Libraries

java.nio.charset

About

The java.nio.charset package provides classes and interfaces for character encoding and decoding. It is part of the Java NIO (New I/O) package introduced in Java 1.4 to provide non-blocking I/O operations, among other features. Understanding character sets is crucial for applications dealing with text processing, file I/O, network communication, and internationalization.

Charset (java.nio.charset.Charset):

Represents a named mapping between sequences of sixteen-bit Unicode characters and sequences of bytes. It defines methods for encoding, decoding, and working with character sets.

Static Methods:

• static Charset forName(String charsetName): Returns a charset object for the given charset name.

• static Charset defaultCharset(): Returns the default charset of this Java virtual machine.

• static SortedMap<String, Charset> availableCharsets(): Returns a map of available charsets.

• static boolean isSupported(String charsetName): Tells whether the named charset is supported.

Methods:

• boolean contains(Charset cs): Tells whether or not this charset contains the given charset.

• boolean canEncode(): Tells whether or not this charset supports encoding.

• String name(): Returns the canonical name of this charset.

• Set<String> aliases(): Returns a set containing this charset's aliases.

• String displayName(): Returns a string that is the canonical name of this charset.

• String displayName(Locale locale): Returns a localized string that is the canonical name of this charset.

• boolean isRegistered(): Tells whether or not this charset is known by its canonical name.

• CharsetEncoder newEncoder(): Constructs a new encoder for this charset.

• CharsetDecoder newDecoder(): Constructs a new decoder for this charset.

• ByteBuffer encode(CharBuffer cb): Convenience method that encodes Unicode characters into bytes.

• ByteBuffer encode(String str): Convenience method that encodes a string into bytes.

• CharBuffer decode(ByteBuffer bb): Convenience method that decodes bytes into Unicode characters.

• int compareTo(Charset that): Compares this charset to another.

CharsetDecoder (java.nio.charset.CharsetDecoder):

Converts a byte sequence into a sequence of sixteen-bit Unicode characters.

Methods:

• Charset charset(): Returns the charset that created this decoder.

• CharsetDecoder onMalformedInput(CodingErrorAction newAction): Changes the action for malformed-input errors.

• CharsetDecoder onUnmappableCharacter(CodingErrorAction newAction): Changes the action for unmappable-character errors.

• CodingErrorAction malformedInputAction(): Returns the current malformed-input action.

• CodingErrorAction unmappableCharacterAction(): Returns the current unmappable-character action.

• CharsetDecoder replaceWith(String newReplacement): Changes this decoder's replacement value.

• String replacement(): Returns this decoder's replacement value.

• boolean isAutoDetecting(): Tells whether or not this decoder implements an auto-detecting charset.

• boolean isCharsetDetected(): Tells whether or not a charset has yet been detected by this decoder.

• Charset detectedCharset(): Returns the charset detected by this decoder, if any.

• CoderResult decode(ByteBuffer in, CharBuffer out, boolean endOfInput): Decodes one or more bytes into one or more characters.

• CoderResult flush(CharBuffer out): Flushes this decoder.

• CharsetDecoder reset(): Resets this decoder, clearing any internal state.

CharsetEncoder (java.nio.charset.CharsetEncoder):

Converts a sequence of sixteen-bit Unicode characters into a byte sequence.

Methods:

• Charset charset(): Returns the charset that created this encoder.

• CharsetEncoder onMalformedInput(CodingErrorAction newAction): Changes the action for malformed-input errors.

• CharsetEncoder onUnmappableCharacter(CodingErrorAction newAction): Changes the action for unmappable-character errors.

• CodingErrorAction malformedInputAction(): Returns the current malformed-input action.

• CodingErrorAction unmappableCharacterAction(): Returns the current unmappable-character action.

• CharsetEncoder replaceWith(byte[] newReplacement): Changes this encoder's replacement value.

• byte[] replacement(): Returns this encoder's replacement value.

• float averageBytesPerChar(): Returns this encoder's average bytes-per-character.

• float maxBytesPerChar(): Returns this encoder's maximum bytes-per-character.

• CoderResult encode(CharBuffer in, ByteBuffer out, boolean endOfInput): Encodes one or more characters into one or more bytes.

• CoderResult flush(ByteBuffer out): Flushes this encoder.

• CharsetEncoder reset(): Resets this encoder, clearing any internal state.

• boolean canEncode(char c): Tells whether or not this encoder can encode the given character.

• boolean canEncode(CharSequence cs): Tells whether or not this encoder can encode the given character sequence.

CodingErrorAction (java.nio.charset.CodingErrorAction):

Describes actions to be taken when encoding/decoding errors occur. Actions include IGNORE, REPLACE, and REPORT.

Static Variables:

• static CodingErrorAction IGNORE: Action indicating that a coding error is to be ignored.

• static CodingErrorAction REPLACE: Action indicating that a coding error is to be handled by dropping the erroneous input and replacing it with the current replacement byte or character sequence.

• static CodingErrorAction REPORT: Action indicating that a coding error is to be reported, either by returning a CoderResult object or by throwing a CharacterCodingException, depending upon the method implementing the coding process.

StandardCharsets (java.nio.charset.StandardCharsets):

Defines constants for standard character sets such as UTF-8, UTF-16, ISO-8859-1, etc.

Static Variables:

• static Charset US_ASCII: Seven-bit ASCII, a.k.a. ISO646-US, a.k.a. the Basic Latin block of the Unicode character set.

• static Charset ISO_8859_1: ISO Latin Alphabet No. 1, a.k.a. ISO-LATIN-1.

• static Charset UTF_8: Eight-bit UCS Transformation Format.

• static Charset UTF_16BE: Sixteen-bit UCS Transformation Format, big-endian byte order.

• static Charset UTF_16LE: Sixteen-bit UCS Transformation Format, little-endian byte order.

• static Charset UTF_16: Sixteen-bit UCS Transformation Format, byte order identified by an optional byte-order mark.

UnsupportedCharsetException (java.nio.charset.UnsupportedCharsetException)

Constructor:

• UnsupportedCharsetException(String charsetName): Constructs an instance of this class.

Methods:

• String getCharsetName(): Retrieves the name of the unsupported charset.

Examples

Encoding and Decoding Strings

import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;

public class CharsetExample {
    public static void main(String[] args) {
        String input = "Hello, World!";
        Charset charset = StandardCharsets.UTF_8;

        // Encoding
        ByteBuffer byteBuffer = charset.encode(input);
        System.out.println("Encoded ByteBuffer: " + byteBuffer);

        // Decoding
        CharBuffer charBuffer = charset.decode(byteBuffer);
        String output = charBuffer.toString();
        System.out.println("Decoded String: " + output);
    }
}

Handling Encoding or Decoding Errors

import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;
import java.nio.charset.CharsetEncoder;
import java.nio.charset.CodingErrorAction;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;

public class ErrorHandlingExample {
    public static void main(String[] args) {
        Charset charset = Charset.forName("US-ASCII");
        CharsetEncoder encoder = charset.newEncoder();
        CharsetDecoder decoder = charset.newDecoder();

        encoder.onMalformedInput(CodingErrorAction.REPLACE);
        encoder.onUnmappableCharacter(CodingErrorAction.REPLACE);
        decoder.onMalformedInput(CodingErrorAction.REPLACE);
        decoder.onUnmappableCharacter(CodingErrorAction.REPLACE);

        String input = "Hello, World! \u00A9";
        ByteBuffer byteBuffer = encoder.encode(CharBuffer.wrap(input));
        CharBuffer charBuffer = decoder.decode(byteBuffer);
        String output = charBuffer.toString();

        System.out.println("Original String: " + input);
        System.out.println("Encoded and Decoded String: " + output);
    }
}

Listing Available Charsets

import java.nio.charset.Charset;
import java.util.SortedMap;

public class ListCharsets {
    public static void main(String[] args) {
        SortedMap<String, Charset> charsets = Charset.availableCharsets();
        for (String charsetName : charsets.keySet()) {
            System.out.println(charsetName);
        }
    }
}