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The Core Camel Java DSL based router
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/**
 * 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.simple;

import org.apache.camel.Expression;
import org.apache.camel.Predicate;
import org.apache.camel.builder.ExpressionBuilder;
import org.apache.camel.support.LanguageSupport;
import org.apache.camel.util.ObjectHelper;
import org.apache.camel.util.PredicateToExpressionAdapter;

/**
 * A simple language
 * which maps simple property style notations to access headers and bodies.
 * Examples of supported expressions are:
 * 
 * exchangeId to access the exchange id
 * id to access the inbound message id
 * in.body or body to access the inbound body
 * in.body.OGNL or body.OGNL to access the inbound body using an OGNL expression
 * mandatoryBodyAs(<classname>) to convert the in body to the given type, will throw exception if not possible to convert
 * bodyAs(<classname>) to convert the in body to the given type, will return null if not possible to convert
 * headerAs(<key>, <classname>) to convert the in header to the given type, will return null if not possible to convert
 * out.body to access the inbound body
 * in.header.foo or header.foo to access an inbound header called 'foo'
 * in.header.foo[bar] or header.foo[bar] to access an inbound header called 'foo' as a Map and lookup the map with 'bar' as key
 * in.header.foo.OGNL or header.OGNL to access an inbound header called 'foo' using an OGNL expression
 * out.header.foo to access an outbound header called 'foo'
 * property.foo to access the exchange property called 'foo'
 * property.foo.OGNL to access the exchange property called 'foo' using an OGNL expression
 * sys.foo to access the system property called 'foo'
 * sysenv.foo to access the system environment called 'foo'
 * exception.messsage to access the exception message
 * threadName to access the current thread name
 * date:<command>:<pattern> for date formatting using the {@link java.text.SimpleDateFormat} patterns.
 *     Supported commands are: now for current timestamp,
 *     in.header.xxx or header.xxx to use the Date object in the in header.
 *     out.header.xxx to use the Date object in the out header.
 * 
 * bean:<bean expression> to invoke a bean using the
 * {@link org.apache.camel.language.bean.BeanLanguage BeanLanguage}
 * properties:<[locations]>:<key> for using property placeholders using the
 *     {@link org.apache.camel.component.properties.PropertiesComponent}.
 *     The locations parameter is optional and you can enter multiple locations separated with comma.
 * 
* 
 * 
 * The simple language supports OGNL notation when accessing either body or header.
 * 

 * The simple language now also includes file language out of the box which means the following expression is also
 * supported:
 * 

 *   file:name to access the file name (is relative, see note below))
 *   file:name.noext to access the file name with no extension
 *   file:name.ext to access the file extension
 *   file:ext to access the file extension
 *   file:onlyname to access the file name (no paths)
 *   file:onlyname.noext to access the file name (no paths) with no extension 
 *   file:parent to access the parent file name
 *   file:path to access the file path name
 *   file:absolute is the file regarded as absolute or relative
 *   file:absolute.path to access the absolute file path name
 *   file:length to access the file length as a Long type
 *   file:size to access the file length as a Long type
 *   file:modified to access the file last modified as a Date type
 *   date:<command>:<pattern> for date formatting using the {@link java.text.SimpleDateFormat} patterns.
 *     Additional Supported commands are: file for the last modified timestamp of the file.
 *     All the commands from {@link SimpleLanguage} is also available.
 *   
 * 
 * The relative file is the filename with the starting directory clipped, as opposed to path that will
 * return the full path including the starting directory.
 * 

 * The only file is the filename only with all paths clipped.
 *
 */
public class SimpleLanguage extends LanguageSupport {

    // singleton for expressions without a result type
    private static final SimpleLanguage SIMPLE = new SimpleLanguage();

    protected boolean allowEscape = true;

    /**
     * Default constructor.
     */
    public SimpleLanguage() {
    }

    public Predicate createPredicate(String expression) {
        ObjectHelper.notNull(expression, "expression");

        expression = loadResource(expression);

        // support old simple language syntax
        @SuppressWarnings("deprecation")
        Predicate answer = SimpleBackwardsCompatibleParser.parsePredicate(expression, allowEscape);
        if (answer == null) {
            // use the new parser
            SimplePredicateParser parser = new SimplePredicateParser(expression, allowEscape);
            answer = parser.parsePredicate();
        }
        return answer;
    }

    public Expression createExpression(String expression) {
        ObjectHelper.notNull(expression, "expression");

        expression = loadResource(expression);

        // support old simple language syntax
        @SuppressWarnings("deprecation")
        Expression answer = SimpleBackwardsCompatibleParser.parseExpression(expression, allowEscape);
        if (answer == null) {
            // use the new parser
            SimpleExpressionParser parser = new SimpleExpressionParser(expression, allowEscape);
            answer = parser.parseExpression();
        }
        return answer;
    }

    /**
     * Creates a new {@link Expression}.
     * 
     * Important: If you need to use a predicate (function to return true|false) then use
     * {@link #predicate(String)} instead.
     */
    public static Expression simple(String expression) {
        return expression(expression);
    }

    /**
     * Creates a new {@link Expression} (or {@link Predicate}
     * if the resultType is a Boolean, or boolean type).
     */
    public static Expression simple(String expression, Class resultType) {
        return new SimpleLanguage().createExpression(expression, resultType);
    }

    public Expression createExpression(String expression, Class resultType) {
        if (resultType == Boolean.class || resultType == boolean.class) {
            // if its a boolean as result then its a predicate
            Predicate predicate = createPredicate(expression);
            return PredicateToExpressionAdapter.toExpression(predicate);
        } else {
            Expression exp = createExpression(expression);
            if (resultType != null) {
                exp = ExpressionBuilder.convertToExpression(exp, resultType);
            }
            return exp;
        }
    }

    /**
     * Creates a new {@link Expression}.
     * 

     * Important: If you need to use a predicate (function to return true|false) then use
     * {@link #predicate(String)} instead.
     */
    public static Expression expression(String expression) {
        return SIMPLE.createExpression(expression);
    }

    /**
     * Creates a new {@link Predicate}.
     */
    public static Predicate predicate(String predicate) {
        return SIMPLE.createPredicate(predicate);
    }

    /**
     * Change the start tokens used for functions.
     * 

     * This can be used to alter the function tokens to avoid clashes with other
     * frameworks etc.
     * 

     * The default start tokens is ${ and $simple{.
     *
     * @param startToken new start token(s) to be used for functions
     */
    public static void changeFunctionStartToken(String... startToken) {
        SimpleTokenizer.changeFunctionStartToken(startToken);
    }
    
    /**
     * Change the end tokens used for functions.
     * 

     * This can be used to alter the function tokens to avoid clashes with other
     * frameworks etc.
     * 

     * The default end token is }
     *
     * @param endToken new end token(s) to be used for functions
     */
    public static void changeFunctionEndToken(String... endToken) {
        SimpleTokenizer.changeFunctionEndToken(endToken);
    }

    /**
     * Change the start token used for functions.
     * 

     * This can be used to alter the function tokens to avoid clashes with other
     * frameworks etc.
     * 

     * The default start tokens is ${ and $simple{.
     *
     * @param startToken new start token to be used for functions
     */
    public void setFunctionStartToken(String startToken) {
        changeFunctionStartToken(startToken);
    }

    /**
     * Change the end token used for functions.
     * 

     * This can be used to alter the function tokens to avoid clashes with other
     * frameworks etc.
     * 
     * The default end token is }
     *
     * @param endToken new end token to be used for functions
     */
    public void setFunctionEndToken(String endToken) {
        changeFunctionEndToken(endToken);
    }
}