/*
* Copyright 2002-2016 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.context.expression;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.BeanExpressionException;
import org.springframework.beans.factory.config.BeanExpressionContext;
import org.springframework.beans.factory.config.BeanExpressionResolver;
import org.springframework.core.convert.ConversionService;
import org.springframework.expression.Expression;
import org.springframework.expression.ExpressionParser;
import org.springframework.expression.ParserContext;
import org.springframework.expression.spel.SpelParserConfiguration;
import org.springframework.expression.spel.standard.SpelExpressionParser;
import org.springframework.expression.spel.support.StandardEvaluationContext;
import org.springframework.expression.spel.support.StandardTypeConverter;
import org.springframework.expression.spel.support.StandardTypeLocator;
import org.springframework.util.Assert;
import org.springframework.util.StringUtils;
/**
* Standard implementation of the
* {@link org.springframework.beans.factory.config.BeanExpressionResolver}
* interface, parsing and evaluating Spring EL using Spring's expression module.
*
* @author Juergen Hoeller
* @since 3.0
* @see org.springframework.expression.ExpressionParser
* @see org.springframework.expression.spel.standard.SpelExpressionParser
* @see org.springframework.expression.spel.support.StandardEvaluationContext
*/
public class StandardBeanExpressionResolver implements BeanExpressionResolver {
/** Default expression prefix: "#{" */
public static final String DEFAULT_EXPRESSION_PREFIX = "#{";
/** Default expression suffix: "}" */
public static final String DEFAULT_EXPRESSION_SUFFIX = "}";
private String expressionPrefix = DEFAULT_EXPRESSION_PREFIX;
private String expressionSuffix = DEFAULT_EXPRESSION_SUFFIX;
private ExpressionParser expressionParser;
private final Map<String, Expression> expressionCache = new ConcurrentHashMap<>(256);
private final Map<BeanExpressionContext, StandardEvaluationContext> evaluationCache =
new ConcurrentHashMap<>(8);
private final ParserContext beanExpressionParserContext = new ParserContext() {
@Override
public boolean isTemplate() {
return true;
}
@Override
public String getExpressionPrefix() {
return expressionPrefix;
}
@Override
public String getExpressionSuffix() {
return expressionSuffix;
}
};
/**
* Create a new {@code StandardBeanExpressionResolver} with default settings.
*/
public StandardBeanExpressionResolver() {
this.expressionParser = new SpelExpressionParser();
}
/**
* Create a new {@code StandardBeanExpressionResolver} with the given bean class loader,
* using it as the basis for expression compilation.
* @param beanClassLoader the factory's bean class loader
*/
public StandardBeanExpressionResolver(ClassLoader beanClassLoader) {
this.expressionParser = new SpelExpressionParser(new SpelParserConfiguration(null, beanClassLoader));
}
/**
* Set the prefix that an expression string starts with.
* The default is "#{".
* @see #DEFAULT_EXPRESSION_PREFIX
*/
public void setExpressionPrefix(String expressionPrefix) {
Assert.hasText(expressionPrefix, "Expression prefix must not be empty");
this.expressionPrefix = expressionPrefix;
}
/**
* Set the suffix that an expression string ends with.
* The default is "}".
* @see #DEFAULT_EXPRESSION_SUFFIX
*/
public void setExpressionSuffix(String expressionSuffix) {
Assert.hasText(expressionSuffix, "Expression suffix must not be empty");
this.expressionSuffix = expressionSuffix;
}
/**
* Specify the EL parser to use for expression parsing.
* <p>Default is a {@link org.springframework.expression.spel.standard.SpelExpressionParser},
* compatible with standard Unified EL style expression syntax.
*/
public void setExpressionParser(ExpressionParser expressionParser) {
Assert.notNull(expressionParser, "ExpressionParser must not be null");
this.expressionParser = expressionParser;
}
@Override
public Object evaluate(String value, BeanExpressionContext evalContext) throws BeansException {
if (!StringUtils.hasLength(value)) {
return value;
}
try {
Expression expr = this.expressionCache.get(value);
if (expr == null) {
expr = this.expressionParser.parseExpression(value, this.beanExpressionParserContext);
this.expressionCache.put(value, expr);
}
StandardEvaluationContext sec = this.evaluationCache.get(evalContext);
if (sec == null) {
sec = new StandardEvaluationContext();
sec.setRootObject(evalContext);
sec.addPropertyAccessor(new BeanExpressionContextAccessor());
sec.addPropertyAccessor(new BeanFactoryAccessor());
sec.addPropertyAccessor(new MapAccessor());
sec.addPropertyAccessor(new EnvironmentAccessor());
sec.setBeanResolver(new BeanFactoryResolver(evalContext.getBeanFactory()));
sec.setTypeLocator(new StandardTypeLocator(evalContext.getBeanFactory().getBeanClassLoader()));
ConversionService conversionService = evalContext.getBeanFactory().getConversionService();
if (conversionService != null) {
sec.setTypeConverter(new StandardTypeConverter(conversionService));
}
customizeEvaluationContext(sec);
this.evaluationCache.put(evalContext, sec);
}
return expr.getValue(sec);
}
catch (Exception ex) {
throw new BeanExpressionException("Expression parsing failed", ex);
}
}
/**
* Template method for customizing the expression evaluation context.
* <p>The default implementation is empty.
*/
protected void customizeEvaluationContext(StandardEvaluationContext evalContext) {
}
}