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DWR is easy Ajax for Java. It makes it simple to call Java code directly from Javascript. It gets rid of almost all the boiler plate code between the web browser and your Java code.

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/*
 * Copyright 2005 Joe Walker
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.directwebremoting.convert;

import java.beans.IntrospectionException;
import java.beans.PropertyDescriptor;
import java.util.Map;

import org.directwebremoting.ConversionException;
import org.directwebremoting.extend.PlainProperty;
import org.directwebremoting.extend.Property;
import org.directwebremoting.extend.PropertyDescriptorProperty;

/**
 * A special case of BeanConverter that doesn't convert StackTraces
 * @author Joe Walker [joe at getahead dot ltd dot uk]
 */
public class ExceptionConverter extends BeanConverter
{
    /* (non-Javadoc)
     * @see org.directwebremoting.convert.BasicBeanConverter#getPropertyDescriptors(java.lang.Class, boolean, boolean)
     */
    @Override
    public Map getPropertyMapFromClass(Class type, boolean readRequired, boolean writeRequired) throws ConversionException
    {
        Map descriptors = super.getPropertyMapFromClass(type, readRequired, writeRequired);
        descriptors.put("javaClassName", new PlainProperty("javaClassName", type.getName()));

        // Make sure Throwable's standard properties are added
        // (fix for Bean Introspector peculiarities)
        try
        {
            fixMissingThrowableProperty(descriptors, "message", "getMessage");
            fixMissingThrowableProperty(descriptors, "cause", "getCause");
        }
        catch (IntrospectionException ex)
        {
            throw new ConversionException(type, ex);
        }

        return descriptors;
    }

    /**
     * Make sure Throwable's standard properties are added
     * (fix for Bean Introspector peculiarities)
     * @param descriptors The Map of the known descriptors
     * @param name The name of the property to add
     * @param readMethodName A method name to use when getting said property
     * @throws IntrospectionException If we fail to build a PropertyDescriptor
     */
    protected void fixMissingThrowableProperty(Map descriptors, String name, String readMethodName) throws IntrospectionException
    {
        if (!descriptors.containsKey(name) && isAllowedByIncludeExcludeRules(name))
        {
            PropertyDescriptor descriptor = new PropertyDescriptor(name, Throwable.class, readMethodName, null);
            descriptors.put(name, new PropertyDescriptorProperty(descriptor));
        }
    }
}