001/* 002 * Copyright 2002-2014 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; 018 019 020/** 021 * A property accessor is able to read from (and possibly write to) an object's properties. 022 * This interface places no restrictions, and so implementors are free to access properties 023 * directly as fields or through getters or in any other way they see as appropriate. 024 * 025 * <p>A resolver can optionally specify an array of target classes for which it should be 026 * called. However, if it returns {@code null} from {@link #getSpecificTargetClasses()}, 027 * it will be called for all property references and given a chance to determine if it 028 * can read or write them. 029 * 030 * <p>Property resolvers are considered to be ordered and each will be called in turn. 031 * The only rule that affects the call order is that any naming the target class directly 032 * in {@link #getSpecificTargetClasses()} will be called first, before the general resolvers. 033 * 034 * @author Andy Clement 035 * @since 3.0 036 */ 037public interface PropertyAccessor { 038 039 /** 040 * Return an array of classes for which this resolver should be called. 041 * <p>>Returning {@code null} indicates this is a general resolver that 042 * can be called in an attempt to resolve a property on any type. 043 * @return an array of classes that this resolver is suitable for 044 * (or {@code null} if a general resolver) 045 */ 046 Class<?>[] getSpecificTargetClasses(); 047 048 /** 049 * Called to determine if a resolver instance is able to access a specified property 050 * on a specified target object. 051 * @param context the evaluation context in which the access is being attempted 052 * @param target the target object upon which the property is being accessed 053 * @param name the name of the property being accessed 054 * @return true if this resolver is able to read the property 055 * @throws AccessException if there is any problem determining whether the property can be read 056 */ 057 boolean canRead(EvaluationContext context, Object target, String name) throws AccessException; 058 059 /** 060 * Called to read a property from a specified target object. 061 * Should only succeed if {@link #canRead} also returns {@code true}. 062 * @param context the evaluation context in which the access is being attempted 063 * @param target the target object upon which the property is being accessed 064 * @param name the name of the property being accessed 065 * @return a TypedValue object wrapping the property value read and a type descriptor for it 066 * @throws AccessException if there is any problem accessing the property value 067 */ 068 TypedValue read(EvaluationContext context, Object target, String name) throws AccessException; 069 070 /** 071 * Called to determine if a resolver instance is able to write to a specified 072 * property on a specified target object. 073 * @param context the evaluation context in which the access is being attempted 074 * @param target the target object upon which the property is being accessed 075 * @param name the name of the property being accessed 076 * @return true if this resolver is able to write to the property 077 * @throws AccessException if there is any problem determining whether the 078 * property can be written to 079 */ 080 boolean canWrite(EvaluationContext context, Object target, String name) throws AccessException; 081 082 /** 083 * Called to write to a property on a specified target object. 084 * Should only succeed if {@link #canWrite} also returns {@code true}. 085 * @param context the evaluation context in which the access is being attempted 086 * @param target the target object upon which the property is being accessed 087 * @param name the name of the property being accessed 088 * @param newValue the new value for the property 089 * @throws AccessException if there is any problem writing to the property value 090 */ 091 void write(EvaluationContext context, Object target, String name, Object newValue) throws AccessException; 092 093}