com.acciente.induction.dispatcher.model.ModelPool.java Source code

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Here is the source code for com.acciente.induction.dispatcher.model.ModelPool.java

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/**
 *   Copyright 2009 Acciente, LLC
 *
 *   Acciente, LLC 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 com.acciente.induction.dispatcher.model;

import com.acciente.commons.reflect.ParameterProviderException;
import com.acciente.induction.init.config.Config;
import com.acciente.induction.util.ConstructorNotFoundException;
import com.acciente.induction.util.MethodNotFoundException;
import com.acciente.induction.util.ObjectFactory;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;
import java.lang.reflect.InvocationTargetException;
import java.util.Hashtable;
import java.util.Iterator;
import java.util.Map;

/**
 * Internal.
 * This class manages access to the pool model objects
 *
 * @created Mar 16, 2008
 *
 * @author Adinath Raveendra Raj
 */
public class ModelPool {
    private Config.ModelDefs _oModelDefs;
    private Map _oAppScopeModelMap;
    private ModelFactory _oModelFactory;

    public ModelPool(Config.ModelDefs oModelDefs, ModelFactory oModelFactory) throws MethodNotFoundException,
            InvocationTargetException, ClassNotFoundException, ConstructorNotFoundException,
            ParameterProviderException, IllegalAccessException, InstantiationException {
        _oModelDefs = oModelDefs;
        _oModelFactory = oModelFactory;
        _oAppScopeModelMap = new Hashtable(); // we use a hashtable instead of a HashMap for safe concurrent access

        Log oLog = LogFactory.getLog(ModelPool.class);

        // initialize the models set to initialize on startup
        for (Iterator oIter = oModelDefs.getModelDefList().iterator(); oIter.hasNext();) {
            Config.ModelDefs.ModelDef oModelDef = (Config.ModelDefs.ModelDef) oIter.next();

            if (oModelDef.isApplicationScope() && oModelDef.isInitOnStartUp()) {
                oLog.info("model-pool: initializing model: " + oModelDef.getModelClassName());

                getApplicationScopeModel(oModelDef, null);
            }
        }
    }

    public Object getModel(String sModelClassName, HttpServletRequest oHttpServletRequest)
            throws MethodNotFoundException, InvocationTargetException, ClassNotFoundException,
            ConstructorNotFoundException, ParameterProviderException, IllegalAccessException,
            InstantiationException {
        // first find the model definition object for this model class to determine the scope of this model
        Config.ModelDefs.ModelDef oModelDef = _oModelDefs.getModelDef(sModelClassName);

        if (oModelDef == null) {
            throw new IllegalArgumentException("model-error: no definition for model class: " + sModelClassName);
        }

        // next see if we already have an object instance
        Object oModel;

        if (oModelDef.isApplicationScope()) {
            oModel = getApplicationScopeModel(oModelDef, oHttpServletRequest);
        } else if (oModelDef.isSessionScope()) {
            oModel = getSessionScopeModel(oModelDef, oHttpServletRequest);
        } else if (oModelDef.isRequestScope()) {
            oModel = getRequestScopeModel(oModelDef, oHttpServletRequest);
        } else {
            throw new IllegalArgumentException("model-error: unknown scope for model class: " + sModelClassName);
        }

        return oModel;
    }

    private Object getApplicationScopeModel(Config.ModelDefs.ModelDef oModelDef,
            HttpServletRequest oHttpServletRequest) throws MethodNotFoundException, ClassNotFoundException,
            InvocationTargetException, ParameterProviderException, ConstructorNotFoundException,
            InstantiationException, IllegalAccessException {
        Object oModel;

        oModel = _oAppScopeModelMap.get(oModelDef.getModelClassName());

        // if the model has not yet been created, we use double-checked locking to ensure that
        // separate threads do not simultaneously instantiate multiple instances of the model
        // I do not think this code will have the potential incorrectness introduced by the
        // double-checked locking, since the model map only contains fully constructed objects
        if (oModel == null) {
            synchronized (oModelDef) {
                // check again to see if it is still not null, we may have waited on the lock while some
                // other thread was creating this model
                oModel = _oAppScopeModelMap.get(oModelDef.getModelClassName());

                // if it is still null then go ahead an create the model
                if (oModel == null) {
                    oModel = _oModelFactory.createModel(oModelDef, oHttpServletRequest);

                    _oAppScopeModelMap.put(oModelDef.getModelClassName(), oModel);
                }
            }
        } else {
            if (_oModelFactory.isModelStale(oModelDef, oModel)) {
                synchronized (oModelDef) {
                    Object oPreviousModel = oModel;

                    oModel = _oModelFactory.createModel(oModelDef, oHttpServletRequest);

                    _oAppScopeModelMap.put(oModelDef.getModelClassName(), oModel);

                    ObjectFactory.destroyObject(oPreviousModel);
                }
            }
        }

        return oModel;
    }

    private Object getSessionScopeModel(Config.ModelDefs.ModelDef oModelDef, HttpServletRequest oHttpServletRequest)
            throws MethodNotFoundException, ClassNotFoundException, InvocationTargetException,
            ParameterProviderException, ConstructorNotFoundException, InstantiationException,
            IllegalAccessException {
        HttpSession oHttpSession;
        Object oModel;

        oHttpSession = oHttpServletRequest.getSession(true);

        oModel = oHttpSession.getAttribute(oModelDef.getModelClassName());

        if (oModel == null) {
            synchronized (oHttpSession) {
                oModel = oHttpSession.getAttribute(oModelDef.getModelClassName());

                if (oModel == null) {
                    oModel = _oModelFactory.createModel(oModelDef, oHttpServletRequest);

                    oHttpSession.setAttribute(oModelDef.getModelClassName(), oModel);
                }
            }
        } else {
            synchronized (oModel) {
                if (_oModelFactory.isModelStale(oModelDef, oModel)) {
                    Object oPreviousModel = oModel;

                    oModel = _oModelFactory.createModel(oModelDef, oHttpServletRequest);

                    oHttpSession.setAttribute(oModelDef.getModelClassName(), oModel);

                    ObjectFactory.destroyObject(oPreviousModel);
                }
            }
        }

        return oModel;
    }

    private Object getRequestScopeModel(Config.ModelDefs.ModelDef oModelDef, HttpServletRequest oRequest)
            throws MethodNotFoundException, ClassNotFoundException, InvocationTargetException,
            ParameterProviderException, ConstructorNotFoundException, InstantiationException,
            IllegalAccessException {
        // a request scope object essentially only lasts for the duration of the method invocation so
        // there is no need to pool a copy of the model instance for reuse
        return _oModelFactory.createModel(oModelDef, oRequest);
    }
}

// EOF