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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.dwrp;

import java.util.Map;

import org.directwebremoting.extend.OutboundVariable;
import org.directwebremoting.util.LocalUtil;

/**
 * An OutboundVariable that creates data from Maps.
 * @author Joe Walker [joe at getahead dot ltd dot uk]
 */
public class ObjectJsonOutboundVariable extends JsonNestedOutboundVariable implements MapOutboundVariable
{
    /* (non-Javadoc)
     * @see org.directwebremoting.dwrp.CollectionOutboundVariable#setChildren(java.lang.Object)
     */
    public void setChildren(Map children)
    {
        this.children = children;
    }

    /* (non-Javadoc)
     * @see org.directwebremoting.extend.OutboundVariable#getAssignCode()
     */
    public String getAssignCode()
    {
        return createJsonString(children);
    }

    /**
     * JSON strings sometimes need to be created in a non JSON mode too, so
     * this method is shared between {@link ObjectJsonOutboundVariable} and it's
     * brother {@link ObjectNonJsonOutboundVariable}.
     * @return A JSON string that represents the set of {@link OutboundVariable}s
     */
    protected static String createJsonString(Map children)
    {
        StringBuffer buffer = new StringBuffer();
        buffer.append('{');

        boolean first = true;
        for (Map.Entry entry : children.entrySet())
        {
            String name = entry.getKey();
            OutboundVariable nested = entry.getValue();

            String innerAssignCode = nested.getAssignCode();

            if (!first)
            {
                buffer.append(',');
            }

            // The compact JSON style syntax is only any good for simple names
            // and when we are not recursive
            if (LocalUtil.isSimpleName(name))
            {
                buffer.append(name);
                buffer.append(':');
                buffer.append(innerAssignCode);
            }
            else
            {
                buffer.append('\'');
                buffer.append(name);
                buffer.append("\':");
                buffer.append(innerAssignCode);
            }

            // we don't need to do this one the hard way
            first = false;
        }
        buffer.append('}');

        return buffer.toString();
    }

    /* (non-Javadoc)
     * @see java.lang.Object#toString()
     */
    @Override
    public String toString()
    {
        return "ObjectJsonOutboundVariable:" + children;
    }

    /**
     * The contained variables
     */
    private Map children;
}