com.talvish.tales.parts.RegularExpressionHelper.java Source code

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Here is the source code for com.talvish.tales.parts.RegularExpressionHelper.java

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// ***************************************************************************
// *  Copyright 2012 Joseph Molnar
// *
// *  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.talvish.tales.parts;

import com.google.common.base.Preconditions;
import com.google.common.base.Strings;

/**
 * A utility class containing helper regular expressions.
 * @author jmolnar
 *
 */
public final class RegularExpressionHelper {
    /**
     * Helper method that makes sure a user supplied regular expression
     * doesn't contain capturing groups, which would otherwise cause problems
     * if the regex is being used for needs where other capturing groups are
     * important
     * @param theRegEx the regex to escape
     * @return the non-capturing regex
     */
    public final static String toNoncapturingExpression(String theRegEx) {
        Preconditions.checkArgument(!Strings.isNullOrEmpty(theRegEx), "need a regex");
        // I feel there is a better way, but this is good enough for now ...
        StringBuilder builder = new StringBuilder();

        int charClassCount = 0;

        int startOffset = 0;
        char currentChar;

        for (int offset = 0; offset < theRegEx.length(); offset += 1) {
            currentChar = theRegEx.charAt(offset);
            if (currentChar == '\\') { // ignore escaping character
                offset += 1;
            } else if (currentChar == '[') { // we are in a capturing group (java supports some nesting, though I don't fully here)
                charClassCount += 1;
            } else if (currentChar == ']') { // we are leaving one
                charClassCount -= 1;
            } else if (currentChar == '(' && charClassCount == 0) {
                if ((offset == theRegEx.length() - 1) || (theRegEx.charAt(offset + 1) != '?')) { // found at the end or next character isn't a quote/meaning non-capturing already
                    builder.append(theRegEx.substring(startOffset, offset + 1));
                    builder.append("?:"); // turn into a non capturing group
                    startOffset = offset + 1;
                }
            }
        }
        builder.append(theRegEx.substring(startOffset, theRegEx.length()));
        return builder.toString();
    }
}