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/*
* Copyright 2002-2019 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
*
* https://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;
import org.springframework.lang.Nullable;
/**
* A property accessor is able to read from (and possibly write to) an object's properties.
*
* This 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. However, if it returns {@code null} from {@link #getSpecificTargetClasses()},
* 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 resolver naming the target
* class directly in {@link #getSpecificTargetClasses()} 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 {@code 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 {@code null} if a general resolver)
*/
@Nullable
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, @Nullable Object target, String name) throws AccessException;
/**
* Called to read a property from a specified target object.
* Should only succeed if {@link #canRead} also returns {@code 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
* @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, @Nullable 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, @Nullable Object target, String name) throws AccessException;
/**
* Called to write to a property on a specified target object.
* Should only succeed if {@link #canWrite} also returns {@code 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, @Nullable Object target, String name, @Nullable Object newValue)
throws AccessException;
}