UnicodeUtil (Lucene 10.5.0 core API)
Description: declaration: package: org.apache.lucene.util, class: UnicodeUtil

Package org.apache.lucene.util

# Class UnicodeUtil

java.lang.Object
org.apache.lucene.util.UnicodeUtil

public final class UnicodeUtil extends Object
Class to encode java's UTF16 char[] into UTF8 byte[] without always allocating a new byte[] as String.getBytes(StandardCharsets.UTF_8) does.

NOTE: This API is for internal purposes only and might change in incompatible ways in the next release.

- ## Nested Class Summary

  Nested Classes
  Modifier and Type
  Class
  Description
  `static final class`
  `UnicodeUtil.UTF8CodePoint`
  Holds a codepoint along with the number of bytes required to represent it in UTF8

- ## Field Summary

  Fields
  Modifier and Type
  Field
  Description
  `static final BytesRef`
  `BIG_TERM`
  A binary term consisting of a number of 0xff bytes, likely to be bigger than other terms (e.g.
  `static final int`
  `MAX_UTF8_BYTES_PER_CHAR`
  Maximum number of UTF8 bytes per UTF16 character.
  `static final int`
  `UNI_REPLACEMENT_CHAR`
  `static final int`
  `UNI_SUR_HIGH_END`
  `static final int`
  `UNI_SUR_HIGH_START`
  `static final int`
  `UNI_SUR_LOW_END`
  `static final int`
  `UNI_SUR_LOW_START`

- ## Method Summary

  Modifier and Type
  Method
  Description
  `static int`
  `calcUTF16toUTF8Length(CharSequence s, int offset, int len)`
  Calculates the number of UTF8 bytes necessary to write a UTF16 string.
  `static UnicodeUtil.UTF8CodePoint`
  `codePointAt(byte[] utf8, int pos, UnicodeUtil.UTF8CodePoint reuse)`
  Computes the codepoint and codepoint length (in bytes) of the specified `offset` in the provided `utf8` byte array, assuming UTF8 encoding.
  `static int`
  `codePointCount(BytesRef utf8)`
  Returns the number of code points in this UTF8 sequence.
  `static int`
  `maxUTF8Length(int utf16Length)`
  Returns the maximum number of utf8 bytes required to encode a utf16 (e.g., java char[], String)
  `static String`
  `newString(int[] codePoints, int offset, int count)`
  Cover JDK 1.5 API.
  `static String`
  `toHexString(String s)`
  `static int`
  `UTF16toUTF8(char[] source, int offset, int length, byte[] out)`
  Encode characters from a char[] source, starting at offset for length chars.
  `static int`
  `UTF16toUTF8(CharSequence s, int offset, int length, byte[] out)`
  Encode characters from this String, starting at offset for length characters.
  `static int`
  `UTF16toUTF8(CharSequence s, int offset, int length, byte[] out, int outOffset)`
  Encode characters from this String, starting at offset for length characters.
  `static int`
  `UTF8toUTF16(byte[] utf8, int offset, int length, char[] out)`
  Interprets the given byte array as UTF-8 and converts to UTF-16.
  `static int`
  `UTF8toUTF16(BytesRef bytesRef, char[] chars)`
  Utility method for `UTF8toUTF16(byte[], int, int, char[])`
  `static int`
  `UTF8toUTF32(BytesRef utf8, int[] ints)`
  This method assumes valid UTF8 input.
  `static boolean`
  `validUTF16String(char[] s, int size)`
  `static boolean`
  `validUTF16String(CharSequence s)`

  ### Methods inherited from class java.lang.Object

  `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- ## Field Details

  - ### BIG_TERM

    public static final BytesRef BIG_TERM
    A binary term consisting of a number of 0xff bytes, likely to be bigger than other terms (e.g. collation keys) one would normally encounter, and definitely bigger than any UTF-8 terms.

    WARNING: This is not a valid UTF8 Term

  - ### UNI_SUR_HIGH_START

    public static final int UNI_SUR_HIGH_START
    See Also:
      - Constant Field Values

  - ### UNI_SUR_HIGH_END

    public static final int UNI_SUR_HIGH_END
    See Also:
      - Constant Field Values

  - ### UNI_SUR_LOW_START

    public static final int UNI_SUR_LOW_START
    See Also:
      - Constant Field Values

  - ### UNI_SUR_LOW_END

    public static final int UNI_SUR_LOW_END
    See Also:
      - Constant Field Values

  - ### UNI_REPLACEMENT_CHAR

    public static final int UNI_REPLACEMENT_CHAR
    See Also:
      - Constant Field Values

  - ### MAX_UTF8_BYTES_PER_CHAR

    public static final int MAX_UTF8_BYTES_PER_CHAR
    Maximum number of UTF8 bytes per UTF16 character.
    See Also:
      - Constant Field Values

- ## Method Details

  - ### UTF16toUTF8

    public static int UTF16toUTF8(char[] source, int offset, int length, byte[] out)
    Encode characters from a char[] source, starting at offset for length chars. It is the responsibility of the caller to make sure that the destination array is large enough.

  - ### UTF16toUTF8

    public static int UTF16toUTF8(CharSequence s, int offset, int length, byte[] out)
    Encode characters from this String, starting at offset for length characters. It is the responsibility of the caller to make sure that the destination array is large enough.

  - ### UTF16toUTF8

    public static int UTF16toUTF8(CharSequence s, int offset, int length, byte[] out, int outOffset)
    Encode characters from this String, starting at offset for length characters. Output to the destination array will begin at `outOffset`. It is the responsibility of the caller to make sure that the destination array is large enough.

    note this method returns the final output offset (outOffset + number of bytes written)

  - ### calcUTF16toUTF8Length

    public static int calcUTF16toUTF8Length(CharSequence s, int offset, int len)
    Calculates the number of UTF8 bytes necessary to write a UTF16 string.
    Returns:
      the number of bytes written

  - ### validUTF16String

    public static boolean validUTF16String(CharSequence s)

  - ### validUTF16String

    public static boolean validUTF16String(char[] s, int size)

  - ### codePointCount

    public static int codePointCount(BytesRef utf8)
    Returns the number of code points in this UTF8 sequence.

    This method assumes valid UTF8 input. This method does not perform full UTF8 validation, it will check only the first byte of each codepoint (for multi-byte sequences any bytes after the head are skipped).

    Throws:
      `IllegalArgumentException` - If invalid codepoint header byte occurs or the content is prematurely truncated.

  - ### UTF8toUTF32

    public static int UTF8toUTF32(BytesRef utf8, int[] ints)
    This method assumes valid UTF8 input. This method does not perform full UTF8 validation, it will check only the first byte of each codepoint (for multi-byte sequences any bytes after the head are skipped). It is the responsibility of the caller to make sure that the destination array is large enough.
    Throws:
      `IllegalArgumentException` - If invalid codepoint header byte occurs or the content is prematurely truncated.

  - ### codePointAt

    public static UnicodeUtil.UTF8CodePoint codePointAt(byte[] utf8, int pos, UnicodeUtil.UTF8CodePoint reuse)
    Computes the codepoint and codepoint length (in bytes) of the specified `offset` in the provided `utf8` byte array, assuming UTF8 encoding. As with other related methods in this class, this assumes valid UTF8 input and does not perform full UTF8 validation. Passing invalid UTF8 or a position that is not a valid header byte position may result in undefined behavior. This makes no attempt to synchronize or validate.

  - ### newString

    public static String newString(int[] codePoints, int offset, int count)
    Cover JDK 1.5 API. Create a String from an array of codePoints.
    Parameters:
      `codePoints` - The code array
      `offset` - The start of the text in the code point array
      `count` - The number of code points
    Returns:
      a String representing the code points between offset and count
    Throws:
      `IllegalArgumentException` - If an invalid code point is encountered
      `IndexOutOfBoundsException` - If the offset or count are out of bounds.

  - ### toHexString

    public static String toHexString(String s)

  - ### UTF8toUTF16

    public static int UTF8toUTF16(byte[] utf8, int offset, int length, char[] out)
    Interprets the given byte array as UTF-8 and converts to UTF-16. It is the responsibility of the caller to make sure that the destination array is large enough.

    NOTE: Full characters are read, even if this reads past the length passed (and can result in an ArrayOutOfBoundsException if invalid UTF-8 is passed). Explicit checks for valid UTF-8 are not performed.

  - ### maxUTF8Length

    public static int maxUTF8Length(int utf16Length)
    Returns the maximum number of utf8 bytes required to encode a utf16 (e.g., java char[], String)

  - ### UTF8toUTF16

    public static int UTF8toUTF16(BytesRef bytesRef, char[] chars)
    Utility method for `UTF8toUTF16(byte[], int, int, char[])`
    See Also:
      - `UTF8toUTF16(byte[], int, int, char[])`