Package com.google.common.net

Class PercentEscaper

  • @Beta
@GwtCompatible
public final class PercentEscaper
extends UnicodeEscaper
    A UnicodeEscaper that escapes some set of Java characters using a UTF-8 based percent encoding scheme. The set of safe characters (those which remain unescaped) can be specified on construction.

    This class is primarily used for creating URI escapers in UrlEscapers but can be used directly if required. While URI escapers impose specific semantics on which characters are considered 'safe', this class has a minimal set of restrictions.

    When escaping a String, the following rules apply:

    • All specified safe characters remain unchanged.
    • If plusForSpace was specified, the space character " " is converted into a plus sign "+".
    • All other characters are converted into one or more bytes using UTF-8 encoding and each byte is then represented by the 3-character string "%XX", where "XX" is the two-digit, uppercase, hexadecimal representation of the byte value.

    For performance reasons the only currently supported character encoding of this class is UTF-8.

    Note: This escaper produces uppercase hexadecimal sequences.

    Since:
    15.0
    Author:
    David Beaumont

    • Constructor Detail

      • PercentEscaper

        public PercentEscaper​(String safeChars,
                      boolean plusForSpace)
        Constructs a percent escaper with the specified safe characters and optional handling of the space character.

        Not that it is allowed, but not necessarily desirable to specify % as a safe character. This has the effect of creating an escaper which has no well defined inverse but it can be useful when escaping additional characters.

        Parameters:
        safeChars - a non null string specifying additional safe characters for this escaper (the ranges 0..9, a..z and A..Z are always safe and should not be specified here)
        plusForSpace - true if ASCII space should be escaped to + rather than %20
        Throws:
        IllegalArgumentException - if any of the parameters were invalid

    • Method Detail

      • nextEscapeIndex

        protected int nextEscapeIndex​(CharSequence csq,
                              int index,
                              int end)
        Description copied from class: UnicodeEscaper
        Scans a sub-sequence of characters from a given CharSequence, returning the index of the next character that requires escaping.

        Note: When implementing an escaper, it is a good idea to override this method for efficiency. The base class implementation determines successive Unicode code points and invokes UnicodeEscaper.escape(int) for each of them. If the semantics of your escaper are such that code points in the supplementary range are either all escaped or all unescaped, this method can be implemented more efficiently using CharSequence.charAt(int).

        Note however that if your escaper does not escape characters in the supplementary range, you should either continue to validate the correctness of any surrogate characters encountered or provide a clear warning to users that your escaper does not validate its input.

        See PercentEscaper for an example.

        Overrides:
        nextEscapeIndex in class UnicodeEscaper
        Parameters:
        csq - a sequence of characters
        index - the index of the first character to be scanned
        end - the index immediately after the last character to be scanned

      • escape

        public String escape​(String s)
        Description copied from class: UnicodeEscaper
        Returns the escaped form of a given literal string.

        If you are escaping input in arbitrary successive chunks, then it is not generally safe to use this method. If an input string ends with an unmatched high surrogate character, then this method will throw IllegalArgumentException. You should ensure your input is valid UTF-16 before calling this method.

        Note: When implementing an escaper it is a good idea to override this method for efficiency by inlining the implementation of UnicodeEscaper.nextEscapeIndex(CharSequence, int, int) directly. Doing this for PercentEscaper more than doubled the performance for unescaped strings (as measured by CharEscapersBenchmark).

        Overrides:
        escape in class UnicodeEscaper
        Parameters:
        s - the literal string to be escaped
        Returns:
        the escaped form of string

      • escape

        protected char[] escape​(int cp)
        Escapes the given Unicode code point in UTF-8.
        Specified by:
        escape in class UnicodeEscaper
        Parameters:
        cp - the Unicode code point to escape if necessary
        Returns:
        the replacement characters, or null if no escaping was needed