001    /*
002     * Copyright (c) 2007-2015 Concurrent, Inc. All Rights Reserved.
003     *
004     * Project and contact information: http://www.cascading.org/
005     *
006     * This file is part of the Cascading project.
007     *
008     * Licensed under the Apache License, Version 2.0 (the "License");
009     * you may not use this file except in compliance with the License.
010     * You may obtain a copy of the License at
011     *
012     *     http://www.apache.org/licenses/LICENSE-2.0
013     *
014     * Unless required by applicable law or agreed to in writing, software
015     * distributed under the License is distributed on an "AS IS" BASIS,
016     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
017     * See the License for the specific language governing permissions and
018     * limitations under the License.
019     */
020    
021    package cascading.operation.expression;
022    
023    import java.beans.ConstructorProperties;
024    
025    import cascading.flow.FlowProcess;
026    import cascading.operation.Filter;
027    import cascading.operation.FilterCall;
028    import cascading.tuple.Tuple;
029    import org.codehaus.janino.ExpressionEvaluator;
030    
031    /**
032     * Class ExpressionFilter dynamically resolves a given expression using argument {@link Tuple} values. Any Tuple that
033     * returns true for the given expression will be removed from the stream. This {@link Filter}
034     * is based on the <a href="http://www.janino.net/">Janino</a> compiler.
035     * <p/>
036     * Specifically this filter uses the {@link ExpressionEvaluator}, thus the syntax from that class is inherited here.
037     * <p/>
038     * An expression may use field names directly as parameters in the expression, or field positions with the syntax
039     * "$n", where n is an integer.
040     * <p/>
041     * Given an argument tuple with the fields "a" and "b", the following expression returns true: <br/>
042     * <code>a + b == $0 + $1</code><br/>
043     * <p/>
044     * Further, the types of the tuple elements will be coerced into the given parameterTypes. Regardless of the actual
045     * tuple element values, they will be converted to the types expected by the expression.
046     * <p/>
047     * Field names used in the expression should be valid Java variable names; for example, '+' or '-' are not allowed.
048     * Also the use of a field name that begins with an upper-case character is likely to fail and should be avoided.
049     */
050    public class ExpressionFilter extends ExpressionOperation implements Filter<ScriptOperation.Context>
051      {
052      /**
053       * Constructor ExpressionFilter creates a new ExpressionFilter instance.
054       * <p/>
055       * This constructor, when used with incoming arguments that have type information, the argument field
056       * names can be used directly in the the expression, for example {@code a + b }. The type of {@code a} and {@code b}
057       * will be inherited from the incoming argument fields.
058       * <p/>
059       * Or, if the incoming argument selector is {@link cascading.tuple.Fields#NONE}, an expression using only static method calls
060       * or constants can be used, for example {@code Math.random() < SomeClass.someValue() }.
061       *
062       * @param expression of type String
063       */
064      @ConstructorProperties( {"expression"} )
065      public ExpressionFilter( String expression )
066        {
067        super( expression );
068        }
069    
070      /**
071       * Constructor ExpressionFilter creates a new ExpressionFilter instance.
072       *
073       * @param expression    of type String
074       * @param parameterType of type Class
075       */
076      @ConstructorProperties({"expression", "parameterType"})
077      public ExpressionFilter( String expression, Class parameterType )
078        {
079        super( expression, parameterType );
080        }
081    
082      /**
083       * Constructor ExpressionFilter creates a new ExpressionFilter instance.
084       *
085       * @param expression     of type String
086       * @param parameterNames of type String[]
087       * @param parameterTypes of type Class[]
088       */
089      @ConstructorProperties({"expression", "parameterNames", "parameterTypes"})
090      public ExpressionFilter( String expression, String[] parameterNames, Class[] parameterTypes )
091        {
092        super( expression, parameterNames, parameterTypes );
093        }
094    
095      @Override
096      public boolean isRemove( FlowProcess flowProcess, FilterCall<Context> filterCall )
097        {
098        return (Boolean) evaluate( filterCall.getContext(), filterCall.getArguments() );
099        }
100      }