001    /*
002     * Created on Jun 28, 2010
003     *
004     * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
005     * the License. You may obtain a copy of the License at
006     *
007     * http://www.apache.org/licenses/LICENSE-2.0
008     *
009     * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
010     * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
011     * specific language governing permissions and limitations under the License.
012     *
013     * Copyright @2010-2011 the original author or authors.
014     */
015    package org.fest.util;
016    
017    import static java.lang.String.format;
018    import static java.lang.reflect.Modifier.isPublic;
019    import static java.util.Locale.ENGLISH;
020    import static org.fest.util.Strings.*;
021    
022    import java.beans.*;
023    import java.lang.reflect.Method;
024    
025    /**
026     * Utility methods related to <a
027     * href="http://java.sun.com/docs/books/tutorial/javabeans/introspection/index.html">JavaBeans Introspection</a>.
028     *
029     * @author Alex Ruiz
030     */
031    public final class Introspection {
032    
033      /**
034       * Returns a <code>{@link PropertyDescriptor}</code> for a property matching the given name in the given object.
035       * @param propertyName the given property name.
036       * @param target the given object.
037       * @return a {@code PropertyDescriptor} for a property matching the given name in the given object.
038       * @throws NullPointerException if the given property name is {@code null}.
039       * @throws IllegalArgumentException if the given property name is empty.
040       * @throws NullPointerException if the given object is {@code null}.
041       * @throws IntrospectionError if a matching property cannot be found or accessed.
042       */
043      public static PropertyDescriptor descriptorForProperty(String propertyName, Object target) {
044        validate(propertyName, target);
045        BeanInfo beanInfo = null;
046        Class<?> type = target.getClass();
047        try {
048          beanInfo = Introspector.getBeanInfo(type);
049        } catch (Exception e) {
050          throw new IntrospectionError(format("Unable to get BeanInfo for type %s", type.getName()), e);
051        }
052        for (PropertyDescriptor d : beanInfo.getPropertyDescriptors())
053          if (propertyName.equals(d.getName())) return d;
054        throw new IntrospectionError(propertyNotFoundErrorMessage(propertyName, target));
055      }
056    
057      private static String propertyNotFoundErrorMessage(String propertyName, Object target) {
058        String targetTypeName = target.getClass().getName();
059        String property = quote(propertyName);
060        // no PropertyDescriptor found, try to give user a precise error message
061        Method getter = beanGetter(propertyName, target);
062        if (getter == null)
063          return format("No getter for property %s in %s", property, targetTypeName);
064        if (!isPublic(getter.getModifiers()))
065          return format("No public getter for property %s in %s", property, targetTypeName);
066        // generic message
067        return format("Unable to find property %s in %s", property, targetTypeName);
068      }
069    
070      private static Method beanGetter(String propertyName, Object target) {
071        validate(propertyName, target);
072        String capitalized = propertyName.substring(0, 1).toUpperCase(ENGLISH) + propertyName.substring(1);
073        // try to find getProperty
074        Method getter = findMethod("get" + capitalized, target);
075        if (getter != null) return getter;
076        // try to find isProperty for boolean properties
077        return findMethod("is" + capitalized, target);
078      }
079    
080      private static Method findMethod(String name, Object target) {
081        // TODO walk class hierarchy to check if any superclass declares the method we are looking for.
082        try {
083          return target.getClass().getDeclaredMethod(name);
084        } catch (Throwable t) {
085          return null;
086        }
087      }
088    
089      private static void validate(String propertyName, Object target) {
090        if (propertyName == null) throw new NullPointerException("The property name should not be null");
091        if (isEmpty(propertyName)) throw new IllegalArgumentException("The property name should not be empty");
092        if (target == null) throw new NullPointerException("The target object should not be null");
093      }
094    
095      private Introspection() {}
096    }