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Java > Open Source Codes > org > apache > turbine > modules > NavigationLoader


1 package org.apache.turbine.modules;
2
3 /*
4  * Copyright 2001-2004 The Apache Software Foundation.
5  *
6  * Licensed under the Apache License, Version 2.0 (the "License")
7  * you may not use this file except in compliance with the License.
8  * You may obtain a copy of the License at
9  *
10  * http://www.apache.org/licenses/LICENSE-2.0
11  *
12  * Unless required by applicable law or agreed to in writing, software
13  * distributed under the License is distributed on an "AS IS" BASIS,
14  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15  * See the License for the specific language governing permissions and
16  * limitations under the License.
17  */
18
19 import java.util.List JavaDoc;
20
21 import org.apache.commons.logging.Log;
22 import org.apache.commons.logging.LogFactory;
23
24 import org.apache.ecs.ConcreteElement;
25
26 import org.apache.turbine.Turbine;
27 import org.apache.turbine.TurbineConstants;
28 import org.apache.turbine.services.assemblerbroker.AssemblerBrokerService;
29 import org.apache.turbine.services.assemblerbroker.TurbineAssemblerBroker;
30 import org.apache.turbine.util.ObjectUtils;
31 import org.apache.turbine.util.RunData;
32
33 /**
34  * The purpose of this class is to allow one to load and execute
35  * Navigation modules.
36  *
37  * @author <a HREF="mailto:mbryson@mont.mindspring.com">Dave Bryson</a>
38  * @author <a HREF="mailto:hps@intermeta.de">Henning P. Schmiedehausen</a>
39  * @version $Id: NavigationLoader.java,v 1.9.2.3 2004/08/16 22:57:50 henning Exp $
40  */
41 public class NavigationLoader
42     extends GenericLoader
43     implements Loader
44 {
45     /** Logging */
46     private static Log log = LogFactory.getLog(NavigationLoader.class);
47
48     /** The single instance of this class. */
49     private static NavigationLoader instance =
50         new NavigationLoader(Turbine.getConfiguration()
51                          .getInt(TurbineConstants.NAVIGATION_CACHE_SIZE_KEY,
52                                  TurbineConstants.NAVIGATION_CACHE_SIZE_DEFAULT));
53
54     /** The Assembler Broker Service */
55     private static AssemblerBrokerService ab = TurbineAssemblerBroker.getService();
56
57     /**
58      * These ctor's are private to force clients to use getInstance()
59      * to access this class.
60      */
61     private NavigationLoader()
62     {
63         super();
64     }
65
66     /**
67      * These ctor's are private to force clients to use getInstance()
68      * to access this class.
69      */
70     private NavigationLoader(int i)
71     {
72         super(i);
73     }
74
75     /**
76      * Adds an instance of an object into the hashtable.
77      *
78      * @param name Name of object.
79      * @param navigation Navigation to be associated with name.
80      */
81     private void addInstance(String JavaDoc name, Navigation navigation)
82     {
83         if (cache())
84         {
85             this.put(name, (Navigation) navigation);
86         }
87     }
88
89     /**
90      * Attempts to load and execute the external Navigation. This is
91      * used when you want to execute a Navigation which returns its
92      * output via a MultiPartElement instead of out the data.getPage()
93      * value. This allows you to easily chain the execution of
94      * Navigation modules together.
95      *
96      * @param data Turbine information.
97      * @param name Name of object that will execute the navigation.
98      * @exception Exception a generic exception.
99      */
100     public ConcreteElement eval(RunData data, String JavaDoc name)
101             throws Exception JavaDoc
102     {
103         // Execute Navigation
104 return getInstance(name).build(data);
105     }
106
107     /**
108      * Attempts to load and execute the external Navigation.
109      *
110      * @param data Turbine information.
111      * @param name Name of object instance.
112      * @exception Exception a generic exception.
113      */
114     public void exec(RunData data, String JavaDoc name)
115             throws Exception JavaDoc
116     {
117         this.eval(data, name);
118     }
119
120     /**
121      * Pulls out an instance of the object by name. Name is just the
122      * single name of the object. This is equal to getInstance but
123      * returns an Assembler object and is needed to fulfil the Loader
124      * interface.
125      *
126      * @param name Name of object instance.
127      * @return A Layout with the specified name, or null.
128      * @exception Exception a generic exception.
129      */
130     public Assembler getAssembler(String JavaDoc name)
131         throws Exception JavaDoc
132     {
133         return getInstance(name);
134     }
135
136     /**
137      * Pulls out an instance of the Navigation by name. Name is just the
138      * single name of the Navigation.
139      *
140      * @param name Name of requested Navigation
141      * @return A Navigation with the specified name, or null.
142      * @exception Exception a generic exception.
143      */
144     public Navigation getInstance(String JavaDoc name)
145             throws Exception JavaDoc
146     {
147         Navigation navigation = null;
148
149         // Check if the navigation is already in the cache
150 if (cache() && this.containsKey(name))
151         {
152             navigation = (Navigation) this.get(name);
153             log.debug("Found Navigation " + name + " in the cache!");
154         }
155         else
156         {
157             log.debug("Loading Navigation " + name + " from the Assembler Broker");
158
159             try
160             {
161                 if (ab != null)
162                 {
163                     // Attempt to load the navigation
164 navigation = (Navigation) ab.getAssembler(
165                         AssemblerBrokerService.NAVIGATION_TYPE, name);
166                 }
167             }
168             catch (ClassCastException JavaDoc cce)
169             {
170                 // This can alternatively let this exception be thrown
171 // So that the ClassCastException is shown in the
172 // browser window. Like this it shows "Screen not Found"
173 navigation = null;
174             }
175
176             if (navigation == null)
177             {
178                 // If we did not find a screen we should try and give
179 // the user a reason for that...
180 // FIX ME: The AssemblerFactories should each add it's
181 // own string here...
182 List JavaDoc packages = Turbine.getConfiguration()
183                     .getList(TurbineConstants.MODULE_PACKAGES);
184
185                 ObjectUtils.addOnce(packages,
186                         GenericLoader.getBasePackage());
187
188                 throw new ClassNotFoundException JavaDoc(
189                         "\n\n\tRequested Navigation not found: " + name +
190                         "\n\tTurbine looked in the following " +
191                         "modules.packages path: \n\t" + packages.toString() + "\n");
192             }
193             else if (cache())
194             {
195                 // The new instance is added to the cache
196 addInstance(name, navigation);
197             }
198         }
199         return navigation;
200     }
201
202     /**
203      * The method through which this class is accessed.
204      *
205      * @return The single instance of this class.
206      */
207     public static NavigationLoader getInstance()
208     {
209         return instance;
210     }
211 }
212
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