org.directwebremoting.extend.OutboundContext Maven / Gradle / Ivy

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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.HashMap;
import java.util.Map;

import org.directwebremoting.util.LocalUtil;

/**
 * We need to keep track of stuff while we are converting on the way out to
 * prevent recurrsion.
 * This class helps track the conversion process.
 * @author Joe Walker [joe at getahead dot ltd dot uk]
 */
public final class OutboundContext
{
    /**
     * JDK14: Can use IdentityHashMap directly
     * Since map needs to have referencial equality rather than object equality
     * this constructor tries to use java.util.IdentityHashMap (>=1.4), and
     * failing that falls back on wrapper objects in a HashMap.
     */
    public OutboundContext()
    {
        // We can only assign to map once, so we use this as a staging post.
        Map assign;

        try
        {
            assign = (Map) LocalUtil.classForName("java.util.IdentityHashMap").newInstance();
            referenceWrappers = false;
        }
        catch (Exception ex)
        {
            assign = new HashMap();
            referenceWrappers = true;
        }

        map = assign;
    }

    /**
     * Have we already converted an object?
     * @param object The object to check
     * @return How it was converted last time or null if we've not seen it before
     */
    public OutboundVariable get(Object object)
    {
        Object key = object;
        if (referenceWrappers)
        {
            key = new ReferenceWrapper(object);
        }

        return (OutboundVariable) map.get(key);
    }

    /**
     * @param object We have converted a new object, remember it
     * @param ss How the object was converted
     */
    public void put(Object object, OutboundVariable ss)
    {
        Object key = object;
        if (referenceWrappers)
        {
            key = new ReferenceWrapper(object);
        }

        map.put(key, ss);
    }

    /**
     * Create a new variable name to keep everything we declare separate
     * @return A new unique variable name
     */
    public String getNextVariableName()
    {
        String varName = OUTBOUND_VARIABLE_PREFIX + nextVarIndex;
        nextVarIndex++;

        return varName;
    }

    /* (non-Javadoc)
     * @see java.lang.Object#toString()
     */
    public String toString()
    {
        return map.toString();
    }

    /**
     * The prefix for outbound variable names the we generate
     */
    private static final String OUTBOUND_VARIABLE_PREFIX = "s";

    /**
     * The map of objects to how we converted them last time
     */
    private final Map map;

    /**
     * Tells if we are to wrap objects in the map to get referencial equality.
     */
    private boolean referenceWrappers;

    /**
     * What index do we tack on the next variable name that we generate
     */
    private int nextVarIndex = 0;

    /**
     * Wrapper class that makes sure that equals() and hashCode() uses
     * referencial equality on the wrapped object. This is used when
     * we can't have a IdentityHashMap in map.
     */
    private static class ReferenceWrapper
    {
        /**
         * @param object The object to wrap
         */
        protected ReferenceWrapper(Object object)
        {
            this.object = object;
        }

        /* (non-Javadoc)
         * @see java.lang.Object#hashCode()
         */
        public int hashCode()
        {
            return System.identityHashCode(object);
        }

        /* (non-Javadoc)
         * @see java.lang.Object#equals(java.lang.Object)
         */
        public boolean equals(Object obj)
        {
            if (!(obj instanceof ReferenceWrapper))
            {
                return false;
            }

            ReferenceWrapper that = (ReferenceWrapper) obj;
            return this.object == that.object;
        }

        /**
         * My wrapped object.
         */
        private Object object;
    }
}