001/*
002 * Copyright 2002-2019 the original author or authors.
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 *      https://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package org.springframework.expression;
018
019import org.springframework.lang.Nullable;
020
021/**
022 * A property accessor is able to read from (and possibly write to) an object's properties.
023 *
024 * <p>This interface places no restrictions, and so implementors are free to access properties
025 * directly as fields or through getters or in any other way they see as appropriate.
026 *
027 * <p>A resolver can optionally specify an array of target classes for which it should be
028 * called. However, if it returns {@code null} from {@link #getSpecificTargetClasses()},
029 * it will be called for all property references and given a chance to determine if it
030 * can read or write them.
031 *
032 * <p>Property resolvers are considered to be ordered, and each will be called in turn.
033 * The only rule that affects the call order is that any resolver naming the target
034 * class directly in {@link #getSpecificTargetClasses()} will be called first, before
035 * the general resolvers.
036 *
037 * @author Andy Clement
038 * @since 3.0
039 */
040public interface PropertyAccessor {
041
042        /**
043         * Return an array of classes for which this resolver should be called.
044         * <p>Returning {@code null} indicates this is a general resolver that
045         * can be called in an attempt to resolve a property on any type.
046         * @return an array of classes that this resolver is suitable for
047         * (or {@code null} if a general resolver)
048         */
049        @Nullable
050        Class<?>[] getSpecificTargetClasses();
051
052        /**
053         * Called to determine if a resolver instance is able to access a specified property
054         * on a specified target object.
055         * @param context the evaluation context in which the access is being attempted
056         * @param target the target object upon which the property is being accessed
057         * @param name the name of the property being accessed
058         * @return true if this resolver is able to read the property
059         * @throws AccessException if there is any problem determining whether the property can be read
060         */
061        boolean canRead(EvaluationContext context, @Nullable Object target, String name) throws AccessException;
062
063        /**
064         * Called to read a property from a specified target object.
065         * Should only succeed if {@link #canRead} also returns {@code true}.
066         * @param context the evaluation context in which the access is being attempted
067         * @param target the target object upon which the property is being accessed
068         * @param name the name of the property being accessed
069         * @return a TypedValue object wrapping the property value read and a type descriptor for it
070         * @throws AccessException if there is any problem accessing the property value
071         */
072        TypedValue read(EvaluationContext context, @Nullable Object target, String name) throws AccessException;
073
074        /**
075         * Called to determine if a resolver instance is able to write to a specified
076         * property on a specified target object.
077         * @param context the evaluation context in which the access is being attempted
078         * @param target the target object upon which the property is being accessed
079         * @param name the name of the property being accessed
080         * @return true if this resolver is able to write to the property
081         * @throws AccessException if there is any problem determining whether the
082         * property can be written to
083         */
084        boolean canWrite(EvaluationContext context, @Nullable Object target, String name) throws AccessException;
085
086        /**
087         * Called to write to a property on a specified target object.
088         * Should only succeed if {@link #canWrite} also returns {@code true}.
089         * @param context the evaluation context in which the access is being attempted
090         * @param target the target object upon which the property is being accessed
091         * @param name the name of the property being accessed
092         * @param newValue the new value for the property
093         * @throws AccessException if there is any problem writing to the property value
094         */
095        void write(EvaluationContext context, @Nullable Object target, String name, @Nullable Object newValue)
096                        throws AccessException;
097
098}