public abstract class UnicodeEscaper extends EscaperAn 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>".
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.
Static Methods
codePointAt(CharSequence seq, int index, int end)
protected static int codePointAt(CharSequence seq, int index, int end)Returns the Unicode code point of the character at the given index.
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:
- If
index >= end, IndexOutOfBoundsException is thrown. - If the character at the specified index is not a surrogate, it is returned.
- If the first character was a high surrogate value, then an attempt is made to read the
next character.
- If the end of the sequence was reached, the negated value of the trailing high surrogate is returned.
- If the next character was a valid low surrogate, the code point value of the high/low surrogate pair is returned.
- If the next character was not a low surrogate value, then IllegalArgumentException is thrown.
| Name | Description |
| seq | CharSequencethe sequence of characters from which to decode the code point |
| index | intthe index of the first character to decode |
| end | intthe index beyond the last valid character to decode |
| Type | Description |
| int | the Unicode code point for the given index or the negated value of the trailing high surrogate character at the end of the sequence |
Constructors
UnicodeEscaper()
public UnicodeEscaper()Methods
escape(int cp)
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. 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.
| Name | Description |
| cp | intthe Unicode code point to escape if necessary |
| Type | Description |
| char[] | the replacement characters, or |
escape(String string)
public abstract String escape(String string)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.
| Name | Description |
| string | Stringthe literal string to be escaped |
| Type | Description |
| String | the escaped form of |
escapeSlow(String s, int index)
protected final String escapeSlow(String s, int index)Returns the escaped form of a given literal string, starting at the given index. This method is called by the #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.
This method is not reentrant and may only be invoked by the top level #escape(String) method.
| Name | Description |
| s | Stringthe literal string to be escaped |
| index | intthe index to start escaping from |
| Type | Description |
| String | the escaped form of |
nextEscapeIndex(CharSequence csq, int start, int end)
protected abstract 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.
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.
| Name | Description |
| csq | CharSequencea sequence of characters |
| start | intthe index of the first character to be scanned |
| end | intthe index immediately after the last character to be scanned |
| Type | Description |
| int |