BeanRule


1   package org.sapia.validator;
2   
3   import org.apache.commons.beanutils.PropertyUtils;
4   
5   /**
6    * This abstract rule class provides the behavior that handles
7    * dynamic attributes (using the BeanUtils library from the
8    * Jakarta project).
9    * <p>
10   * This class allows to set the name of an accessor that will be
11   * used against the current object in the validation context
12   * stack. The accessor is invoked on the object, and the return
13   * value will be the object that is validated. If no accessor is
14   * specified, the current object on the stack will be validated.
15   * <p>
16   * If there is no object on the stack, or if the object returned
17   * by the accessor is <code>null</code>, an instance of this class
18   * can optionally throw an <code>IllegalStateException</code>; for this
19   * to occur, inheriting classes must call this class' 
20   * <code>throwExceptionOnNull(true)</code> method.
21   * <p>
22   * Classes inheriting from this class must implement the <code>doValidate()</code>
23   * method, which is passed the object to validate. This implies that implementations
24   * must "know" what type of object to expect as a parameter.
25   * 
26   * @see #validate(ValidationContext)
27   * @see #doValidate(Object)
28   * @see #throwExceptionOnNull(boolean)
29   * 
30   * @author Yanick Duchesne
31   * <dl>
32   * <dt><b>Copyright:</b><dd>Copyright &#169; 2002-2003 <a HREF="http://www.sapia-oss.org">Sapia Open Source Software</a>. All Rights Reserved.</dd></dt>
33   * <dt><b>License:</b><dd>Read the license.txt file of the jar or visit the
34   *        <a HREF="http://www.sapia-oss.org/license.html">license page</a> at the Sapia OSS web site</dd></dt>
35   * </dl>
36   */
37  public abstract class BeanRule extends Rule {
38    protected String   _attribute;
39    private boolean  _throw;
40    
41    /**
42     * Sets the name of the accessor that should be invoked on
43     * the current object in the validation context's stack.
44     * 
45     * @param attr the name of the accessor to invoke.
46     * @see ValidationContext
47     */
48    public void setAttribute(String   attr) {
49      _attribute = attr;
50    }
51  
52    /**
53     * If called with <code>true</code> as an argument, indicates
54     * that this instance should throw an <code>IllegalStateException</code>
55     * if there is no object on the validation context's stack, or
56     * if the accessor invoked on the current object on stack returns
57     * <code>null</code>.
58     * 
59     * @param throwExc if <code>true</code>, an <code>IllegalStateException</code>
60     * will be thrown by this instance's <code>validate()</code> method if
61     * there is no current object on stack, or if the accessor returns <code>null</code>.
62     */
63    protected void throwExceptionOnNull(boolean throwExc) {
64      _throw = throwExc;
65    }
66  
67    /**
68     * If this instance was specified an accessor (through the 
69     * <code>setAttribute()</code> method), the accessor is invoked
70     * on the current object in the given validation context.
71     * <p>
72     * If no accessor was specified, the current object remains.
73     * <p>
74     * If the current object is null (no object in stack), or if the accessor returns 
75     * <code>null</code>, and if the instance's <code>throwExceptionOnNull(true)</code>
76     * method was called, then this method throws an <code>IllegalStateException</code>.
77     * <p>
78     * If no problem is detected, this method calls its <code>doValidate()<code> method,
79     * passing it either: a) the current object on the stack; or b) the object returned
80     * by the specified accessor.
81     * <p>
82     * If the <code>doValidate()</code> method returns <code>false</code>, this instance
83     * signals a validation error to the validation context's status.
84     * 
85     * @see #setAttribute(String)
86     * @see #doValidate(Object)
87     * 
88     * @see org.sapia.validator.Rule#validate(ValidationContext)
89     */
90    public final void validate(ValidationContext context) {
91      Object   toValidate;
92  
93      if (_attribute == null) {
94        toValidate = context.get();
95  
96        if ((toValidate == null) && _throw) {
97          throw new IllegalStateException  ("No object on validation context stack at " + qualifiedName());
98        }
99      } else {
100       try {
101         toValidate = PropertyUtils.getProperty(context.get(), _attribute);
102 
103         if ((toValidate == null) && _throw) {
104           throw new IllegalStateException  ("Attribute " + _attribute
105             + " evaluates to null on rule " + qualifiedName());
106         }
107       } catch (Throwable   err) {
108         context.getStatus().error(this, err);
109 
110         return;
111       }
112     }
113 
114     if (!doValidate(toValidate)) {
115       context.getStatus().error(this);
116     }
117   }
118 
119   /**
120    * This template method must be implemented by inheriting classes, and is called
121    * by this class' <code>validate()</code>.
122    * <p>
123    * Inheriting classes should implement their validation logic in this method, and
124    * return <code>false</code> if the validation fails. 
125    * 
126    * @param toValidate the object to validate.
127    *
128    * @return <code>false</code> if the validation logic implemented by this method
129    * detects a validation error.
130    */
131   protected abstract boolean doValidate(Object   toValidate);
132 }
133
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