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/*
* Copyright 2002-2024 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* https://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.springframework.expression.spel;
import org.jspecify.annotations.Nullable;
import org.springframework.asm.MethodVisitor;
import org.springframework.expression.EvaluationException;
import org.springframework.expression.TypedValue;
/**
* Represents a node in the abstract syntax tree (AST) for a parsed Spring
* Expression Language (SpEL) expression.
*
* @author Andy Clement
* @author Sam Brannen
* @since 3.0
*/
public interface SpelNode {
/**
* Evaluate the expression node in the context of the supplied expression state
* and return the value.
* @param expressionState the current expression state (includes the context)
* @return the value of this node evaluated against the specified state
* @throws EvaluationException if any problem occurs evaluating the expression
*/
@Nullable Object getValue(ExpressionState expressionState) throws EvaluationException;
/**
* Evaluate the expression node in the context of the supplied expression state
* and return the typed value.
* @param expressionState the current expression state (includes the context)
* @return the typed value of this node evaluated against the specified state
* @throws EvaluationException if any problem occurs evaluating the expression
*/
TypedValue getTypedValue(ExpressionState expressionState) throws EvaluationException;
/**
* Determine if this expression node will support a setValue() call.
* @param expressionState the current expression state (includes the context)
* @return true if the expression node will allow setValue()
* @throws EvaluationException if something went wrong trying to determine
* if the node supports writing
*/
boolean isWritable(ExpressionState expressionState) throws EvaluationException;
/**
* Evaluate the expression to a node and then set the new value on that node.
* For example, if the expression evaluates to a property reference, then the
* property will be set to the new value.
* @param expressionState the current expression state (includes the context)
* @param newValue the new value
* @throws EvaluationException if any problem occurs evaluating the expression or
* setting the new value
*/
void setValue(ExpressionState expressionState, @Nullable Object newValue) throws EvaluationException;
/**
* Return the string form of this AST node.
* @return the string form
*/
String toStringAST();
/**
* Return the number of children under this node.
* @return the child count
* @see #getChild(int)
*/
int getChildCount();
/**
* Return the nth child under this node.
* @return the child node
* @see #getChildCount()
*/
SpelNode getChild(int index);
/**
* Determine the class of the object passed in, unless it is already a class object.
* @param obj the object that the caller wants the class of
* @return the class of the object if it is not already a class object,
* or {@code null} if the object is {@code null}
*/
@Nullable Class getObjectClass(@Nullable Object obj);
/**
* Return the start position of this AST node in the expression string.
* @return the start position
*/
int getStartPosition();
/**
* Return the end position of this AST node in the expression string.
* @return the end position
*/
int getEndPosition();
/**
* Determine if this node can be compiled to bytecode.
* The reasoning in each node may be different but will typically involve
* checking whether the exit type descriptor of the node is known and any
* relevant child nodes are compilable.
*
The default implementation returns {@code false}.
*
If you override this method, you must also override
* {@link #generateCode(MethodVisitor, CodeFlow)}.
* @return {@code true} if this node can be compiled to bytecode
* @since 6.2
* @see #generateCode(MethodVisitor, CodeFlow)
*/
default boolean isCompilable() {
return false;
}
/**
* Generate the bytecode for this node into the supplied {@link MethodVisitor}.
*
Context information about the current expression being compiled is
* available in the supplied {@link CodeFlow} object — for example,
* information about the type of the object currently on the stack.
*
This method will not be invoked unless {@link #isCompilable()} returns
* {@code true}.
*
The default implementation throws an {@link IllegalStateException}
* since {@link #isCompilable()} returns {@code false} by default.
*
If you override this method, you must also override {@link #isCompilable()}.
* @param methodVisitor the ASM {@code MethodVisitor} into which code should
* be generated
* @param codeFlow a context object with information about what is on the stack
* @since 6.2
* @see #isCompilable()
*/
default void generateCode(MethodVisitor methodVisitor, CodeFlow codeFlow) {
throw new IllegalStateException(getClass().getName() + " does not support bytecode generation");
}
}