Package org.apache.commons.beanutils.converters

Class AbstractConverter

java.lang.Object
org.apache.commons.beanutils.converters.AbstractConverter
All Implemented Interfaces:
Converter
Direct Known Subclasses:
ArrayConverter, BooleanConverter, CharacterConverter, ClassConverter, DateTimeConverter, FileConverter, NumberConverter, StringConverter, URLConverter
public abstract class AbstractConverter extends Object implements Converter
Base Converter implementation that provides the structure for handling conversion to and from a specified type.

This implementation provides the basic structure for converting to/from a specified type optionally using a default value or throwing a ConversionException if a conversion error occurs.

Implementations should provide conversion to the specified type and from the specified type to a String value by implementing the following methods:

  • convertToString(value) - convert to a String (default implementation uses the objects toString() method).
  • convertToType(Class, value) - convert to the specified type

The default value has to be compliant to the default type of this converter - which is enforced by the generic type parameter. If a conversion is not possible and a default value is set, the converter tries to transform the default value to the requested target type. If this fails, a ConversionException if thrown.

Since:
1.8.0
Version:
$Id$

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    private static final String
    DEFAULT_CONFIG_MSG
    Debug logging message to indicate default value configuration
    private Object
    defaultValue
    The default value specified to our Constructor, if any.
    private org.apache.commons.logging.Log
    log
    Logging for this instance.
    private static final String
    PACKAGE
    Current package name
    private boolean
    useDefault
    Should we return the default value on conversion errors?

  • Constructor Summary

    Constructors
    Constructor
    Description
    AbstractConverter()
    Construct a Converter that throws a ConversionException if an error occurs.
    AbstractConverter(Object defaultValue)
    Construct a Converter that returns a default value if an error occurs.

  • Method Summary

    Modifier and Type
    Method
    Description
    protected ConversionException
    conversionException(Class<?> type, Object value)
    Generates a standard conversion exception with a message indicating that the passed in value cannot be converted to the desired target type.
    <T> T
    convert(Class<T> type, Object value)
    Convert the input object into an output object of the specified type.
    protected Object
    convertArray(Object value)
    Return the first element from an Array (or Collection) or the value unchanged if not an Array (or Collection).
    private <T> T
    convertToDefaultType(Class<T> targetClass, Object value)
    Performs a conversion to the default type.
    protected String
    convertToString(Object value)
    Convert the input object into a String.
    protected abstract <T> T
    convertToType(Class<T> type, Object value)
    Convert the input object into an output object of the specified type.
    protected Object
    getDefault(Class<?> type)
    Return the default value for conversions to the specified type.
    protected abstract Class<?>
    getDefaultType()
    Return the default type this Converter handles.
    protected <T> T
    handleError(Class<T> type, Object value, Throwable cause)
    Handle Conversion Errors.
    protected <T> T
    handleMissing(Class<T> type)
    Handle missing values.
    boolean
    isUseDefault()
    Indicates whether a default value will be returned or exception thrown in the event of a conversion error.
    (package private) org.apache.commons.logging.Log
    log()
    Accessor method for Log instance.
    protected void
    setDefaultValue(Object defaultValue)
    Set the default value, converting as required.
    String
    toString()
    Provide a String representation of this converter.
    (package private) String
    toString(Class<?> type)
    Provide a String representation of a java.lang.Class.

    Methods inherited from class java.lang.Object

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

  • Field Details

    • DEFAULT_CONFIG_MSG

      private static final String DEFAULT_CONFIG_MSG
      Debug logging message to indicate default value configuration
      See Also:

    • PACKAGE

      private static final String PACKAGE
      Current package name
      See Also:

    • log

      private transient org.apache.commons.logging.Log log
      Logging for this instance.

    • useDefault

      private boolean useDefault
      Should we return the default value on conversion errors?

    • defaultValue

      private Object defaultValue
      The default value specified to our Constructor, if any.

  • Constructor Details

    • AbstractConverter

      public AbstractConverter()
      Construct a Converter that throws a ConversionException if an error occurs.

    • AbstractConverter

      public AbstractConverter(Object defaultValue)
      Construct a Converter that returns a default value if an error occurs.
      Parameters:
      defaultValue - The default value to be returned if the value to be converted is missing or an error occurs converting the value.

  • Method Details

    • isUseDefault

      public boolean isUseDefault()
      Indicates whether a default value will be returned or exception thrown in the event of a conversion error.
      Returns:
      true if a default value will be returned for conversion errors or false if a ConversionException will be thrown.

    • convert

      public <T> T convert(Class<T> type, Object value)
      Convert the input object into an output object of the specified type.
      Specified by:
      convert in interface Converter
      Type Parameters:
      T - the target type of the conversion
      Parameters:
      type - Data type to which this value should be converted
      value - The input value to be converted
      Returns:
      The converted value.
      Throws:
      ConversionException - if conversion cannot be performed successfully and no default is specified.

    • convertToString

      protected String convertToString(Object value) throws Throwable
      Convert the input object into a String.

      N.B.This implementation simply uses the value's toString() method and should be overriden if a more sophisticated mechanism for conversion to a String is required.

      Parameters:
      value - The input value to be converted.
      Returns:
      the converted String value.
      Throws:
      Throwable - if an error occurs converting to a String

    • convertToType

      protected abstract <T> T convertToType(Class<T> type, Object value) throws Throwable
      Convert the input object into an output object of the specified type.

      Typical implementations will provide a minimum of String --> type conversion.

      Type Parameters:
      T - Target type of the conversion.
      Parameters:
      type - Data type to which this value should be converted.
      value - The input value to be converted.
      Returns:
      The converted value.
      Throws:
      Throwable - if an error occurs converting to the specified type

    • convertArray

      protected Object convertArray(Object value)
      Return the first element from an Array (or Collection) or the value unchanged if not an Array (or Collection). N.B. This needs to be overriden for array/Collection converters.
      Parameters:
      value - The value to convert
      Returns:
      The first element in an Array (or Collection) or the value unchanged if not an Array (or Collection)

    • handleError

      protected <T> T handleError(Class<T> type, Object value, Throwable cause)
      Handle Conversion Errors.

      If a default value has been specified then it is returned otherwise a ConversionException is thrown.

      Type Parameters:
      T - Target type of the conversion.
      Parameters:
      type - Data type to which this value should be converted.
      value - The input value to be converted
      cause - The exception thrown by the convert method
      Returns:
      The default value.
      Throws:
      ConversionException - if no default value has been specified for this Converter.

    • handleMissing

      protected <T> T handleMissing(Class<T> type)
      Handle missing values.

      If a default value has been specified, then it is returned (after a cast to the desired target class); otherwise a ConversionException is thrown.

      Type Parameters:
      T - the desired target type
      Parameters:
      type - Data type to which this value should be converted.
      Returns:
      The default value.
      Throws:
      ConversionException - if no default value has been specified for this Converter.

    • setDefaultValue

      protected void setDefaultValue(Object defaultValue)
      Set the default value, converting as required.

      If the default value is different from the type the Converter handles, it will be converted to the handled type.

      Parameters:
      defaultValue - The default value to be returned if the value to be converted is missing or an error occurs converting the value.
      Throws:
      ConversionException - if an error occurs converting the default value

    • getDefaultType

      protected abstract Class<?> getDefaultType()
      Return the default type this Converter handles.
      Returns:
      The default type this Converter handles.

    • getDefault

      protected Object getDefault(Class<?> type)
      Return the default value for conversions to the specified type.
      Parameters:
      type - Data type to which this value should be converted.
      Returns:
      The default value for the specified type.

    • toString

      public String toString()
      Provide a String representation of this converter.
      Overrides:
      toString in class Object
      Returns:
      A String representation of this converter

    • log

      org.apache.commons.logging.Log log()
      Accessor method for Log instance.

      The Log instance variable is transient and accessing it through this method ensures it is re-initialized when this instance is de-serialized.

      Returns:
      The Log instance.

    • toString

      String toString(Class<?> type)
      Provide a String representation of a java.lang.Class.
      Parameters:
      type - The java.lang.Class.
      Returns:
      The String representation.

    • convertToDefaultType

      private <T> T convertToDefaultType(Class<T> targetClass, Object value)
      Performs a conversion to the default type. This method is called if we do not have a target class. In this case, the T parameter is not set. Therefore, we can cast to it (which is required to fulfill the contract of the method signature).
      Type Parameters:
      T - the type of the result object
      Parameters:
      targetClass - the target class of the conversion
      value - the value to be converted
      Returns:
      the converted value

    • conversionException

      protected ConversionException conversionException(Class<?> type, Object value)
      Generates a standard conversion exception with a message indicating that the passed in value cannot be converted to the desired target type.
      Parameters:
      type - the target type
      value - the value to be converted
      Returns:
      a ConversionException with a standard message
      Since:
      1.9