Rules Guide

Chapter 3   Developing Custom Conditions and Actions

This chapter describes how to write your own classes for special-purpose conditions and actions. It includes the following topics:

• About custom conditions and actions

• Designing a condition or action

• Defining logic

• Defining properties

This chapter assumes you are familiar with rules-based applications and using the Rule Editor in Workbench. For background information, see Rule Development Basics.

About custom conditions and actions

Conditions and actions are Java classes used to build rules fired by components. The Rule Editor provides a selection of prebuilt conditions and actions. You can also write custom conditions and actions to meet your application's specific requirements.

Conditions and actions are typically implemented as JavaBeans, with properties you can set in the Rule Editor.

Designing a condition or action

Designing a condition or action involves several decision points.

What logic should be implemented?    When designing rule-based logic, consider how conditions and actions will interact with each other and with the firing component. Here are key considerations:

• What condition should be tested?

• What action should be executed if the condition is true?

• What action should be executed if the condition is false?

• What components will fire the rule that contains these conditions and actions?

• What data must be passed by the condition to its actions and by actions back to the firing component?

Will any of the installed conditions or actions meet my requirements?   Before you begin your development, you should become familiar with the installed conditions and actions. There may be one that will meet your requirements, or you may want to modify one of the installed versions.

    For more information, see Installed Conditions and Installed Actions.

What kind of user interface should be rendered by the Rule Editor?   By default, the Rule Editor generates a generic property panel as the interface for interacting with conditions and actions you use to build rules. If a condition or action has properties, the property panel provides controls—such as check boxes and text boxes—for choosing or entering required values.

You can also specify a custom user interface in your condition and action class, which the Rule Editor then uses to render the property panel.

    For more information, see Defining properties.

What supporting classes will be needed?   Conditions and actions often rely on supporting classes such as:

Does the rule need to access runtime values?   You can define properties to access session whiteboard values that can be set dynamically at runtime.

    For more information, see Defining runtime properties.

Defining logic

Conditions and actions each have three methods that define their implementations:

These methods are included in the templates generated by the Condition Wizard and Action Wizard in Workbench.

    For on overview of the templates and core methods, see About the template methods.

Defining logic for a condition

Typically a condition compares property values entered in the Rule Editor and returns a Boolean. This logic is coded within the doCondition() method.

The doCondition() method includes an EbiContext object, allowing you to access runtime values.

Example of doCondition()

This example shows code from the installed condition CheckTime, which checks whether the current time of day is within the time range specified for the condition in the Rule Editor:

  // ...
  // JavaBean get/set accessor methods
  	 public int getFrom() {
  	 	 return from;
  	 }
  
  	 public void setFrom( int from ) {
  	 	 this.from = from;
  	 }
  
  /	 public int getTo() {
  	 	 return to;
  	 
  	 public void setTo( int to ) {
      	 this.to = to;
  	 }
  // Check to see if the current time of day is within the specified range
  public boolean doCondition( com.sssw.re.api.EbiContext context ) throws com.sssw.re.exception.EboConditionException {
  	 	 int hour = new GregorianCalendar().get( Calendar.HOUR_OF_DAY );
  
      	 if ( from < to ) {
  	 	 	 // daytime check
  	 	 	 if ( hour >= from ) {
  	 	 	 	 if ( hour <= to ) {
  	 	 	 	 	 return true;
  	 	 	 	 }
  	 	 	 }
  	 	 	 return false;
  	 	 }
  	 	 else {
  	 	 	 // cross over check
  	 	 	 if ( hour >= to ) {
  	 	 	 	 if ( hour <= from ) {
  	 	 	 	 	 return false;
  	 	 	 	 }
  	 	 	 }
  	 	 	 return true;
  	 	 }
  
  	 }
  // ...

Notes about the condition example

get/set methods   These are JavaBean accessor methods that define two properties for this condition: from a specified time and to a specified time (inclusive). These values are accessed from the property panel in the Rule Editor.

    For information, see Defining JavaBeans.

doCondition()    This method is the workhorse of condition classes. In this example the property values are compared to the current time, which is obtained from a Java GregorianCalendar object. The code does two checks—for within current day and for crossover times—in each case returning a Boolean.

Defining logic for an action

An action returns the result of a rule, based on the return value of one or more conditions. The logic for an action is coded in the doAction() method.

Actions can perform virtually any activity, ranging from accessing a database via SQL, manipulating whiteboard values, returning HTTP and HTML values, performing operations, and controlling user access to objects. Like conditions, actions typically have properties settable in the Rule Editor.

Returning values to the caller

Because actions return the result of a rule, you need to understand how the result is handled by the caller, typically a component or JSP page. Here is a summary of the common HTTP response methods you might use to return a value from an action to the component that fired the rule:

Example of doAction()

The following shows code from the installed action ReturnAsHTMLBold. It returns the text entered by the user in bold format:

  public void doAction( com.sssw.re.api.EbiContext context ) throws
     com.sssw.re.exception.EboActionException {
  context.setResponsePhrase( "<b>" + getValue().getValue( context ) + "</b>" );

Defining a condition or action rule descriptor

The toString() method provided by the template returns a description of the condition or action that appears in the Rule Editor when a condition or action is selected. Typically, toString() calls the properties' get methods to include property values.

Example of toString()

Here is how toString() is implemented in the installed condition CheckTime:

  // Use resource bundle, "caResource" instantiated with Class definition, 
  // for string processing
  public String toString() {
  	 	 return caResource.getString("the hour is between <b>") + getHours().elementAt( from ) + caResource.getString("</b> and <b>") + getHours().elementAt( to );
  	 }
  // Implement a JPanel using getParameterPanel() using getHours() to get
  // selected property values..
  
  private Vector getHours() {
  	 	 if ( hours == null ) {
  	 	 	 hours = new Vector();
  	 	 	 hours.addElement( caResource.getString("12 am"));
  	 	 	 hours.addElement( caResource.getString("1 am"));
  	 	 	 hours.addElement( caResource.getString("2 am"));
          // ...

Notes about toString() example

A local method, getHours(), uses a Vector to store property values. The toString() method calls getHours() to display the hours selected in the Rule Editor.

NOTE   In this example, toString() directs processing to a resource bundle that is instantiated with the condition class. This provides support for localization. For more information, see Using resource bundles.

Here is what the result looks like in the Rule Editor:

Defining properties

There are several ways to define properties and property panels for conditions and actions. The Rule subsystem supports Java constructs like JavaBeans and JPanels, and also provides default controls for certain data types and objects and support for using runtime values in properties. You can also follow the implementation of resource bundles and BeanInfo classes used in the installed conditions and actions.

This section provides descriptions and examples of each approach.

Defining JavaBeans

Like other JavaBeans, conditions and actions can have properties. By defining properties, you allow conditions and actions to be customized in the Rule Editor for use in a variety of rules.

When you add properties in a custom condition or action, you must follow JavaBeans standards. For each property, define:

• A member variable whose name has all lowercase letters

• A pair of get and set accessor methods

  By convention, each method name consists of get or set prepended to the property name starting with an initial capital letter (such as getTime).

The Rule Editor can use these constructs to automatically generate a property panel for the condition or action, based on the data type of the property. For a model implementation, see Example of doCondition().

You can also use a JDK BeanInfo class to enhance the display properties. See Writing a BeanInfo class.

Defining runtime properties

The Rule subsystem provides two string template data types that allow properties in conditions and actions to be set dynamically from runtime values:

• EboStringTemplateSingle: single-line text box, rendered as a TextField

• EboStringTemplateMulti: multiline text box, rendered as a TextArea

When you define properties using these data types, the Rule Editor lets you specify values for these properties by referencing whiteboard keys. When the rule is fired, the property will be set to the real-time value associated with the whiteboard key.

    For information about using the whiteboard, see Rule Development Basics.

Working with the !valueOf construct

For each property you want to set dynamically, you need to define a member variable of type EboStringTemplateSingle or EboStringTemplateMulti. The Rule Editor will generate the associated TextField or TextArea, labeled with a string that ends with the caret (^) symbol. This symbol indicates that the property has been defined as a string template that can be set either statically by entering a literal string or dynamically by using the construct !valueOf. With this construct, you specify the value associated with a whiteboard key. Here is the syntax:

  !valueOf.whiteboard key

Certain session values, such as userID, are automatically provided. For example, to set the property to the value associated with the whiteboard key UserID, enter !valueOf.UserID.

Resolving the valueOf! expression   When you write a condition or action that needs to evaluate a runtime value, use one of these methods to get the value:

Example of using string template values

This example shows code from the installed action SaveToWhiteBoard. The action saves data to the whiteboard in the specified whiteboard key:

  public boolean resolve;
  	 public com.sssw.re.core.EboStringTemplateSingle data = new
    com.sssw.re.core.EboStringTemplateSingle();
  	 public com.sssw.re.core.EboStringTemplateSingle template = new
    com.sssw.re.core.EboStringTemplateSingle();
  
  // Sets the template value for the whiteboard key that will be used to
  // store the data value.
   	 public void setKeyTemplate( EboStringTemplateSingle detailKey ) {
  	 	 this.template = detailKey;
  	 }
  // Returns the template for the whiteboard key.
   	 public EboStringTemplateSingle getKeyTemplate() {
  	 	 return template;
  	 }
  
  // Returns the template for the data.
   	 public EboStringTemplateSingle getData() {
  	 	 return data;
  	 }
  
  // Sets the template value for the data to be saved to the whiteboard
   	 public void setData( EboStringTemplateSingle data ) {
  	 	 this.data = data;
  	 }
  
  // Return boolean true if the data value is a templatized string that needs
  // to be  resolved, false if the data value is the value to be saved.
  	 public boolean getResolve() {
  	 	 return resolve;
  	 }
  
  // Sets the value which determines if the data value needs to be resolved.
   	 public void setResolve( boolean resolve ) {
  	 	 this.resolve = resolve;
  	 }
  
  // Saves the data value, or resolved data value if resolved is true, to the
  // whiteboard in the specified whiteboard key.
  public void doAction( com.sssw.re.api.EbiContext context ) throws com.sssw.re.exception.EboActionException {
  	 	 String merged = getKeyTemplate().getValue( context );
  	 	 context.setValue( merged, ( getResolve() ? getData().getValue( context
       ) : getData().getTemplate() ) );
      }

Notes on string template example

This action defines three properties that appear in the Rule Editor:

EboStringTemplateSingle   The code instantiates two template objects for each template property. The first property (Key-template) will be resolved to get its data representation. The second property (Data) is resolved only if the Resolve control is selected.

doAction()    Gets the properties and implements these methods:

Using generic property panels

The Rule subsystem supports a set of data types for which it can automatically generate generic property panels. For each supported data type, the Rule Editor renders a preselected GUI control in the property panel. All you need to do is implement JavaBean accessor methods for each property.

Here is a list of the supported data types and the associated controls:

Creating a custom property panel

If you prefer to create your own property panel rather than use the generic controls, you can implement the getParameterPanel() method to specify a custom user interface. The Rule Editor requires the custom interface to be defined as a JPanel; it will not create a custom property panel based on any other type of component returned by getParameterPanel().

When including the getParameterPanel() method in a condition or action, you must implement a listener interface to allow the controls in the JPanel to respond to user actions.

Example of using a custom JPanel

This is the code that defines the property panel for the installed condition CheckTime:

  // ...
  // Returns a custom ui component to be used for editing this condition.
   	 public java.awt.Component getParameterPanel() {
  	 	 JPanel p = new JPanel();
  	 	 p.setLayout( new BoxLayout( p, BoxLayout.X_AXIS ) );
  	 	 p.add( new JLabel( caResource.getString("between the hours of") ) );
  	 	 p.add( FROM = new JComboBox( getHours() ) );
  	 	 p.add( new JLabel( caResource.getString("and") ) );
  	 	 p.add( TO = new JComboBox( getHours() ) );
  	 	 FROM.setAlignmentY( JComponent.CENTER_ALIGNMENT );
  	 	 TO.setAlignmentY( JComponent.CENTER_ALIGNMENT );
  	 	 FROM.setSelectedIndex( from );
  	 	 TO.setSelectedIndex( to );
  	 	 FROM.addItemListener( this );
  	 	 TO.addItemListener( this );
  	 	 return p;
  	 }
  
  // Returns a vector of hours for selection in the ui.
   	 private Vector getHours() {
  	 	 if ( hours == null ) {
  	 	 	 hours = new Vector();
  	 	 	 hours.addElement( caResource.getString("12 am"));
  	 	 	 hours.addElement( caResource.getString("1 am"));
  	 	 	 hours.addElement( caResource.getString("2 am"));
          // ...

Notes on custom JPanel example

Here is the custom property panel generated by the code:

JComboBox implementation    The variables TO and FROM are defined as ints. Using a generic panel would result in text fields for each property. Instead, getParameterPanel() instantiates a JPanel and implements a pair of JComboBox controls, providing a dropdown list of time selections in the Rule Editor.

The code defines a local method, getHours(), that uses a Vector to fill in the values of the combo boxes.

Resource bundle    The code uses a resource bundle caResource to localize the labels for the ComboBox. For information, see Using resource bundles.

Writing a BeanInfo class

You can write a BeanInfo class for any condition and action to specify the appearance of attributes in the property panel. For example, you can use a BeanInfo class for:

• Specifying a display name for each property

• Implementing localization for property names and static text strings that appear on the panel for each property

NOTE   Using a BeanInfo class is the recommended way to implement resource bundles for localization. For information about resource bundles, see Using resource bundles.

Like JavaBeans, BeanInfo classes require their associated condition or action classes to specify properties as member variables with associated get and set methods.

To create a BeanInfo class:

1. Create a Java class in your preferred Java editor. The class must extend EboBeanInfo and implement these code elements:

   Code element	Description
   imports	For conditions: package com.sssw.re.condition.* For actions: package com.sssw.re.action.* For conditions and actions: com.sssw.re.core.* java.beans.*
   getClazz() method	Returns the condition or action class associated with the BeanInfo class
   PropertyDescriptor[] pds	Provides information to the Rule Editor for generating the property panel for the condition or action The array should be the same size as the number of properties you want to appear in the property panel
   PropertyDescriptor pd	Defines a descriptor for (each) property Each individual property descriptor is added to the property descriptor array

2. Name the BeanInfo class by appending BeanInfo to the name of the associated condition or action class.

   For example, if your class name is CheckCondition, the BeanInfo class must be named CheckConditionBeanInfo.

    For an example of a BeanInfo class, see Example of a BeanInfo class.

Using resource bundles

Resource bundles are a standard feature of the Java JDK used for localization. You can store any object, string, number, or other data in a resource bundle. To create a resource bundle, you need to create either a Java class that extends ListResourceBundle or a properties file that contains static strings. For each locale you want to support, you provide a separate version of the resource bundle.

You can use resource bundles to implement localization in conditions, actions, and associated BeanInfo classes. Here is a recommended approach:

1. Create resource bundles for all locales supported by your application.

2. In your condition, action, or BeanInfo class, declare ResourceBundle objects that reference your resource bundles by calling the EboResourceBundle.getBundle() method. This simplest version of this method takes one argument, the fully qualified name of your resource bundle class.

   Example    If your resource bundle is MyBundle.class located in package locales, your declaration should look like this:

     static com.sssw.re.util.EboResourceBundle eoCABundle = com.sssw.re.util.EboResourceBundle.getBundle("locales.MyBundle")
   

3. Access the data in the resource bundle by calling get methods on the ResourceBundle object.

   Example    If your resource bundle contains localized strings, call the getString() method on the ResourceBundle object, passing the key associated with the desired string value.

NOTE   For complete information on creating resource bundles, see the reference documentation for the ResourceBundle, ListResourceBundle, and PropertyResourceBundle classes in the Java standard API documentation. All these classes are in the java.util package.

Example of a BeanInfo class

This is the code that defines the BeanInfo class for the installed condition CheckTime:

  package com.sssw.re.condition;
  import com.sssw.re.core.*;
  import java.beans.*;
  
  public class CheckTimeBeanInfo extends EboBeanInfo {
  
  	 // Resource Bundle definition
      static com.sssw.re.util.EboResourceBundle eoCABundle =
        com.sssw.re.util.EboResourceBundle.getBundle( EboConstant.CA_BUNDLE,
          getClass().getClassLoader() );
          
  	 public Class getClazz() {
  	 	 return com.sssw.re.condition.CheckTime.class;
  	 }
  
  	 public PropertyDescriptor[] getPropertyDescriptors() {
  	 	 PropertyDescriptor[] pds = new PropertyDescriptor[ 2 ];
  	 	 PropertyDescriptor pd;
  	 	 pd = super.getPropertyDescriptor( "From" );
  	 	 pd.setDisplayName( eoCABundle.getString( "From" ) );
  	 	 pds[ 0 ] = pd;
  	 	 pd = super.getPropertyDescriptor( "To" );
  	 	 pd.setDisplayName( eoCABundle.getString( "To" ) );
  	 	 pds[ 1 ] = pd;
  	 	 return pds;
  	 }
  
  }

Notes on the BeanInfoClass example

Getting the resource bundle   Uses EboResourceBundle.getBundle() to get the name of the resource bundle for the installed conditions and actions stored in CA_BUNDLE, and the class loader.

Defining property descriptors   Since the CheckTime condition defines two properties, it requires two property descriptors—as indicated in the array declaration.

Specifying a display name for a property   You can use the setDisplayName() method to specify a property name. When the Rule Editor generates the property panel, it uses this display name as the label for the UI control associated with the property.

The setDisplayName() method is called on the property descriptor and takes a string argument. This example shows the recommended approach for implementing resource bundles. It uses key values To and From—passing them to the resource bundle so that the Rule Editor displays a localized string.

Rules Guide

Copyright © 2002, SilverStream Software, LLC, a wholly owned subsidiary of Novell, Inc. All rights reserved.