001    package org.apache.turbine.services.assemblerbroker.util.java;
002    
003    
004    /*
005     * Licensed to the Apache Software Foundation (ASF) under one
006     * or more contributor license agreements.  See the NOTICE file
007     * distributed with this work for additional information
008     * regarding copyright ownership.  The ASF licenses this file
009     * to you under the Apache License, Version 2.0 (the
010     * "License"); you may not use this file except in compliance
011     * with the License.  You may obtain a copy of the License at
012     *
013     *   http://www.apache.org/licenses/LICENSE-2.0
014     *
015     * Unless required by applicable law or agreed to in writing,
016     * software distributed under the License is distributed on an
017     * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
018     * KIND, either express or implied.  See the License for the
019     * specific language governing permissions and limitations
020     * under the License.
021     */
022    
023    import java.util.Collections;
024    import java.util.HashMap;
025    import java.util.List;
026    import java.util.Map;
027    
028    import org.apache.commons.lang.StringUtils;
029    import org.apache.commons.logging.Log;
030    import org.apache.commons.logging.LogFactory;
031    import org.apache.turbine.modules.Assembler;
032    import org.apache.turbine.modules.GenericLoader;
033    import org.apache.turbine.modules.Loader;
034    import org.apache.turbine.services.assemblerbroker.util.AssemblerFactory;
035    
036    /**
037     * A screen factory that attempts to load a java class from
038     * the module packages defined in the TurbineResource.properties.
039     *
040     * @author <a href="mailto:leon@opticode.co.za">Leon Messerschmidt</a>
041     * @author <a href="mailto:hps@intermeta.de">Henning P. Schmiedehausen</a>
042     * @version $Id: JavaBaseFactory.java 1078552 2011-03-06 19:58:46Z tv $
043     */
044    public abstract class JavaBaseFactory<T extends Assembler>
045        implements AssemblerFactory<T>
046    {
047        /** A vector of packages. */
048        private static List<String> packages = GenericLoader.getPackages();
049    
050        /** Logging */
051        protected Log log = LogFactory.getLog(this.getClass());
052    
053        /**
054         * A cache for previously obtained Class instances, which we keep in order
055         * to reduce the Class.forName() overhead (which can be sizable).
056         */
057        private final Map<String, Class<T>> classCache =
058            Collections.synchronizedMap(new HashMap<String, Class<T>>());
059    
060        /**
061         * Get an Assembler.
062         *
063         * @param packageName java package name
064         * @param name name of the requested Assembler
065         * @return an Assembler
066         */
067        @SuppressWarnings("unchecked")
068        public T getAssembler(String packageName, String name)
069        {
070            T assembler = null;
071    
072            log.debug("Class Fragment is " + name);
073    
074            if (StringUtils.isNotEmpty(name))
075            {
076                for (String p : packages)
077                {
078                    StringBuffer sb = new StringBuffer();
079    
080                    sb.append(p).append('.').append(packageName).append('.').append(name);
081    
082                    String className = sb.toString();
083    
084                    log.debug("Trying " + className);
085    
086                    try
087                    {
088                        Class<T> servClass = classCache.get(className);
089                        if(servClass == null)
090                        {
091                            servClass = (Class<T>) Class.forName(className.toString());
092                            classCache.put(className, servClass);
093                        }
094                        assembler = servClass.newInstance();
095                        break; // for()
096                    }
097                    catch (ClassNotFoundException cnfe)
098                    {
099                        // Do this so we loop through all the packages.
100                        log.debug(className + ": Not found");
101                    }
102                    catch (NoClassDefFoundError ncdfe)
103                    {
104                        // Do this so we loop through all the packages.
105                        log.debug(className + ": No Class Definition found");
106                    }
107                    catch (ClassCastException cce)
108                    {
109                        // This means trouble!
110                        // Alternatively we can throw this exception so
111                        // that it will appear on the client browser
112                        log.error("Could not load "+className, cce);
113                        break; // for()
114                    }
115                    catch (InstantiationException ine)
116                    {
117                        // This means trouble!
118                        // Alternatively we can throw this exception so
119                        // that it will appear on the client browser
120                        log.error("Could not load "+className, ine);
121                        break; // for()
122                    }
123                    catch (IllegalAccessException ilae)
124                    {
125                        // This means trouble!
126                        // Alternatively we can throw this exception so
127                        // that it will appear on the client browser
128                        log.error("Could not load "+className, ilae);
129                        break; // for()
130                    }
131                    // With ClassCastException, InstantiationException we hit big problems
132                }
133            }
134            log.debug("Returning: " + assembler);
135    
136            return assembler;
137        }
138    
139        /**
140         * Get the loader for this type of assembler
141         *
142         * @return a Loader
143         */
144        public abstract Loader<T> getLoader();
145    
146        /**
147         * Get the size of a possibly configured cache
148         *
149         * @return the size of the cache in bytes
150         */
151        public int getCacheSize()
152        {
153            return getLoader().getCacheSize();
154        }
155    }