001/* 002 * Copyright 2002-2017 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.core.convert.TypeDescriptor; 020import org.springframework.lang.Nullable; 021 022/** 023 * A type converter can convert values between different types encountered during 024 * expression evaluation. This is an SPI for the expression parser; see 025 * {@link org.springframework.core.convert.ConversionService} for the primary 026 * user API to Spring's conversion facilities. 027 * 028 * @author Andy Clement 029 * @author Juergen Hoeller 030 * @since 3.0 031 */ 032public interface TypeConverter { 033 034 /** 035 * Return {@code true} if the type converter can convert the specified type 036 * to the desired target type. 037 * @param sourceType a type descriptor that describes the source type 038 * @param targetType a type descriptor that describes the requested result type 039 * @return {@code true} if that conversion can be performed 040 */ 041 boolean canConvert(@Nullable TypeDescriptor sourceType, TypeDescriptor targetType); 042 043 /** 044 * Convert (or coerce) a value from one type to another, for example from a 045 * {@code boolean} to a {@code String}. 046 * <p>The {@link TypeDescriptor} parameters enable support for typed collections: 047 * A caller may prefer a {@code List<Integer>}, for example, rather than 048 * simply any {@code List}. 049 * @param value the value to be converted 050 * @param sourceType a type descriptor that supplies extra information about the 051 * source object 052 * @param targetType a type descriptor that supplies extra information about the 053 * requested result type 054 * @return the converted value 055 * @throws EvaluationException if conversion failed or is not possible to begin with 056 */ 057 @Nullable 058 Object convertValue(@Nullable Object value, @Nullable TypeDescriptor sourceType, TypeDescriptor targetType); 059 060}