Guava: Google Core Libraries for Java 32.1.2-jre · com.google.common.escape.UnicodeEscaper

An 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 com.google.common.html.HtmlEscapers and com.google.common.xml.XmlEscapers. To create your own escapers extend this class and implement the escape(int) method.

Field Summary

Modifier and Type	Field and Description
private static final int	DEST_PAD The amount of padding (chars) to use when growing the escape buffer.

Constructor Summary

Access	Constructor and Description
protected	UnicodeEscaper() Constructor for use by subclasses.

Method Summary

Modifier and Type	Method and Description
protected static int	Returns: the Unicode code point for the given index or the negated value of the trailing high surrogate character at the end of the sequence codePointAt(CharSequence the sequence of characters from which to decode the code point seq, int the index of the first character to decode index, int the index beyond the last valid character to decode end) Returns the Unicode code point of the character at the given index.
protected abstract char[]	Returns: the replacement characters, or `null` if no escaping was needed escape(int the Unicode code point to escape if necessary cp) Returns the escaped form of the given Unicode code point, or `null` if this code point does not need to be escaped.
public String	Returns: the escaped form of `string` escape(String the literal string to be escaped string) Implements abstract com.google.common.escape.Escaper.escape. Returns the escaped form of a given literal string.
protected final String	Returns: the escaped form of `string` escapeSlow(String the literal string to be escaped s, int the index to start escaping from index) Returns the escaped form of a given literal string, starting at the given index.
private static char[]	growBuffer(char[] dest, int index, int size) Helper method to grow the character buffer as needed, this only happens once in a while so it's ok if it's in a method call.
protected int	nextEscapeIndex(CharSequence a sequence of characters csq, int the index of the first character to be scanned start, int the index immediately after the last character to be scanned end) Scans a sub-sequence of characters from a given `CharSequence`, returning the index of the next character that requires escaping.

Inherited from com.google.common.escape.Escaper:: asFunction

Field Detail

DEST_PAD	back to summary
private static final int DEST_PAD The amount of padding (chars) to use when growing the escape buffer.

Constructor Detail

UnicodeEscaper	back to summary
protected UnicodeEscaper() Constructor for use by subclasses.

Method Detail

codePointAt back to summary

codePointAt	back to summary
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. If the first character was a low surrogate value, `IllegalArgumentException` is thrown. Parameters seq:CharSequence the sequence of characters from which to decode the code point index:int the index of the first character to decode end:int the index beyond the last valid character to decode Returns: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

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.
1. If the end of the sequence was reached, the negated value of the trailing high surrogate is returned.
2. If the next character was a valid low surrogate, the code point value of the high/low surrogate pair is returned.
3. If the next character was not a low surrogate value, then IllegalArgumentException is thrown.
If the first character was a low surrogate value, IllegalArgumentException is thrown.

Parameters

seq:CharSequence: the sequence of characters from which to decode the code point
index:int: the index of the first character to decode
end:int: the index beyond the last valid character to decode

Returns: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

escape back to summary

escape	back to summary
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. Parameters cp:int the Unicode code point to escape if necessary Returns:char[] the replacement characters, or `null` if no escaping was needed Annotations @CheckForNull

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.

Parameters

cp:int: the Unicode code point to escape if necessary

Returns:char[]

the replacement characters, or null if no escaping was needed

Annotations

@CheckForNull

escape back to summary

escape	back to summary
public String escape(String string) Implements abstract com.google.common.escape.Escaper.escape. 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. 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 `com.google.common.net.PercentEscaper` more than doubled the performance for unescaped strings (as measured by `CharEscapersBenchmark`). Parameters string:String the literal string to be escaped Returns:String the escaped form of `string` Annotations @Override Exceptions NullPointerException: if `string` is null IllegalArgumentException: if invalid surrogate characters are encountered

public String escape(String string)

Implements abstract com.google.common.escape.Escaper.escape.

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.

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 com.google.common.net.PercentEscaper more than doubled the performance for unescaped strings (as measured by CharEscapersBenchmark).

Parameters

string:String: the literal string to be escaped

Returns:String

the escaped form of string

Annotations

@Override

Exceptions

NullPointerException:: if string is null
IllegalArgumentException:: if invalid surrogate characters are encountered

escapeSlow back to summary

escapeSlow	back to summary
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. See `CharEscaperBuilder` for an example usage. This method is not reentrant and may only be invoked by the top level `escape(String)` method. Parameters s:String the literal string to be escaped index:int the index to start escaping from Returns:String the escaped form of `string` Exceptions NullPointerException: if `string` is null IllegalArgumentException: if invalid surrogate characters are encountered

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. See CharEscaperBuilder for an example usage.

This method is not reentrant and may only be invoked by the top level escape(String) method.

Parameters

s:String: the literal string to be escaped
index:int: the index to start escaping from

Returns:String

the escaped form of string

Exceptions

NullPointerException:: if string is null
IllegalArgumentException:: if invalid surrogate characters are encountered

growBuffer	back to summary
private static char[] growBuffer(char[] dest, int index, int size) Helper method to grow the character buffer as needed, this only happens once in a while so it's ok if it's in a method call. If the index passed in is 0 then no copying will be done.

nextEscapeIndex back to summary

nextEscapeIndex	back to summary
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. 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 `com.google.common.net.PercentEscaper` for an example. Parameters csq:CharSequence a sequence of characters start:int the index of the first character to be scanned end:int the index immediately after the last character to be scanned Exceptions IllegalArgumentException: if the scanned sub-sequence of `csq` contains invalid surrogate pairs

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.

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 com.google.common.net.PercentEscaper for an example.

Parameters

csq:CharSequence: a sequence of characters
start:int: the index of the first character to be scanned
end:int: the index immediately after the last character to be scanned

Exceptions

IllegalArgumentException:: if the scanned sub-sequence of csq contains invalid surrogate pairs

public abstract Class UnicodeEscaper

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