1 /* 2 * Copyright 2002-2014 the original author or authors. 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package org.springframework.expression; 18 19 20 /** 21 * A property accessor is able to read from (and possibly write to) an object's properties. 22 * This interface places no restrictions, and so implementors are free to access properties 23 * directly as fields or through getters or in any other way they see as appropriate. 24 * 25 * <p>A resolver can optionally specify an array of target classes for which it should be 26 * called. However, if it returns {@code null} from {@link #getSpecificTargetClasses()}, 27 * it will be called for all property references and given a chance to determine if it 28 * can read or write them. 29 * 30 * <p>Property resolvers are considered to be ordered and each will be called in turn. 31 * The only rule that affects the call order is that any naming the target class directly 32 * in {@link #getSpecificTargetClasses()} will be called first, before the general resolvers. 33 * 34 * @author Andy Clement 35 * @since 3.0 36 */ 37 public interface PropertyAccessor { 38 39 /** 40 * Return an array of classes for which this resolver should be called. 41 * <p>>Returning {@code null} indicates this is a general resolver that 42 * can be called in an attempt to resolve a property on any type. 43 * @return an array of classes that this resolver is suitable for 44 * (or {@code null} if a general resolver) 45 */ 46 Class<?>[] getSpecificTargetClasses(); 47 48 /** 49 * Called to determine if a resolver instance is able to access a specified property 50 * on a specified target object. 51 * @param context the evaluation context in which the access is being attempted 52 * @param target the target object upon which the property is being accessed 53 * @param name the name of the property being accessed 54 * @return true if this resolver is able to read the property 55 * @throws AccessException if there is any problem determining whether the property can be read 56 */ 57 boolean canRead(EvaluationContext context, Object target, String name) throws AccessException; 58 59 /** 60 * Called to read a property from a specified target object. 61 * Should only succeed if {@link #canRead} also returns {@code true}. 62 * @param context the evaluation context in which the access is being attempted 63 * @param target the target object upon which the property is being accessed 64 * @param name the name of the property being accessed 65 * @return a TypedValue object wrapping the property value read and a type descriptor for it 66 * @throws AccessException if there is any problem accessing the property value 67 */ 68 TypedValue read(EvaluationContext context, Object target, String name) throws AccessException; 69 70 /** 71 * Called to determine if a resolver instance is able to write to a specified 72 * property on a specified target object. 73 * @param context the evaluation context in which the access is being attempted 74 * @param target the target object upon which the property is being accessed 75 * @param name the name of the property being accessed 76 * @return true if this resolver is able to write to the property 77 * @throws AccessException if there is any problem determining whether the 78 * property can be written to 79 */ 80 boolean canWrite(EvaluationContext context, Object target, String name) throws AccessException; 81 82 /** 83 * Called to write to a property on a specified target object. 84 * Should only succeed if {@link #canWrite} also returns {@code true}. 85 * @param context the evaluation context in which the access is being attempted 86 * @param target the target object upon which the property is being accessed 87 * @param name the name of the property being accessed 88 * @param newValue the new value for the property 89 * @throws AccessException if there is any problem writing to the property value 90 */ 91 void write(EvaluationContext context, Object target, String name, Object newValue) throws AccessException; 92 93 }