• net.sf.jasperreports.extension.registry.factory.{registry_id} - the extension registry factory class for custom functions
• net.sf.jasperreports.extension.{registry_id}.{property_suffix} - one or more properties providing a comma separated list of function classes

• Class-level annotations:
  • @FunctionCategories - stores metadata for an array of FunctionCategory classes, used as category identifiers when functions are grouped by categories. A given function may belong to different categories. The annotation can be declared as class or method-level. As class-level declaration, it applies to all methods in the class.
  • @FunctionCategory - stores metadata for any element in the @FunctionCategories array
  • @FunctionMessagesBundle - stores metadata for the message bundle file, including package information. If not provided, the default message bundle is considered a jasperreports_messages.properties file in the current package.
• Method-level annotations:
  • @FunctionCategories - stores metadata for an array of FunctionCategory classes at method level
  • @FunctionCategory - stores metadata for any element in the above @FunctionCategories array
  • @FunctionParameters - stores metadata for an array of FunctionParameter elements
  • @FunctionParameter - stores metadata for any element in the above @FunctionParameters array.

1. Depending on your specific criteria, create one or many category classes. Or you can use the existing built-in classes in the net.sf.jasperreports.functions.standard package: DateTimeCategory, LogicalCategory, MathCategory, TextCategory.
2. Implement one or many function classes with annotated methods. In this example, a function class is implemented for each category, but keep in mind that methods in different categories may be placed together in the same file, since we have the possibility to declare categories at method-level. There are 4 function classes in the net.sf.jasperreports.functions.standard package: DateTimeFunctions, LogicalFunctions, MathFunctions, TextFunctions
3. Create a properties file to store i18n labels for categories, functions and parameters: names, descriptions, other useful informations. Each category, function or parameter require a name and a description entry in the properties file. Entry keys are formed according to following rules:
   • Category name key: the category class name (including package) + .name suffix. For instance: net.sf.jasperreports.functions.standard.DateTimeCategory.name
   • Category description key: the category class name (including package) + .description suffix. For instance: net.sf.jasperreports.functions.standard.DateTimeCategory.description
   • Function name key: the function class name (including package) + the function name (as declared in the @Function method annotation) + .name suffix. For instance: net.sf.jasperreports.functions.standard.DateTimeFunctions.DATE.name
   • Function description key: the function class name (including package) + the function name (as declared in the @Function method annotation) + .description suffix. For instance: net.sf.jasperreports.functions.standard.DateTimeFunctions.DATE.description
   • Parameter name key: the function class name (including package) + the function name (as declared in the @Function method annotation) + the related parameter name (as declared in the related @FunctionParameter method annotation) + .name suffix. For instance: net.sf.jasperreports.functions.standard.DateTimeFunctions.DATE.dayOfMonth.name
   • Parameter description key: the function class name (including package) + the function name (as declared in the @Function method annotation) + the related parameter name (as declared in the related @FunctionParameter method annotation) + .description suffix. For instance: net.sf.jasperreports.functions.standard.DateTimeFunctions.DATE.dayOfMonth.description
4. Write the appropriate information in a jasperreports_extension.properties file as shown above.
5. Finally, archive your classes and properties files in a jar file and place it in your application classpath. Your custom functions are now ready to use.

  package net.sf.jasperreports.functions.standard;
  
  import net.sf.jasperreports.functions.annotations.FunctionCategory;
  
  /**
   * This class should maintain all function methods that belongs to the category {@link #DATE_TIME}.
   */
  @FunctionCategory(
    //"DATE_TIME" // if not specified, the value is the name of the category class
    )
  public final class DateTimeCategory 
  {
  }

package net.sf.jasperreports.functions.standard;

// import declarations here
// ...

/**
 * This class should maintain all function methods that belongs to the category {@link #DATE_TIME}.
 */
@FunctionCategories({DateTimeCategory.class})
public final class DateTimeFunctions
{
  private static final Log log = LogFactory.getLog(DateTimeFunctions.class);
  
  // ===================== TODAY function ===================== //
  /**
   * Returns the current date as date object.
   */
  @Function("TODAY")
  public static Date TODAY(){
    return new Date();
  }
  
  // other methods declared here 
  // ...
  
  // ===================== DAY function ===================== //
  /**
   * 
   * Returns the day of a given date. Date object can be a String, long value (milliseconds) or Date instance itself.
   */
  @Function("DAY")
  @FunctionParameters({
    @FunctionParameter("dateObject")})
  public static Integer DAY(Object dateObject){
    return getCalendarFieldFromDate(dateObject,Calendar.DAY_OF_MONTH);
  }
  
  // ===================== WEEKDAY function ===================== //
  /**
   * Returns the day of the week for a given date. Date object can be a String, long value (milliseconds) or Date instance itself.
   */
  @Function("WEEKDAY")
  @FunctionParameters({
    @FunctionParameter("dateObject"),
    @FunctionParameter("isSundayFirstDay")})
  public static Integer WEEKDAY(Object dateObject){
    return WEEKDAY(dateObject, false);
  }
  
  public static Integer WEEKDAY(Object dateObject, Boolean isSundayFirstDay){
    Integer dayOfWeek = getCalendarFieldFromDate(dateObject,Calendar.DAY_OF_WEEK);
    if(dayOfWeek==null) {
      if(log.isDebugEnabled()){
        log.debug("Unable to get the correct day of the week.");
      }
      return null;
    }
    if(isSundayFirstDay){
      // By default Sunday is considered first day in Java 
      // Calendar.SUNDAY should be a constant with value 1.
      // See the Calendar.DAY_OF_WEEK javadoc    
      return dayOfWeek;
    }
    else{
      // shift the days
      if(dayOfWeek==Calendar.SUNDAY){
        return 7;
      }
      else{
        return dayOfWeek-1;
      }
    }
  }

  // other public methods declared here 
  // ...
  
  // private methods declared here
  // ...
}  

net.sf.jasperreports.functions.standard.DateTimeCategory.description                           = Category for date and time manipulation functions
net.sf.jasperreports.functions.standard.DateTimeCategory.name                                  = Date & Time
net.sf.jasperreports.functions.standard.DateTimeFunctions.DATE.dayOfMonth.description          = The day of the new date
net.sf.jasperreports.functions.standard.DateTimeFunctions.DATE.dayOfMonth.name                 = Day of month
net.sf.jasperreports.functions.standard.DateTimeFunctions.DATE.description                     = Creates a date object using the specified information on day, month and year.
net.sf.jasperreports.functions.standard.DateTimeFunctions.DATE.month.description               = The month of the new date
net.sf.jasperreports.functions.standard.DateTimeFunctions.DATE.month.name                      = Month
net.sf.jasperreports.functions.standard.DateTimeFunctions.DATE.name                            = DATE
net.sf.jasperreports.functions.standard.DateTimeFunctions.DATE.year.description                = The year of the new date
net.sf.jasperreports.functions.standard.DateTimeFunctions.DATE.year.name                       = Year

net.sf.jasperreports.functions.standard.DateTimeCategory.description                           = Categoria di funzioni per la manipolazione di date e tempo
net.sf.jasperreports.functions.standard.DateTimeCategory.name                                  = Data e tempo
net.sf.jasperreports.functions.standard.DateTimeFunctions.DATE.dayOfMonth.description          = Il giorno della data
net.sf.jasperreports.functions.standard.DateTimeFunctions.DATE.dayOfMonth.name                 = Giorno
net.sf.jasperreports.functions.standard.DateTimeFunctions.DATE.description                     = Crea una nuova data utilizzando le informazioni di giorno, mese e anno specificati.
net.sf.jasperreports.functions.standard.DateTimeFunctions.DATE.month.description               = Il mese della data
net.sf.jasperreports.functions.standard.DateTimeFunctions.DATE.month.name                      = Mese
net.sf.jasperreports.functions.standard.DateTimeFunctions.DATE.name                            = DATE
net.sf.jasperreports.functions.standard.DateTimeFunctions.DATE.year.description                = L''anno della data
net.sf.jasperreports.functions.standard.DateTimeFunctions.DATE.year.name                       = Anno

net.sf.jasperreports.extension.registry.factory.functions=net.sf.jasperreports.functions.FunctionsRegistryFactory
net.sf.jasperreports.extension.functions.datetime=net.sf.jasperreports.functions.standard.DateTimeFunctions
net.sf.jasperreports.extension.functions.math=net.sf.jasperreports.functions.standard.MathFunctions, net.sf.jasperreports.functions.standard.LogicalFunctions
net.sf.jasperreports.extension.functions.text=net.sf.jasperreports.functions.standard.TextFunctions