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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    *
9    *     http://www.apache.org/licenses/LICENSE-2.0
10   *
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  package org.apache.commons.configuration2.beanutils;
18  
19  import java.util.Objects;
20  
21  /**
22   * <p>
23   * A class representing an argument for a constructor invocation to be used by a {@link BeanDeclaration}.
24   * </p>
25   * <p>
26   * A {@code BeanDeclaration} can provide a list of instances of this class to define the constructor to be invoked on
27   * the bean class. Each constructor argument can either be a simple value or a nested {@code BeanDeclaration}. In the
28   * latter case, the bean is resolved recursively.
29   * </p>
30   * <p>
31   * The constructor to be invoked on the bean class has to be determined based on the types of the constructor arguments.
32   * To avoid ambiguity, the type name can be explicitly provided.
33   * </p>
34   *
35   * @since 2.0
36   */
37  public final class ConstructorArg {
38  
39      /** The bean declaration referenced by this constructor argument. */
40      private final BeanDeclaration beanDeclaration;
41  
42      /** The value of this constructor argument. */
43      private final Object value;
44  
45      /** The name of the argument type. */
46      private final String typeName;
47  
48      /**
49       * Constructs a new instance of {@code ConstructorArg}.
50       *
51       * @param decl the associated bean declaration
52       * @param val the value of the argument
53       * @param type the type name
54       */
55      private ConstructorArg(final BeanDeclaration decl, final Object val, final String type) {
56          beanDeclaration = decl;
57          value = val;
58          typeName = type;
59      }
60  
61      /**
62       * Creates a new instance of {@code ConstructorArg} for the specified {@code BeanDeclaration}. The actual value of this
63       * argument is the resolved {@code BeanDeclaration}.
64       *
65       * @param decl the {@code BeanDeclaration}
66       * @return the newly created instance of this class
67       * @throws NullPointerException if the {@code BeanDeclaration} is <b>null</b>
68       */
69      public static ConstructorArg forBeanDeclaration(final BeanDeclaration decl) {
70          return forBeanDeclaration(decl, null);
71      }
72  
73      /**
74       * Creates a new instance of {@code ConstructorArg} for the specified {@code BeanDeclaration} and sets the type name
75       * explicitly. The type name is used to match this argument against the parameter type of a constructor or the bean
76       * class.
77       *
78       * @param beanDeclaration the {@code BeanDeclaration}
79       * @param typeName the name of the data type of this argument
80       * @return the newly created instance of this class
81       * @throws NullPointerException if the {@code BeanDeclaration} is <b>null</b>
82       */
83      public static ConstructorArg forBeanDeclaration(final BeanDeclaration beanDeclaration, final String typeName) {
84          Objects.requireNonNull(beanDeclaration, "beanDeclaration");
85          return new ConstructorArg(beanDeclaration, null, typeName);
86      }
87  
88      /**
89       * Creates a new instance of {@code ConstructorArg} for the specified simple value. The value is passed to the
90       * constructor invocation.
91       *
92       * @param value the value of this constructor argument (may be <b>null</b>)
93       * @return the newly created instance of this class
94       */
95      public static ConstructorArg forValue(final Object value) {
96          return forValue(value, null);
97      }
98  
99      /**
100      * Creates a new instance of {@code ConstructorArg} for the specified simple value and sets the type name explicitly.
101      * The type name is used to match this argument against the parameter type of a constructor or the bean class.
102      *
103      * @param value the value of this constructor argument (may be <b>null</b>)
104      * @param typeName the name of the data type of this argument
105      * @return the newly created instance of this class
106      */
107     public static ConstructorArg forValue(final Object value, final String typeName) {
108         return new ConstructorArg(null, value, typeName);
109     }
110 
111     /**
112      * Gets the {@code BeanDeclaration} referenced by this constructor argument. A return value of <b>null</b> means that
113      * this constructor argument does not have a bean declaration as value; in this case, the value can be queried using the
114      * {@link #getValue()} method.
115      *
116      * @return the referenced {@code BeanDeclaration} or <b>null</b>
117      */
118     public BeanDeclaration getBeanDeclaration() {
119         return beanDeclaration;
120     }
121 
122     /**
123      * Tests whether this constructor argument represents a {@code BeanDeclaration}. If this method returns
124      * <b>true</b>, the actual value of this argument can be obtained by resolving the bean declaration returned by
125      * {@link #getBeanDeclaration()}. Otherwise, this argument has a simple value which can be queried using
126      * {@link #getValue()}.
127      *
128      * @return whether this constructor argument references a bean declaration
129      */
130     public boolean isNestedBeanDeclaration() {
131         return getBeanDeclaration() != null;
132     }
133 
134     /**
135      * Gets the value of this constructor argument. This method can be queried if {@link #isNestedBeanDeclaration()}
136      * returns <b>false</b>. Note that a return value of <b>null</b> is legal (to pass <b>null</b> to a constructor
137      * argument).
138      *
139      * @return the simple value of this constructor argument
140      */
141     public Object getValue() {
142         return value;
143     }
144 
145     /**
146      * Gets the optional data type name of this constructor argument. The type name can be specified as a hint to select
147      * a specific constructor if there are ambiguities. Note that it does not necessarily has to match the data type of this
148      * argument's value because a type conversion may be performed before invoking the constructor.
149      *
150      * @return the data type name of this argument if defined or <b>null</b> otherwise
151      */
152     public String getTypeName() {
153         return typeName;
154     }
155 
156     /**
157      * Checks whether this constructor argument is compatible with the given class. This method is called to determine a
158      * matching constructor. It compares the argument's data type with the class name if it is defined. If no type name has
159      * been set, result is <b>true</b> as it is assumed that a type conversion can be performed when calling the
160      * constructor. This means that per default only the number of constructor arguments is checked to find a matching
161      * constructor. Only if there are multiple constructors with the same number of arguments, explicit type names have to
162      * be provided to select a specific constructor.
163      *
164      * @param argCls the class of the constructor argument to compare with
165      * @return <b>true</b> if this constructor argument is compatible with this class, <b>false</b> otherwise
166      */
167     public boolean matches(final Class<?> argCls) {
168         if (argCls == null) {
169             return false;
170         }
171 
172         return getTypeName() == null || getTypeName().equals(argCls.getName());
173     }
174 
175     /**
176      * Gets a string representation of this object. This string contains the value of this constructor argument and the
177      * explicit type if provided.
178      *
179      * @return a string for this object
180      */
181     @Override
182     public String toString() {
183         final StringBuilder buf = new StringBuilder();
184         buf.append(getClass().getSimpleName());
185         buf.append(" [ value = ");
186         buf.append(isNestedBeanDeclaration() ? getBeanDeclaration() : getValue());
187         if (getTypeName() != null) {
188             buf.append(" (").append(getTypeName()).append(')');
189         }
190         buf.append(" ]");
191         return buf.toString();
192     }
193 }