Emulate a non supported class in GWT

To develop with GWT, only a Java SDK subset is available, plus GWT specific classes. Mainly (look at JRE emulation for details):

• java.lang
• java.lang.annotation
• java.util
• java.io
• java.sql

This emulation mechanism is used to bypass GWT limitations, such as, no reflection due to the JavaScript translation.

As GWT support only a few JDK classes, as developers, we often miss something to do the work. To fill the gap, it is easy to use emulation to implement a full GWT compliant class. To do so, the best practice is to create a directory out of the class path named super, that will contain the emulations. The name of this directory has no importance, it is just done that way in GWT sources. Your package structure takes place under this directory. At this place, a module must be created, it contains only a super-source directive as following:

<super-source path="source_location"/>

path attribute provides the root directory of simulated classes. For example, to simulate a class from package java.io:

The reason to not include emulated classes in classpath, is, these classes must declare the package name from the class they emulate, not the package previously defined:

package java.io;

Now, to use these classes, you should only inherits from the emulation module.