com.ibm.icu.charset

Class CharsetICU

java.lang.Object

java.nio.charset.Charset

com.ibm.icu.charset.CharsetICU

All Implemented Interfaces:

Comparable<Charset>

public abstract class CharsetICU
extends Charset

A subclass of java.nio.Charset for providing implementation of ICU's charset converters. This API is used to convert codepage or character encoded data to and from UTF-16. You can open a converter with Charset.forName(java.lang.String) and forNameICU(java.lang.String). With that converter, you can get its properties, set options, convert your data.

Since many software programs recognize different converter names for different types of converters, there are other functions in this API to iterate over the converter aliases.

Note that Charset.name() cannot always return a unique charset name. Charset documents that, for charsets listed in the IANA Charset Registry, the Charset.name() must be listed there, and it “must be the MIME-preferred name” if there are multiple names.

However, there are different implementations of many if not most charsets, ICU provides multiple variants for some of them, ICU provides variants of some java.nio-system-supported charsets, and ICU users are free to add more variants. This is so that applications can be compatible with multiple implementations at the same time.

This is in conflict with the Charset.name() requirements. It is not possible to offer variants of an IANA charset and always use the MIME-preferred name and also have those names be unique.

Charset.name() returns the MIME-preferred name, or IANA name, so that it can always be used for the charset field in internet protocols.

Same-name charsets are accessible via Charset.forName(java.lang.String) or forNameICU(java.lang.String) by using unique aliases (e.g., the ICU-canonical names).

Charset also documents that “Two charsets are equal if, and only if, they have the same canonical names.” This is not possible.

Unfortunately, Charset.equals(java.lang.Object) is final, and Charset.availableCharsets() returns “a sorted map from canonical charset names to charset objects”. Since Charset.name() cannot be unique, Charset.equals(java.lang.Object) cannot work properly in such cases, and Charset.availableCharsets() can only include one variant for a name.

Status:

Stable ICU 3.6.

Field Summary

Fields

Modifier and Type	Field and Description
static int	ROUNDTRIP_AND_FALLBACK_SET Deprecated. This API is ICU internal only.
static int	ROUNDTRIP_SET Parameter that select the set of roundtrippable Unicode code points.

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	CharsetICU(String icuCanonicalName, String canonicalName, String[] aliases)

Method Summary

Modifier and Type	Method and Description
boolean	contains(Charset cs) Ascertains if a charset is a sub set of this charset Implements the abstract method of super class.
static Charset	forNameICU(String charsetName) Returns a charset object for the named charset.
void	getUnicodeSet(UnicodeSet setFillIn, int which) Returns the set of Unicode code points that can be converted by an ICU Converter.
boolean	isFixedWidth() Returns whether or not the charset of the converter has a fixed number of bytes per charset character.

Methods inherited from class java.nio.charset.Charset

aliases, availableCharsets, canEncode, compareTo, decode, defaultCharset, displayName, displayName, encode, encode, equals, forName, hashCode, isRegistered, isSupported, name, newDecoder, newEncoder, toString

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

ROUNDTRIP_SET

public static final int ROUNDTRIP_SET

Parameter that select the set of roundtrippable Unicode code points.

See Also:

Constant Field Values

Status:

Stable ICU 4.0.

ROUNDTRIP_AND_FALLBACK_SET

@Deprecated
public static final int ROUNDTRIP_AND_FALLBACK_SET

Deprecated. This API is ICU internal only.

Select the set of Unicode code points with roundtrip or fallback mappings. Not supported at this point.

See Also:

Constant Field Values

Status:

Internal. This API is ICU internal only.

Constructor Detail

CharsetICU

protected CharsetICU(String icuCanonicalName,
                     String canonicalName,
                     String[] aliases)

Parameters:

icuCanonicalName -

canonicalName -

aliases -

Status:

Stable ICU 3.6.

Method Detail

contains

public boolean contains(Charset cs)

Ascertains if a charset is a sub set of this charset Implements the abstract method of super class.

Specified by:

contains in class Charset

Parameters:

cs - charset to test

Returns:

true if the given charset is a subset of this charset

Status:

Stable ICU 3.6.

forNameICU

public static Charset forNameICU(String charsetName)
                          throws IllegalCharsetNameException,
                                 UnsupportedCharsetException

Returns a charset object for the named charset. This method guarantees that ICU charset is returned when available. If the ICU charset provider does not support the specified charset, then try other charset providers including the standard Java charset provider.

Parameters:

charsetName - The name of the requested charset, may be either a canonical name or an alias

Returns:

A charset object for the named charset

Throws:

IllegalCharsetNameException - If the given charset name is illegal

UnsupportedCharsetException - If no support for the named charset is available in this instance of th Java virtual machine

Status:

Stable ICU 3.6.

getUnicodeSet

public void getUnicodeSet(UnicodeSet setFillIn,
                          int which)

Returns the set of Unicode code points that can be converted by an ICU Converter.

The current implementation returns only one kind of set (UCNV_ROUNDTRIP_SET): The set of all Unicode code points that can be roundtrip-converted (converted without any data loss) with the converter This set will not include code points that have fallback mappings or are only the result of reverse fallback mappings. See UTR #22 "Character Mapping Markup Language" at http://www.unicode.org/reports/tr22/

In the future, there may be more UConverterUnicodeSet choices to select sets with different properties.

This is useful for example for

• checking that a string or document can be roundtrip-converted with a converter, without/before actually performing the conversion
• testing if a converter can be used for text for typical text for a certain locale, by comparing its roundtrip set with the set of ExemplarCharacters from ICU's locale data or other sources

Parameters:

setFillIn - A valid UnicodeSet. It will be cleared by this function before the converter's specific set is filled in.

which - A selector; currently ROUNDTRIP_SET is the only supported value.

Throws:

IllegalArgumentException - if the parameters does not match.

Status:

Stable ICU 4.0.

isFixedWidth

public boolean isFixedWidth()

Returns whether or not the charset of the converter has a fixed number of bytes per charset character. An example of this are converters that are of the type UCNV_SBCS or UCNV_DBCS. Another example is UTF-32 which is always 4 bytes per character. A UTF-32 code point may represent more than one UTF-8 or UTF-16 code units but always have size of 4 bytes. Note: This method is not intended to be used to determine whether the charset has a fixed ratio of bytes to Unicode codes units for any particular Unicode encoding form.

Returns:

true if the converter is fixed-width

Status:

Stable ICU 4.8.