org.springframework.core

## Class Constants

- java.lang.Object
- - org.springframework.core.Constants

-     public class Constants
      extends Object

  This class can be used to parse other classes containing constant definitions in public static final members. The `asXXXX` methods of this class allow these constant values to be accessed via their string names.

  Consider class Foo containing `public final static int CONSTANT1 = 66;` An instance of this class wrapping `Foo.class` will return the constant value of 66 from its `asNumber` method given the argument `"CONSTANT1"`.

  This class is ideal for use in PropertyEditors, enabling them to recognize the same names as the constants themselves, and freeing them from maintaining their own mapping.

  Since:
    16.03.2003
  Author:
    Rod Johnson, Juergen Hoeller

- - ### Nested Class Summary

    Nested Classes
    Modifier and Type | Class and Description
    --- | ---
    `static class` | `Constants.ConstantException` Exception thrown when the `Constants` class is asked for an invalid constant name.

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `Constants(Class<?> clazz)` Create a new Constants converter class wrapping the given class.

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `Number` | `asNumber(String code)` Return a constant value cast to a Number.
    `Object` | `asObject(String code)` Parse the given String (upper or lower case accepted) and return the appropriate value if it's the name of a constant field in the class that we're analysing.
    `String` | `asString(String code)` Return a constant value as a String.
    `String` | `getClassName()` Return the name of the analyzed class.
    `protected Map<String,Object>` | `getFieldCache()` Exposes the field cache to subclasses: a Map from String field name to object value.
    `Set<String>` | `getNames(String namePrefix)` Return all names of the given group of constants.
    `Set<String>` | `getNamesForProperty(String propertyName)` Return all names of the group of constants for the given bean property name.
    `Set<String>` | `getNamesForSuffix(String nameSuffix)` Return all names of the given group of constants.
    `int` | `getSize()` Return the number of constants exposed.
    `Set<Object>` | `getValues(String namePrefix)` Return all values of the given group of constants.
    `Set<Object>` | `getValuesForProperty(String propertyName)` Return all values of the group of constants for the given bean property name.
    `Set<Object>` | `getValuesForSuffix(String nameSuffix)` Return all values of the given group of constants.
    `String` | `propertyToConstantNamePrefix(String propertyName)` Convert the given bean property name to a constant name prefix.
    `String` | `toCode(Object value, String namePrefix)` Look up the given value within the given group of constants.
    `String` | `toCodeForProperty(Object value, String propertyName)` Look up the given value within the group of constants for the given bean property name.
    `String` | `toCodeForSuffix(Object value, String nameSuffix)` Look up the given value within the given group of constants.

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

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

- - ### Constructor Detail

    - #### Constants

          public Constants(Class<?> clazz)

      Create a new Constants converter class wrapping the given class.

      All public static final variables will be exposed, whatever their type.

      Parameters:
        `clazz` - the class to analyze
      Throws:
        `IllegalArgumentException` - if the supplied `clazz` is `null`

  - ### Method Detail

    - #### getClassName

          public final String getClassName()

      Return the name of the analyzed class.

    - #### getSize

          public final int getSize()

      Return the number of constants exposed.

    - #### getFieldCache

          protected final Map<String,Object> getFieldCache()

      Exposes the field cache to subclasses: a Map from String field name to object value.

    - #### asNumber

          public Number asNumber(String code)
                          throws Constants.ConstantException

      Return a constant value cast to a Number.
      Parameters:
        `code` - the name of the field (never `null`)
      Returns:
        the Number value
      Throws:
        `Constants.ConstantException` - if the field name wasn't found or if the type wasn't compatible with Number
      See Also:
        `asObject(java.lang.String)`

    - #### asString

          public String asString(String code)
                          throws Constants.ConstantException

      Return a constant value as a String.
      Parameters:
        `code` - the name of the field (never `null`)
      Returns:
        the String value Works even if it's not a string (invokes `toString()`).
      Throws:
        `Constants.ConstantException` - if the field name wasn't found
      See Also:
        `asObject(java.lang.String)`

    - #### asObject

          public Object asObject(String code)
                          throws Constants.ConstantException

      Parse the given String (upper or lower case accepted) and return the appropriate value if it's the name of a constant field in the class that we're analysing.
      Parameters:
        `code` - the name of the field (never `null`)
      Returns:
        the Object value
      Throws:
        `Constants.ConstantException` - if there's no such field

    - #### getNames

          public Set<String> getNames(@Nullable
                                      String namePrefix)

      Return all names of the given group of constants.

      Note that this method assumes that constants are named in accordance with the standard Java convention for constant values (i.e. all uppercase). The supplied `namePrefix` will be uppercased (in a locale-insensitive fashion) prior to the main logic of this method kicking in.

      Parameters:
        `namePrefix` - prefix of the constant names to search (may be `null`)
      Returns:
        the set of constant names

    - #### getNamesForProperty

          public Set<String> getNamesForProperty(String propertyName)

      Return all names of the group of constants for the given bean property name.
      Parameters:
        `propertyName` - the name of the bean property
      Returns:
        the set of values
      See Also:
        `propertyToConstantNamePrefix(java.lang.String)`

    - #### getNamesForSuffix

          public Set<String> getNamesForSuffix(@Nullable
                                               String nameSuffix)

      Return all names of the given group of constants.

      Note that this method assumes that constants are named in accordance with the standard Java convention for constant values (i.e. all uppercase). The supplied `nameSuffix` will be uppercased (in a locale-insensitive fashion) prior to the main logic of this method kicking in.

      Parameters:
        `nameSuffix` - suffix of the constant names to search (may be `null`)
      Returns:
        the set of constant names

    - #### getValues

          public Set<Object> getValues(@Nullable
                                       String namePrefix)

      Return all values of the given group of constants.

      Note that this method assumes that constants are named in accordance with the standard Java convention for constant values (i.e. all uppercase). The supplied `namePrefix` will be uppercased (in a locale-insensitive fashion) prior to the main logic of this method kicking in.

      Parameters:
        `namePrefix` - prefix of the constant names to search (may be `null`)
      Returns:
        the set of values

    - #### getValuesForProperty

          public Set<Object> getValuesForProperty(String propertyName)

      Return all values of the group of constants for the given bean property name.
      Parameters:
        `propertyName` - the name of the bean property
      Returns:
        the set of values
      See Also:
        `propertyToConstantNamePrefix(java.lang.String)`

    - #### getValuesForSuffix

          public Set<Object> getValuesForSuffix(@Nullable
                                                String nameSuffix)

      Return all values of the given group of constants.

      Note that this method assumes that constants are named in accordance with the standard Java convention for constant values (i.e. all uppercase). The supplied `nameSuffix` will be uppercased (in a locale-insensitive fashion) prior to the main logic of this method kicking in.

      Parameters:
        `nameSuffix` - suffix of the constant names to search (may be `null`)
      Returns:
        the set of values

    - #### toCode

          public String toCode(Object value,
                               @Nullable
                               String namePrefix)
                        throws Constants.ConstantException

      Look up the given value within the given group of constants.

      Will return the first match.

      Parameters:
        `value` - constant value to look up
        `namePrefix` - prefix of the constant names to search (may be `null`)
      Returns:
        the name of the constant field
      Throws:
        `Constants.ConstantException` - if the value wasn't found

    - #### toCodeForProperty

          public String toCodeForProperty(Object value,
                                          String propertyName)
                                   throws Constants.ConstantException

      Look up the given value within the group of constants for the given bean property name. Will return the first match.
      Parameters:
        `value` - constant value to look up
        `propertyName` - the name of the bean property
      Returns:
        the name of the constant field
      Throws:
        `Constants.ConstantException` - if the value wasn't found
      See Also:
        `propertyToConstantNamePrefix(java.lang.String)`

    - #### toCodeForSuffix

          public String toCodeForSuffix(Object value,
                                        @Nullable
                                        String nameSuffix)
                                 throws Constants.ConstantException

      Look up the given value within the given group of constants.

      Will return the first match.

      Parameters:
        `value` - constant value to look up
        `nameSuffix` - suffix of the constant names to search (may be `null`)
      Returns:
        the name of the constant field
      Throws:
        `Constants.ConstantException` - if the value wasn't found

    - #### propertyToConstantNamePrefix

          public String propertyToConstantNamePrefix(String propertyName)

      Convert the given bean property name to a constant name prefix.

      Uses a common naming idiom: turning all lower case characters to upper case, and prepending upper case characters with an underscore.

      Example: "imageSize" → "IMAGE_SIZE"
      Example: "imagesize" → "IMAGESIZE".
      Example: "ImageSize" → "_IMAGE_SIZE".
      Example: "IMAGESIZE" → "_I_M_A_G_E_S_I_Z_E"

      Parameters:
        `propertyName` - the name of the bean property
      Returns:
        the corresponding constant name prefix
      See Also:
        `getValuesForProperty(java.lang.String)`, `toCodeForProperty(java.lang.Object, java.lang.String)`