Add SimpleEvaluationContext

Issue: SPR-16588

Author: rstoyanchev

spring-expression/src/main/java/org/springframework/expression/spel/support/SimpleEvaluationContext.java

@@ -0,0 +1,195 @@
+/*
+ * Copyright 2002-2018 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
+ *
+ *      http://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.support;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+import org.springframework.expression.BeanResolver;
+import org.springframework.expression.ConstructorResolver;
+import org.springframework.expression.EvaluationContext;
+import org.springframework.expression.EvaluationException;
+import org.springframework.expression.MethodResolver;
+import org.springframework.expression.OperatorOverloader;
+import org.springframework.expression.PropertyAccessor;
+import org.springframework.expression.TypeComparator;
+import org.springframework.expression.TypeConverter;
+import org.springframework.expression.TypeLocator;
+import org.springframework.expression.TypedValue;
+import org.springframework.expression.spel.SpelEvaluationException;
+import org.springframework.expression.spel.SpelMessage;
+
+/**
+ * A basic implementation of {@link EvaluationContext} that focuses on a subset
+ * of essential SpEL features and configuration options, and relies on default
+ * strategies otherwise.
+ *
+ * <p>In many cases, the full extent of the SpEL is not
+ * required and should be meaningfully restricted. Examples include but are not
+ * limited to data binding expressions, property-based filters, and others. To
+ * that effect, {@code SimpleEvaluationContext} supports only a subset of the
+ * SpEL language syntax that excludes references to Java types, constructors,
+ * and bean references.
+ *
+ * <p>Note that {@code SimpleEvaluationContext} cannot be configured with a
+ * default root object. Instead it is meant to be created once and used
+ * repeatedly through method variants on
+ * {@link org.springframework.expression.Expression Expression} that accept
+ * both an {@code EvaluationContext} and a root object.
+ *
+ * @author Rossen Stoyanchev
+ * @since 4.3.15
+ */
+public class SimpleEvaluationContext implements EvaluationContext {
+
+	private static final TypeLocator typeNotFoundTypeLocator = new TypeLocator() {
+
+		@Override
+		public Class<?> findType(String typeName) throws EvaluationException {
+			throw new SpelEvaluationException(SpelMessage.TYPE_NOT_FOUND, typeName);
+		}
+	};
+
+
+	private final List<PropertyAccessor> propertyAccessors;
+
+	private final List<ConstructorResolver> constructorResolvers =
+			Collections.<ConstructorResolver>singletonList(new ReflectiveConstructorResolver());
+
+	private final List<MethodResolver> methodResolvers =
+			Collections.<MethodResolver>singletonList(new ReflectiveMethodResolver());
+
+	private final TypeConverter typeConverter;
+
+	private final TypeComparator typeComparator = new StandardTypeComparator();
+
+	private final OperatorOverloader operatorOverloader = new StandardOperatorOverloader();
+
+	private final Map<String, Object> variables = new HashMap<String, Object>();
+
+
+	public SimpleEvaluationContext() {
+		this(null, null);
+	}
+
+	public SimpleEvaluationContext(List<PropertyAccessor> accessors, TypeConverter converter) {
+		this.propertyAccessors = initPropertyAccessors(accessors);
+		this.typeConverter = converter != null ? converter : new StandardTypeConverter();
+	}
+
+
+	private static List<PropertyAccessor> initPropertyAccessors(List<PropertyAccessor> accessors) {
+		if (accessors == null) {
+			accessors = new ArrayList<PropertyAccessor>(5);
+			accessors.add(new ReflectivePropertyAccessor());
+		}
+		return accessors;
+	}
+
+
+	/**
+	 * {@code SimpleEvaluationContext} cannot be configured with a root object.
+	 * It is meant for repeated use with
+	 * {@link org.springframework.expression.Expression Expression} method
+	 * variants that accept both an {@code EvaluationContext} and a root object.
+	 * @return Always returns {@link TypedValue#NULL}.
+	 */
+	@Override
+	public TypedValue getRootObject() {
+		return TypedValue.NULL;
+	}
+
+	@Override
+	public List<PropertyAccessor> getPropertyAccessors() {
+		return this.propertyAccessors;
+	}
+
+	/**
+	 * Return a single {@link ReflectiveConstructorResolver}.
+	 */
+	@Override
+	public List<ConstructorResolver> getConstructorResolvers() {
+		return this.constructorResolvers;
+	}
+
+	/**
+	 * Return a single {@link ReflectiveMethodResolver}.
+	 */
+	@Override
+	public List<MethodResolver> getMethodResolvers() {
+		return this.methodResolvers;
+	}
+
+	/**
+	 * {@code SimpleEvaluationContext} does not support use of bean references.
+	 * @return Always returns {@code null}
+	 */
+	@Override
+	public BeanResolver getBeanResolver() {
+		return null;
+	}
+
+	/**
+	 * {@code SimpleEvaluationContext} does not support use of type references.
+	 * @return {@code TypeLocator} implementation that raises a
+	 * {@link SpelEvaluationException} with {@link SpelMessage#TYPE_NOT_FOUND}.
+	 */
+	@Override
+	public TypeLocator getTypeLocator() {
+		return typeNotFoundTypeLocator;
+	}
+
+	/**
+	 * The configured {@link TypeConverter}.
+	 * <p>By default this is {@link StandardTypeConverter}.
+	 */
+	@Override
+	public TypeConverter getTypeConverter() {
+		return this.typeConverter;
+	}
+
+	/**
+	 * Return an instance of {@link StandardTypeComparator}.
+	 */
+	@Override
+	public TypeComparator getTypeComparator() {
+		return this.typeComparator;
+	}
+
+
+	/**
+	 * Return an instance of {@link StandardOperatorOverloader}.
+	 */
+	@Override
+	public OperatorOverloader getOperatorOverloader() {
+		return this.operatorOverloader;
+	}
+
+	@Override
+	public void setVariable(String name, Object value) {
+		this.variables.put(name, value);
+	}
+
+	@Override
+	public Object lookupVariable(String name) {
+		return this.variables.get(name);
+	}
+
+}