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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.util.Collection;

/**
 * A helper for implementing OutboundVariable when you have children
 * @author Joe Walker [joe at getahead dot ltd dot uk]
 */
public abstract class NestedOutboundVariable implements OutboundVariable
{
    /**
     * OutboundVariable may need to create variables or deny outlining
     */
    protected NestedOutboundVariable(OutboundContext context)
    {
        this.context = context;
    }

    /**
     * We setup the children later than construction time so we can check for
     * recursive references.
     */
    public void setChildren(Collection children)
    {
        this.children = children;
    }

    /**
     * The objects that we contain
     */
    public Collection getChildren()
    {
        return children;
    }

    /**
     * @return The {@link #getDeclareCode()}s of all our children
     */
    protected String getChildDeclareCodes()
    {
        StringBuilder builder = new StringBuilder();

        for (OutboundVariable child : children)
        {
            builder.append(child.getDeclareCode());
        }

        return builder.toString();
    }

    /**
     * @return The {@link #getBuildCode()}s of all our children
     */
    protected String getChildBuildCodes()
    {
        StringBuilder builder = new StringBuilder();

        for (OutboundVariable child : children)
        {
            builder.append(child.getBuildCode());
        }

        return builder.toString();
    }

    /* (non-Javadoc)
     * @see org.directwebremoting.OutboundVariable#getReference()
     */
    public OutboundVariable getReferenceVariable()
    {
        if (reference == null)
        {
            reference = new NonNestedOutboundVariable(getVariableName());
        }

        referenced = true;
        return reference;
    }

    /**
     * If outline then we need a variable so we can be referred to
     */
    protected String getVariableName()
    {
        if (varName == null)
        {
            varName = context.getNextVariableName();
        }

        return varName;
    }

    /**
     * Is there something (like JSON mode) that forces us to inline or maybe we
     * are referred to by multiple other things
     */
    protected boolean isInline()
    {
        return context.isJsonMode() || !referenced;
    }

    /**
     * Are we in JSON mode, and therefore must quote property names?
     */
    public boolean isJsonMode()
    {
        return context.isJsonMode();
    }

    /**
     * Are there references to us (forcing outline)?
     */
    private boolean referenced = false;

    /**
     * When we create buildCode and declareCode, what do we need to add?
     */
    private Collection children;

    /**
     * Does anything refer to us?
     */
    private OutboundVariable reference;

    /**
     * If we get recursive, this is the variable name we declare
     */
    private String varName;

    /**
     * The conversion context, from which we get variable names
     */
    private final OutboundContext context;
}