    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017package org.apache.commons.beanutils;
    018
    019import java.beans.IntrospectionException;
    020import java.beans.Introspector;
    021import java.beans.PropertyDescriptor;
    022import java.lang.reflect.Method;
    023import java.util.Locale;
    024
    025import org.apache.commons.logging.Log;
    026import org.apache.commons.logging.LogFactory;
    027
    028/**
    029 * <p>
    030 * An implementation of the <code>BeanIntrospector</code> interface which can
    031 * detect write methods for properties used in fluent API scenario.
    032 * </p>
    033 * <p>
    034 * A <em>fluent API</em> allows setting multiple properties using a single
    035 * statement by supporting so-called <em>method chaining</em>: Methods for
    036 * setting a property value do not return <b>void</b>, but an object which can
    037 * be called for setting another property. An example of such a fluent API could
    038 * look as follows:
    039 *
    040 * <pre>
    041 * public class FooBuilder {
    042 *     public FooBuilder setFooProperty1(String value) {
    043 *        ...
    044 *        return this;
    045 *    }
    046 *
    047 *     public FooBuilder setFooProperty2(int value) {
    048 *        ...
    049 *        return this;
    050 *    }
    051 * }
    052 * </pre>
    053 *
    054 * Per default, <code>PropertyUtils</code> does not detect methods like this
    055 * because, having a non-<b>void</b> return type, they violate the Java Beans
    056 * specification.
    057 * </p>
    058 * <p>
    059 * This class is more tolerant with regards to the return type of a set method.
    060 * It basically iterates over all methods of a class and filters them for a
    061 * configurable prefix (the default prefix is <code>set</code>). It then
    062 * generates corresponding <code>PropertyDescriptor</code> objects for the
    063 * methods found which use these methods as write methods.
    064 * </p>
    065 * <p>
    066 * An instance of this class is intended to collaborate with a
    067 * {@link DefaultBeanIntrospector} object. So best results are achieved by
    068 * adding this instance as custom {@code BeanIntrospector} after the
    069 * <code>DefaultBeanIntrospector</code> object. Then default introspection finds
    070 * read-only properties because it does not detect the write methods with a
    071 * non-<b>void</b> return type. {@code FluentPropertyBeanIntrospector}
    072 * completes the descriptors for these properties by setting the correct write
    073 * method.
    074 * </p>
    075 *
    076 * @version $Id$
    077 * @since 1.9
    078 */
    079public class FluentPropertyBeanIntrospector implements BeanIntrospector {
    080    /** The default prefix for write methods. */
    081    public static final String DEFAULT_WRITE_METHOD_PREFIX = "set";
    082
    083    /** The logger. */
    084    private final Log log = LogFactory.getLog(getClass());
    085
    086    /** The prefix of write methods to search for. */
    087    private final String writeMethodPrefix;
    088
    089    /**
    090     *
    091     * Creates a new instance of <code>FluentPropertyBeanIntrospector</code> and
    092     * initializes it with the prefix for write methods used by the classes to
    093     * be inspected.
    094     *
    095     * @param writePrefix the prefix for write methods (must not be <b>null</b>)
    096     * @throws IllegalArgumentException if the prefix is <b>null</b>
    097     */
    098    public FluentPropertyBeanIntrospector(final String writePrefix) {
    099        if (writePrefix == null) {
    100            throw new IllegalArgumentException(
    101                    "Prefix for write methods must not be null!");
    102        }
    103        writeMethodPrefix = writePrefix;
    104    }
    105
    106    /**
    107     *
    108     * Creates a new instance of <code>FluentPropertyBeanIntrospector</code> and
    109     * sets the default prefix for write methods.
    110     */
    111    public FluentPropertyBeanIntrospector() {
    112        this(DEFAULT_WRITE_METHOD_PREFIX);
    113    }
    114
    115    /**
    116     * Returns the prefix for write methods this instance scans for.
    117     *
    118     * @return the prefix for write methods
    119     */
    120    public String getWriteMethodPrefix() {
    121        return writeMethodPrefix;
    122    }
    123
    124    /**
    125     * Performs introspection. This method scans the current class's methods for
    126     * property write methods which have not been discovered by default
    127     * introspection.
    128     *
    129     * @param icontext the introspection context
    130     * @throws IntrospectionException if an error occurs
    131     */
    132    public void introspect(final IntrospectionContext icontext)
    133            throws IntrospectionException {
    134        for (final Method m : icontext.getTargetClass().getMethods()) {
    135            if (m.getName().startsWith(getWriteMethodPrefix())) {
    136                final String propertyName = propertyName(m);
    137                final PropertyDescriptor pd = icontext
    138                        .getPropertyDescriptor(propertyName);
    139                try {
    140                    if (pd == null) {
    141                        icontext.addPropertyDescriptor(createFluentPropertyDescritor(
    142                                m, propertyName));
    143                    } else if (pd.getWriteMethod() == null) {
    144                        pd.setWriteMethod(m);
    145                    }
    146                } catch (final IntrospectionException e) {
    147                    log.info("Error when creating PropertyDescriptor for " + m
    148                            + "! Ignoring this property.");
    149                    log.debug("Exception is:", e);
    150                }
    151            }
    152        }
    153    }
    154
    155    /**
    156     * Derives the name of a property from the given set method.
    157     *
    158     * @param m the method
    159     * @return the corresponding property name
    160     */
    161    private String propertyName(final Method m) {
    162        final String methodName = m.getName().substring(
    163                getWriteMethodPrefix().length());
    164        return (methodName.length() > 1) ? Introspector.decapitalize(methodName) : methodName
    165                .toLowerCase(Locale.ENGLISH);
    166    }
    167
    168    /**
    169     * Creates a property descriptor for a fluent API property.
    170     *
    171     * @param m the set method for the fluent API property
    172     * @param propertyName the name of the corresponding property
    173     * @return the descriptor
    174     * @throws IntrospectionException if an error occurs
    175     */
    176    private PropertyDescriptor createFluentPropertyDescritor(final Method m,
    177            final String propertyName) throws IntrospectionException {
    178        return new PropertyDescriptor(propertyName(m), null, m);
    179    }
    180}