ) I can see them in Chrome->F12->Console or (during debug) in IDEA->Debug->Dev Mode. But if the System.out.println() was used in IDEA the messages appear in the same place as the logged ones, but what about when I am not debugging? where do they go?

Answer 1

System.out.println() are just removed by the compiler in production mode.

If you want to check just create this simple module:

public class Foo implements EntryPoint {

  public void onModuleLoad() {

    System.out.println("Hello World!");
  }
}

And look at the generated javascript.

Answer 2

The preferred way to do logging (at development time) is com.google.gwt.core.client.GWT.log() . Messages logged this way will also wind up in your browser's console like you mention. Likely System.out.println is mapped to the same functionality for convenience. From the GWT.log Javadoc:

Logs a message to the development shell logger in Development Mode, or to the console in Super Dev Mode. Calls are optimized out in Production Mode.