easyexcel/src/main/java/com/alibaba/excel/util/StringUtils.java

package com.alibaba.excel.util;

/*
 * Copyright 2002-2017 the original author or authors.
 *
 * 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.
 */


import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.Locale;
import java.util.Properties;
import java.util.Set;
import java.util.StringTokenizer;
import java.util.TimeZone;
import java.util.UUID;

import org.apache.commons.codec.binary.CharSequenceUtils;

/**
 * Miscellaneous {@link String} utility methods.
 *
 * <p>Mainly for internal use within the framework; consider
 * <a href="http://commons.apache.org/proper/commons-lang/">Apache's Commons Lang</a>
 * for a more comprehensive suite of {@code String} utilities.
 *
 * <p>This class delivers some simple functionality that should really be
 * provided by the core Java {@link String} and {@link StringBuilder}
 * classes. It also provides easy-to-use methods to convert between
 * delimited strings, such as CSV strings, and collections and arrays.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @author Keith Donald
 * @author Rob Harrop
 * @author Rick Evans
 * @author Arjen Poutsma
 * @author Sam Brannen
 * @author Brian Clozel
 * @since 16 April 2001
 */
public abstract class StringUtils {

    private static final String FOLDER_SEPARATOR = "/";

    private static final String WINDOWS_FOLDER_SEPARATOR = "\\";

    private static final String TOP_PATH = "..";

    private static final String CURRENT_PATH = ".";

    private static final char EXTENSION_SEPARATOR = '.';


    //---------------------------------------------------------------------
    // General convenience methods for working with Strings
    //---------------------------------------------------------------------

    /**
     * Check whether the given {@code String} is empty.
     * <p>This method accepts any Object as an argument, comparing it to
     * {@code null} and the empty String. As a consequence, this method
     * will never return {@code true} for a non-null non-String object.
     * <p>The Object signature is useful for general attribute handling code
     * that commonly deals with Strings but generally has to iterate over
     * Objects since attributes may e.g. be primitive value objects as well.
     * @param str the candidate String
     * @since 3.2.1
     */
    public static boolean isEmpty(Object str) {
        return (str == null || "".equals(str));
    }

    /**
     * Check that the given {@code CharSequence} is neither {@code null} nor
     * of length 0.
     * <p>Note: this method returns {@code true} for a {@code CharSequence}
     * that purely consists of whitespace.
     * <p><pre class="code">
     * StringUtils.hasLength(null) = false
     * StringUtils.hasLength("") = false
     * StringUtils.hasLength(" ") = true
     * StringUtils.hasLength("Hello") = true
     * </pre>
     * @param str the {@code CharSequence} to check (may be {@code null})
     * @return {@code true} if the {@code CharSequence} is not {@code null} and has length
     * @see #hasText(String)
     */
    public static boolean hasLength(CharSequence str) {
        return (str != null && str.length() > 0);
    }

    /**
     * Check that the given {@code String} is neither {@code null} nor of length 0.
     * <p>Note: this method returns {@code true} for a {@code String} that
     * purely consists of whitespace.
     * @param str the {@code String} to check (may be {@code null})
     * @return {@code true} if the {@code String} is not {@code null} and has length
     * @see #hasLength(CharSequence)
     * @see #hasText(String)
     */
    public static boolean hasLength(String str) {
        return (str != null && !str.isEmpty());
    }

    /**
     * Check whether the given {@code CharSequence} contains actual <em>text</em>.
     * <p>More specifically, this method returns {@code true} if the
     * {@code CharSequence} is not {@code null}, its length is greater than
     * 0, and it contains at least one non-whitespace character.
     * <p><pre class="code">
     * StringUtils.hasText(null) = false
     * StringUtils.hasText("") = false
     * StringUtils.hasText(" ") = false
     * StringUtils.hasText("12345") = true
     * StringUtils.hasText(" 12345 ") = true
     * </pre>
     * @param str the {@code CharSequence} to check (may be {@code null})
     * @return {@code true} if the {@code CharSequence} is not {@code null},
     * its length is greater than 0, and it does not contain whitespace only
     * @see Character#isWhitespace
     */
    public static boolean hasText(CharSequence str) {
        return (hasLength(str) && containsText(str));
    }

    /**
     * Check whether the given {@code String} contains actual <em>text</em>.
     * <p>More specifically, this method returns {@code true} if the
     * {@code String} is not {@code null}, its length is greater than 0,
     * and it contains at least one non-whitespace character.
     * @param str the {@code String} to check (may be {@code null})
     * @return {@code true} if the {@code String} is not {@code null}, its
     * length is greater than 0, and it does not contain whitespace only
     * @see #hasText(CharSequence)
     */
    public static boolean hasText(String str) {
        return (hasLength(str) && containsText(str));
    }

    private static boolean containsText(CharSequence str) {
        int strLen = str.length();
        for (int i = 0; i < strLen; i++) {
            if (!Character.isWhitespace(str.charAt(i))) {
                return true;
            }
        }
        return false;
    }

    /**
     * Check whether the given {@code CharSequence} contains any whitespace characters.
     * @param str the {@code CharSequence} to check (may be {@code null})
     * @return {@code true} if the {@code CharSequence} is not empty and
     * contains at least 1 whitespace character
     * @see Character#isWhitespace
     */
    public static boolean containsWhitespace(CharSequence str) {
        if (!hasLength(str)) {
            return false;
        }

        int strLen = str.length();
        for (int i = 0; i < strLen; i++) {
            if (Character.isWhitespace(str.charAt(i))) {
                return true;
            }
        }
        return false;
    }

    /**
     * Check whether the given {@code String} contains any whitespace characters.
     * @param str the {@code String} to check (may be {@code null})
     * @return {@code true} if the {@code String} is not empty and
     * contains at least 1 whitespace character
     * @see #containsWhitespace(CharSequence)
     */
    public static boolean containsWhitespace(String str) {
        return containsWhitespace((CharSequence) str);
    }

    /**
     * Trim leading and trailing whitespace from the given {@code String}.
     * @param str the {@code String} to check
     * @return the trimmed {@code String}
     * @see Character#isWhitespace
     */
    public static String trimWhitespace(String str) {
        if (!hasLength(str)) {
            return str;
        }

        StringBuilder sb = new StringBuilder(str);
        while (sb.length() > 0 && Character.isWhitespace(sb.charAt(0))) {
            sb.deleteCharAt(0);
        }
        while (sb.length() > 0 && Character.isWhitespace(sb.charAt(sb.length() - 1))) {
            sb.deleteCharAt(sb.length() - 1);
        }
        return sb.toString();
    }

    /**
     * Trim <i>all</i> whitespace from the given {@code String}:
     * leading, trailing, and in between characters.
     * @param str the {@code String} to check
     * @return the trimmed {@code String}
     * @see Character#isWhitespace
     */
    public static String trimAllWhitespace(String str) {
        if (!hasLength(str)) {
            return str;
        }

        int len = str.length();
        StringBuilder sb = new StringBuilder(str.length());
        for (int i = 0; i < len; i++) {
            char c = str.charAt(i);
            if (!Character.isWhitespace(c)) {
                sb.append(c);
            }
        }
        return sb.toString();
    }

    /**
     * Trim leading whitespace from the given {@code String}.
     * @param str the {@code String} to check
     * @return the trimmed {@code String}
     * @see Character#isWhitespace
     */
    public static String trimLeadingWhitespace(String str) {
        if (!hasLength(str)) {
            return str;
        }

        StringBuilder sb = new StringBuilder(str);
        while (sb.length() > 0 && Character.isWhitespace(sb.charAt(0))) {
            sb.deleteCharAt(0);
        }
        return sb.toString();
    }

    /**
     * Trim trailing whitespace from the given {@code String}.
     * @param str the {@code String} to check
     * @return the trimmed {@code String}
     * @see Character#isWhitespace
     */
    public static String trimTrailingWhitespace(String str) {
        if (!hasLength(str)) {
            return str;
        }

        StringBuilder sb = new StringBuilder(str);
        while (sb.length() > 0 && Character.isWhitespace(sb.charAt(sb.length() - 1))) {
            sb.deleteCharAt(sb.length() - 1);
        }
        return sb.toString();
    }

    /**
     * Trim all occurrences of the supplied leading character from the given {@code String}.
     * @param str the {@code String} to check
     * @param leadingCharacter the leading character to be trimmed
     * @return the trimmed {@code String}
     */
    public static String trimLeadingCharacter(String str, char leadingCharacter) {
        if (!hasLength(str)) {
            return str;
        }

        StringBuilder sb = new StringBuilder(str);
        while (sb.length() > 0 && sb.charAt(0) == leadingCharacter) {
            sb.deleteCharAt(0);
        }
        return sb.toString();
    }

    /**
     * Trim all occurrences of the supplied trailing character from the given {@code String}.
     * @param str the {@code String} to check
     * @param trailingCharacter the trailing character to be trimmed
     * @return the trimmed {@code String}
     */
    public static String trimTrailingCharacter(String str, char trailingCharacter) {
        if (!hasLength(str)) {
            return str;
        }

        StringBuilder sb = new StringBuilder(str);
        while (sb.length() > 0 && sb.charAt(sb.length() - 1) == trailingCharacter) {
            sb.deleteCharAt(sb.length() - 1);
        }
        return sb.toString();
    }

    /**
     * Test if the given {@code String} starts with the specified prefix,
     * ignoring upper/lower case.
     * @param str the {@code String} to check
     * @param prefix the prefix to look for
     * @see String#startsWith
     */
    public static boolean startsWithIgnoreCase(String str, String prefix) {
        return (str != null && prefix != null && str.length() >= prefix.length() &&
            str.regionMatches(true, 0, prefix, 0, prefix.length()));
    }

    /**
     * Test if the given {@code String} ends with the specified suffix,
     * ignoring upper/lower case.
     * @param str the {@code String} to check
     * @param suffix the suffix to look for
     * @see String#endsWith
     */
    public static boolean endsWithIgnoreCase(String str, String suffix) {
        return (str != null && suffix != null && str.length() >= suffix.length() &&
            str.regionMatches(true, str.length() - suffix.length(), suffix, 0, suffix.length()));
    }

    /**
     * Test whether the given string matches the given substring
     * at the given index.
     * @param str the original string (or StringBuilder)
     * @param index the index in the original string to start matching against
     * @param substring the substring to match at the given index
     */
    public static boolean substringMatch(CharSequence str, int index, CharSequence substring) {
        if (index + substring.length() > str.length()) {
            return false;
        }
        for (int i = 0; i < substring.length(); i++) {
            if (str.charAt(index + i) != substring.charAt(i)) {
                return false;
            }
        }
        return true;
    }

    /**
     * Count the occurrences of the substring {@code sub} in string {@code str}.
     * @param str string to search in
     * @param sub string to search for
     */
    public static int countOccurrencesOf(String str, String sub) {
        if (!hasLength(str) || !hasLength(sub)) {
            return 0;
        }

        int count = 0;
        int pos = 0;
        int idx;
        while ((idx = str.indexOf(sub, pos)) != -1) {
            ++count;
            pos = idx + sub.length();
        }
        return count;
    }

    /**
     * Replace all occurrences of a substring within a string with another string.
     * @param inString {@code String} to examine
     * @param oldPattern {@code String} to replace
     * @param newPattern {@code String} to insert
     * @return a {@code String} with the replacements
     */
    public static String replace(String inString, String oldPattern, String newPattern) {
        if (!hasLength(inString) || !hasLength(oldPattern) || newPattern == null) {
            return inString;
        }
        int index = inString.indexOf(oldPattern);
        if (index == -1) {
            // no occurrence -> can return input as-is
            return inString;
        }

        int capacity = inString.length();
        if (newPattern.length() > oldPattern.length()) {
            capacity += 16;
        }
        StringBuilder sb = new StringBuilder(capacity);

        int pos = 0;  // our position in the old string
        int patLen = oldPattern.length();
        while (index >= 0) {
            sb.append(inString.substring(pos, index));
            sb.append(newPattern);
            pos = index + patLen;
            index = inString.indexOf(oldPattern, pos);
        }

        // append any characters to the right of a match
        sb.append(inString.substring(pos));
        return sb.toString();
    }

    /**
     * Delete all occurrences of the given substring.
     * @param inString the original {@code String}
     * @param pattern the pattern to delete all occurrences of
     * @return the resulting {@code String}
     */
    public static String delete(String inString, String pattern) {
        return replace(inString, pattern, "");
    }

    /**
     * Delete any character in a given {@code String}.
     * @param inString the original {@code String}
     * @param charsToDelete a set of characters to delete.
     * E.g. "az\n" will delete 'a's, 'z's and new lines.
     * @return the resulting {@code String}
     */
    public static String deleteAny(String inString, String charsToDelete) {
        if (!hasLength(inString) || !hasLength(charsToDelete)) {
            return inString;
        }

        StringBuilder sb = new StringBuilder(inString.length());
        for (int i = 0; i < inString.length(); i++) {
            char c = inString.charAt(i);
            if (charsToDelete.indexOf(c) == -1) {
                sb.append(c);
            }
        }
        return sb.toString();
    }


    //---------------------------------------------------------------------
    // Convenience methods for working with formatted Strings
    //---------------------------------------------------------------------

    /**
     * Quote the given {@code String} with single quotes.
     * @param str the input {@code String} (e.g. "myString")
     * @return the quoted {@code String} (e.g. "'myString'"),
     * or {@code null} if the input was {@code null}
     */
    public static String quote(String str) {
        return (str != null ? "'" + str + "'" : null);
    }

    /**
     * Turn the given Object into a {@code String} with single quotes
     * if it is a {@code String}; keeping the Object as-is else.
     * @param obj the input Object (e.g. "myString")
     * @return the quoted {@code String} (e.g. "'myString'"),
     * or the input object as-is if not a {@code String}
     */
    public static Object quoteIfString(Object obj) {
        return (obj instanceof String ? quote((String) obj) : obj);
    }

    /**
     * Unqualify a string qualified by a '.' dot character. For example,
     * "this.name.is.qualified", returns "qualified".
     * @param qualifiedName the qualified name
     */
    public static String unqualify(String qualifiedName) {
        return unqualify(qualifiedName, '.');
    }

    /**
     * Unqualify a string qualified by a separator character. For example,
     * "this:name:is:qualified" returns "qualified" if using a ':' separator.
     * @param qualifiedName the qualified name
     * @param separator the separator
     */
    public static String unqualify(String qualifiedName, char separator) {
        return qualifiedName.substring(qualifiedName.lastIndexOf(separator) + 1);
    }

    /**
     * Capitalize a {@code String}, changing the first letter to
     * upper case as per {@link Character#toUpperCase(char)}.
     * No other letters are changed.
     * @param str the {@code String} to capitalize
     * @return the capitalized {@code String}
     */
    public static String capitalize(String str) {
        return changeFirstCharacterCase(str, true);
    }

    /**
     * Uncapitalize a {@code String}, changing the first letter to
     * lower case as per {@link Character#toLowerCase(char)}.
     * No other letters are changed.
     * @param str the {@code String} to uncapitalize
     * @return the uncapitalized {@code String}
     */
    public static String uncapitalize(String str) {
        return changeFirstCharacterCase(str, false);
    }

    private static String changeFirstCharacterCase(String str, boolean capitalize) {
        if (!hasLength(str)) {
            return str;
        }

        char baseChar = str.charAt(0);
        char updatedChar;
        if (capitalize) {
            updatedChar = Character.toUpperCase(baseChar);
        }
        else {
            updatedChar = Character.toLowerCase(baseChar);
        }
        if (baseChar == updatedChar) {
            return str;
        }

        char[] chars = str.toCharArray();
        chars[0] = updatedChar;
        return new String(chars, 0, chars.length);
    }

    /**
     * Extract the filename from the given Java resource path,
     * e.g. {@code "mypath/myfile.txt" -> "myfile.txt"}.
     * @param path the file path (may be {@code null})
     * @return the extracted filename, or {@code null} if none
     */
    public static String getFilename(String path) {
        if (path == null) {
            return null;
        }

        int separatorIndex = path.lastIndexOf(FOLDER_SEPARATOR);
        return (separatorIndex != -1 ? path.substring(separatorIndex + 1) : path);
    }

    /**
     * Extract the filename extension from the given Java resource path,
     *
     * @param path the file path (may be {@code null})
     * @return the extracted filename extension, or {@code null} if none
     */
    public static String getFilenameExtension(String path) {
        if (path == null) {
            return null;
        }

        int extIndex = path.lastIndexOf(EXTENSION_SEPARATOR);
        if (extIndex == -1) {
            return null;
        }

        int folderIndex = path.lastIndexOf(FOLDER_SEPARATOR);
        if (folderIndex > extIndex) {
            return null;
        }

        return path.substring(extIndex + 1);
    }

    /**
     * Strip the filename extension from the given Java resource path,
     *
     * @param path the file path
     * @return the path with stripped filename extension
     */
    public static String stripFilenameExtension(String path) {
        if (path == null) {
            return null;
        }

        int extIndex = path.lastIndexOf(EXTENSION_SEPARATOR);
        if (extIndex == -1) {
            return path;
        }

        int folderIndex = path.lastIndexOf(FOLDER_SEPARATOR);
        if (folderIndex > extIndex) {
            return path;
        }

        return path.substring(0, extIndex);
    }

    /**
     * Apply the given relative path to the given Java resource path,
     * assuming standard Java folder separation (i.e. "/" separators).
     * @param path the path to start from (usually a full file path)
     * @param relativePath the relative path to apply
     * (relative to the full file path above)
     * @return the full file path that results from applying the relative path
     */
    public static String applyRelativePath(String path, String relativePath) {
        int separatorIndex = path.lastIndexOf(FOLDER_SEPARATOR);
        if (separatorIndex != -1) {
            String newPath = path.substring(0, separatorIndex);
            if (!relativePath.startsWith(FOLDER_SEPARATOR)) {
                newPath += FOLDER_SEPARATOR;
            }
            return newPath + relativePath;
        }
        else {
            return relativePath;
        }
    }

    /**
     * Normalize the path by suppressing sequences like "path/.." and
     * inner simple dots.
     * <p>The result is convenient for path comparison. For other uses,
     * notice that Windows separators ("\") are replaced by simple slashes.
     * @param path the original path
     * @return the normalized path
     */
    public static String cleanPath(String path) {
        if (path == null) {
            return null;
        }
        String pathToUse = replace(path, WINDOWS_FOLDER_SEPARATOR, FOLDER_SEPARATOR);

        // Strip prefix from path to analyze, to not treat it as part of the
        // first path element. This is necessary to correctly parse paths like
        // "file:core/../core/io/Resource.class", where the ".." should just
        // strip the first "core" directory while keeping the "file:" prefix.
        int prefixIndex = pathToUse.indexOf(":");
        String prefix = "";
        if (prefixIndex != -1) {
            prefix = pathToUse.substring(0, prefixIndex + 1);
            if (prefix.contains("/")) {
                prefix = "";
            }
            else {
                pathToUse = pathToUse.substring(prefixIndex + 1);
            }
        }
        if (pathToUse.startsWith(FOLDER_SEPARATOR)) {
            prefix = prefix + FOLDER_SEPARATOR;
            pathToUse = pathToUse.substring(1);
        }

        String[] pathArray = delimitedListToStringArray(pathToUse, FOLDER_SEPARATOR);
        List<String> pathElements = new LinkedList<String>();
        int tops = 0;

        for (int i = pathArray.length - 1; i >= 0; i--) {
            String element = pathArray[i];
            if (CURRENT_PATH.equals(element)) {
                // Points to current directory - drop it.
            }
            else if (TOP_PATH.equals(element)) {
                // Registering top path found.
                tops++;
            }
            else {
                if (tops > 0) {
                    // Merging path element with element corresponding to top path.
                    tops--;
                }
                else {
                    // Normal path element found.
                    pathElements.add(0, element);
                }
            }
        }

        // Remaining top paths need to be retained.
        for (int i = 0; i < tops; i++) {
            pathElements.add(0, TOP_PATH);
        }

        return prefix + collectionToDelimitedString(pathElements, FOLDER_SEPARATOR);
    }

    /**
     * Compare two paths after normalization of them.
     * @param path1 first path for comparison
     * @param path2 second path for comparison
     * @return whether the two paths are equivalent after normalization
     */
    public static boolean pathEquals(String path1, String path2) {
        return cleanPath(path1).equals(cleanPath(path2));
    }

    /**
     * Parse the given {@code localeString} value into a {@link Locale}.
     * <p>This is the inverse operation of {@link Locale#toString Locale's toString}.
     * @param localeString the locale {@code String}, following {@code Locale's}
     * {@code toString()} format ("en", "en_UK", etc);
     * also accepts spaces as separators, as an alternative to underscores
     * @return a corresponding {@code Locale} instance, or {@code null} if none
     * @throws IllegalArgumentException in case of an invalid locale specification
     */
    public static Locale parseLocaleString(String localeString) {
        String[] parts = tokenizeToStringArray(localeString, "_ ", false, false);
        String language = (parts.length > 0 ? parts[0] : "");
        String country = (parts.length > 1 ? parts[1] : "");

        validateLocalePart(language);
        validateLocalePart(country);

        String variant = "";
        if (parts.length > 2) {
            // There is definitely a variant, and it is everything after the country
            // code sans the separator between the country code and the variant.
            int endIndexOfCountryCode = localeString.indexOf(country, language.length()) + country.length();
            // Strip off any leading '_' and whitespace, what's left is the variant.
            variant = trimLeadingWhitespace(localeString.substring(endIndexOfCountryCode));
            if (variant.startsWith("_")) {
                variant = trimLeadingCharacter(variant, '_');
            }
        }
        return (language.length() > 0 ? new Locale(language, country, variant) : null);
    }

    private static void validateLocalePart(String localePart) {
        for (int i = 0; i < localePart.length(); i++) {
            char ch = localePart.charAt(i);
            if (ch != ' ' && ch != '_' && ch != '#' && !Character.isLetterOrDigit(ch)) {
                throw new IllegalArgumentException(
                    "Locale part \"" + localePart + "\" contains invalid characters");
            }
        }
    }

    /**
     * Determine the RFC 3066 compliant language tag,
     * as used for the HTTP "Accept-Language" header.
     * @param locale the Locale to transform to a language tag
     * @return the RFC 3066 compliant language tag as {@code String}
     */
    public static String toLanguageTag(Locale locale) {
        return locale.getLanguage() + (hasText(locale.getCountry()) ? "-" + locale.getCountry() : "");
    }

    /**
     * Parse the given {@code timeZoneString} value into a {@link TimeZone}.
     * @param timeZoneString the time zone {@code String}, following {@link TimeZone#getTimeZone(String)}
     * but throwing {@link IllegalArgumentException} in case of an invalid time zone specification
     * @return a corresponding {@link TimeZone} instance
     * @throws IllegalArgumentException in case of an invalid time zone specification
     */
    public static TimeZone parseTimeZoneString(String timeZoneString) {
        TimeZone timeZone = TimeZone.getTimeZone(timeZoneString);
        if ("GMT".equals(timeZone.getID()) && !timeZoneString.startsWith("GMT")) {
            // We don't want that GMT fallback...
            throw new IllegalArgumentException("Invalid time zone specification '" + timeZoneString + "'");
        }
        return timeZone;
    }


    //---------------------------------------------------------------------
    // Convenience methods for working with String arrays
    //---------------------------------------------------------------------

    /**
     * Append the given {@code String} to the given {@code String} array,
     * returning a new array consisting of the input array contents plus
     * the given {@code String}.
     * @param array the array to append to (can be {@code null})
     * @param str the {@code String} to append
     * @return the new array (never {@code null})
     */
    public static String[] addStringToArray(String[] array, String str) {
        if (ObjectUtils.isEmpty(array)) {
            return new String[] {str};
        }

        String[] newArr = new String[array.length + 1];
        System.arraycopy(array, 0, newArr, 0, array.length);
        newArr[array.length] = str;
        return newArr;
    }

    /**
     * Concatenate the given {@code String} arrays into one,
     * with overlapping array elements included twice.
     * <p>The order of elements in the original arrays is preserved.
     * @param array1 the first array (can be {@code null})
     * @param array2 the second array (can be {@code null})
     * @return the new array ({@code null} if both given arrays were {@code null})
     */
    public static String[] concatenateStringArrays(String[] array1, String[] array2) {
        if (ObjectUtils.isEmpty(array1)) {
            return array2;
        }
        if (ObjectUtils.isEmpty(array2)) {
            return array1;
        }

        String[] newArr = new String[array1.length + array2.length];
        System.arraycopy(array1, 0, newArr, 0, array1.length);
        System.arraycopy(array2, 0, newArr, array1.length, array2.length);
        return newArr;
    }

    /**
     * Merge the given {@code String} arrays into one, with overlapping
     * array elements only included once.
     * <p>The order of elements in the original arrays is preserved
     * (with the exception of overlapping elements, which are only
     * included on their first occurrence).
     * @param array1 the first array (can be {@code null})
     * @param array2 the second array (can be {@code null})
     * @return the new array ({@code null} if both given arrays were {@code null})
     */
    public static String[] mergeStringArrays(String[] array1, String[] array2) {
        if (ObjectUtils.isEmpty(array1)) {
            return array2;
        }
        if (ObjectUtils.isEmpty(array2)) {
            return array1;
        }

        List<String> result = new ArrayList<String>();
        result.addAll(Arrays.asList(array1));
        for (String str : array2) {
            if (!result.contains(str)) {
                result.add(str);
            }
        }
        return toStringArray(result);
    }

    /**
     * Turn given source {@code String} array into sorted array.
     * @param array the source array
     * @return the sorted array (never {@code null})
     */
    public static String[] sortStringArray(String[] array) {
        if (ObjectUtils.isEmpty(array)) {
            return new String[0];
        }

        Arrays.sort(array);
        return array;
    }

    /**
     * Copy the given {@code Collection} into a {@code String} array.
     * <p>The {@code Collection} must contain {@code String} elements only.
     * @param collection the {@code Collection} to copy
     * @return the {@code String} array
     */
    public static String[] toStringArray(Collection<String> collection) {
        if (collection == null) {
            return null;
        }

        return collection.toArray(new String[collection.size()]);
    }

    /**
     * Copy the given Enumeration into a {@code String} array.
     * The Enumeration must contain {@code String} elements only.
     * @param enumeration the Enumeration to copy
     * @return the {@code String} array
     */
    public static String[] toStringArray(Enumeration<String> enumeration) {
        if (enumeration == null) {
            return null;
        }

        List<String> list = Collections.list(enumeration);
        return list.toArray(new String[list.size()]);
    }

    /**
     * Trim the elements of the given {@code String} array,
     * calling {@code String.trim()} on each of them.
     * @param array the original {@code String} array
     * @return the resulting array (of the same size) with trimmed elements
     */
    public static String[] trimArrayElements(String[] array) {
        if (ObjectUtils.isEmpty(array)) {
            return new String[0];
        }

        String[] result = new String[array.length];
        for (int i = 0; i < array.length; i++) {
            String element = array[i];
            result[i] = (element != null ? element.trim() : null);
        }
        return result;
    }

    /**
     * Remove duplicate strings from the given array.
     * <p>As of 4.2, it preserves the original order, as it uses a {@link LinkedHashSet}.
     * @param array the {@code String} array
     * @return an array without duplicates, in natural sort order
     */
    public static String[] removeDuplicateStrings(String[] array) {
        if (ObjectUtils.isEmpty(array)) {
            return array;
        }

        Set<String> set = new LinkedHashSet<String>();
        for (String element : array) {
            set.add(element);
        }
        return toStringArray(set);
    }

    /**
     * Split a {@code String} at the first occurrence of the delimiter.
     * Does not include the delimiter in the result.
     * @param toSplit the string to split
     * @param delimiter to split the string up with
     * @return a two element array with index 0 being before the delimiter, and
     * index 1 being after the delimiter (neither element includes the delimiter);
     * or {@code null} if the delimiter wasn't found in the given input {@code String}
     */
    public static String[] split(String toSplit, String delimiter) {
        if (!hasLength(toSplit) || !hasLength(delimiter)) {
            return null;
        }
        int offset = toSplit.indexOf(delimiter);
        if (offset < 0) {
            return null;
        }

        String beforeDelimiter = toSplit.substring(0, offset);
        String afterDelimiter = toSplit.substring(offset + delimiter.length());
        return new String[] {beforeDelimiter, afterDelimiter};
    }

    /**
     * Take an array of strings and split each element based on the given delimiter.
     * A {@code Properties} instance is then generated, with the left of the
     * delimiter providing the key, and the right of the delimiter providing the value.
     * <p>Will trim both the key and value before adding them to the
     * {@code Properties} instance.
     * @param array the array to process
     * @param delimiter to split each element using (typically the equals symbol)
     * @return a {@code Properties} instance representing the array contents,
     * or {@code null} if the array to process was {@code null} or empty
     */
    public static Properties splitArrayElementsIntoProperties(String[] array, String delimiter) {
        return splitArrayElementsIntoProperties(array, delimiter, null);
    }

    /**
     * Take an array of strings and split each element based on the given delimiter.
     * A {@code Properties} instance is then generated, with the left of the
     * delimiter providing the key, and the right of the delimiter providing the value.
     * <p>Will trim both the key and value before adding them to the
     * {@code Properties} instance.
     * @param array the array to process
     * @param delimiter to split each element using (typically the equals symbol)
     * @param charsToDelete one or more characters to remove from each element
     * prior to attempting the split operation (typically the quotation mark
     * symbol), or {@code null} if no removal should occur
     * @return a {@code Properties} instance representing the array contents,
     * or {@code null} if the array to process was {@code null} or empty
     */
    public static Properties splitArrayElementsIntoProperties(
        String[] array, String delimiter, String charsToDelete) {

        if (ObjectUtils.isEmpty(array)) {
            return null;
        }

        Properties result = new Properties();
        for (String element : array) {
            if (charsToDelete != null) {
                element = deleteAny(element, charsToDelete);
            }
            String[] splittedElement = split(element, delimiter);
            if (splittedElement == null) {
                continue;
            }
            result.setProperty(splittedElement[0].trim(), splittedElement[1].trim());
        }
        return result;
    }

    /**
     * Tokenize the given {@code String} into a {@code String} array via a
     * {@link StringTokenizer}.
     * <p>Trims tokens and omits empty tokens.
     * <p>The given {@code delimiters} string can consist of any number of
     * delimiter characters. Each of those characters can be used to separate
     * tokens. A delimiter is always a single character; for multi-character
     * delimiters, consider using {@link #delimitedListToStringArray}.
     * @param str the {@code String} to tokenize
     * @param delimiters the delimiter characters, assembled as a {@code String}
     * (each of the characters is individually considered as a delimiter)
     * @return an array of the tokens
     * @see StringTokenizer
     * @see String#trim()
     * @see #delimitedListToStringArray
     */
    public static String[] tokenizeToStringArray(String str, String delimiters) {
        return tokenizeToStringArray(str, delimiters, true, true);
    }

    /**
     * Tokenize the given {@code String} into a {@code String} array via a
     * {@link StringTokenizer}.
     * <p>The given {@code delimiters} string can consist of any number of
     * delimiter characters. Each of those characters can be used to separate
     * tokens. A delimiter is always a single character; for multi-character
     * delimiters, consider using {@link #delimitedListToStringArray}.
     * @param str the {@code String} to tokenize
     * @param delimiters the delimiter characters, assembled as a {@code String}
     * (each of the characters is individually considered as a delimiter)
     * @param trimTokens trim the tokens via {@link String#trim()}
     * @param ignoreEmptyTokens omit empty tokens from the result array
     * (only applies to tokens that are empty after trimming; StringTokenizer
     * will not consider subsequent delimiters as token in the first place).
     * @return an array of the tokens
     * @see StringTokenizer
     * @see String#trim()
     * @see #delimitedListToStringArray
     */
    public static String[] tokenizeToStringArray(
        String str, String delimiters, boolean trimTokens, boolean ignoreEmptyTokens) {

        if (str == null) {
            return null;
        }

        StringTokenizer st = new StringTokenizer(str, delimiters);
        List<String> tokens = new ArrayList<String>();
        while (st.hasMoreTokens()) {
            String token = st.nextToken();
            if (trimTokens) {
                token = token.trim();
            }
            if (!ignoreEmptyTokens || token.length() > 0) {
                tokens.add(token);
            }
        }
        return toStringArray(tokens);
    }

    /**
     * Take a {@code String} that is a delimited list and convert it into a
     * {@code String} array.
     * <p>A single {@code delimiter} may consist of more than one character,
     * but it will still be considered as a single delimiter string, rather
     * than as bunch of potential delimiter characters, in contrast to
     * {@link #tokenizeToStringArray}.
     * @param str the input {@code String}
     * @param delimiter the delimiter between elements (this is a single delimiter,
     * rather than a bunch individual delimiter characters)
     * @return an array of the tokens in the list
     * @see #tokenizeToStringArray
     */
    public static String[] delimitedListToStringArray(String str, String delimiter) {
        return delimitedListToStringArray(str, delimiter, null);
    }

    /**
     * Take a {@code String} that is a delimited list and convert it into
     * a {@code String} array.
     * <p>A single {@code delimiter} may consist of more than one character,
     * but it will still be considered as a single delimiter string, rather
     * than as bunch of potential delimiter characters, in contrast to
     * {@link #tokenizeToStringArray}.
     * @param str the input {@code String}
     * @param delimiter the delimiter between elements (this is a single delimiter,
     * rather than a bunch individual delimiter characters)
     * @param charsToDelete a set of characters to delete; useful for deleting unwanted
     * line breaks: e.g. "\r\n\f" will delete all new lines and line feeds in a {@code String}
     * @return an array of the tokens in the list
     * @see #tokenizeToStringArray
     */
    public static String[] delimitedListToStringArray(String str, String delimiter, String charsToDelete) {
        if (str == null) {
            return new String[0];
        }
        if (delimiter == null) {
            return new String[] {str};
        }

        List<String> result = new ArrayList<String>();
        if ("".equals(delimiter)) {
            for (int i = 0; i < str.length(); i++) {
                result.add(deleteAny(str.substring(i, i + 1), charsToDelete));
            }
        }
        else {
            int pos = 0;
            int delPos;
            while ((delPos = str.indexOf(delimiter, pos)) != -1) {
                result.add(deleteAny(str.substring(pos, delPos), charsToDelete));
                pos = delPos + delimiter.length();
            }
            if (str.length() > 0 && pos <= str.length()) {
                // Add rest of String, but not in case of empty input.
                result.add(deleteAny(str.substring(pos), charsToDelete));
            }
        }
        return toStringArray(result);
    }

    /**
     * Convert a comma delimited list (e.g., a row from a CSV file) into an
     * array of strings.
     * @param str the input {@code String}
     * @return an array of strings, or the empty array in case of empty input
     */
    public static String[] commaDelimitedListToStringArray(String str) {
        return delimitedListToStringArray(str, ",");
    }

    /**
     * Convert a comma delimited list (e.g., a row from a CSV file) into a set.
     * <p>Note that this will suppress duplicates, and as of 4.2, the elements in
     * the returned set will preserve the original order in a {@link LinkedHashSet}.
     * @param str the input {@code String}
     * @return a set of {@code String} entries in the list
     * @see #removeDuplicateStrings(String[])
     */
    public static Set<String> commaDelimitedListToSet(String str) {
        Set<String> set = new LinkedHashSet<String>();
        String[] tokens = commaDelimitedListToStringArray(str);
        for (String token : tokens) {
            set.add(token);
        }
        return set;
    }

    /**
     * Convert a {@link Collection} to a delimited {@code String} (e.g. CSV).
     * <p>Useful for {@code toString()} implementations.
     * @param coll the {@code Collection} to convert
     * @param delim the delimiter to use (typically a ",")
     * @param prefix the {@code String} to start each element with
     * @param suffix the {@code String} to end each element with
     * @return the delimited {@code String}
     */
    public static String collectionToDelimitedString(Collection<?> coll, String delim, String prefix, String suffix) {
        if (CollectionUtils.isEmpty(coll)) {
            return "";
        }

        StringBuilder sb = new StringBuilder();
        Iterator<?> it = coll.iterator();
        while (it.hasNext()) {
            sb.append(prefix).append(it.next()).append(suffix);
            if (it.hasNext()) {
                sb.append(delim);
            }
        }
        return sb.toString();
    }

    /**
     * Convert a {@code Collection} into a delimited {@code String} (e.g. CSV).
     * <p>Useful for {@code toString()} implementations.
     * @param coll the {@code Collection} to convert
     * @param delim the delimiter to use (typically a ",")
     * @return the delimited {@code String}
     */
    public static String collectionToDelimitedString(Collection<?> coll, String delim) {
        return collectionToDelimitedString(coll, delim, "", "");
    }

    /**
     * Convert a {@code Collection} into a delimited {@code String} (e.g., CSV).
     * <p>Useful for {@code toString()} implementations.
     * @param coll the {@code Collection} to convert
     * @return the delimited {@code String}
     */
    public static String collectionToCommaDelimitedString(Collection<?> coll) {
        return collectionToDelimitedString(coll, ",");
    }

    /**
     * Convert a {@code String} array into a delimited {@code String} (e.g. CSV).
     * <p>Useful for {@code toString()} implementations.
     * @param arr the array to display
     * @param delim the delimiter to use (typically a ",")
     * @return the delimited {@code String}
     */
    public static String arrayToDelimitedString(Object[] arr, String delim) {
        if (ObjectUtils.isEmpty(arr)) {
            return "";
        }
        if (arr.length == 1) {
            return ObjectUtils.nullSafeToString(arr[0]);
        }

        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < arr.length; i++) {
            if (i > 0) {
                sb.append(delim);
            }
            sb.append(arr[i]);
        }
        return sb.toString();
    }

    /**
     * Convert a {@code String} array into a comma delimited {@code String}
     * (i.e., CSV).
     * <p>Useful for {@code toString()} implementations.
     * @param arr the array to display
     * @return the delimited {@code String}
     */
    public static String arrayToCommaDelimitedString(Object[] arr) {
        return arrayToDelimitedString(arr, ",");
    }

    /**
     * <p>Compares two CharSequences, returning {@code true} if they represent
     * equal sequences of characters.</p>
     *
     * <p>{@code null}s are handled without exceptions. Two {@code null}
     * references are considered to be equal. The comparison is case sensitive.</p>
     *
     * <pre>
     * StringUtils.equals(null, null)   = true
     * StringUtils.equals(null, "abc")  = false
     * StringUtils.equals("abc", null)  = false
     * StringUtils.equals("abc", "abc") = true
     * StringUtils.equals("abc", "ABC") = false
     * </pre>
     *
     * @see Object#equals(Object)
     * @param cs1  the first CharSequence, may be {@code null}
     * @param cs2  the second CharSequence, may be {@code null}
     * @return {@code true} if the CharSequences are equal (case-sensitive), or both {@code null}
     * @since 3.0 Changed signature from equals(String, String) to equals(CharSequence, CharSequence)
     */
    public static boolean equals(final CharSequence cs1, final CharSequence cs2) {
        if (cs1 == cs2) {
            return true;
        }
        if (cs1 == null || cs2 == null) {
            return false;
        }
        if (cs1.length() != cs2.length()) {
            return false;
        }
        if (cs1 instanceof String && cs2 instanceof String) {
            return cs1.equals(cs2);
        }
        return regionMatches(cs1, false, 0, cs2, 0, cs1.length());
    }

    /**
     * Green implementation of regionMatches.
     *
     * @param cs the {@code CharSequence} to be processed
     * @param ignoreCase whether or not to be case insensitive
     * @param thisStart the index to start on the {@code cs} CharSequence
     * @param substring the {@code CharSequence} to be looked for
     * @param start the index to start on the {@code substring} CharSequence
     * @param length character length of the region
     * @return whether the region matched
     */
    static boolean regionMatches(final CharSequence cs, final boolean ignoreCase, final int thisStart,
                                 final CharSequence substring, final int start, final int length)    {
        if (cs instanceof String && substring instanceof String) {
            return ((String) cs).regionMatches(ignoreCase, thisStart, (String) substring, start, length);
        }
        int index1 = thisStart;
        int index2 = start;
        int tmpLen = length;

        // Extract these first so we detect NPEs the same as the java.lang.String version
        final int srcLen = cs.length() - thisStart;
        final int otherLen = substring.length() - start;

        // Check for invalid parameters
        if (thisStart < 0 || start < 0 || length < 0) {
            return false;
        }

        // Check that the regions are long enough
        if (srcLen < length || otherLen < length) {
            return false;
        }

        while (tmpLen-- > 0) {
            final char c1 = cs.charAt(index1++);
            final char c2 = substring.charAt(index2++);

            if (c1 == c2) {
                continue;
            }

            if (!ignoreCase) {
                return false;
            }

            // The same check as in String.regionMatches():
            if (Character.toUpperCase(c1) != Character.toUpperCase(c2)
                && Character.toLowerCase(c1) != Character.toLowerCase(c2)) {
                return false;
            }
        }

        return true;
    }

}