    001/*
    002 * Copyright (c) 2007-2016 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  }