How to call GWT java function from Javascript?

Question

Is it possible to call Java (GWT) methods from Javascript? It is also unclear from documentation. All samples here http://code.google.com/intl/ru/webtoolkit/doc/latest/DevGuideCodingBasicsJSNI.html demonstrate calling java functions from JSNI (not JS) functions.

UPDATE 1

Here is a Java code:

public class Test_GoogleWeb_JSNI_02 implements EntryPoint {
/**
 * This is the entry point method.
 */
public void onModuleLoad() {
}

public static void Callee() {
    Window.alert("Callee");
}
}

Here is caller button samples in html:

<input type='button' value='Call' onclick='Test02()'>

And here are some functions I tried and which were not worked:

<script type="text/javascript">

    function Test01() {
        @com.inthemoon.tests.client.Test_GoogleWeb_JSNI_02::Callee()();
    }

    function Test02() {
        com.inthemoon.tests.client.Test_GoogleWeb_JSNI_02::Callee()();
    }


</script>

UPDATE 2

The following worked.

Java preparation:

public void onModuleLoad() {
    Prepare();
}

public static native void Prepare() /*-{
    $doc.calleeRunner = @com.inthemoon.tests.client.Test_GoogleWeb_JSNI_02::Callee();
}-*/;

public static void Callee() {
    Window.alert("Callee");
}

Caller:

function Test03() {
        document.calleeRunner();
}

Is there a better way?

Solution

your example is not going to work, since you are trying to use JSNI in some external script. If you want to call something from external JS you need to use approach described in this question or use GWT exporter

UPDATE:

The safest way to expose the GWT stuff is to wrap invocation in some other function. For example:

    public native void expose()/*-{
    $wnd.exposedMethod = function(param){
         @com.my.MyClass::myFunction(*)(param);
    }
}-*/;

Otherwise you might encounter some strange bugs in production mode=)

Comments

[Dims]

Thanks! Is you update concerns my Update2? I mean do you suggest not to write [email protected]::myFunction(*)(param)? Why?

[jusio]

It might prevent GWT from doing some basic optimization. Performance impact most likely won't be big, but you should keep it in mind. Also your way will only work with exposure of static methods, it most likely break if you try to call some instance method.

[chelo_c]

can you call a javascrypt method that returns an object? and use that object?

[haui]

The exposed function should be wrapped with the $entry(...) function, see gwtproject.org/doc/latest/DevGuideCodingBasicsJSNI.html#call‌​ing: `$wnd.exposedMethod = $entry(function(param) {...});

[sushmitha shenoy]

Can non static methods be called this way?