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A Java library to parse, migrate and validate crons as well as describe them in human readable language
There is a newer version: 9.2.1
/*
 * Copyright 2014 jmrozanec
 *
 * 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.cronutils.parser;

import com.cronutils.model.CompositeCron;
import com.cronutils.model.Cron;
import com.cronutils.model.SingleCron;
import com.cronutils.model.definition.CronDefinition;
import com.cronutils.model.field.CronField;
import com.cronutils.model.field.definition.FieldDefinition;
import com.cronutils.utils.Preconditions;
import com.cronutils.utils.StringUtils;

import java.util.*;
import java.util.stream.Collectors;

/**
 * Parser for cron expressions.
 */
public class CronParser {

    private final Map> expressions = new HashMap<>();
    private final CronDefinition cronDefinition;

    /**
     * @param cronDefinition - cronDefinition of cron expressions to be parsed if null, a NullPointerException will be raised.
     */
    public CronParser(final CronDefinition cronDefinition) {
        this.cronDefinition = Preconditions.checkNotNull(cronDefinition, "CronDefinition must not be null");
        buildPossibleExpressions(cronDefinition);
    }

    /**
     * Build possible cron expressions from definitions. One is built for sure. A second one may be build if last field is optional.
     *
     * @param cronDefinition - cron definition instance
     */
    private void buildPossibleExpressions(final CronDefinition cronDefinition) {
        final List sortedExpression = cronDefinition.getFieldDefinitions().stream()
                .map(this::toCronParserField)
                .sorted(CronParserField.createFieldTypeComparator())
                .collect(Collectors.toList());

        List tempExpression = sortedExpression;

        while(lastFieldIsOptional(tempExpression)) {
            int expressionLength = tempExpression.size() - 1;
            ArrayList possibleExpression = new ArrayList<>(tempExpression.subList(0, expressionLength));

            expressions.put(expressionLength, possibleExpression);
            tempExpression = possibleExpression;
        }

        expressions.put(sortedExpression.size(), sortedExpression);
    }

    private CronParserField toCronParserField(final FieldDefinition fieldDefinition) {
        return new CronParserField(fieldDefinition.getFieldName(), fieldDefinition.getConstraints(), fieldDefinition.isOptional());
    }

    private boolean lastFieldIsOptional(final List fields) {
        return !fields.isEmpty() && fields.get(fields.size() - 1).isOptional();
    }

    /**
     * Parse string with cron expression.
     *
     * @param expression - cron expression, never null
     * @return Cron instance, corresponding to cron expression received
     * @throws java.lang.IllegalArgumentException if expression does not match cron definition
     */
    public Cron parse(final String expression) {
        Preconditions.checkNotNull(expression, "Expression must not be null");
        final String replaced = expression.replaceAll("\\s+", " ").trim();
        if (StringUtils.isEmpty(replaced)) {
            throw new IllegalArgumentException("Empty expression!");
        }

        if(expression.contains("||")) {
            List crons = Arrays.stream(expression.split("\\|\\|")).map(this::parse).collect(Collectors.toList());
            return new CompositeCron(crons);
        }
        if(expression.contains("|")){
            List crons = new ArrayList<>();
            int cronscount = Arrays.stream(expression.split("\\s+")).mapToInt(s->s.split("\\|").length).max().orElse(0);
            for(int j=0; j x.endsWith(",")).findAny().orElse(null);
            if(fieldWithTrailingCommas!=null){
                throw new IllegalArgumentException(String.format("Invalid field value! Trailing commas not permitted! '%s'", fieldWithTrailingCommas));
            }
            final List fields = expressions.get(expressionLength);
            if (fields == null) {
                throw new IllegalArgumentException(
                        String.format("Cron expression contains %s parts but we expect one of %s", expressionLength, expressions.keySet()));
            }
            try {

                final int size = expressionParts.length;
                final List results = new ArrayList<>(size + 1);
                for (int j = 0; j < size; j++) {
                    results.add(fields.get(j).parse(expressionParts[j]));
                }
                return new SingleCron(cronDefinition, results).validate();
            } catch (final IllegalArgumentException e) {
                throw new IllegalArgumentException(String.format("Failed to parse '%s'. %s", expression, e.getMessage()), e);
            }
        }
    }
}