Struts example source code file (GxpInstance.java)

This example Struts source code file (GxpInstance.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Struts tags/keywords

class, class, error, exception, function, gxpinstance, gxpinstance, interface, interface, log, logging, map, object, object, objectfactory, override, util

The Struts GxpInstance.java source code

/*
 * $Id$
 *
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.apache.struts2.views.gxp;

import com.google.common.base.Function;
import com.google.common.collect.MapMaker;
import com.opensymphony.xwork2.ObjectFactory;
import com.opensymphony.xwork2.inject.Inject;

import java.util.Map;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 * Struts 2 to GXP adapter that uses instances of GXP Interfaces, as created by
 * the {@link ObjectFactory}. Can be used to write a GXP or create a
 * HtmlClosure. Pulls non-constructor GXP parameters from Struts 2 value stack.
 *
 * @author David P. Baker
 */
public class GxpInstance extends Gxp {

    private static final Logger logger = Logger.getLogger(GxpInstance.class.getCanonicalName());

    private Class<?> gxpInterface;
    private Class<?> gxpInstance;
    private ObjectFactory objectFactory;

    GxpInstance(Class<?> gxpClass) {
        super(gxpClass,
                lookupMethodByName(getNestedClass(gxpClass, "Interface"), "write"),
                lookupMethodByName(getNestedClass(gxpClass, "Interface"), "getGxpClosure"));
        this.gxpInterface = getNestedClass(gxpClass, "Interface");
        this.gxpInstance = getNestedClass(gxpClass, "Instance");
    }

    private static Class<?> getNestedClass(Class clazz, String nestedClassName) {
        for (Class<?> nested : clazz.getDeclaredClasses()) {
            if (nestedClassName.equals(nested.getSimpleName())) {
                return nested;
            }
        }
        throw new IllegalArgumentException(String.format("Cannot find class %s.%s", clazz.getCanonicalName(), nestedClassName));
    }

    /**
     * {@inheritDoc}
     * <p> This implementation uses the {@link ObjectFactory} to try to create an
     * instance of the {@code Interface} class that is nested within the GXP
     * class. If that doesn't work, it falls back to trying to use the
     * {@code ObjectFactory} to create an instance of the nested {@code Instance}
     * class, in case there is no binding for the {@code Interface}.
     */
    @Override
    protected Object getGxpInstance() {
        try {
            return objectFactory.buildBean(gxpInterface, null);
        } catch (Exception e) {
            logger.log(
                    Level.INFO, "Error instantiating {0}; trying {1}",
                    new Object[]{gxpInterface.getCanonicalName(), gxpInstance.getCanonicalName(),});
            try {
                return objectFactory.buildBean(gxpInstance, null);
            } catch (Exception e1) {
                throw new RuntimeException(String.format("Error instantiating %s",
                        gxpInterface.getCanonicalName(), gxpInstance.getCanonicalName()),
                        e1);
            }
        }
    }

    @Override
    public Class<?> getGxpClass() {
        return this.gxpInterface;
    }

    private static final Map<Class classToGxpInstance = new MapMaker().weakKeys().softValues()
            .makeComputingMap(new Function<Class() {
                public GxpInstance apply(Class<?> from) {
                    return classToGxpInstance.containsKey(from) ? classToGxpInstance.get(from) : new GxpInstance(from);
                }
            });

    private static final Map<String, GxpInstance> pathToGxpInstance = new MapMaker().softValues()
            .makeComputingMap(new Function<String, GxpInstance>() {
                public GxpInstance apply(String from) {
                    return pathToGxpInstance.containsKey(from) ? pathToGxpInstance.get(from) : getInstance(getGxpClassForPath(from));
                }
            });

    /**
     * Looks up Gxp instance for GXP with given path.
     */
    public static GxpInstance getInstance(String gxpPath) {
        try {
            return pathToGxpInstance.get(gxpPath);
        } catch (RuntimeException e) {
            if (e.getCause() instanceof ClassNotFoundException) {
                // Couldn't find or load the GXP class.  Return null.
                // It would be simpler if classToGxp.create() could return null,
                // but the contract of ReferenceCache doesn't allow it to.
                return null;
            }
            throw e;
        }
    }

    /**
     * Looks up {@code GxpInstance} instance for the given GXP class.
     */
    public static GxpInstance getInstance(Class<?> gxpClass) {
        return classToGxpInstance.get(gxpClass);
    }

    @Inject
    public void setObjectFactory(ObjectFactory objectFactory) {
        this.objectFactory = objectFactory;
    }

}