ReflectionUtils.java

/*
 * Copyright 2011 Martin Grotzke
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package de.hashcode.validation;

import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.Locale;

import javax.annotation.CheckForNull;
import javax.annotation.Nonnull;
import javax.persistence.Id;

/**
 * A utility class for reflection tasks.
 *
 * @author Martin Grotzke
 */
public class ReflectionUtils {

    private ReflectionUtils() {
        // utility class
    }

    /**
     * Determines which field of the given class is annotated with {@link Id},
     * including the inheritence tree up to {@link Object}.
     *
     * @return the Id field, never <code>null</code>.
     * @throws IllegalArgumentException
     *             thrown if there's no field annotated with {@link Id}.
     */
    public static Field getIdField(final Class<?> entityClass) throws IllegalArgumentException {
        final Field[] fields = entityClass.getDeclaredFields();
        for (final Field field : fields) {
            final Id annotation = field.getAnnotation(Id.class);
            if (annotation != null) {
                return field;
            }
        }
        if (entityClass.getSuperclass() != Object.class) {
            return getIdField(entityClass.getSuperclass());
        }
        throw new IllegalArgumentException("No id field found on class " + entityClass);
    }

    /**
     * Read the value of the specified propertyName from the given object. This
     * implementation allows properties/fields with only getters (immutable
     * beans) and does not rely on java beans standard (PropertyDescriptor)
     * which would require also a setter method (the alternative would be s.th.
     * like
     * <code>new PropertyDescriptor(propertyName, entityClass).getReadMethod().invoke(target);</code>
     * ).
     */
    @CheckForNull
    public static Object getPropertyValue(@Nonnull final Object object, @Nonnull final String propertyName)
            throws IllegalArgumentException, IllegalAccessException, InvocationTargetException {
        final Method method = getGetter(object.getClass(), propertyName);
        return method.invoke(object, (Object[]) null);
    }

    @Nonnull
    private static String toMethodName(@Nonnull final String methodPrefix, @Nonnull final String propertyName) {
        return methodPrefix + propertyName.substring(0, 1).toUpperCase(Locale.ENGLISH) + propertyName.substring(1);
    }

    @Nonnull
    private static Method getGetter(@Nonnull final Class<?> clazz, @Nonnull final String property) {
        final String get = toMethodName("get", property);
        final String is = toMethodName("is", property);
        Method getter;
        try {
            getter = clazz.getMethod(get);
        } catch (final NoSuchMethodException noSuchMethodException) {
            try {
                getter = clazz.getMethod(is);
            } catch (final NoSuchMethodException noSuchMethodException2) {
                throw new RuntimeException("Getter for '" + clazz.getSimpleName() + '#' + property + "' not found.",
                        noSuchMethodException2);
            } catch (final SecurityException securityException) {
                throw new RuntimeException("Method '" + clazz.getSimpleName() + '#' + is
                        + "()' is protected by the security manager.");
            }
        } catch (final SecurityException securityException) {
            try {
                getter = clazz.getMethod(is);
            } catch (final NoSuchMethodException noSuchMethodException) {
                throw new RuntimeException("Method '" + clazz.getSimpleName() + '#' + get
                        + "()' is protected by the security manager.");
            } catch (final SecurityException securityException2) {
                throw new RuntimeException("Methods '" + clazz.getSimpleName() + '#' + get + "()' and "
                        + clazz.getSimpleName() + '#' + is + "()' are protected by the security manager.");
            }
        }
        return getter;
    }

}