Package org.pentaho.reporting.engine.classic.core.function

The function package contains statefull functions and stateless expression for JFreeReport.


Interface Summary
AggregationFunction Todo: Document Me
Expression An expression is a lightweight function that does not maintain a state.
ExpressionRuntime The expression runtime encapsulates all properties of the current report processing run that might be needed to successfully evaluate an expression.
FieldAggregationFunction Todo: Document Me
Function The interface for report functions.
LayoutProcessorFunction A tagging interface that allows the system to differentiate between functions that compute values and functions that modify the report-definiton.
OutputFunction A simple tagging interface for the transition from function-based layouting back to explicit layouting.
ProcessingContext The processing context hold information about the progress of the report processing and contains global properties used during the report processing.
StructureFunction A structure function is a annonymous function that modifes the structure of the report or computes changes to the report definition on the current report.
ValidateableExpression A decorator interface that allows an expression to validate it's parameters.

Class Summary
AbstractCompareExpression Deprecated. This can be better handled in a formula.
AbstractElementFormatFunction The AbstractElementFormatFunction provides a common base implementation for all functions that need to modify the report definition or the style of an report element or band during the report processing.
AbstractExpression An abstract base class for implementing new report expressions.
AbstractFunction Base class for implementing new report functions.
AverageExpression Deprecated. this has been replaced by the ColumnAverageExpression.
ColumnAggregationExpression The base-class for all expressions that aggregate values from multiple columns.
ColumnAverageExpression Deprecated. the same can be achived with a formula "AVG([column1], [column2], [column3])"
ColumnDifferenceExpression Deprecated. This can be done easier with a formula.
ColumnDivisionExpression Deprecated. Use a formula
ColumnMaximumExpression Deprecated. Use a formula
ColumnMinimumExpression Deprecated. Use a formula
ColumnMultiplyExpression Deprecated. Use a formula
ColumnSumExpression Deprecated. Use a formula
CompareFieldsExpression Deprecated. Use a formula instead.
ConditionalItemSumFunction Deprecated. Filter the values by using a plain formula.
ConvertToDateExpression Parses a string into a date using the given date-format.
ConvertToNumberExpression Parses a string into a number using the given decimal-format.
CountDistinctFunction Counts the distinct occurences of an certain value of an column.
CreateGroupAnchorsFunction Deprecated. It is easier to create anchors using a Style-expression.
CreateHyperLinksFunction Deprecated. add style expressions to the 'href-target' and 'href-window' instead.
DateCutExpression Deprecated. The VariableDateExpression is much better suited for this purpose.
ElementColorFunction Deprecated. add a style expression for the 'paint' style instead
ElementTrafficLightFunction Deprecated. This function can be safely replaced by a formula.
ElementVisibilityFunction Deprecated. add a style-expression for the visible style-key instead.
ElementVisibilitySwitchFunction Deprecated. Use the RowBandingFunction to modify the band's background color directly.
EventMonitorFunction A function that logs each event that it receives.
ExpressionCollection Collects all expressions used in the report.
ExpressionUtilities A collection of utility methods which may be useful for expression-implementors.
FormulaExpression The formula expression is used to evaluate a LibFormula/OpenFormula expression.
FormulaFunction The formula function is a stateful version of the FormulaExpression and is used to evaluate a LibFormula/OpenFormula expression.
FunctionUtilities A collection of utility methods relating to functions.
GenericExpressionRuntime Todo: Document me!

Date: 13.05.2010 Time: 16:53:49

GroupCountFunction A report function that counts groups in a report.
HideElementByNameFunction Deprecated. Use a formula
HideElementIfDataAvailableExpression Deprecated. Use a Style-Expression or make proper use of the No-Data-Band
HideNullValuesFunction Deprecated. This should be done using Style-Expressions.
HidePageBandForTableExportFunction Hides the page header and footer if the export type is not pageable.
IsEmptyExpression Deprecated. Use a Formula Instead
IsNullExpression Deprecated. Use a Formula Instead
ItemAvgFunction A report function that calculates the average of one field (column) from the TableModel.
ItemColumnQuotientExpression Deprecated. Use PercentageExpression instead, it's name is much clearer
ItemCountFunction A report function that counts items in a report.
ItemHideFunction The ItemHideFunction hides equal values in a group.
ItemMaxFunction A report function that calculates the maximum value of one field (column) from the data-row.
ItemMinFunction A report function that calculates the minimum value of one field (column) from the data-row.
ItemPercentageFunction Calculates the percentage value of a numeric field.
ItemSumFunction A report function that calculates the sum of one field (column) from the data-row.
NegativeNumberPaintChangeFunction Deprecated. The same thing can be achieved using a simple StyleExpression on the element's PAINT stylekey.
PageFunction A report function that counts pages.
PageItemCountFunction An ItemCount function, that is reset to zero on every new page.
PageItemSumFunction An ItemSum function, that is reset to zero on every new page.
PageOfPagesFunction A report function that combines PageFunctionand PageTotalFunction.
PageTotalFunction Prints the total number of pages of an report.
PaintComponentFunction Deprecated. Use the new Component-Element instead.
PaintDynamicComponentFunction Deprecated. Use the new Component-Element instead.
PercentageExpression Deprecated. The same can be achieved using a simple ValueExpression.
ReportFormulaContext The report formula context is a FormulaContext implementation that connects the formula evaluator with the current data-row of the report process.
RowBandingFunction A function that alternates the background-color for each item-band within a group.
ShowElementByNameFunction Deprecated. This can be done easier using style-expressions
ShowElementIfDataAvailableExpression Deprecated. Use a formula instead.
TextFormatExpression Deprecated. Use the MessageFormatExpression instead.
TotalCalculationFunction A report function that stores the result of a calculation for a group or the complete report.
TotalGroupCountFunction A report function that counts the total of groups in a report.
TotalGroupSumFunction A report function that calculates the sum of one field (column) from the Data-Row.
TotalGroupSumQuotientFunction A report function that calculates the quotient of two summed fields (columns) from the report's data row.
TotalGroupSumQuotientPercentFunction A report function that calculates the quotient of two summed fields (columns) from the data-row.
TotalItemCountFunction A report function that counts the total number of items contained in groups in a report.
TotalItemMaxFunction A report function that pre-computes the largest item in a group.
TotalItemMinFunction A report function that pre-computes the smallest item in a group.
TotalPageItemCountFunction A report function that counts the total number of items contained in groups in a report.
TriggerPageFooterFunction This function enables a "PageFooter only on last page" functionality.

Exception Summary
FunctionProcessingException An exception that indicates that a function has not been correctly initialised.

Package org.pentaho.reporting.engine.classic.core.function Description

The function package contains statefull functions and stateless expression for JFreeReport.

The following lines apply to both functions and expressions.

JFreeReport supports 2 kinds of user defined calculations: Functions are statefull calculations, when the report proceedes they change their state, they sum up, calculate averages, count etc. Statefull means in that case, given you feed the same event multiple times into the function,you are not guaranteed to get the same result.

Expressions in contrast do not maintain a state, they calculate a value or change the report-elements depending on the current Event feed to them. If you feed the same Event into the Expression multiple times, you will always get the same result.

Common to both variants is: Data is fed into the function/expression by using a DataRow object. This object provides the (among others) these methods

to read the values of a function, expression, a column from the tablemodel or a ReportProperty.

Expressions are simple and easily explained: Expression have the method

Object getValue() which is called when the expression is queried. All expression have to override this method to perform the calculation and to return the value.

Functions are more complex:
Functions have several notification methods, where the system informs the function that a new event is processed.

By using the Event-object, you have access to the ReportState. The state can be used for getting the current group, current item and for gaining access to the dataRow. In case you want to manipulate the ReportElements, you also have access to the JFreeReport object.

Functions live in an own environment, separated from the outside world. Changing the original JFreeReport object does not affect the inner JFreeReport-Object. You are also unable to add new Functions or expressions to the report from inside, so all functions and expression have to be set before the report processing has begun.

All Functions have to be cloneable. It is not guaranteed that the report is processed in an linear order, but it is guaranteed that a single instance of a function does pass a reportstate only once.

That means: When processing the report, the system clones the functions on certain save-points (for instance whenever a page is finished). This saved copy can later be used to restart the report processing on that saved point. The copy-state made will never return to a previous save point, but it can (and certainly will occur) that this copy is used to process the report from that saved point on.

So when saving a state after page 2, it will never happen, that this page-2-copy gets used to process page 2 a second time, but it could happen that copies of this page-2-state process the page 3 again and again.

The best way to avoid cloning problems is to use Unmodifiable objects or primitive datatypes when storing a state. Using java.lang.String, one of the java.lang.Number implementers or any other unmodifiable object type is always save. If you use complex objects, lists or hashtables and you get weird results, try to implement a deep-object-copy in the clone() method of the function for these objects.

Using the functions

The function implementation is loaded via its default constructor by the report parser, all function implementations which should be used from within the xml-definitions must define a public default constructor. The functions implementation is defined by specifiying the "class" attribute of the "function" tag and is loaded by using the default class loader. Your function implementation must be in the classloaders classpath.

As with every function, a single function can return one value, something mathematicans express like y = f(x) where x is the data from your report processing.

A function is called several times, for every state change (whenever the report advances) one of the ReportListener methods are called (reportStarted, groupStarted etc). Expressions do not receive events, they just perform their computations based on the current state.

The functions value is returned by the "getValue()" function. You can return any Object, but make sure, that this object does not get modified anymore after it was returned to the caller. (A simple way to obey to this rule is to create a new object whenever the computed object changes).

Functions may reuse results from other functions by using and querying the DataRow object supplied in the report state or the function.

The order of the functions and the order for receiving events is undefined for functions of the same dependency level. So if you define a function which reads values from an other function, it is wise to define the dependencies for these functions.

Defining dependencies is easy: A function with an higher dependency is called before any function with a lower dependency. By default all user functions have the dependency of "0", the lowest possible level. The dependency is defined by specifying the "deplevel" attribute of the function or expression tag.

When using the API, the dependency level is read by "getDependencyLevel()" and can be set with "setDependencyLevel(int)".

For the example above, the caller function would have the dependency level of '0' and the called function the level of '1' or higher.