How to print to the console in GWT

Question

I am debugging a GWT application and I need to print some stuff to the console for testing purposes. System.out.println and GWT.log don\'t work. Do

Answer 1

Just summing up the different possibilities shown in the answer's of mreppy and Strelok in one snippet. I also added one possible workaround for IE exceptions as described here: Why does JavaScript only work after opening developer tools in IE once?

    java.util.logging.Logger logger = Logger.getLogger(this.getClass().getSimpleName());

    native void jsConsoleLog(String message) /*-{
        try {
            console.log(message);
        } catch (e) {
        }
    }-*/;

    private void log(final String message) {
        // Logs to Dev mode console only
        GWT.log(message);
        // Logs to Dev mode and JavaScript console (requires configuration)
        this.logger.log(Level.FINEST, message);
        // Logs to JavaScript console only
        jsConsoleLog(message);

Answer 2

I suggest you use GWT Developer mode It adds a little overhead cause the automatic compilation and code-allocating on the code server, but it's pretty clear when some exceptions arises in client side of your application. I mean, some times chrome console (or firebug or whatever browser debugging built-in tool) doesn't say too much in those situations, trust me, finding a NullPointerException is a pain in the neck when you try to figure out what is happening by alerting your code.

Answer 3

In GWT version 2.6.0, method GWT.log writes message to browser console, you don't need to write native methods.

Answer 4

Quoting the documentation:

Adding GWT logging is really quite simple, as simple as the following code example. However — understanding how logging works, and how to correctly configure it is important, so please do take the time to read the rest of this document.

http://code.google.com/webtoolkit/doc/latest/DevGuideLogging.html

The simplest way to enable logging is:

# In your .gwt.xml file
<inherits name="com.google.gwt.logging.Logging"/>

# In your .java file
Logger logger = java.util.logging.Logger.getLogger("NameOfYourLogger");
logger.log(Level.SEVERE, "this message should get logged");