beanelresolver.java

java属性邦定的（JSR-295）的一个实现

     * <p>If this resolver was constructed in read-only mode, this method will
     * always throw <code>PropertyNotWritableException</code>.</p>
     *
     * <p>The provided property name will first be coerced to a
     * <code>String</code>. If property is a writable property of 
     * <code>base</code> (as per the JavaBeans Specification), the setter 
     * method is called (passing <code>value</code>). If the property exists
     * but does not have a setter, then a
     * <code>PropertyNotFoundException</code> is thrown. If the property
     * does not exist, a <code>PropertyNotFoundException</code> is thrown.</p>
     *
     * @param context The context of this evaluation.
     * @param base The bean on which to set the property.
     * @param property The name of the property to set. Will be coerced to
     *     a <code>String</code>.
     * @param val The value to be associated with the specified key.
     * @throws NullPointerException if context is <code>null</code>.
     * @throws PropertyNotFoundException if <code>base</code> is not
     *     <code>null</code> and the specified property does not exist.
     * @throws PropertyNotWritableException if this resolver was constructed
     *     in read-only mode, or if there is no setter for the property.
     * @throws ELException if an exception was thrown while performing
     *     the property or variable resolution. The thrown exception
     *     must be included as the cause property of this exception, if
     *     available.
     */
    public void setValue(ELContext context,
                         Object base,
                         Object property,
                         Object val) {

        if (context == null) {
            throw new NullPointerException();
        }

        if (base == null || property == null){
            return;
        }

        if (isReadOnly) {
            throw new PropertyNotWritableException(
                        ELUtil.getExceptionMessageString(context,
                            "resolverNotwritable",
                            new Object[] { base.getClass().getName() }));
        } 

        BeanProperty bp = getBeanProperty(context, base, property);
        Method method = bp.getWriteMethod();
        if (method == null) {
            throw new PropertyNotWritableException(
                        ELUtil.getExceptionMessageString(context,
                            "propertyNotWritable",
                            new Object[] { base.getClass().getName(),
                                           property.toString()}));
        }

        try {
            method.invoke(base, new Object[] {val});
            context.setPropertyResolved(true);
        } catch (ELException ex) {
            throw ex;
        } catch (InvocationTargetException ite) {
            throw new ELException(ite.getCause());
        } catch (Exception ex) {
            if (null == val) {
                val = "null";
            }
            String message = ELUtil.getExceptionMessageString(context,
                    "setPropertyFailed",
                    new Object[] { property.toString(),
                                   base.getClass().getName(), val });
            throw new ELException(message, ex);
        }
    }

    /**
     * If the base object is not <code>null</code>, returns whether a call
     * to {@link #setValue} will always fail.
     *
     * <p>If the base is not <code>null</code>, the 
     * <code>propertyResolved</code> property of the <code>ELContext</code>
     * object must be set to <code>true</code> by this resolver, before
     * returning. If this property is not <code>true</code> after this 
     * method is called, the caller can safely assume no value was set.</p>
     *
     * <p>If this resolver was constructed in read-only mode, this method will
     * always return <code>true</code>.</p>
     *
     * <p>The provided property name will first be coerced to a
     * <code>String</code>. If property is a writable property of 
     * <code>base</code>, <code>false</code> is returned. If the property is
     * found but is not writable, <code>true</code> is returned. If the
     * property is not found, a <code>PropertyNotFoundException</code>
     * is thrown.</p>
     *
     * @param context The context of this evaluation.
     * @param base The bean to analyze.
     * @param property The name of the property to analyzed. Will be coerced to
     *     a <code>String</code>.
     * @return If the <code>propertyResolved</code> property of 
     *     <code>ELContext</code> was set to <code>true</code>, then
     *     <code>true</code> if calling the <code>setValue</code> method
     *     will always fail or <code>false</code> if it is possible that
     *     such a call may succeed; otherwise undefined.
     * @throws NullPointerException if context is <code>null</code>
     * @throws PropertyNotFoundException if <code>base</code> is not
     *     <code>null</code> and the specified property does not exist.
     * @throws ELException if an exception was thrown while performing
     *     the property or variable resolution. The thrown exception
     *     must be included as the cause property of this exception, if
     *     available.
     */
    public boolean isReadOnly(ELContext context,
                              Object base,
                              Object property) {

        if (context == null) {
            throw new NullPointerException();
        }

        if (base == null || property == null){
            return false;
        }

        context.setPropertyResolved(true);
        if (isReadOnly) {
            return true;
        }

        BeanProperty bp = getBeanProperty(context, base, property);
        return bp.isReadOnly();
    }

    /**
     * If the base object is not <code>null</code>, returns an
     * <code>Iterator</code> containing the set of JavaBeans properties
     * available on the given object. Otherwise, returns <code>null</code>.
     *
     * <p>The <code>Iterator</code> returned must contain zero or more 
     * instances of {@link java.beans.FeatureDescriptor}. Each info object 
     * contains information about a property in the bean, as obtained by
     * calling the <code>BeanInfo.getPropertyDescriptors</code> method.
     * The <code>FeatureDescriptor</code> is initialized using the same
     * fields as are present in the <code>PropertyDescriptor</code>,
     * with the additional required named attributes "<code>type</code>" and 
     * "<code>resolvableAtDesignTime</code>" set as follows:
     * <dl>
     *     <li>{@link ELResolver#TYPE} - The runtime type of the property, from
     *         <code>PropertyDescriptor.getPropertyType()</code>.</li>
     *     <li>{@link ELResolver#RESOLVABLE_AT_DESIGN_TIME} - <code>true</code>.</li>
     * </dl>
     * </p>
     * 
     * @param context The context of this evaluation.
     * @param base The bean to analyze.
     * @return An <code>Iterator</code> containing zero or more 
     *     <code>FeatureDescriptor</code> objects, each representing a property
     *     on this bean, or <code>null</code> if the <code>base</code>
     *     object is <code>null</code>.
     */
    public Iterator<FeatureDescriptor> getFeatureDescriptors(
                                          ELContext context,
                                          Object base) {
        if (base == null){
            return null;
        }

        BeanInfo info = null;
        try {
            info = Introspector.getBeanInfo(base.getClass());
        } catch (Exception ex) {
        }
        if (info == null) {
            return null;
        }
        ArrayList<FeatureDescriptor> list = new ArrayList<FeatureDescriptor>(
                info.getPropertyDescriptors().length);
        for (PropertyDescriptor pd: info.getPropertyDescriptors()) {
            if (pd.getPropertyType() != null) {
                pd.setValue("type", pd.getPropertyType());
                pd.setValue("resolvableAtDesignTime", Boolean.TRUE);
            }
            list.add(pd);
        }
        return list.iterator();
    }

    /**
     * If the base object is not <code>null</code>, returns the most 
     * general type that this resolver accepts for the 
     * <code>property</code> argument. Otherwise, returns <code>null</code>.
     *
     * <p>Assuming the base is not <code>null</code>, this method will always
     * return <code>Object.class</code>. This is because any object is
     * accepted as a key and is coerced into a string.</p>
     *
     * @param context The context of this evaluation.
     * @param base The bean to analyze.
     * @return <code>null</code> if base is <code>null</code>; otherwise
     *     <code>Object.class</code>.
     */
    public Class<?> getCommonPropertyType(ELContext context,
                                               Object base) {
        if (base == null){
            return null;
        }

        return Object.class;
    }

    /*
     * Get a public method form a public class or interface of a given method.
     * Note that if a PropertyDescriptor is obtained for a non-public class that
     * implements a public interface, the read/write methods will be for the
     * class, and therefore inaccessible.  To correct this, a version of the
     * same method must be found in a superclass or interface.
     **/

    static private Method getMethod(Class cl, Method method) {

        if (Modifier.isPublic (cl.getModifiers ())) {
            return method;
        }
        Class [] interfaces = cl.getInterfaces ();
        for (int i = 0; i < interfaces.length; i++) {
            Class c = interfaces[i];
            Method m = null;
            try {
                m = c.getMethod(method.getName(), method.getParameterTypes());
                c = m.getDeclaringClass();
                if ((m = getMethod(c, m)) != null)
                    return m;
            } catch (NoSuchMethodException ex) {
            }
        }
        Class c = cl.getSuperclass();
        if (c != null) {
            Method m = null;
            try {
                m = c.getMethod(method.getName(), method.getParameterTypes());
                c = m.getDeclaringClass();
                if ((m = getMethod(c, m)) != null)
                    return m;
            } catch (NoSuchMethodException ex) {
            }
        }
        return null;
    }

    private BeanProperty getBeanProperty(ELContext context,
                                         Object base,
                                         Object prop) {

        String property = prop.toString();
        Class baseClass = base.getClass();
        BeanProperties bps = properties.get(baseClass);
        if (bps == null && (bps = properties2.get(baseClass)) == null) {
            if (properties.size() > SIZE) {
                // Discard the old map to limit the cache size.
                properties2.clear();
                properties2.putAll(properties);
                properties.clear();
            }
            bps = new BeanProperties(baseClass);
            properties.put(baseClass, bps);
        }
        return bps.getBeanProperty(property);
    }
}