    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.configuration2.beanutils;
    018
    019/**
    020 * <p>
    021 * A class representing an argument for a constructor invocation to be used by a
    022 * {@link BeanDeclaration}.
    023 * </p>
    024 * <p>
    025 * A {@code BeanDeclaration} can provide a list of instances of this class to
    026 * define the constructor to be invoked on the bean class. Each constructor
    027 * argument can either be a simple value or a nested {@code BeanDeclaration}. In
    028 * the latter case, the bean is resolved recursively.
    029 * </p>
    030 * <p>
    031 * The constructor to be invoked on the bean class has to be determined based on
    032 * the types of the constructor arguments. To avoid ambiguity, the type name can
    033 * be explicitly provided.
    034 * </p>
    035 *
    036 * @since 2.0
    037 */
    038public final class ConstructorArg
    039{
    040    /** The bean declaration referenced by this constructor argument. */
    041    private final BeanDeclaration beanDeclaration;
    042
    043    /** The value of this constructor argument. */
    044    private final Object value;
    045
    046    /** The name of the argument type. */
    047    private final String typeName;
    048
    049    /**
    050     * Creates a new instance of {@code ConstructorArg}.
    051     *
    052     * @param decl the associated bean declaration
    053     * @param val the value of the argument
    054     * @param type the type name
    055     */
    056    private ConstructorArg(final BeanDeclaration decl, final Object val, final String type)
    057    {
    058        beanDeclaration = decl;
    059        value = val;
    060        typeName = type;
    061    }
    062
    063    /**
    064     * Creates a new instance of {@code ConstructorArg} for the specified
    065     * {@code BeanDeclaration}. The actual value of this argument is the
    066     * resolved {@code BeanDeclaration}.
    067     *
    068     * @param decl the {@code BeanDeclaration}
    069     * @return the newly created instance of this class
    070     * @throws NullPointerException if the {@code BeanDeclaration} is
    071     *         <b>null</b>
    072     */
    073    public static ConstructorArg forBeanDeclaration(final BeanDeclaration decl)
    074    {
    075        return forBeanDeclaration(decl, null);
    076    }
    077
    078    /**
    079     * Creates a new instance of {@code ConstructorArg} for the specified
    080     * {@code BeanDeclaration} and sets the type name explicitly. The type name
    081     * is used to match this argument against the parameter type of a
    082     * constructor or the bean class.
    083     *
    084     * @param decl the {@code BeanDeclaration}
    085     * @param typeName the name of the data type of this argument
    086     * @return the newly created instance of this class
    087     * @throws NullPointerException if the {@code BeanDeclaration} is
    088     *         <b>null</b>
    089     */
    090    public static ConstructorArg forBeanDeclaration(final BeanDeclaration decl,
    091            final String typeName)
    092    {
    093        if (decl == null)
    094        {
    095            throw new NullPointerException("BeanDeclaration must not be null!");
    096        }
    097        return new ConstructorArg(decl, null, typeName);
    098    }
    099
    100    /**
    101     * Creates a new instance of {@code ConstructorArg} for the specified simple
    102     * value. The value is passed to the constructor invocation.
    103     *
    104     * @param value the value of this constructor argument (may be <b>null</b>)
    105     * @return the newly created instance of this class
    106     */
    107    public static ConstructorArg forValue(final Object value)
    108    {
    109        return forValue(value, null);
    110    }
    111
    112    /**
    113     * Creates a new instance of {@code ConstructorArg} for the specified simple
    114     * value and sets the type name explicitly. The type name is used to match
    115     * this argument against the parameter type of a constructor or the bean
    116     * class.
    117     *
    118     * @param value the value of this constructor argument (may be <b>null</b>)
    119     * @param typeName the name of the data type of this argument
    120     * @return the newly created instance of this class
    121     */
    122    public static ConstructorArg forValue(final Object value, final String typeName)
    123    {
    124        return new ConstructorArg(null, value, typeName);
    125    }
    126
    127    /**
    128     * Returns the {@code BeanDeclaration} referenced by this constructor
    129     * argument. A return value of <b>null</b> means that this constructor
    130     * argument does not have a bean declaration as value; in this case, the
    131     * value can be queried using the {@link #getValue()} method.
    132     *
    133     * @return the referenced {@code BeanDeclaration} or <b>null</b>
    134     */
    135    public BeanDeclaration getBeanDeclaration()
    136    {
    137        return beanDeclaration;
    138    }
    139
    140    /**
    141     * Returns a flag whether this constructor argument represents a
    142     * {@code BeanDeclaration}. If this method returns <b>true</b>, the actual
    143     * value of this argument can be obtained by resolving the bean declaration
    144     * returned by {@link #getBeanDeclaration()}. Otherwise, this argument has a
    145     * simple value which can be queried using {@link #getValue()}.
    146     *
    147     * @return a flag whether this constructor argument references a bean
    148     *         declaration
    149     */
    150    public boolean isNestedBeanDeclaration()
    151    {
    152        return getBeanDeclaration() != null;
    153    }
    154
    155    /**
    156     * Returns the value of this constructor argument. This method can be
    157     * queried if {@link #isNestedBeanDeclaration()} returns <b>false</b>. Note
    158     * that a return value of <b>null</b> is legal (to pass <b>null</b> to a
    159     * constructor argument).
    160     *
    161     * @return the simple value of this constructor argument
    162     */
    163    public Object getValue()
    164    {
    165        return value;
    166    }
    167
    168    /**
    169     * Returns the optional data type name of this constructor argument. The
    170     * type name can be specified as a hint to select a specific constructor if
    171     * there are ambiguities. Note that it does not necessarily has to match the
    172     * data type of this argument's value because a type conversion may be
    173     * performed before invoking the constructor.
    174     *
    175     * @return the data type name of this argument if defined or <b>null</b>
    176     *         otherwise
    177     */
    178    public String getTypeName()
    179    {
    180        return typeName;
    181    }
    182
    183    /**
    184     * Checks whether this constructor argument is compatible with the given
    185     * class. This method is called to determine a matching constructor. It
    186     * compares the argument's data type with the class name if it is defined.
    187     * If no type name has been set, result is <b>true</b> as it is assumed that
    188     * a type conversion can be performed when calling the constructor. This
    189     * means that per default only the number of constructor arguments is
    190     * checked to find a matching constructor. Only if there are multiple
    191     * constructors with the same number of arguments, explicit type names have
    192     * to be provided to select a specific constructor.
    193     *
    194     * @param argCls the class of the constructor argument to compare with
    195     * @return <b>true</b> if this constructor argument is compatible with this
    196     *         class, <b>false</b> otherwise
    197     */
    198    public boolean matches(final Class<?> argCls)
    199    {
    200        if (argCls == null)
    201        {
    202            return false;
    203        }
    204
    205        return getTypeName() == null || getTypeName().equals(argCls.getName());
    206    }
    207
    208    /**
    209     * Returns a string representation of this object. This string contains the
    210     * value of this constructor argument and the explicit type if provided.
    211     *
    212     * @return a string for this object
    213     */
    214    @Override
    215    public String toString()
    216    {
    217        final StringBuilder buf = new StringBuilder();
    218        buf.append(getClass().getSimpleName());
    219        buf.append(" [ value = ");
    220        buf.append(isNestedBeanDeclaration() ? getBeanDeclaration()
    221                : getValue());
    222        if (getTypeName() != null)
    223        {
    224            buf.append(" (").append(getTypeName()).append(')');
    225        }
    226        buf.append(" ]");
    227        return buf.toString();
    228    }
    229}