https://github.com/spring-projects/spring-framework: Spring Expression Language (SpEL) (Spring IO)
  • Juergen Hoeller 
/*
 * Copyright 2002-2017 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;

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 null from 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 naming the target class directly in getSpecificTargetClasses() will be called first, before the general resolvers. 
Author:Andy Clement
Since:3.0
/**
 * 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.
 *
 * <p>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.
 *
 * <p>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 {@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 null indicates this is a general resolver that can be called in an attempt to resolve a property on any type. 
Returns:an array of classes that this resolver is suitable for (or null if a general resolver)
/**
	 * Return an array of classes for which this resolver should be called.
	 * <p>>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.

Params:
  • context – the evaluation context in which the access is being attempted
  • target – the target object upon which the property is being accessed
  • name – the name of the property being accessed
Throws:
  • AccessException – if there is any problem determining whether the property can be read
Returns:true if this resolver is able to read the property
/**
	 * 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 canRead also returns true. 
Params:
  • context – the evaluation context in which the access is being attempted
  • target – the target object upon which the property is being accessed
  • name – the name of the property being accessed
Throws:
Returns:a TypedValue object wrapping the property value read and a type descriptor for it
/**
	 * 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.

Params:
  • context – the evaluation context in which the access is being attempted
  • target – the target object upon which the property is being accessed
  • name – the name of the property being accessed
Throws:
  • AccessException – if there is any problem determining whether the
property can be written to
Returns:true if this resolver is able to write to the property
/**
	 * 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 canWrite also returns true. 
Params:
  • context – the evaluation context in which the access is being attempted
  • target – the target object upon which the property is being accessed
  • name – the name of the property being accessed
  • newValue – the new value for the property
Throws:
/**
	 * 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;

}