@Beta @GwtCompatible public abstract class UnicodeEscaper extends Escaper
Escaperthat 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>" to prevent
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
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.
UnicodeEscaper instance is required to be stateless, and safe
when used concurrently by multiple threads.
Several popular escapers are defined as constants in classes like
SourceCodeEscapers. To create
your own escapers extend this class and implement the
|Modifier||Constructor and Description|
Constructor for use by subclasses.
|Modifier and Type||Method and Description|
Returns the Unicode code point of the character at the given index.
Returns the escaped form of the given Unicode code point, or
Returns the escaped form of a given literal string.
Returns the escaped form of a given literal string, starting at the given index.
Scans a sub-sequence of characters from a given
protected abstract char escape(int cp)
nullif 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
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 necessary
nullif no escaping was needed
protected 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
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.
PercentEscaper for an example.
csq- a sequence of characters
start- the index of the first character to be scanned
end- the index immediately after the last character to be scanned
IllegalArgumentException- if the scanned sub-sequence of
csqcontains invalid surrogate pairs
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
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
protected 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
CharEscaperBuilderfor an example usage.
This method is not reentrant and may only be invoked by the top level
protected static int codePointAt(CharSequence seq, int index, int end)
The behaviour of this method is as follows:
index >= end,
seq- the sequence of characters from which to decode the code point
index- the index of the first character to decode
end- the index beyond the last valid character to decode
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