@Beta @GwtCompatible public abstract class UnicodeEscaper extends 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.
Popular escapers are defined as constants in classes like HtmlEscapers
and XmlEscapers
. To create
your own escapers extend this class and implement the escape(int)
method.
Modifier | Constructor and Description |
---|---|
protected |
UnicodeEscaper()
Constructor for use by subclasses.
|
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.
|
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. |
asFunction
protected UnicodeEscaper()
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 neededpublic 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 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 nextEscapeIndex(CharSequence, int, int)
directly. Doing this for PercentEscaper
more than doubled the
performance for unescaped strings (as measured by CharEscapersBenchmark
).
escape
in class Escaper
string
- the literal string to be escapedstring
NullPointerException
- if string
is nullIllegalArgumentException
- if invalid surrogate characters are encounteredprotected 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 pairsprotected 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 fromstring
NullPointerException
- if string
is nullIllegalArgumentException
- if invalid surrogate characters are encounteredprotected static 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 © 2010–2019. All rights reserved.