com.epam.dlab.core.parser.ConditionEvaluate.java Source code

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/***************************************************************************
    
Copyright (c) 2016, EPAM SYSTEMS INC
    
Licensed 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 com.epam.dlab.core.parser;

import java.util.ArrayList;
import java.util.List;

import org.apache.commons.jexl3.JexlBuilder;
import org.apache.commons.jexl3.JexlContext;
import org.apache.commons.jexl3.JexlEngine;
import org.apache.commons.jexl3.MapContext;
import org.apache.commons.jexl3.internal.Script;
import org.apache.commons.lang3.StringUtils;

import com.epam.dlab.exceptions.InitializationException;
import com.epam.dlab.exceptions.ParseException;
import com.google.common.base.MoreObjects;
import com.google.common.base.MoreObjects.ToStringHelper;

/** Evaluate condition for filtering source data.
 */
public class ConditionEvaluate {

    /** Names of columns for condition. */
    private String[] columnNames;

    /** Indexes of columns for condition. */
    private int[] columnIndexes;

    /** JEXL expression for evaluation. */
    private final Script expression;

    /** JEXL context to evaluate row. */
    private final JexlContext jexlContext;

    /** Instantiate the engine to evaluate condition. 
     * @param columnNames the list of column names.
     * @param condition condition for filtering data.
     * @throws InitializationException
     */
    public ConditionEvaluate(List<String> columnNames, String condition) throws InitializationException {
        //Replace : to . in column names
        List<String> colNames = new ArrayList<>(columnNames.size());
        for (int i = 0; i < columnNames.size(); i++) {
            String name = columnNames.get(i);
            if (name.indexOf(':') > -1 && condition.indexOf(name) > -1) {
                String newName = StringUtils.replaceChars(name, ':', '.');
                colNames.add(newName);
                condition = StringUtils.replace(condition, name, newName);
            } else {
                colNames.add(name);
            }
        }

        try {
            JexlEngine engine = new JexlBuilder().strict(true).silent(false).debug(true).create();
            expression = (Script) engine.createExpression(condition);
            jexlContext = new MapContext();
        } catch (Exception e) {
            throw new InitializationException(
                    "Cannot initialize JEXL engine for condition: " + condition + ". " + e.getLocalizedMessage(),
                    e);
        }

        // Create mapping of columns for evaluations. 
        List<String> names = new ArrayList<>();
        List<Integer> indexes = new ArrayList<>();
        for (List<String> variableList : expression.getVariables()) {
            String columnName = StringUtils.join(variableList, '.');
            int index = getColumnIndex(colNames, columnName);
            if (index == -1) {
                throw new InitializationException("Unknow source column name \"" + columnName + "\" in condition: "
                        + expression.getSourceText() + ". Known column names: "
                        + StringUtils.join(columnNames, ", ") + ".");
            }
            names.add(columnName);
            indexes.add(index);
        }

        this.columnNames = new String[names.size()];
        this.columnIndexes = new int[indexes.size()];
        for (int i = 0; i < indexes.size(); i++) {
            this.columnNames[i] = names.get(i);
            this.columnIndexes[i] = indexes.get(i);
        }
    }

    /** Find and return the index of column in the given column list.
     * @param columnNames the list of column names.
     * @param columnName the name of column to find.
     */
    private int getColumnIndex(List<String> columnNames, String columnName) {
        for (int i = 0; i < columnNames.size(); i++) {
            if (columnName.equals(columnNames.get(i))) {
                return i;
            }
        }
        return -1;
    }

    /** Evaluate condition for given row.
     * @param row the row to evaluate.
     * @return <true> if condition is true.
     * @throws ParseException if condition is not return boolean type.
     */
    public boolean evaluate(List<String> row) throws ParseException {
        for (int i = 0; i < columnNames.length; i++) {
            jexlContext.set(columnNames[i], row.get(columnIndexes[i]));
        }
        Object value;
        try {
            value = expression.evaluate(jexlContext);
        } catch (Exception e) {
            throw new ParseException(
                    "Cannot evaluate condition: " + expression.getSourceText() + ". " + e.getLocalizedMessage(), e);
        }
        if (value instanceof Boolean) {
            return (Boolean) value;
        }
        throw new ParseException("Invalid condition: " + expression.getSourceText());
    }

    /** Returns a string representation of the object.
     * @param self the object to generate the string for (typically this), used only for its class name.
     */
    public ToStringHelper toStringHelper(Object self) {
        return MoreObjects.toStringHelper(self).add("columnNames", columnNames).add("columnIndexes", columnIndexes);
    }

    @Override
    public String toString() {
        return toStringHelper(this).toString();
    }
}