org.apache.lucene.queryparser.ext

## Class Extensions

- java.lang.Object
- - org.apache.lucene.queryparser.ext.Extensions

-     public class Extensions
      extends Object

  The `Extensions` class represents an extension mapping to associate `ParserExtension` instances with extension keys. An extension key is a string encoded into a Lucene standard query parser field symbol recognized by `ExtendableQueryParser`. The query parser passes each extension field token to `splitExtensionField(String, String)` to separate the extension key from the field identifier.

  In addition to the key to extension mapping this class also defines the field name overloading scheme. `ExtendableQueryParser` uses the given extension to split the actual field name and extension key by calling `splitExtensionField(String, String)`. To change the order or the key / field name encoding scheme users can subclass `Extensions` to implement their own.

  See Also:
    `ExtendableQueryParser`, `ParserExtension`

- - ### Nested Class Summary

    Nested Classes
    Modifier and Type | Class and Description
    --- | ---
    `static class` | `Extensions.Pair<Cur,Cud>` This class represents a generic pair.

  - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `static char` | `DEFAULT_EXTENSION_FIELD_DELIMITER` The default extension field delimiter character.

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `Extensions()` Creates a new `Extensions` instance with the `DEFAULT_EXTENSION_FIELD_DELIMITER` as a delimiter character.
    `Extensions(char extensionFieldDelimiter)` Creates a new `Extensions` instance

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `void` | `add(String key, ParserExtension extension)` Adds a new `ParserExtension` instance associated with the given key.
    `String` | `buildExtensionField(String extensionKey)` Builds an extension field string from a given extension key and the default query field.
    `String` | `buildExtensionField(String extensionKey, String field)` Builds an extension field string from a given extension key and the extensions field.
    `String` | `escapeExtensionField(String extfield)` Escapes an extension field.
    `ParserExtension` | `getExtension(String key)` Returns the `ParserExtension` instance for the given key or `null` if no extension can be found for the key.
    `char` | `getExtensionFieldDelimiter()` Returns the extension field delimiter
    `Extensions.Pair<String,String>` | `splitExtensionField(String defaultField, String field)` Splits a extension field and returns the field / extension part as a `Extensions.Pair`.

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

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

- - ### Field Detail

    - #### DEFAULT_EXTENSION_FIELD_DELIMITER

          public static final char DEFAULT_EXTENSION_FIELD_DELIMITER

      The default extension field delimiter character. This constant is set to ':'
      See Also:
        Constant Field Values

  - ### Constructor Detail

    - #### Extensions

          public Extensions()

      Creates a new `Extensions` instance with the `DEFAULT_EXTENSION_FIELD_DELIMITER` as a delimiter character.

    - #### Extensions

          public Extensions(char extensionFieldDelimiter)

      Creates a new `Extensions` instance
      Parameters:
        `extensionFieldDelimiter` - the extensions field delimiter character

  - ### Method Detail

    - #### add

          public void add(String key,
                          ParserExtension extension)

      Adds a new `ParserExtension` instance associated with the given key.
      Parameters:
        `key` - the parser extension key
        `extension` - the parser extension

    - #### getExtension

          public final ParserExtension getExtension(String key)

      Returns the `ParserExtension` instance for the given key or `null` if no extension can be found for the key.
      Parameters:
        `key` - the extension key
      Returns:
        the `ParserExtension` instance for the given key or `null` if no extension can be found for the key.

    - #### getExtensionFieldDelimiter

          public char getExtensionFieldDelimiter()

      Returns the extension field delimiter
      Returns:
        the extension field delimiter

    - #### splitExtensionField

          public Extensions.Pair<String,String> splitExtensionField(String defaultField,
                                                                    String field)

      Splits a extension field and returns the field / extension part as a `Extensions.Pair`. This method tries to split on the first occurrence of the extension field delimiter, if the delimiter is not present in the string the result will contain a `null` value for the extension key and the given field string as the field value. If the given extension field string contains no field identifier the result pair will carry the given default field as the field value.
      Parameters:
        `defaultField` - the default query field
        `field` - the extension field string
      Returns:
        a `Extensions.Pair` with the field name as the `Extensions.Pair.cur` and the extension key as the `Extensions.Pair.cud`

    - #### escapeExtensionField

          public String escapeExtensionField(String extfield)

      Escapes an extension field. The default implementation is equivalent to `QueryParserBase.escape(String)`.
      Parameters:
        `extfield` - the extension field identifier
      Returns:
        the extension field identifier with all special chars escaped with a backslash character.

    - #### buildExtensionField

          public String buildExtensionField(String extensionKey)

      Builds an extension field string from a given extension key and the default query field. The default field and the key are delimited with the extension field delimiter character. This method makes no assumption about the order of the extension key and the field. By default the extension key is appended to the end of the returned string while the field is added to the beginning. Special Query characters are escaped in the result.

      Note: `Extensions` subclasses must maintain the contract between `buildExtensionField(String)` and `splitExtensionField(String, String)` where the latter inverts the former.

    - #### buildExtensionField

          public String buildExtensionField(String extensionKey,
                                            String field)

      Builds an extension field string from a given extension key and the extensions field. The field and the key are delimited with the extension field delimiter character. This method makes no assumption about the order of the extension key and the field. By default the extension key is appended to the end of the returned string while the field is added to the beginning. Special Query characters are escaped in the result.

      Note: `Extensions` subclasses must maintain the contract between `buildExtensionField(String, String)` and `splitExtensionField(String, String)` where the latter inverts the former.

      Parameters:
        `extensionKey` - the extension key
        `field` - the field to apply the extension on.
      Returns:
        escaped extension field identifier
      See Also:
        `to use the default query field`

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