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.spel;
18
19 import org.springframework.expression.EvaluationException;
20 import org.springframework.expression.TypedValue;
21
22 /**
23 * Represents a node in the Ast for a parsed expression.
24 *
25 * @author Andy Clement
26 * @since 3.0
27 */
28 public interface SpelNode {
29
30 /**
31 * Evaluate the expression node in the context of the supplied expression state
32 * and return the value.
33 * @param expressionState the current expression state (includes the context)
34 * @return the value of this node evaluated against the specified state
35 */
36 Object getValue(ExpressionState expressionState) throws EvaluationException;
37
38 /**
39 * Evaluate the expression node in the context of the supplied expression state
40 * and return the typed value.
41 * @param expressionState the current expression state (includes the context)
42 * @return the type value of this node evaluated against the specified state
43 */
44 TypedValue getTypedValue(ExpressionState expressionState) throws EvaluationException;
45
46 /**
47 * Determine if this expression node will support a setValue() call.
48 * @param expressionState the current expression state (includes the context)
49 * @return true if the expression node will allow setValue()
50 * @throws EvaluationException if something went wrong trying to determine
51 * if the node supports writing
52 */
53 boolean isWritable(ExpressionState expressionState) throws EvaluationException;
54
55 /**
56 * Evaluate the expression to a node and then set the new value on that node.
57 * For example, if the expression evaluates to a property reference, then the
58 * property will be set to the new value.
59 * @param expressionState the current expression state (includes the context)
60 * @param newValue the new value
61 * @throws EvaluationException if any problem occurs evaluating the expression or
62 * setting the new value
63 */
64 void setValue(ExpressionState expressionState, Object newValue) throws EvaluationException;
65
66 /**
67 * @return the string form of this AST node
68 */
69 String toStringAST();
70
71 /**
72 * @return the number of children under this node
73 */
74 int getChildCount();
75
76 /**
77 * Helper method that returns a SpelNode rather than an Antlr Tree node.
78 * @return the child node cast to a SpelNode
79 */
80 SpelNode getChild(int index);
81
82 /**
83 * Determine the class of the object passed in, unless it is already a class object.
84 * @param obj the object that the caller wants the class of
85 * @return the class of the object if it is not already a class object,
86 * or {@code null} if the object is {@code null}
87 */
88 Class<?> getObjectClass(Object obj);
89
90 /**
91 * @return the start position of this Ast node in the expression string
92 */
93 int getStartPosition();
94
95 /**
96 * @return the end position of this Ast node in the expression string
97 */
98 int getEndPosition();
99
100 }