最小的String实用程序类。专为内部jsoup使用而设计。

喜欢ヅ旅行 2023-10-05 13:43 22阅读 0赞

package org.jsoup.helper;
    
    import java.net.MalformedURLException;
    import java.net.URL;
    import java.util.Arrays;
    import java.util.Collection;
    import java.util.Iterator;
    
    /**
     * A minimal String utility class. Designed for internal jsoup use only.
     */
    public final class StringUtil {
        // memoised padding up to 21
        static final String[] padding = {"", " ", "  ", "   ", "    ", "     ", "      ", "       ", "        ",
            "         ", "          ", "           ", "            ", "             ", "              ", "               ",
            "                ", "                 ", "                  ", "                   ", "                    "};
    
        /**
         * Join a collection of strings by a separator
         * @param strings collection of string objects
         * @param sep string to place between strings
         * @return joined string
         */
        public static String join(Collection strings, String sep) {
            return join(strings.iterator(), sep);
        }
    
        /**
         * Join a collection of strings by a separator
         * @param strings iterator of string objects
         * @param sep string to place between strings
         * @return joined string
         */
        public static String join(Iterator strings, String sep) {
            if (!strings.hasNext())
                return "";
    
            String start = strings.next().toString();
            if (!strings.hasNext()) // only one, avoid builder
                return start;
    
            StringBuilder sb = new StringBuilder(64).append(start);
            while (strings.hasNext()) {
                sb.append(sep);
                sb.append(strings.next());
            }
            return sb.toString();
        }
    
        /**
         * Join an array of strings by a separator
         * @param strings collection of string objects
         * @param sep string to place between strings
         * @return joined string
         */
        public static String join(String[] strings, String sep) {
            return join(Arrays.asList(strings), sep);
        }
    
        /**
         * Returns space padding
         * @param width amount of padding desired
         * @return string of spaces * width
         */
        public static String padding(int width) {
            if (width < 0)
                throw new IllegalArgumentException("width must be > 0");
    
            if (width < padding.length)
                return padding[width];
            char[] out = new char[width];
            for (int i = 0; i < width; i++)
                out[i] = ' ';
            return String.valueOf(out);
        }
    
        /**
         * Tests if a string is blank: null, empty, or only whitespace (" ", \r\n, \t, etc)
         * @param string string to test
         * @return if string is blank
         */
        public static boolean isBlank(String string) {
            if (string == null || string.length() == 0)
                return true;
    
            int l = string.length();
            for (int i = 0; i < l; i++) {
                if (!StringUtil.isWhitespace(string.codePointAt(i)))
                    return false;
            }
            return true;
        }
    
        /**
         * Tests if a string is numeric, i.e. contains only digit characters
         * @param string string to test
         * @return true if only digit chars, false if empty or null or contains non-digit chars
         */
        public static boolean isNumeric(String string) {
            if (string == null || string.length() == 0)
                return false;
    
            int l = string.length();
            for (int i = 0; i < l; i++) {
                if (!Character.isDigit(string.codePointAt(i)))
                    return false;
            }
            return true;
        }
    
        /**
         * Tests if a code point is "whitespace" as defined in the HTML spec. Used for output HTML.
         * @param c code point to test
         * @return true if code point is whitespace, false otherwise
         * @see #isActuallyWhitespace(int)
         */
        public static boolean isWhitespace(int c){
            return c == ' ' || c == '\t' || c == '\n' || c == '\f' || c == '\r';
        }
    
        /**
         * Tests if a code point is "whitespace" as defined by what it looks like. Used for Element.text etc.
         * @param c code point to test
         * @return true if code point is whitespace, false otherwise
         */
        public static boolean isActuallyWhitespace(int c){
            return c == ' ' || c == '\t' || c == '\n' || c == '\f' || c == '\r' || c == 160;
            // 160 is   (non-breaking space). Not in the spec but expected.
        }
    
        public static boolean isInvisibleChar(int c) {
            return Character.getType(c) == 16 && (c == 8203 || c == 8204 || c == 8205 || c == 173);
            // zero width sp, zw non join, zw join, soft hyphen
        }
    
        /**
         * Normalise the whitespace within this string; multiple spaces collapse to a single, and all whitespace characters
         * (e.g. newline, tab) convert to a simple space
         * @param string content to normalise
         * @return normalised string
         */
        public static String normaliseWhitespace(String string) {
            StringBuilder sb = StringUtil.stringBuilder();
            appendNormalisedWhitespace(sb, string, false);
            return sb.toString();
        }
    
        /**
         * After normalizing the whitespace within a string, appends it to a string builder.
         * @param accum builder to append to
         * @param string string to normalize whitespace within
         * @param stripLeading set to true if you wish to remove any leading whitespace
         */
        public static void appendNormalisedWhitespace(StringBuilder accum, String string, boolean stripLeading) {
            boolean lastWasWhite = false;
            boolean reachedNonWhite = false;
    
            int len = string.length();
            int c;
            for (int i = 0; i < len; i+= Character.charCount(c)) {
                c = string.codePointAt(i);
                if (isActuallyWhitespace(c)) {
                    if ((stripLeading && !reachedNonWhite) || lastWasWhite)
                        continue;
                    accum.append(' ');
                    lastWasWhite = true;
                }
                else if (!isInvisibleChar(c)) {
                    accum.appendCodePoint(c);
                    lastWasWhite = false;
                    reachedNonWhite = true;
                }
            }
        }
    
        public static boolean in(final String needle, final String... haystack) {
            final int len = haystack.length;
            for (int i = 0; i < len; i++) {
                if (haystack[i].equals(needle))
                return true;
            }
            return false;
        }
    
        public static boolean inSorted(String needle, String[] haystack) {
            return Arrays.binarySearch(haystack, needle) >= 0;
        }
    
        /**
         * Create a new absolute URL, from a provided existing absolute URL and a relative URL component.
         * @param base the existing absolute base URL
         * @param relUrl the relative URL to resolve. (If it's already absolute, it will be returned)
         * @return the resolved absolute URL
         * @throws MalformedURLException if an error occurred generating the URL
         */
        public static URL resolve(URL base, String relUrl) throws MalformedURLException {
            // workaround: java resolves '//path/file + ?foo' to '//path/?foo', not '//path/file?foo' as desired
            if (relUrl.startsWith("?"))
                relUrl = base.getPath() + relUrl;
            // workaround: //example.com + ./foo = //example.com/./foo, not //example.com/foo
            if (relUrl.indexOf('.') == 0 && base.getFile().indexOf('/') != 0) {
                base = new URL(base.getProtocol(), base.getHost(), base.getPort(), "/" + base.getFile());
            }
            return new URL(base, relUrl);
        }
    
        /**
         * Create a new absolute URL, from a provided existing absolute URL and a relative URL component.
         * @param baseUrl the existing absolute base URL
         * @param relUrl the relative URL to resolve. (If it's already absolute, it will be returned)
         * @return an absolute URL if one was able to be generated, or the empty string if not
         */
        public static String resolve(final String baseUrl, final String relUrl) {
            URL base;
            try {
                try {
                    base = new URL(baseUrl);
                } catch (MalformedURLException e) {
                    // the base is unsuitable, but the attribute/rel may be abs on its own, so try that
                    URL abs = new URL(relUrl);
                    return abs.toExternalForm();
                }
                return resolve(base, relUrl).toExternalForm();
            } catch (MalformedURLException e) {
                return "";
            }
        }
    
        /**
         * Maintains a cached StringBuilder, to minimize new StringBuilder GCs. Prevents it from growing too big per thread.
         * Care must be taken to not grab more than one in the same stack (not locked or mutexed or anything).
         * @return an empty StringBuilder
         */
        public static StringBuilder stringBuilder() {
            StringBuilder sb = stringLocal.get();
            if (sb.length() > MaxCachedBuilderSize) {
                sb = new StringBuilder(MaxCachedBuilderSize);
                stringLocal.set(sb);
            } else {
                sb.delete(0, sb.length());
            }
            return sb;
    
        }
    
        private static final int MaxCachedBuilderSize = 8 * 1024;
        private static final ThreadLocal<StringBuilder> stringLocal = new ThreadLocal<StringBuilder>(){
            @Override
            protected StringBuilder initialValue() {
                return new StringBuilder(MaxCachedBuilderSize);
            }
        };
    
    
    }