Spring源码解析 StringUtils

这个类是spring的工具类，用于一些常用的字符串处理，但是这些方法不在jdk的String中。

know more about this class,write less code.

apache中的commmons lang中也有一个StringUtils，比spring中这个功能更全面。

下面是我把方法声明以及部分实现摘抄下来。

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 = '.';

判断“空”串
    public static boolean isEmpty(Object str) {
        return (str == null || "".equals(str));
    }

判断是否是“真串”
     * StringUtils.hasLength(null) = false
     * StringUtils.hasLength("") = false
     * StringUtils.hasLength(" ") = true
     * StringUtils.hasLength("Hello") = true
    public static boolean hasLength(CharSequence str) {
        return (str != null && str.length() > 0);
    }

 
    public static boolean hasLength(String str) {
        return hasLength((CharSequence) str);
    }

判断是否是有内容的“真串” Check whether the given String has actual text.
     * StringUtils.hasText(null) = false
     * StringUtils.hasText("") = false
     * StringUtils.hasText(" ") = false
     * StringUtils.hasText("12345") = true
     * StringUtils.hasText(" 12345 ") = true
    public static boolean hasText(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;
    }

    
    public static boolean hasText(String str) {
        return hasText((CharSequence) str);
    }

 判断是否包含空格
    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;
    }

   
    public static boolean containsWhitespace(String str) {
        return containsWhitespace((CharSequence) str);
    }

去掉头尾的空格
    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();
    }

    去掉所有空格
    public static String trimAllWhitespace(String str) {
        if (!hasLength(str)) {
            return str;
        }
        StringBuilder sb = new StringBuilder(str);
        int index = 0;
        while (sb.length() > index) {
            if (Character.isWhitespace(sb.charAt(index))) {
                sb.deleteCharAt(index);
            }
            else {
                index++;
            }
        }
        return sb.toString();
    }

  去头部空格
    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();
    }

去尾部空格
    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();
    }

去头部指定字符
    public static String trimLeadingCharacter(String str, char leadingCharacter)

    去尾部指定字符
    public static String trimTrailingCharacter(String str, char trailingCharacter)



  判断字符串的prefix，不区分大小写
    public static boolean startsWithIgnoreCase(String str, String prefix) {
        if (str == null || prefix == null) {
            return false;
        }
        if (str.startsWith(prefix)) {
            return true;
        }
        if (str.length() < prefix.length()) {
            return false;
        }
        String lcStr = str.substring(0, prefix.length()).toLowerCase();
        String lcPrefix = prefix.toLowerCase();
        return lcStr.equals(lcPrefix);
    }

   判断字符串的suffix，不区分大小写


    /**
     * 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) {
        for (int j = 0; j < substring.length(); j++) {
            int i = index + j;
            if (i >= str.length() || str.charAt(i) != substring.charAt(j)) {
                return false;
            }
        }
        return true;
    }

统计子串出现次数。
    public static int countOccurrencesOf(String str, String sub) {
        if (str == null || sub == null || str.length() == 0 || sub.length() == 0) {
            return 0;
        }
        int count = 0;
        int pos = 0;
        int idx;
        while ((idx = str.indexOf(sub, pos)) != -1) {
            ++count;
            pos = idx + sub.length();
        }
        return count;
    }

  替换掉所有某子串
    public static String replace(String inString, String oldPattern, String newPattern) {
        if (!hasLength(inString) || !hasLength(oldPattern) || newPattern == null) {
            return inString;
        }
        StringBuilder sb = new StringBuilder();
        int pos = 0; // our position in the old string
        int index = inString.indexOf(oldPattern);
        // the index of an occurrence we've found, or -1
        int patLen = oldPattern.length();
        while (index >= 0) {
            sb.append(inString.substring(pos, index));
            sb.append(newPattern);
            pos = index + patLen;
            index = inString.indexOf(oldPattern, pos);
        }
        sb.append(inString.substring(pos));
        // remember to append any characters to the right of a match
        return sb.toString();
    }

    删除所有出现的指定的子串
    public static String delete(String inString, String pattern) {
        return replace(inString, pattern, "");
    }

    删除指定的char
    public static String deleteAny(String inString, String charsToDelete) {
        if (!hasLength(inString) || !hasLength(charsToDelete)) {
            return inString;
        }
        StringBuilder sb = new StringBuilder();
        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 String with single quotes.
     * @param str the input String (e.g. "myString")
     * @return the quoted 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 String with single quotes
     * if it is a String; keeping the Object as-is else.
     * @param obj the input Object (e.g. "myString")
     * @return the quoted String (e.g. "'myString'"),
     * or the input object as-is if not a 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 String to capitalize, may be {@code null}
     * @return the capitalized String, {@code null} if null
     */
    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 String to uncapitalize, may be {@code null}
     * @return the uncapitalized String, {@code null} if null
     */
    public static String uncapitalize(String str) {
        return changeFirstCharacterCase(str, false);
    }

    private static String changeFirstCharacterCase(String str, boolean capitalize) {
        if (str == null || str.length() == 0) {
            return str;
        }
        StringBuilder sb = new StringBuilder(str.length());
        if (capitalize) {
            sb.append(Character.toUpperCase(str.charAt(0)));
        }
        else {
            sb.append(Character.toLowerCase(str.charAt(0)));
        }
        sb.append(str.substring(1));
        return sb.toString();
    }

    /**
     * Extract the filename from the given path,
     * e.g. "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 path,
     * e.g. "mypath/myfile.txt" -> "txt".
     * @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 path,
     * e.g. "mypath/myfile.txt" -> "mypath/myfile".
     * @param path the file path (may be {@code null})
     * @return the path with stripped filename extension,
     * or {@code null} if none
     */
    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 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.
     *

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);
            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 pathElements = new LinkedList();
        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}.
     *

This is the inverse operation of {@link Locale#toString Locale's toString}.
     * @param localeString the locale 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
     */
    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.lastIndexOf(country) + 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 != ' ' && !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 String
     */
    public static String toLanguageTag(Locale locale) {
        return locale.getLanguage() + (hasText(locale.getCountry()) ? "-" + locale.getCountry() : "");
    }


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

    /**
     * Append the given String to the given String array, returning a new array
     * consisting of the input array contents plus the given String.
     * @param array the array to append to (can be {@code null})
     * @param str the 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 String arrays into one,
     * with overlapping array elements included twice.
     *

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 String arrays into one, with overlapping
     * array elements only included once.
     *

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

    /**
     * Turn given source 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 Collection into a String array.
     * The Collection must contain String elements only.
     * @param collection the Collection to copy
     * @return the String array ({@code null} if the passed-in
     * Collection was {@code null})
     */
    public static String[] toStringArray(Collection collection) {
        if (collection == null) {
            return null;
        }
        return collection.toArray(new String[collection.size()]);
    }

    /**
     * Copy the given Enumeration into a String array.
     * The Enumeration must contain String elements only.
     * @param enumeration the Enumeration to copy
     * @return the String array ({@code null} if the passed-in
     * Enumeration was {@code null})
     */
    public static String[] toStringArray(Enumeration enumeration) {
        if (enumeration == null) {
            return null;
        }
        List list = Collections.list(enumeration);
        return list.toArray(new String[list.size()]);
    }

    /**
     * Trim the elements of the given String array,
     * calling {@code String.trim()} on each of them.
     * @param array the original 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.
     * Also sorts the array, as it uses a TreeSet.
     * @param array the String array
     * @return an array without duplicates, in natural sort order
     */
    public static String[] removeDuplicateStrings(String[] array) {
        if (ObjectUtils.isEmpty(array)) {
            return array;
        }
        Set set = new TreeSet();
        for (String element : array) {
            set.add(element);
        }
        return toStringArray(set);
    }

    /**
     * Split a 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 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 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.
     *

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 null or empty
     */
    public static Properties splitArrayElementsIntoProperties(String[] array, String delimiter) {
        return splitArrayElementsIntoProperties(array, delimiter, null);
    }

    /**
     * Take an array 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.
     *

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 String into a String array via a StringTokenizer.
     * Trims tokens and omits empty tokens.
     *

The given delimiters string is supposed to 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 {@code delimitedListToStringArray}
     * @param str the String to tokenize
     * @param delimiters the delimiter characters, assembled as String
     * (each of those characters is individually considered as delimiter).
     * @return an array of the tokens
     * @see java.util.StringTokenizer
     * @see String#trim()
     * @see #delimitedListToStringArray
     */
    public static String[] tokenizeToStringArray(String str, String delimiters) {
        return tokenizeToStringArray(str, delimiters, true, true);
    }

    /**
     * Tokenize the given String into a String array via a StringTokenizer.
     *

The given delimiters string is supposed to 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 {@code delimitedListToStringArray}
     * @param str the String to tokenize
     * @param delimiters the delimiter characters, assembled as String
     * (each of those characters is individually considered as delimiter)
     * @param trimTokens trim the tokens via String's {@code 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 ({@code null} if the input String
     * was {@code null})
     * @see java.util.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 tokens = new ArrayList();
        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 String which is a delimited list and convert it to a String array.
     *

A single delimiter can consists of more than one character: It will still
     * be considered as single delimiter string, rather than as bunch of potential
     * delimiter characters - in contrast to {@code tokenizeToStringArray}.
     * @param str the input 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 String which is a delimited list and convert it to a String array.
     *

A single delimiter can consists of more than one character: It will still
     * be considered as single delimiter string, rather than as bunch of potential
     * delimiter characters - in contrast to {@code tokenizeToStringArray}.
     * @param str the input 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 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 result = new ArrayList();
        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 CSV list into an array of Strings.
     * @param str the input String
     * @return an array of Strings, or the empty array in case of empty input
     */
    public static String[] commaDelimitedListToStringArray(String str) {
        return delimitedListToStringArray(str, ",");
    }

    /**
     * Convenience method to convert a CSV string list to a set.
     * Note that this will suppress duplicates.
     * @param str the input String
     * @return a Set of String entries in the list
     */
    public static Set commaDelimitedListToSet(String str) {
        Set set = new TreeSet();
        String[] tokens = commaDelimitedListToStringArray(str);
        for (String token : tokens) {
            set.add(token);
        }
        return set;
    }

    /**
     * Convenience method to return a Collection as a delimited (e.g. CSV)
     * String. E.g. useful for {@code toString()} implementations.
     * @param coll the Collection to display
     * @param delim the delimiter to use (probably a ",")
     * @param prefix the String to start each element with
     * @param suffix the String to end each element with
     * @return the delimited 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();
    }

    /**
     * Convenience method to return a Collection as a delimited (e.g. CSV)
     * String. E.g. useful for {@code toString()} implementations.
     * @param coll the Collection to display
     * @param delim the delimiter to use (probably a ",")
     * @return the delimited String
     */
    public static String collectionToDelimitedString(Collection coll, String delim) {
        return collectionToDelimitedString(coll, delim, "", "");
    }

    /**
     * Convenience method to return a Collection as a CSV String.
     * E.g. useful for {@code toString()} implementations.
     * @param coll the Collection to display
     * @return the delimited String
     */
    public static String collectionToCommaDelimitedString(Collection coll) {
        return collectionToDelimitedString(coll, ",");
    }

  将字符串转换成用指定分割符分割的格式
    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();
    }

   
   Convenience method to return a String array as a CSV String.
将数组转制成CSV格式，CSV即common separated value,就是以逗号分割的格式啦，跟js里面的join(",")是一样的效果的。
    public static String arrayToCommaDelimitedString(Object[] arr) {
        return arrayToDelimitedString(arr, ",");
    }

}