ConstructorArg.java
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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 org.apache.commons.configuration2.beanutils;
import java.util.Objects;
/**
* <p>
* A class representing an argument for a constructor invocation to be used by a {@link BeanDeclaration}.
* </p>
* <p>
* A {@code BeanDeclaration} can provide a list of instances of this class to define the constructor to be invoked on
* the bean class. Each constructor argument can either be a simple value or a nested {@code BeanDeclaration}. In the
* latter case, the bean is resolved recursively.
* </p>
* <p>
* The constructor to be invoked on the bean class has to be determined based on the types of the constructor arguments.
* To avoid ambiguity, the type name can be explicitly provided.
* </p>
*
* @since 2.0
*/
public final class ConstructorArg {
/**
* Creates a new instance of {@code ConstructorArg} for the specified {@code BeanDeclaration}. The actual value of this
* argument is the resolved {@code BeanDeclaration}.
*
* @param decl the {@code BeanDeclaration}
* @return the newly created instance of this class
* @throws NullPointerException if the {@code BeanDeclaration} is <b>null</b>
*/
public static ConstructorArg forBeanDeclaration(final BeanDeclaration decl) {
return forBeanDeclaration(decl, null);
}
/**
* Creates a new instance of {@code ConstructorArg} for the specified {@code BeanDeclaration} and sets the type name
* explicitly. The type name is used to match this argument against the parameter type of a constructor or the bean
* class.
*
* @param beanDeclaration the {@code BeanDeclaration}
* @param typeName the name of the data type of this argument
* @return the newly created instance of this class
* @throws NullPointerException if the {@code BeanDeclaration} is <b>null</b>
*/
public static ConstructorArg forBeanDeclaration(final BeanDeclaration beanDeclaration, final String typeName) {
Objects.requireNonNull(beanDeclaration, "beanDeclaration");
return new ConstructorArg(beanDeclaration, null, typeName);
}
/**
* Creates a new instance of {@code ConstructorArg} for the specified simple value. The value is passed to the
* constructor invocation.
*
* @param value the value of this constructor argument (may be <b>null</b>)
* @return the newly created instance of this class
*/
public static ConstructorArg forValue(final Object value) {
return forValue(value, null);
}
/**
* Creates a new instance of {@code ConstructorArg} for the specified simple value and sets the type name explicitly.
* The type name is used to match this argument against the parameter type of a constructor or the bean class.
*
* @param value the value of this constructor argument (may be <b>null</b>)
* @param typeName the name of the data type of this argument
* @return the newly created instance of this class
*/
public static ConstructorArg forValue(final Object value, final String typeName) {
return new ConstructorArg(null, value, typeName);
}
/** The bean declaration referenced by this constructor argument. */
private final BeanDeclaration beanDeclaration;
/** The value of this constructor argument. */
private final Object value;
/** The name of the argument type. */
private final String typeName;
/**
* Constructs a new instance of {@code ConstructorArg}.
*
* @param decl the associated bean declaration
* @param val the value of the argument
* @param type the type name
*/
private ConstructorArg(final BeanDeclaration decl, final Object val, final String type) {
beanDeclaration = decl;
value = val;
typeName = type;
}
/**
* Gets the {@code BeanDeclaration} referenced by this constructor argument. A return value of <b>null</b> means that
* this constructor argument does not have a bean declaration as value; in this case, the value can be queried using the
* {@link #getValue()} method.
*
* @return the referenced {@code BeanDeclaration} or <b>null</b>
*/
public BeanDeclaration getBeanDeclaration() {
return beanDeclaration;
}
/**
* Gets the optional data type name of this constructor argument. The type name can be specified as a hint to select
* a specific constructor if there are ambiguities. Note that it does not necessarily has to match the data type of this
* argument's value because a type conversion may be performed before invoking the constructor.
*
* @return the data type name of this argument if defined or <b>null</b> otherwise
*/
public String getTypeName() {
return typeName;
}
/**
* Gets the value of this constructor argument. This method can be queried if {@link #isNestedBeanDeclaration()}
* returns <b>false</b>. Note that a return value of <b>null</b> is legal (to pass <b>null</b> to a constructor
* argument).
*
* @return the simple value of this constructor argument
*/
public Object getValue() {
return value;
}
/**
* Tests whether this constructor argument represents a {@code BeanDeclaration}. If this method returns
* <b>true</b>, the actual value of this argument can be obtained by resolving the bean declaration returned by
* {@link #getBeanDeclaration()}. Otherwise, this argument has a simple value which can be queried using
* {@link #getValue()}.
*
* @return whether this constructor argument references a bean declaration
*/
public boolean isNestedBeanDeclaration() {
return getBeanDeclaration() != null;
}
/**
* Checks whether this constructor argument is compatible with the given class. This method is called to determine a
* matching constructor. It compares the argument's data type with the class name if it is defined. If no type name has
* been set, result is <b>true</b> as it is assumed that a type conversion can be performed when calling the
* constructor. This means that per default only the number of constructor arguments is checked to find a matching
* constructor. Only if there are multiple constructors with the same number of arguments, explicit type names have to
* be provided to select a specific constructor.
*
* @param argCls the class of the constructor argument to compare with
* @return <b>true</b> if this constructor argument is compatible with this class, <b>false</b> otherwise
*/
public boolean matches(final Class<?> argCls) {
if (argCls == null) {
return false;
}
return getTypeName() == null || getTypeName().equals(argCls.getName());
}
/**
* Gets a string representation of this object. This string contains the value of this constructor argument and the
* explicit type if provided.
*
* @return a string for this object
*/
@Override
public String toString() {
final StringBuilder buf = new StringBuilder();
buf.append(getClass().getSimpleName());
buf.append(" [ value = ");
buf.append(isNestedBeanDeclaration() ? getBeanDeclaration() : getValue());
if (getTypeName() != null) {
buf.append(" (").append(getTypeName()).append(')');
}
buf.append(" ]");
return buf.toString();
}
}