Coverage Report - org.apache.tapestry.binding.ExpressionBinding
 
Classes in this File Line Coverage Branch Coverage Complexity
ExpressionBinding
0%
0/53
0%
0/18
3.5
 
 1  
 // Copyright 2004, 2005 The Apache Software Foundation
 2  
 //
 3  
 // Licensed under the Apache License, Version 2.0 (the "License");
 4  
 // you may not use this file except in compliance with the License.
 5  
 // You may obtain a copy of the License at
 6  
 //
 7  
 //     http://www.apache.org/licenses/LICENSE-2.0
 8  
 //
 9  
 // Unless required by applicable law or agreed to in writing, software
 10  
 // distributed under the License is distributed on an "AS IS" BASIS,
 11  
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 12  
 // See the License for the specific language governing permissions and
 13  
 // limitations under the License.
 14  
 
 15  
 package org.apache.tapestry.binding;
 16  
 
 17  
 import ognl.Node;
 18  
 import ognl.enhance.ExpressionAccessor;
 19  
 import org.apache.hivemind.Location;
 20  
 import org.apache.tapestry.BindingException;
 21  
 import org.apache.tapestry.IComponent;
 22  
 import org.apache.tapestry.coerce.ValueConverter;
 23  
 import org.apache.tapestry.services.ExpressionCache;
 24  
 import org.apache.tapestry.services.ExpressionEvaluator;
 25  
 
 26  
 /**
 27  
  * Implements a dynamic binding, based on evaluating an expression using an expression language.
 28  
  * Tapestry's default expression language is the <a href="http://www.ognl.org/">Object Graph
 29  
  * Navigation Language </a>.
 30  
  *
 31  
  * @see org.apache.tapestry.services.ExpressionEvaluator
 32  
  * @author Howard Lewis Ship
 33  
  * @since 2.2
 34  
  */
 35  
 
 36  
 public class ExpressionBinding extends AbstractBinding
 37  
 {
 38  
     /**
 39  
      * The root object against which the nested property name is evaluated.
 40  
      */
 41  
 
 42  
     private final IComponent _root;
 43  
 
 44  
     /**
 45  
      * If true, then the binding is invariant.
 46  
      */
 47  
 
 48  0
     private boolean _invariant = false;
 49  
 
 50  
     /**
 51  
      * Parsed OGNL expression.
 52  
      */
 53  
 
 54  
     private Node _parsedExpression;
 55  
 
 56  
     /**
 57  
      * Compiled OGNL expression.
 58  
      */
 59  
 
 60  
     private ExpressionAccessor _accessor;
 61  
 
 62  
     /**
 63  
      * Flag set to true once the binding has initialized.
 64  
      */
 65  
 
 66  
     private boolean _initialized;
 67  
 
 68  
     /**
 69  
      * @since 4.0
 70  
      */
 71  
 
 72  
     private ExpressionEvaluator _evaluator;
 73  
 
 74  
     /** @since 4.0 */
 75  
 
 76  
     private ExpressionCache _cache;
 77  
 
 78  
     /**
 79  
      * Used to detect previous failed attempts at writing values when compiling expressions so
 80  
      * that as many expressions as possible can be fully compiled into their java byte form when
 81  
      * all objects in the expression are available.
 82  
      */
 83  
     private boolean _writeFailed;
 84  
 
 85  
     /**
 86  
      * Creates a {@link ExpressionBinding} from the root object and an OGNL expression.
 87  
      *
 88  
      * @param description
 89  
      *          Used by superclass constructor - {@link AbstractBinding#AbstractBinding(String, org.apache.tapestry.coerce.ValueConverter, org.apache.hivemind.Location)}.
 90  
      * @param location
 91  
      *          Used by superclass constructor - {@link AbstractBinding#AbstractBinding(String, org.apache.tapestry.coerce.ValueConverter, org.apache.hivemind.Location)}.
 92  
      * @param valueConverter
 93  
      *          Used by superclass constructor - {@link AbstractBinding#AbstractBinding(String, org.apache.tapestry.coerce.ValueConverter, org.apache.hivemind.Location)}.
 94  
      * @param root
 95  
      *          The object this binding should be resolved against.
 96  
      * @param expression
 97  
      *          The string expression.
 98  
      * @param evaluator
 99  
      *          Evaluator used to parse and run the expression.
 100  
      * @param cache
 101  
      *          Expression cache which does efficient caching of parsed expressions.
 102  
      */
 103  
     public ExpressionBinding(String description, Location location, ValueConverter valueConverter,
 104  
                              IComponent root, String expression, ExpressionEvaluator evaluator,
 105  
                              ExpressionCache cache)
 106  
     {
 107  0
         super(expression, valueConverter, location);
 108  
 
 109  0
         _root = root;
 110  0
         _evaluator = evaluator;
 111  0
         _cache = cache;
 112  0
     }
 113  
 
 114  
     /**
 115  
      * Gets the value of the property path, with the assistance of the {@link ExpressionEvaluator}.
 116  
      *
 117  
      * @throws BindingException
 118  
      *             if an exception is thrown accessing the property.
 119  
      */
 120  
 
 121  
     public Object getObject()
 122  
     {
 123  0
         initialize();
 124  
 
 125  0
         return resolveExpression();
 126  
     }
 127  
 
 128  
     private Object resolveExpression()
 129  
     {
 130  
         try
 131  
         {
 132  0
             if (_accessor == null && !_writeFailed)
 133  
             {
 134  0
                 _parsedExpression = (Node)_cache.getCompiledExpression(_root, _description);
 135  0
                 _accessor = _parsedExpression.getAccessor();
 136  
             }
 137  
 
 138  0
             if (_accessor != null)
 139  0
                 return _evaluator.read(_root, _accessor);
 140  
 
 141  0
             return _evaluator.readCompiled(_root, _parsedExpression);
 142  
         }
 143  0
         catch (Throwable t)
 144  
         {
 145  0
             throw new BindingException(t.getMessage(), this, t);
 146  
         }
 147  
     }
 148  
 
 149  
     /**
 150  
      * Returns true if the binding is expected to always return the same value.
 151  
      */
 152  
 
 153  
     public boolean isInvariant()
 154  
     {
 155  0
         initialize();
 156  
 
 157  0
         return _invariant;
 158  
     }
 159  
 
 160  
     /**
 161  
      * Sets up the helper object, but also optimizes the property path and determines if the binding
 162  
      * is invarant.
 163  
      */
 164  
 
 165  
     private void initialize()
 166  
     {
 167  0
         if (_initialized)
 168  0
             return;
 169  
 
 170  0
         _initialized = true;
 171  
 
 172  
         try
 173  
         {
 174  0
             _parsedExpression = (Node)_cache.getCompiledExpression(_description);
 175  0
             _invariant = _evaluator.isConstant(_description);
 176  
         }
 177  0
         catch (Exception ex)
 178  
         {
 179  0
             throw new BindingException(ex.getMessage(), this, ex);
 180  0
         }
 181  0
     }
 182  
 
 183  
     /**
 184  
      * Updates the property for the binding to the given value.
 185  
      *
 186  
      * @throws BindingException
 187  
      *             if the property can't be updated (typically due to an security problem, or a
 188  
      *             missing mutator method).
 189  
      */
 190  
 
 191  
     public void setObject(Object value)
 192  
     {
 193  0
         initialize();
 194  
 
 195  0
         if (_invariant)
 196  0
             throw createReadOnlyBindingException(this);
 197  
 
 198  
         try
 199  
         {
 200  0
             if (_accessor == null)
 201  
             {
 202  0
                 _evaluator.writeCompiled(_root, _parsedExpression, value);
 203  
 
 204  0
                 if (!_writeFailed)
 205  
                 {    
 206  
                     // re-parse expression as compilation may be possible now that it potentially has a value
 207  
                     try {
 208  0
                         _parsedExpression = (Node)_cache.getCompiledExpression(_root, _description);
 209  
 
 210  0
                         _accessor = _parsedExpression.getAccessor();
 211  0
                     } catch (Throwable t) {
 212  
 
 213  
                         // ignore re-read failures as they aren't supposed to be happening now anyways
 214  
                         // and a more user friendly version will be available if someone actually calls
 215  
                         // getObject
 216  
 
 217  
                         // if writing fails then we're probably screwed...so don't do it again
 218  0
                         if (value != null)
 219  0
                             _writeFailed = true;
 220  0
                     }
 221  
                 }
 222  
             } else
 223  
             {
 224  0
                 _evaluator.write(_root, _accessor, value);
 225  
             }
 226  
         }
 227  0
         catch (Throwable ex)
 228  
         {
 229  0
             throw new BindingException(ex.getMessage(), this, ex);
 230  0
         }
 231  0
     }
 232  
 
 233  
     /**
 234  
      * Returns the a String representing the property path. This includes the
 235  
      * {@link IComponent#getExtendedId() extended id}of the root component and the property path
 236  
      * ... once the binding is used, these may change due to optimization of the property path.
 237  
      */
 238  
 
 239  
     public String toString()
 240  
     {
 241  0
         StringBuffer buffer = new StringBuffer();
 242  
 
 243  0
         buffer.append("ExpressionBinding[");
 244  0
         buffer.append(_root.getExtendedId());
 245  
 
 246  0
         if (_description != null)
 247  
         {
 248  0
             buffer.append(' ');
 249  0
             buffer.append(_description);
 250  
         }
 251  
 
 252  0
         buffer.append(']');
 253  
 
 254  0
         return buffer.toString();
 255  
     }
 256  
 
 257  
     /** @since 4.0 */
 258  
     public Object getComponent()
 259  
     {
 260  0
         return _root;
 261  
     }
 262  
 }