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 021package cascading.operation.expression; 022 023import java.beans.ConstructorProperties; 024 025import cascading.flow.FlowProcess; 026import cascading.operation.Function; 027import cascading.operation.FunctionCall; 028import cascading.tuple.Fields; 029import cascading.tuple.Tuple; 030import org.codehaus.janino.ExpressionEvaluator; 031 032/** 033 * Class ExpressionFunction dynamically resolves a given expression using argument {@link Tuple} values. This {@link Function} 034 * is based on the <a href="http://www.janino.net/">Janino</a> compiler. 035 * <p/> 036 * Specifically this function 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 */ 050public class ExpressionFunction extends ExpressionOperation implements Function<ScriptOperation.Context> 051 { 052 /** 053 * Constructor ExpressionFunction creates a new ExpressionFunction 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 Fields#NONE}, an expression using only static method calls 060 * or constants can be used. 061 * <p/> 062 * This is useful when inserting random numbers for example, {@code (int) (Math.random() * Integer.MAX_VALUE) }. 063 * 064 * @param fieldDeclaration of type Fields 065 * @param expression of type String 066 */ 067 @ConstructorProperties({"fieldDeclaration", "expression"}) 068 public ExpressionFunction( Fields fieldDeclaration, String expression ) 069 { 070 super( fieldDeclaration, expression ); 071 072 verify( fieldDeclaration ); 073 } 074 075 /** 076 * Constructor ExpressionFunction creates a new ExpressionFunction instance. 077 * <p/> 078 * This constructor assumes all parameter are of the same type. 079 * 080 * @param fieldDeclaration of type Fields 081 * @param expression of type String 082 * @param parameterType of type Class 083 */ 084 @ConstructorProperties({"fieldDeclaration", "expression", "parameterType"}) 085 public ExpressionFunction( Fields fieldDeclaration, String expression, Class parameterType ) 086 { 087 super( fieldDeclaration, expression, parameterType ); 088 089 verify( fieldDeclaration ); 090 } 091 092 /** 093 * Constructor ExpressionFunction creates a new ExpressionFunction instance. 094 * <p/> 095 * This constructor expects all parameter type names to be declared with their types. Positional parameters must 096 * be named the same as in the given expression with the "$" sign prepended. 097 * 098 * @param fieldDeclaration of type Fields 099 * @param expression of type String 100 * @param parameterNames of type String[] 101 * @param parameterTypes of type Class[] 102 */ 103 @ConstructorProperties({"fieldDeclaration", "expression", "parameterNames", "parameterTypes"}) 104 public ExpressionFunction( Fields fieldDeclaration, String expression, String[] parameterNames, Class[] parameterTypes ) 105 { 106 super( fieldDeclaration, expression, parameterNames, parameterTypes ); 107 108 verify( fieldDeclaration ); 109 } 110 111 private void verify( Fields fieldDeclaration ) 112 { 113 if( !fieldDeclaration.isSubstitution() && fieldDeclaration.size() != 1 ) 114 throw new IllegalArgumentException( "fieldDeclaration may only declare one field, was " + fieldDeclaration.print() ); 115 } 116 117 @Override 118 public void operate( FlowProcess flowProcess, FunctionCall<ExpressionOperation.Context> functionCall ) 119 { 120 functionCall.getContext().result.set( 0, evaluate( functionCall.getContext(), functionCall.getArguments() ) ); 121 functionCall.getOutputCollector().add( functionCall.getContext().result ); 122 } 123 }