org.picocontainer.parameters.NullParameter Maven / Gradle / Ivy
/*******************************************************************************
* Copyright (C) PicoContainer Organization. All rights reserved.
* ---------------------------------------------------------------------------
* The software in this package is published under the terms of the BSD style
* license a copy of which has been included with this distribution in the
* LICENSE.txt file.
******************************************************************************/
package org.picocontainer.parameters;
import java.io.Serializable;
import java.lang.annotation.Annotation;
import java.lang.reflect.Type;
import org.picocontainer.ComponentAdapter;
import org.picocontainer.NameBinding;
import org.picocontainer.PicoCompositionException;
import org.picocontainer.PicoContainer;
import org.picocontainer.PicoVisitor;
/**
* Once in a great while, you actually want to pass in 'null' as an argument. Instead
* of bypassing the type checking mechanisms available in
* {@link org.picocontainer.parameters.ConstantParameter ConstantParameter}, we provide a Special Type
* geared to marking nulls.
* @author Michael Rimov
*
*/
@SuppressWarnings("serial")
public class NullParameter extends AbstractParameter implements Serializable {
/**
* The one and only instance of null parameter.
*/
public static final NullParameter INSTANCE = new NullParameter();
/**
* Only once instance of Null parameter needed.
*/
protected NullParameter() {
}
/**
* {@inheritDoc}
* @see org.picocontainer.Parameter#accept(org.picocontainer.PicoVisitor)
*/
public void accept(PicoVisitor visitor) {
visitor.visitParameter(this);
}
/**
* {@inheritDoc}
* @see org.picocontainer.Parameter#resolve(org.picocontainer.PicoContainer, org.picocontainer.ComponentAdapter, org.picocontainer.ComponentAdapter, java.lang.reflect.Type, org.picocontainer.NameBinding, boolean, java.lang.annotation.Annotation)
*/
public Resolver resolve(PicoContainer container,
ComponentAdapter forAdapter,
ComponentAdapter injecteeAdapter, Type expectedType,
NameBinding expectedNameBinding, boolean useNames,
Annotation binding) {
return new ValueResolver(isAssignable(expectedType), null, null);
}
/**
* {@inheritDoc}
* @see org.picocontainer.Parameter#verify(org.picocontainer.PicoContainer, org.picocontainer.ComponentAdapter, java.lang.reflect.Type, org.picocontainer.NameBinding, boolean, java.lang.annotation.Annotation)
*/
public void verify(PicoContainer container, ComponentAdapter adapter,
Type expectedType, NameBinding expectedNameBinding,
boolean useNames, Annotation binding) {
if (!isAssignable(expectedType)) {
throw new PicoCompositionException(expectedType + " cannot be assigned a null value");
}
}
/**
* Nulls cannot be assigned to primitives.
* @param expectedType
* @return
*/
protected boolean isAssignable(Type expectedType) {
if (expectedType instanceof Class) {
Class expectedClass = Class.class.cast(expectedType);
if (expectedClass.isPrimitive()) {
return false;
}
}
return true;
}
}