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 * @version $Id: ConstructorArg.java 1842194 2018-09-27 22:24:23Z ggregory $
037 * @since 2.0
038 */
039public final class ConstructorArg
040{
041    /** The bean declaration referenced by this constructor argument. */
042    private final BeanDeclaration beanDeclaration;
043
044    /** The value of this constructor argument. */
045    private final Object value;
046
047    /** The name of the argument type. */
048    private final String typeName;
049
050    /**
051     * Creates a new instance of {@code ConstructorArg}.
052     *
053     * @param decl the associated bean declaration
054     * @param val the value of the argument
055     * @param type the type name
056     */
057    private ConstructorArg(final BeanDeclaration decl, final Object val, final String type)
058    {
059        beanDeclaration = decl;
060        value = val;
061        typeName = type;
062    }
063
064    /**
065     * Creates a new instance of {@code ConstructorArg} for the specified
066     * {@code BeanDeclaration}. The actual value of this argument is the
067     * resolved {@code BeanDeclaration}.
068     *
069     * @param decl the {@code BeanDeclaration}
070     * @return the newly created instance of this class
071     * @throws NullPointerException if the {@code BeanDeclaration} is
072     *         <b>null</b>
073     */
074    public static ConstructorArg forBeanDeclaration(final BeanDeclaration decl)
075    {
076        return forBeanDeclaration(decl, null);
077    }
078
079    /**
080     * Creates a new instance of {@code ConstructorArg} for the specified
081     * {@code BeanDeclaration} and sets the type name explicitly. The type name
082     * is used to match this argument against the parameter type of a
083     * constructor or the bean class.
084     *
085     * @param decl the {@code BeanDeclaration}
086     * @param typeName the name of the data type of this argument
087     * @return the newly created instance of this class
088     * @throws NullPointerException if the {@code BeanDeclaration} is
089     *         <b>null</b>
090     */
091    public static ConstructorArg forBeanDeclaration(final BeanDeclaration decl,
092            final String typeName)
093    {
094        if (decl == null)
095        {
096            throw new NullPointerException("BeanDeclaration must not be null!");
097        }
098        return new ConstructorArg(decl, null, typeName);
099    }
100
101    /**
102     * Creates a new instance of {@code ConstructorArg} for the specified simple
103     * value. The value is passed to the constructor invocation.
104     *
105     * @param value the value of this constructor argument (may be <b>null</b>)
106     * @return the newly created instance of this class
107     */
108    public static ConstructorArg forValue(final Object value)
109    {
110        return forValue(value, null);
111    }
112
113    /**
114     * Creates a new instance of {@code ConstructorArg} for the specified simple
115     * value and sets the type name explicitly. The type name is used to match
116     * this argument against the parameter type of a constructor or the bean
117     * class.
118     *
119     * @param value the value of this constructor argument (may be <b>null</b>)
120     * @param typeName the name of the data type of this argument
121     * @return the newly created instance of this class
122     */
123    public static ConstructorArg forValue(final Object value, final String typeName)
124    {
125        return new ConstructorArg(null, value, typeName);
126    }
127
128    /**
129     * Returns the {@code BeanDeclaration} referenced by this constructor
130     * argument. A return value of <b>null</b> means that this constructor
131     * argument does not have a bean declaration as value; in this case, the
132     * value can be queried using the {@link #getValue()} method.
133     *
134     * @return the referenced {@code BeanDeclaration} or <b>null</b>
135     */
136    public BeanDeclaration getBeanDeclaration()
137    {
138        return beanDeclaration;
139    }
140
141    /**
142     * Returns a flag whether this constructor argument represents a
143     * {@code BeanDeclaration}. If this method returns <b>true</b>, the actual
144     * value of this argument can be obtained by resolving the bean declaration
145     * returned by {@link #getBeanDeclaration()}. Otherwise, this argument has a
146     * simple value which can be queried using {@link #getValue()}.
147     *
148     * @return a flag whether this constructor argument references a bean
149     *         declaration
150     */
151    public boolean isNestedBeanDeclaration()
152    {
153        return getBeanDeclaration() != null;
154    }
155
156    /**
157     * Returns the value of this constructor argument. This method can be
158     * queried if {@link #isNestedBeanDeclaration()} returns <b>false</b>. Note
159     * that a return value of <b>null</b> is legal (to pass <b>null</b> to a
160     * constructor argument).
161     *
162     * @return the simple value of this constructor argument
163     */
164    public Object getValue()
165    {
166        return value;
167    }
168
169    /**
170     * Returns the optional data type name of this constructor argument. The
171     * type name can be specified as a hint to select a specific constructor if
172     * there are ambiguities. Note that it does not necessarily has to match the
173     * data type of this argument's value because a type conversion may be
174     * performed before invoking the constructor.
175     *
176     * @return the data type name of this argument if defined or <b>null</b>
177     *         otherwise
178     */
179    public String getTypeName()
180    {
181        return typeName;
182    }
183
184    /**
185     * Checks whether this constructor argument is compatible with the given
186     * class. This method is called to determine a matching constructor. It
187     * compares the argument's data type with the class name if it is defined.
188     * If no type name has been set, result is <b>true</b> as it is assumed that
189     * a type conversion can be performed when calling the constructor. This
190     * means that per default only the number of constructor arguments is
191     * checked to find a matching constructor. Only if there are multiple
192     * constructors with the same number of arguments, explicit type names have
193     * to be provided to select a specific constructor.
194     *
195     * @param argCls the class of the constructor argument to compare with
196     * @return <b>true</b> if this constructor argument is compatible with this
197     *         class, <b>false</b> otherwise
198     */
199    public boolean matches(final Class<?> argCls)
200    {
201        if (argCls == null)
202        {
203            return false;
204        }
205
206        return getTypeName() == null || getTypeName().equals(argCls.getName());
207    }
208
209    /**
210     * Returns a string representation of this object. This string contains the
211     * value of this constructor argument and the explicit type if provided.
212     *
213     * @return a string for this object
214     */
215    @Override
216    public String toString()
217    {
218        final StringBuilder buf = new StringBuilder();
219        buf.append(getClass().getSimpleName());
220        buf.append(" [ value = ");
221        buf.append(isNestedBeanDeclaration() ? getBeanDeclaration()
222                : getValue());
223        if (getTypeName() != null)
224        {
225            buf.append(" (").append(getTypeName()).append(')');
226        }
227        buf.append(" ]");
228        return buf.toString();
229    }
230}