001 /* 002 * Copyright (c) 2007-2014 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 * 055 * @param expression of type String 056 * @param parameterType of type Class 057 */ 058 @ConstructorProperties({"expression", "parameterType"}) 059 public ExpressionFilter( String expression, Class parameterType ) 060 { 061 super( expression, parameterType ); 062 } 063 064 /** 065 * Constructor ExpressionFilter creates a new ExpressionFilter instance. 066 * 067 * @param expression of type String 068 * @param parameterNames of type String[] 069 * @param parameterTypes of type Class[] 070 */ 071 @ConstructorProperties({"expression", "parameterNames", "parameterTypes"}) 072 public ExpressionFilter( String expression, String[] parameterNames, Class[] parameterTypes ) 073 { 074 super( expression, parameterNames, parameterTypes ); 075 } 076 077 @Override 078 public boolean isRemove( FlowProcess flowProcess, FilterCall<Context> filterCall ) 079 { 080 return (Boolean) evaluate( filterCall.getContext(), filterCall.getArguments() ); 081 } 082 }