public abstract class UnicodeEscaper extends Object implements Escaper
Escaper that converts literal text into a format safe for
inclusion in a particular context (such as an XML document). Typically (but
not always), the inverse process of "unescaping" the text is performed
automatically by the relevant parser.
For example, an XML escaper would convert the literal string "Foo<Bar>" into "Foo<Bar>" to prevent "<Bar>" from
being confused with an XML tag. When the resulting XML document is parsed,
the parser API will return this text as the original literal string "Foo<Bar>".
Note: This class is similar to CharEscaper but with one
very important difference. A CharEscaper can only process Java
UTF16 characters in
isolation and may not cope when it encounters surrogate pairs. This class
facilitates the correct escaping of all Unicode characters.
As there are important reasons, including potential security issues, to handle Unicode correctly if you are considering implementing a new escaper you should favor using UnicodeEscaper wherever possible.
A UnicodeEscaper instance is required to be stateless, and safe
when used concurrently by multiple threads.
Several popular escapers are defined as constants in the class CharEscapers. To create your own escapers extend this class and implement
the escape(int) method.
| Constructor and Description |
|---|
UnicodeEscaper() |
| Modifier and Type | Method and Description |
|---|---|
protected static int |
codePointAt(CharSequence seq,
int index,
int end)
Returns the Unicode code point of the character at the given index.
|
Appendable |
escape(Appendable out)
Returns an
Appendable instance which automatically escapes all
text appended to it before passing the resulting text to an underlying
Appendable. |
protected abstract char[] |
escape(int cp)
Returns the escaped form of the given Unicode code point, or
null
if this code point does not need to be escaped. |
String |
escape(String string)
Returns the escaped form of a given literal string.
|
protected String |
escapeSlow(String s,
int index)
Returns the escaped form of a given literal string, starting at the given
index.
|
protected int |
nextEscapeIndex(CharSequence csq,
int start,
int end)
Scans a sub-sequence of characters from a given
CharSequence,
returning the index of the next character that requires escaping. |
protected abstract char[] escape(int cp)
null
if this code point does not need to be escaped. When called as part of an
escaping operation, the given code point is guaranteed to be in the range
0 <= cp <= Character#MAX_CODE_POINT.
If an empty array is returned, this effectively strips the input character from the resulting text.
If the character does not need to be escaped, this method should return
null, rather than an array containing the character representation
of the code point. This enables the escaping algorithm to perform more
efficiently.
If the implementation of this method cannot correctly handle a particular code point then it should either throw an appropriate runtime exception or return a suitable replacement character. It must never silently discard invalid input as this may constitute a security risk.
cp - the Unicode code point to escape if necessarynull if no escaping was
neededprotected int nextEscapeIndex(CharSequence csq, int start, int end)
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 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.
csq - a sequence of charactersstart - the index of the first character to be scannedend - the index immediately after the last character to be scannedIllegalArgumentException - if the scanned sub-sequence of csq
contains invalid surrogate pairspublic String escape(String 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).
escape in interface Escaperstring - the literal string to be escapedstringNullPointerException - if string is nullIllegalArgumentException - if invalid surrogate characters are
encounteredprotected final String escapeSlow(String s, int index)
escape(String) method when it
discovers that escaping is required. It is protected to allow subclasses
to override the fastpath escaping function to inline their escaping test.
See CharEscaperBuilder for an example usage.
This method is not reentrant and may only be invoked by the top level
escape(String) method.
s - the literal string to be escapedindex - the index to start escaping fromstringNullPointerException - if string is nullIllegalArgumentException - if invalid surrogate characters are
encounteredpublic Appendable escape(Appendable out)
Appendable instance which automatically escapes all
text appended to it before passing the resulting text to an underlying
Appendable.
Unlike escape(String) it is permitted to append arbitrarily
split input to this Appendable, including input that is split over a
surrogate pair. In this case the pending high surrogate character will not
be processed until the corresponding low surrogate is appended. This means
that a trailing high surrogate character at the end of the input cannot be
detected and will be silently ignored. This is unavoidable since the
Appendable interface has no close() method, and it is impossible to
determine when the last characters have been appended.
The methods of the returned object will propagate any exceptions thrown
by the underlying Appendable.
For well formed UTF-16
the escaping behavior is identical to that of escape(String) and
the following code is equivalent to (but much slower than)
escaper.escape(string):
StringBuilder sb = new StringBuilder();
escaper.escape(sb).append(string);
return sb.toString();escape in interface Escaperout - the underlying Appendable to append escaped output toAppendable which passes text to out after
escaping itNullPointerException - if out is nullIllegalArgumentException - if invalid surrogate characters are
encounteredprotected static final int codePointAt(CharSequence seq, int index, int end)
Unlike Character.codePointAt(CharSequence, int) or
String.codePointAt(int) this method will never fail silently when
encountering an invalid surrogate pair.
The behaviour of this method is as follows:
index >= end, IndexOutOfBoundsException is thrown.
IllegalArgumentException is thrown.
IllegalArgumentException is thrown.
seq - the sequence of characters from which to decode the code pointindex - the index of the first character to decodeend - the index beyond the last valid character to decodeCopyright © 2012. All Rights Reserved.