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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.extend;

import java.beans.PropertyDescriptor;
import java.lang.reflect.Member;

import org.directwebremoting.ConversionException;

/**
 * Describes some way to get or set a bit of data on an object.
 * There are obvious Properties for a getter/setter pair
 * {@link PropertyDescriptorProperty}, for a field {@link FieldProperty} and
 * also for a constructor parameter {@link ConstructorProperty}. There is a
 * {@link PlainProperty} for when we have a collection of Properties of a bean,
 * but need to augment it in some way and {@link NestedProperty} which is used
 * when we're digging into nested generic type info.
 * It would be nice if {@link PropertyDescriptor}, and the various reflection
 * types like {@link Member} had a common supertype, but they don't. In a way
 * this is it.
 * @author Joe Walker [joe at getahead dot ltd dot uk]
 */
public interface Property
{
    /**
     * Gets the name of this property
     * @return The property name
     */
    String getName();

    /**
     * What type does this property
     * @return The type of object that will be returned by {@link #getValue(Object)}
     */
    Class getPropertyType();

    /**
     * Get the value of this property of the passed in java bean
     * @param bean The bean to introspect
     * @return The value assigned to this property of the passed in bean
     * @throws ConversionException If the reflection access fails
     */
    Object getValue(Object bean) throws ConversionException;

    /**
     * Set the value of this property of the passed in java bean
     * @param bean The bean to introspect
     * @param value The value assigned to this property of the passed in bean
     * @throws ConversionException If the reflection access fails
     */
    void setValue(Object bean, Object value) throws ConversionException;

    /**
     * Properties may have children where we have nested generic type info.
     * For example with {@code setFoo(List> x)} we can
     * find type information about the nested bits of generic data.
     * 
     * If calling this method then you almost certainly want to check for an
     * overridden property as defined by the {@link ConverterManager} by calling
     * {@link ConverterManager#checkOverride(Property)}
     * @param index Generally the parameter offset.
     * @return A Property to describe the nested bit of data
     */
    Property createChild(int index) throws ConversionException;
}