Package org.apache.commons.configuration2.convert

Class DefaultConversionHandler

java.lang.Object
org.apache.commons.configuration2.convert.DefaultConversionHandler
All Implemented Interfaces:
ConversionHandler
Direct Known Subclasses:
DataConfiguration.DataConversionHandler
public class DefaultConversionHandler extends Object implements ConversionHandler

A default implementation of the ConversionHandler interface.

This class implements the standard data type conversions as used by AbstractConfiguration and derived classes. There is a central conversion method - convert() - for converting a passed in object to a given target class. The basic implementation already handles a bunch of standard data type conversions. If other conversions are to be supported, this method can be overridden.

The object passed to convert() can be a single value or a complex object (like an array, a collection, etc.) containing multiple values. It lies in the responsibility of convert() to deal with such complex objects. The implementation provided by this class tries to extract the first child element and then delegates to convertValue() which does the actual conversion.

Since:
2.0

  • Field Details

    • INSTANCE

      public static final DefaultConversionHandler INSTANCE
      A default instance of this class. Because an instance of this class can be shared between arbitrary objects it is possible to make use of this default instance anywhere.

    • DEFAULT_DATE_FORMAT

      public static final String DEFAULT_DATE_FORMAT
      The default format for dates.
      See Also:

    • NULL_INTERPOLATOR

      private static final ConfigurationInterpolator NULL_INTERPOLATOR
      Constant for a default ConfigurationInterpolator to be used if none is provided by the caller.

    • LIST_DELIMITER_HANDLER

      static final ListDelimiterHandler LIST_DELIMITER_HANDLER
      The default ListDelimiterHandler used for extracting values from complex objects.

    • dateFormat

      private volatile String dateFormat
      The current date format.

    • listDelimiterHandler

      private volatile ListDelimiterHandler listDelimiterHandler
      The default ListDelimiterHandler used for extracting values from complex objects.

  • Constructor Details

    • DefaultConversionHandler

      public DefaultConversionHandler()

  • Method Details

    • fetchInterpolator

      private static ConfigurationInterpolator fetchInterpolator(ConfigurationInterpolator ci)
      Obtains a ConfigurationInterpolator. If the passed in one is not null, it is used. Otherwise, a default one is returned.
      Parameters:
      ci - the ConfigurationInterpolator provided by the caller
      Returns:
      the ConfigurationInterpolator to be used

    • convert

      protected <T> T convert(Object src, Class<T> targetCls, ConfigurationInterpolator ci)
      Performs the conversion from the passed in source object to the specified target class. This method is called for each conversion to be done. The source object has already been passed to the ConfigurationInterpolator, so interpolation does not have to be done again. (The passed in ConfigurationInterpolator may still be necessary for extracting values from complex objects; it is guaranteed to be non null.) The source object may be a complex object, e.g. a collection or an array. This base implementation checks whether the source object is complex. If so, it delegates to extractConversionValue(Object, Class, ConfigurationInterpolator) to obtain a single value. Eventually, convertValue(Object, Class, ConfigurationInterpolator) is called with the single value to be converted.
      Type Parameters:
      T - the desired target type of the conversion
      Parameters:
      src - the source object to be converted
      targetCls - the desired target class
      ci - the ConfigurationInterpolator (not null)
      Returns:
      the converted value
      Throws:
      ConversionException - if conversion is not possible

    • convertToCollection

      private <T> void convertToCollection(Object src, Class<T> elemClass, ConfigurationInterpolator ci, Collection<T> dest)
      Helper method for converting all values of a source object and storing them in a collection.
      Type Parameters:
      T - the target type of the conversion
      Parameters:
      src - the source object
      elemClass - the target class of the conversion
      ci - the ConfigurationInterpolator
      dest - the collection in which to store the results
      Throws:
      ConversionException - if a conversion cannot be performed

    • convertValue

      protected <T> T convertValue(Object src, Class<T> targetCls, ConfigurationInterpolator ci)
      Performs a conversion of a single value to the specified target class. The passed in source object is guaranteed to be a single value, but it can be null. Derived classes that want to extend the available conversions, but are happy with the handling of complex objects, just need to override this method.
      Type Parameters:
      T - the desired target type of the conversion
      Parameters:
      src - the source object (a single value)
      targetCls - the target class of the conversion
      ci - the ConfigurationInterpolator (not null)
      Returns:
      the converted value
      Throws:
      ConversionException - if conversion is not possible

    • extractConversionValue

      protected Object extractConversionValue(Object container, Class<?> targetCls, ConfigurationInterpolator ci)
      Extracts a single value from a complex object. This method is called by convert() if the source object is complex. This implementation extracts the first value from the complex object and returns it.
      Parameters:
      container - the complex object
      targetCls - the target class of the conversion
      ci - the ConfigurationInterpolator (not null)
      Returns:
      the value to be converted (may be null if no values are found)

    • extractValues

      protected Collection<?> extractValues(Object source)
      Extracts all values contained in the given source object and returns them as a flat collection.
      Parameters:
      source - the source object (may be a single value or a complex object)
      Returns:
      a collection with all extracted values

    • extractValues

      protected Collection<?> extractValues(Object source, int limit)
      Extracts a maximum number of values contained in the given source object and returns them as flat collection. This method is useful if the caller only needs a subset of values, e.g. only the first one.
      Parameters:
      source - the source object (may be a single value or a complex object)
      limit - the number of elements to extract
      Returns:
      a collection with all extracted values

    • getDateFormat

      public String getDateFormat()
      Gets the date format used by this conversion handler.
      Returns:
      the date format

    • getListDelimiterHandler

      public ListDelimiterHandler getListDelimiterHandler()
      Gets the ListDelimiterHandler used for extracting values from complex objects.
      Returns:
      the ListDelimiterHandler used for extracting values from complex objects, never null.
      Since:
      2.9.0

    • isComplexObject

      protected boolean isComplexObject(Object src)
      Tests whether the passed in object is complex (which means that it contains multiple values). This method is called by convert(Object, Class, ConfigurationInterpolator) to figure out whether a actions are required to extract a single value from a complex source object. This implementation considers the following objects as complex:
      • Iterable objects
      • Iterator objects
      • Arrays
      Parameters:
      src - the source object
      Returns:
      true if this is a complex object, false otherwise

    • isEmptyElement

      protected boolean isEmptyElement(Object src)
      Tests whether the passed in object represents an empty element. This method is called by conversion methods to arrays or collections. If it returns true, the resulting array or collection will be empty. This implementation returns true if and only if the passed in object is an empty string. With this method it can be controlled if and how empty elements in configurations are handled.
      Parameters:
      src - the object to be tested
      Returns:
      a flag whether this object is an empty element

    • setDateFormat

      public void setDateFormat(String dateFormat)
      Sets the date format to be used by this conversion handler. This format is applied by conversions to Date or Calendar objects. The string is passed to the SimpleDateFormat class, so it must be compatible with this class. If no date format has been set, a default format is used.
      Parameters:
      dateFormat - the date format string
      See Also:

    • setListDelimiterHandler

      public void setListDelimiterHandler(ListDelimiterHandler listDelimiterHandler)
      Sets the ListDelimiterHandler used for extracting values from complex objects.
      Parameters:
      listDelimiterHandler - the ListDelimiterHandler used for extracting values from complex objects. Setting the value to null resets the value to its default.
      Since:
      2.9.0

    • to

      public <T> T to(Object src, Class<T> targetCls, ConfigurationInterpolator ci)
      Description copied from interface: ConversionHandler
      Converts a single object to the specified target type. A concrete implementation has to attempt a conversion. If this is not possible, a ConversionException is thrown. It is up to a concrete implementation how null values are handled; a default strategy would be to return null if the source object is null.
      Specified by:
      to in interface ConversionHandler
      Type Parameters:
      T - the type of the desired result
      Parameters:
      src - the object to be converted
      targetCls - the target class of the conversion
      ci - an object for performing variable substitution
      Returns:
      the converted object

    • toArray

      public Object toArray(Object src, Class<?> elemClass, ConfigurationInterpolator ci)
      Converts the given object to an array of the specified element type. The object can be a single value (e.g. a String, a primitive, etc.) or a complex object containing multiple values (like a collection or another array). In the latter case all elements contained in the complex object are converted to the target type. If the value(s) cannot be converted to the desired target class, a ConversionException is thrown. Note that the result type of this method is Object; because this method can also produce arrays of a primitive type the return type Object[] cannot be used. This implementation extracts all values stored in the passed in source object, converts them to the target type, and adds them to a result array. Arrays of objects and of primitive types are supported. If the source object is null, result is null, too.
      Specified by:
      toArray in interface ConversionHandler
      Parameters:
      src - the object to be converted
      elemClass - the element class of the resulting array
      ci - an object for performing variable substitution
      Returns:
      the array with the converted values

    • toCollection

      public <T> void toCollection(Object src, Class<T> elemClass, ConfigurationInterpolator ci, Collection<T> dest)
      Converts the given object to a collection of the specified type. The target collection must be provided (here callers have the option to specify different types of collections like lists or sets). All values contained in the specified source object (or the source object itself if it is a single value) are converted to the desired target class and added to the destination collection. If the conversion of an element is not possible, a ConversionException is thrown. This implementation extracts all values stored in the passed in source object, converts them to the target type, and adds them to the target collection. The target collection must not be null. If the source object is null, nothing is added to the collection.
      Specified by:
      toCollection in interface ConversionHandler
      Type Parameters:
      T - the type of the elements of the destination collection
      Parameters:
      src - the object to be converted
      elemClass - the element class of the destination collection
      ci - an object for performing variable substitution
      dest - the destination collection
      Throws:
      IllegalArgumentException - if the target collection is null

    • toObjectArray

      private <T> T[] toObjectArray(Object src, Class<T> elemClass, ConfigurationInterpolator ci)
      Converts the given source object to an array of objects.
      Parameters:
      src - the source object
      elemClass - the element class of the array
      ci - the ConfigurationInterpolator
      Returns:
      the result array
      Throws:
      ConversionException - if a conversion cannot be performed

    • toPrimitiveArray

      private Object toPrimitiveArray(Object src, Class<?> elemClass, ConfigurationInterpolator ci)
      Converts the given source object to an array of a primitive type. This method performs some checks whether the source object is already an array of the correct type or a corresponding wrapper type. If not, all values are extracted, converted one by one, and stored in a newly created array.
      Parameters:
      src - the source object
      elemClass - the element class of the array
      ci - the ConfigurationInterpolator
      Returns:
      the result array
      Throws:
      ConversionException - if a conversion cannot be performed