org.apache.camel.language.spel.SpelExpression Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of camel-spring Show documentation
Camel Spring
There is a newer version: 4.9.0
/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.apache.camel.language.spel;

import org.apache.camel.CamelContext;
import org.apache.camel.Exchange;
import org.apache.camel.ExpressionEvaluationException;
import org.apache.camel.spring.SpringCamelContext;
import org.apache.camel.spring.util.RegistryBeanResolver;
import org.apache.camel.support.ExpressionSupport;
import org.springframework.context.ApplicationContext;
import org.springframework.context.expression.BeanFactoryResolver;
import org.springframework.context.expression.MapAccessor;
import org.springframework.expression.BeanResolver;
import org.springframework.expression.EvaluationContext;
import org.springframework.expression.Expression;
import org.springframework.expression.ParserContext;
import org.springframework.expression.common.TemplateParserContext;
import org.springframework.expression.spel.standard.SpelExpressionParser;
import org.springframework.expression.spel.support.StandardEvaluationContext;

/**
 * Class responsible for evaluating
 *  Spring
 * Expression Language (SpEL) in the context of Camel.
 */
public class SpelExpression extends ExpressionSupport {

    private final String expressionString;
    private final Class type;
    private final BeanResolver beanResolver;

    // SpelExpressionParser is thread-safe according to the docs
    private final SpelExpressionParser expressionParser;

    private volatile Expression expression;

    public SpelExpression(String expressionString, Class type) {
        this(expressionString, type, null);
    }

    public SpelExpression(String expressionString, Class type, BeanResolver beanResolver) {
        this.expressionString = expressionString;
        this.type = type;
        this.beanResolver = beanResolver;
        this.expressionParser = new SpelExpressionParser();
    }

    public static SpelExpression spel(String expression) {
        return new SpelExpression(expression, Object.class);
    }

    @Override
    public  T evaluate(Exchange exchange, Class tClass) {
        if (expression == null) {
            init(exchange.getContext());
        }
        try {
            EvaluationContext evaluationContext = createEvaluationContext(exchange);
            Object value = expression.getValue(evaluationContext);
            // Let Camel handle the type conversion
            return exchange.getContext().getTypeConverter().convertTo(tClass, value);
        } catch (Exception e) {
            throw new ExpressionEvaluationException(this, exchange, e);
        }
    }

    private EvaluationContext createEvaluationContext(Exchange exchange) {
        StandardEvaluationContext evaluationContext = new StandardEvaluationContext(new RootObject(exchange));
        evaluationContext.addPropertyAccessor(new MapAccessor());
        if (beanResolver != null) {
            evaluationContext.setBeanResolver(beanResolver);
        } else if (exchange.getContext() instanceof SpringCamelContext) {
            // Support references (like @foo) in expressions to beans defined in the Registry/ApplicationContext
            ApplicationContext applicationContext = ((SpringCamelContext) exchange.getContext()).getApplicationContext();
            evaluationContext.setBeanResolver(new BeanFactoryResolver(applicationContext));
        } else {
            evaluationContext.setBeanResolver(new RegistryBeanResolver(exchange.getContext().getRegistry()));
        }
        return evaluationContext;
    }

    private Expression parseExpression() {
        // Support template parsing with #{ } delimiters
        ParserContext parserContext = new TemplateParserContext();
        return expressionParser.parseExpression(expressionString, parserContext);
    }

    public Class getType() {
        return type;
    }

    @Override
    protected String assertionFailureMessage(Exchange exchange) {
        return expressionString;
    }

    @Override
    public void init(CamelContext context) {
        expression = parseExpression();
    }

    @Override
    public String toString() {
        return "SpelExpression[" + expressionString + "]";
    }
}