1 /*
2 * Copyright 2002-2013 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 import org.springframework.core.convert.TypeDescriptor;
20
21 /**
22 * A type converter can convert values between different types encountered during
23 * expression evaluation. This is an SPI for the expression parser; see
24 * {@link org.springframework.core.convert.ConversionService} for the primary
25 * user API to Spring's conversion facilities.
26 *
27 * @author Andy Clement
28 * @author Juergen Hoeller
29 * @since 3.0
30 */
31 public interface TypeConverter {
32
33 /**
34 * Return {@code true} if the type converter can convert the specified type
35 * to the desired target type.
36 * @param sourceType a type descriptor that describes the source type
37 * @param targetType a type descriptor that describes the requested result type
38 * @return {@code true} if that conversion can be performed
39 */
40 boolean canConvert(TypeDescriptor sourceType, TypeDescriptor targetType);
41
42 /**
43 * Convert (or coerce) a value from one type to another, for example from a
44 * {@code boolean} to a {@code String}.
45 * <p>The {@link TypeDescriptor} parameters enable support for typed collections:
46 * A caller may prefer a {@code List<Integer>}, for example, rather than
47 * simply any {@code List}.
48 * @param value the value to be converted
49 * @param sourceType a type descriptor that supplies extra information about the
50 * source object
51 * @param targetType a type descriptor that supplies extra information about the
52 * requested result type
53 * @return the converted value
54 * @throws EvaluationException if conversion failed or is not possible to begin with
55 */
56 Object convertValue(Object value, TypeDescriptor sourceType, TypeDescriptor targetType);
57
58 }