Re: How To : Write a GWT Generator

Thanks to you, it just took me 15 minutes :)

On Monday, December 10, 2007 10:10:11 PM UTC-5, Riyaz Mansoor wrote:

It took me a week to write my first generator (with help - thanks mP).
Am hoping that this How-To will save time for others.

This How-To is targetted for newbies and upwards.

A generator that returns a properties file as a Map.

Usage :: Map myPropertiesMap = (Map) GWT.create(MyPropertiesMap.class)
Valid :: HashMap myPropertiesMap = (HashMap)
GWT.create(MyPropertiesMap.class)


*** Step 1 ***  Write a marker interface/class.
**************

In the following example, "extends Map" is not necessary. I have
included it as it is more *descriptive*. This interface/class *must*
reside in a "client side" folder as it needs to be accessed by the
GWTCompiler to generate client side code (example location:
module.client[.generator])

file :: PropertyMap.java
========================

package rm.gwt.core.client.generator;


import java.util.Map;


public interface PropertyMap extends Map {

}





*** Step 2 ***  Write your generator.
**************

Writes out the source code for the new class. The source code is self
explanatory. This class *must* *not* reside in a "client side" folder.
This class can use *any* class available to it - it is *not* limited
to the GWT runtimes. By convention, it is placed in the module.rebind
folder.


file :: PropertyMapGenerator.java
=================================


package rm.gwt.core.rebind;


import com.google.gwt.core.ext.Generator;
import com.google.gwt.core.ext.GeneratorContext;
import com.google.gwt.core.ext.TreeLogger;
import com.google.gwt.core.ext.UnableToCompleteException;

import com.google.gwt.core.ext.typeinfo.JClassType;
import com.google.gwt.core.ext.typeinfo.TypeOracle;

import com.google.gwt.user.rebind.ClassSourceFileComposerFactory;
import com.google.gwt.user.rebind.SourceWriter;

import java.io.PrintWriter;

import java.util.Enumeration;
import java.util.HashMap;
import java.util.ResourceBundle;


/**
 * GWT generator that returns a <code>Map</code> (<code>HashMap</
code>)
 * from a properties file.
 * Usage :: Map myPropertyMap = (Map) GWT.create(MyPropertyMap.class);
 * Where :: MyProperMap extends PropertyMap (marker interface)
 *       :: MyPropertyMap.properties is in same package as
MyPropertyMap.java
 *
 * @author riyaz....@gmail.com
 * @version 2007.12-1
 */
public class PropertyMapGenerator extends Generator {


    /** Simple name of class to be generated */
    private String className = null;

    /** Package name of class to be generated */
    private String packageName = null;

    /** Fully qualified class name passed into GWT.create() */
    private String typeName = null;


    // inherited generator method
    public String generate(TreeLogger logger, GeneratorContext
context,
                String typeName) throws UnableToCompleteException {

        this.typeName = typeName;
        TypeOracle typeOracle = context.getTypeOracle();

        try {

            // get classType and save instance variables
            JClassType classType = typeOracle.getType(typeName);
            packageName = classType.getPackage().getName();
            className = classType.getSimpleSourceName() + "Wrapper";
            // Generate class source code
            generateClass(logger, context);

        } catch (Exception e) {

            // record to logger that Map generation threw an exception
            logger.log(TreeLogger.ERROR, "PropertyMap ERROR!!!", e);

        }

        // return the fully qualifed name of the class generated
        return packageName + "." + className;

    }

    /**
     * Generate source code for new class. Class extends
<code>HashMap</code>.
     *
     * @param logger Logger object
     * @param context Generator context
     */
    private void generateClass(TreeLogger logger, GeneratorContext
context) {

        // get print writer that receives the source code
        PrintWriter printWriter = null;
        printWriter = context.tryCreate(logger, packageName, className);
        // print writer if null, source code has ALREADY been generated,
return
        if (printWriter == null) return;

        // init composer, set class properties, create source writer
        ClassSourceFileComposerFactory composer = null;
        composer = new ClassSourceFileComposerFactory(packageName,
className);
        composer.setSuperclass("java.util.HashMap");
        SourceWriter sourceWriter = null;
        sourceWriter = composer.createSourceWriter(context, printWriter);

        // generator constructor source code
        generateConstructor(sourceWriter);
        // close generated class
        sourceWriter.outdent();
        sourceWriter.println("}");

        // commit generated class
        context.commit(logger, printWriter);

    }

    /**
     * Generate source code for the default constructor. Create
default
     * constructor, call super(), and insert all key/value pairs from
     * the resoruce bundle.
     *
     * @param sourceWriter Source writer to output source code
     */
    private void generateConstructor(SourceWriter sourceWriter) {

        // init resource bundle
        ResourceBundle bundle = ResourceBundle.getBundle(typeName);

        // start constructor source generation
        sourceWriter.println("public " + className + "() { ");
        sourceWriter.indent();
        sourceWriter.println("super();");

        // add statements to pub key/value pairs from the resrouce bundle
        for (Enumeration<String> keys = bundle.getKeys();
                    keys.hasMoreElements();) {
            String key = keys.nextElement();
            sourceWriter.println("put(\"" + Generator.escape(key) +
"\", \""
                                 + bundle.getString(key) + "\");");
        }

        // end constructor source generation
        sourceWriter.outdent();
        sourceWriter.println("}");

    }

}




*** Step 3 ***  Update the module.gwt.xml file
**************

Include generator info as the last element within your xml file.

Module.xml (sample) ::
======================

<?xml version="1.0" encoding="UTF-8"?>
<module>
    <inherits name="com.google.gwt.user.User"/>
    <generate-with class="rm.gwt.core.rebind.PropertyMapGenerator" >
        <when-type-assignable
class="rm.gwt.core.client.generator.PropertyMap"/>
    </generate-with>
</module>




*** Step 4 *** Write sample files. *Must* be in the same folder.
**************

file :: MyPropertiesMap.java
============================
package <package>;
import <imports>;
public interface MyPropertiesMap extends PropertiesMap {}

file :: MyPropertiesMap.properties
==================================
key1=value1
key2=value2


END

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