org.springframework.expression.PropertyAccessor Maven / Gradle / Ivy

/*
 * Copyright 2002-2009 the original author or authors.
 *
 * Licensed 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.springframework.expression;


/**
 * A property accessor is able to read (and possibly write) to object properties. The interface places no restrictions
 * and so implementors are free to access properties directly as fields or through getters or in any other way they see
 * as appropriate. A resolver can optionally specify an array of target classes for which it should be called - but if
 * it returns null from getSpecificTargetClasses() then it will be called for all property references and given a chance
 * to determine if it can read or write them. Property resolvers are considered to be ordered and each will be called in
 * turn. The only rule that affects the call order is that any naming the target class directly in
 * getSpecifiedTargetClasses() will be called first, before the general resolvers.
 * 
 * @author Andy Clement
 * @since 3.0
 */
public interface PropertyAccessor {

	/**
	 * Return an array of classes for which this resolver should be called. Returning null indicates this is a general
	 * resolver that can be called in an attempt to resolve a property on any type.
	 * @return an array of classes that this resolver is suitable for (or null if a general resolver)
	 */
	Class[] getSpecificTargetClasses();

	/**
	 * Called to determine if a resolver instance is able to access a specified property on a specified target object.
	 * @param context the evaluation context in which the access is being attempted
	 * @param target the target object upon which the property is being accessed
	 * @param name the name of the property being accessed
	 * @return true if this resolver is able to read the property
	 * @throws AccessException if there is any problem determining whether the property can be read
	 */
	boolean canRead(EvaluationContext context, Object target, String name) throws AccessException;

	/**
	 * Called to read a property from a specified target object
	 * @param context the evaluation context in which the access is being attempted
	 * @param target the target object upon which the property is being accessed
	 * @param name the name of the property being accessed
	 * @return a TypedValue object wrapping the property value read and a type descriptor for it
	 * @throws AccessException if there is any problem accessing the property value
	 */
	TypedValue read(EvaluationContext context, Object target, String name) throws AccessException;

	/**
	 * Called to determine if a resolver instance is able to write to a specified property on a specified target object.
	 * @param context the evaluation context in which the access is being attempted
	 * @param target the target object upon which the property is being accessed
	 * @param name the name of the property being accessed
	 * @return true if this resolver is able to write to the property
	 * @throws AccessException if there is any problem determining whether the property can be written to
	 */
	boolean canWrite(EvaluationContext context, Object target, String name) throws AccessException;

	/**
	 * Called to write to a property on a specified target object. Should only succeed if canWrite() also returns true.
	 * @param context the evaluation context in which the access is being attempted
	 * @param target the target object upon which the property is being accessed
	 * @param name the name of the property being accessed
	 * @param newValue the new value for the property
	 * @throws AccessException if there is any problem writing to the property value
	 */
	void write(EvaluationContext context, Object target, String name, Object newValue) throws AccessException;

}