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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;
import java.util.List;
import java.util.function.Supplier;
import org.springframework.lang.Nullable;
/**
* Expressions are executed in an evaluation context. It is in this context that
* references are resolved when encountered during expression evaluation.
*
* There are two default implementations of this interface.
*
* - {@link org.springframework.expression.spel.support.SimpleEvaluationContext
* SimpleEvaluationContext}: a simpler builder-style {@code EvaluationContext}
* variant for data-binding purposes, which allows for opting into several SpEL
* features as needed.
* - {@link org.springframework.expression.spel.support.StandardEvaluationContext
* StandardEvaluationContext}: a powerful and highly configurable {@code EvaluationContext}
* implementation, which can be extended, rather than having to implement everything
* manually.
*
*
* @author Andy Clement
* @author Juergen Hoeller
* @author Sam Brannen
* @since 3.0
*/
public interface EvaluationContext {
/**
* Return the default root context object against which unqualified
* properties/methods/etc should be resolved. This can be overridden
* when evaluating an expression.
*/
TypedValue getRootObject();
/**
* Return a list of accessors that will be asked in turn to read/write a property.
*/
List getPropertyAccessors();
/**
* Return a list of resolvers that will be asked in turn to locate a constructor.
*/
List getConstructorResolvers();
/**
* Return a list of resolvers that will be asked in turn to locate a method.
*/
List getMethodResolvers();
/**
* Return a bean resolver that can look up beans by name.
*/
@Nullable
BeanResolver getBeanResolver();
/**
* Return a type locator that can be used to find types, either by short or
* fully qualified name.
*/
TypeLocator getTypeLocator();
/**
* Return a type converter that can convert (or coerce) a value from one type to another.
*/
TypeConverter getTypeConverter();
/**
* Return a type comparator for comparing pairs of objects for equality.
*/
TypeComparator getTypeComparator();
/**
* Return an operator overloader that may support mathematical operations
* between more than the standard set of types.
*/
OperatorOverloader getOperatorOverloader();
/**
* Assign the value created by the specified {@link Supplier} to a named variable
* within this evaluation context.
* In contrast to {@link #setVariable(String, Object)}, this method should only
* be invoked to support the assignment operator ({@code =}) within an expression.
*
By default, this method delegates to {@code setVariable(String, Object)},
* providing the value created by the {@code valueSupplier}. Concrete implementations
* may override this default method to provide different semantics.
* @param name the name of the variable to assign
* @param valueSupplier the supplier of the value to be assigned to the variable
* @return a {@link TypedValue} wrapping the assigned value
* @since 5.2.24
*/
default TypedValue assignVariable(String name, Supplier valueSupplier) {
TypedValue typedValue = valueSupplier.get();
setVariable(name, typedValue.getValue());
return typedValue;
}
/**
* Set a named variable in this evaluation context to a specified value.
* In contrast to {@link #assignVariable(String, Supplier)}, this method
* should only be invoked programmatically when interacting directly with the
* {@code EvaluationContext} — for example, to provide initial
* configuration for the context.
* @param name the name of the variable to set
* @param value the value to be placed in the variable
*/
void setVariable(String name, @Nullable Object value);
/**
* Look up a named variable within this evaluation context.
* @param name the name of the variable to look up
* @return the value of the variable, or {@code null} if not found
*/
@Nullable
Object lookupVariable(String name);
/**
* Determine if assignment is enabled within expressions evaluated by this evaluation
* context.
*
If this method returns {@code false}, the assignment ({@code =}), increment
* ({@code ++}), and decrement ({@code --}) operators are disabled.
*
By default, this method returns {@code true}. Concrete implementations may override
* this default method to disable assignment.
* @return {@code true} if assignment is enabled; {@code false} otherwise
* @since 5.3.38
*/
default boolean isAssignmentEnabled() {
return true;
}
}