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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one
3    * or more contributor license agreements.  See the NOTICE file
4    * distributed with this work for additional information
5    * regarding copyright ownership.  The ASF licenses this file
6    * to you under the Apache License, Version 2.0 (the
7    * "License"); you may not use this file except in compliance
8    * with the License.  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,
13   * software distributed under the License is distributed on an
14   * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
15   * KIND, either express or implied.  See the License for the
16   * specific language governing permissions and limitations
17   * under the License.
18   */
19  package org.apache.myfaces.webapp;
20  
21  import java.util.logging.Level;
22  import java.util.logging.Logger;
23  
24  import javax.el.ELContext;
25  import javax.el.ExpressionFactory;
26  import javax.el.MethodExpression;
27  import javax.el.ValueExpression;
28  import javax.faces.FacesException;
29  import javax.faces.context.ExternalContext;
30  import javax.servlet.ServletContext;
31  
32  /**
33   * Initializes MyFaces in a JSP 2.0 (or less) environment.
34   * 
35   */
36  public class Jsp20FacesInitializer extends AbstractFacesInitializer
37  {
38      /**
39       * The logger instance for this class.
40       */
41      //private static final Log log = LogFactory.getLog(Jsp20FacesInitializer.class);
42      private static final Logger log = Logger.getLogger(Jsp20FacesInitializer.class.getName());
43  
44      /**
45       * The ExpressionFactory implementation of the EL-RI.
46       */
47      private static final String EL_RI_EXPRESSION_FACTORY_IMPL = "com.sun.el.ExpressionFactoryImpl";
48  
49      /**
50       * Jasper's ExpressionFactory implementation.
51       */
52      private static final String JASPER_EL_EXPRESSION_FACTORY_IMPL = "org.apache.el.ExpressionFactoryImpl";
53  
54      /**
55       * All known ExpressionFactory implementations.
56       */
57      private static final String[] KNOWN_EXPRESSION_FACTORIES =
58              new String[] { EL_RI_EXPRESSION_FACTORY_IMPL, JASPER_EL_EXPRESSION_FACTORY_IMPL };
59  
60      @Override
61      protected void initContainerIntegration(ServletContext servletContext, ExternalContext externalContext)
62      {
63          if (log.isLoggable(Level.INFO))
64          {
65              log.info("This application isn't running in a JSP 2.1 container.");
66          }
67  
68          // It's possible to run MyFaces in a JSP 2.0 Container, but the user has to provide
69          // the ExpressionFactory implementation to use as there is no JspApplicationContext
70          // we could ask for. Having said that, though, the user only has to provide it, if
71          // there is no known ExpressionFactory available (i.e. if neither
72          // "com.sun.el.ExpressionFactoryImpl" nor "org.apache.el.ExpressionFactoryImpl"
73          // are available).
74          ExpressionFactory expressionFactory = getUserDefinedExpressionFactory(externalContext);
75  
76          if (expressionFactory == null) {
77              if (log.isLoggable(Level.INFO)) {
78                  log.info("Either you haven't specified the ExpressionFactory implementation, or an " 
79                          + "error occured while instantiating the implementation you've specified. "
80                          + "However, attempting to load a known implementation.");
81              }
82  
83              expressionFactory = findExpressionFactory(KNOWN_EXPRESSION_FACTORIES);
84              if (expressionFactory == null)
85              { // if we still haven't got a valid implementation
86                  if (log.isLoggable(Level.SEVERE))
87                  {
88                      log.severe("No valid ExpressionFactory implementation is available "
89                              + "but that's required as this application isn't running in a JSP 2.1 container.");
90                  }
91  
92                  // use a dummy implementation that reports the error again
93                  expressionFactory = new ErrorExpressionFactory();
94              }
95          }
96  
97          if (log.isLoggable(Level.FINE))
98          {
99              log.fine("The following ExpressionFactory implementation will " + "be used: '" + expressionFactory + "'.");
100         }
101 
102         buildConfiguration(servletContext, externalContext, expressionFactory);
103     }
104 
105     /**
106      * Attempts to find a valid ExpressionFactory implementation. Each of the given
107      * "ExpressionFactory implementation candidates" will be tried to instantiate. If an attempt succeeded, the
108      * ExpressionFactory implementation will be returned (i.e. the first valid ExpressionFactory implementation will be
109      * returned) and if no attempt succeeds, <code>null</code> will be returned.
110      * 
111      * @param expressionFactoryClassNames
112      *            "ExpresionFactory implementation candidates"
113      * 
114      * @return the newly created ExpressionFactory implementation, or <code>null</code>, if there is no valid
115      *         implementation
116      */
117     private static ExpressionFactory findExpressionFactory(String[] expressionFactoryClassNames)
118     {
119         for (String expressionFactoryClassName : expressionFactoryClassNames)
120         {
121             ExpressionFactory expressionFactory = loadExpressionFactory(expressionFactoryClassName);
122             if (expressionFactory != null)
123             {
124                 return expressionFactory;
125             }
126         }
127 
128         return null;
129     }
130 
131     /**
132      * Dummy implementation informing the user that there is no valid ExpressionFactory implementation available. This
133      * class makes it easier for the user to understand why the application crashes. Otherwise he would have to deal
134      * with NullPointerExceptions.
135      * 
136      */
137     private class ErrorExpressionFactory extends ExpressionFactory
138     {
139 
140         @Override
141         public Object coerceToType(Object obj, Class<?> targetType)
142         {
143             throw new FacesException("No valid ExpressionFactory implementation is available "
144                     + "but that's required as this application isn't running in a JSP 2.1 container.");
145         }
146 
147         @Override
148         public MethodExpression createMethodExpression(ELContext context, String expression,
149                                                        Class<?> expectedReturnType, Class<?>[] expectedParamTypes)
150         {
151             throw new FacesException("No valid ExpressionFactory implementation is available "
152                     + "but that's required as this application isn't running in a JSP 2.1 container.");
153         }
154 
155         @Override
156         public ValueExpression createValueExpression(Object instance, Class<?> expectedType)
157         {
158             throw new FacesException("No valid ExpressionFactory implementation is available "
159                     + "but that's required as this application isn't running in a JSP 2.1 container.");
160         }
161 
162         @Override
163         public ValueExpression createValueExpression(ELContext context, String expression, Class<?> expectedType)
164         {
165             throw new FacesException("No valid ExpressionFactory implementation is available "
166                     + "but that's required as this application isn't running in a JSP 2.1 container.");
167         }
168 
169     }
170 
171 }