public class

PercentEscaper

extends UnicodeEscaper
java.lang.Object
   ↳ com.google.gdata.util.common.base.UnicodeEscaper
     ↳ com.google.gdata.util.common.base.PercentEscaper

Class Overview

A UnicodeEscaper that escapes some set of Java characters using the URI percent encoding scheme. The set of safe characters (those which remain unescaped) can be specified on construction.

For details on escaping URIs for use in web pages, see section 2.4 of RFC 3986.

In most cases this class should not need to be used directly. If you have no special requirements for escaping your URIs, you should use either uriEscaper() or uriEscaper(boolean).

When encoding a String, the following rules apply:

  • The alphanumeric characters "a" through "z", "A" through "Z" and "0" through "9" remain the same.
  • Any additionally specified safe characters remain the same.
  • 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 "%XY", where "XY" is the two-digit, uppercase, hexadecimal representation of the byte value.

RFC 2396 specifies the set of unreserved characters as "-", "_", ".", "!", "~", "*", "'", "(" and ")". It goes on to state:

Unreserved characters can be escaped without changing the semantics of the URI, but this should not be done unless the URI is being used in a context that does not allow the unescaped character to appear.

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

Note: This escaper produces uppercase hexidecimal sequences. From RFC 3986:
"URI producers and normalizers should use uppercase hexadecimal digits for all percent-encodings."

Summary

Constants
String SAFECHARS_URLENCODER A string of safe characters that mimics the behavior of java.net.URLEncoder.
String SAFEPATHCHARS_URLENCODER A string of characters that do not need to be encoded when used in URI path segments, as specified in RFC 3986.
String SAFEQUERYSTRINGCHARS_URLENCODER A string of characters that do not need to be encoded when used in URI query strings, as specified in RFC 3986.
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Inherited Constants
From class com.google.gdata.util.common.base.UnicodeEscaper
Fields
private static final char[] UPPER_HEX_DIGITS
private static final char[] URI_ESCAPED_SPACE
private final boolean plusForSpace If true we should convert space to the + character.
private final boolean[] safeOctets An array of flags where for any char c if safeOctets[c] is true then c should remain unmodified in the output.
[Expand]
Inherited Fields
From class com.google.gdata.util.common.base.UnicodeEscaper
Public Constructors
PercentEscaper(String safeChars, boolean plusForSpace)
Constructs a URI escaper with the specified safe characters and optional handling of the space character.
Public Methods
String escape(String s)
Returns the escaped form of a given literal string.
Protected Methods
char[] escape(int cp)
Escapes the given Unicode code point in UTF-8.
int nextEscapeIndex(CharSequence csq, int index, int end)
Scans a sub-sequence of characters from a given CharSequence, returning the index of the next character that requires escaping.
[Expand]
Inherited Methods
From class com.google.gdata.util.common.base.UnicodeEscaper
From class java.lang.Object
From interface com.google.gdata.util.common.base.Escaper

Constants

public static final String SAFECHARS_URLENCODER

A string of safe characters that mimics the behavior of java.net.URLEncoder.

Constant Value: "-_.*"

public static final String SAFEPATHCHARS_URLENCODER

A string of characters that do not need to be encoded when used in URI path segments, as specified in RFC 3986. Note that some of these characters do need to be escaped when used in other parts of the URI.

Constant Value: "-_.!~*'()@:$&,;="

public static final String SAFEQUERYSTRINGCHARS_URLENCODER

A string of characters that do not need to be encoded when used in URI query strings, as specified in RFC 3986. Note that some of these characters do need to be escaped when used in other parts of the URI.

Constant Value: "-_.!~*'()@:$,;/?:"

Fields

private static final char[] UPPER_HEX_DIGITS

private static final char[] URI_ESCAPED_SPACE

private final boolean plusForSpace

If true we should convert space to the + character.

private final boolean[] safeOctets

An array of flags where for any char c if safeOctets[c] is true then c should remain unmodified in the output. If c > safeOctets.length then it should be escaped.

Public Constructors

public PercentEscaper (String safeChars, boolean plusForSpace)

Constructs a URI escaper with the specified safe characters and optional handling of the space character.

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

Public Methods

public String escape (String s)

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 either ensure your input is valid UTF-16 before calling this method or use an escaped Appendable (as returned by escape(Appendable)) which can cope with arbitrarily split input.

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

Parameters
s The literal string to be escaped
Returns
  • the escaped form of string

Protected Methods

protected char[] escape (int cp)

Escapes the given Unicode code point in UTF-8.

Parameters
cp The Unicode code point to escape if necessary
Returns
  • the replacement characters, or null if no escaping was needed

protected int nextEscapeIndex (CharSequence csq, int index, int end)

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 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 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.

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