ConstructorInjector.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
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 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
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 */
package org.apache.felix.ipojo;

/**
 * Interface implemented to support constructor parameter injection.
 * When a new POJO object has to be created, all constructor injectors are
 * called to gets the objects to injects as well as the type (to discover
 * the constructor).
 * Handlers willing to inject constructor parameters must register themselves
 * using {@link InstanceManager#register(int, ConstructorInjector)} where
 * the integer is the parameter index. Only one injector can inject a value
 * for a specific index. If several injectors are registered for the same index,
 * the component type is declared as invalid.
 * @author <a href="mailto:dev@felix.apache.org">Felix Project Team</a>
 */
public interface ConstructorInjector {

    /**
     * Gets the object to inject in the constructor parameter.
     * @param index the parameter index
     * @return the object to be injected.
     */
	Object getConstructorParameter(int index);

    /**
     * Gets the type of the object to inject in the constructor parameter.
     * This is the type looked into the Pojo class, so it must match.
     * Returning <code>null</code> will try to get the class from the
     * injected object, however this can be wrong (implementation instead of interface,
     * boxed objects...) and error-prone.
     * @param index the parameter index
     * @return the Class object (must fit also for primitive type)
     */
	Class getConstructorParameterType(int index);

}