Tutorials : A Closer Look at the Java Rules Engine API (JSR 94) :

Runtime API

The Runtime API provides a JDBC type access to vendor implementations of the Rules Engine API. Vendors can expose their rule engine implementations to the clients through the RuleServiceProvider class. The RuleServiceProvider provides access to the Runtime and the Administrative APIs of the specific rules engine implementation. Every vendor who wishes to expose a RuleServiceProvider will have a RuleServiceProvider URL, which uniquely identifies the implementation. The recommended standard is to have an Internet domain namespace convention like "com.mycompany.myrulesengine.rules. RuleServiceProvider". This would help in having uniqueness of the access URL. The RuleServiceProvider internally implements the interfaces required for rules administration and runtime access. All RuleServiceProviders should be registered with a RuleServiceProviderManager so that they can be accessible to clients. The registration is done in a manner similar to the DriverManager and Driver of the JDBC API. Only RuleServiceProvider registered with the RuleServiceProviderManager are exposed to the clients.

The RuleRuntime Interface is the heart of the Runtime API. The RuleRuntime interface provides methods to create a RuleSession, which in turn is used to run the rules. The RuleRuntime also provides a mechanism to access the list of all the RuleExecutionSets registered with the service provider. The RuleSession Interface also defines the type of session that will be used by the client. The clients have an option of having a stateful session or a stateless session depending on the way the client want to run the rules.

The StatelessRuleSession behaves like a stateless session bean, it works on a per request basis. Clients can send either a single input object or a list of objects and expect an output object. A StatefulRuleSession is useful when the client needs a dedicated session with the rules engine. Input objects can be added to the session through the addObject method. Any number of objects can be added to the same session. Existing objects on the session can be updated using the updateObject method. The objects are not lost as long as the session exists between the client and the rules engine.

RuleExecutionSetMetaData interface is provided to the clients to find out about the metadata of the RuleExecutionSets. The information is not directly exposed to clients as rule administrators without notice might modify the information about the RuleExecutionSet. The metadata information is exposed through the RuleSession Interface.

A snippet of sample code for the using the Runtime API is shown below:

RuleServiceProvider ruleProvider = 
RuleServiceProviderManager.getRuleServiceProvider
(“com.mycompany.myrulesengine.rules. RuleServiceProvider”);   
RuleRuntime ruleRuntime = ruleProvider.getRuleRuntime();
StatelessRuleSession ruleSession = (StatelessRuleSession)  
ruleRuntime.createRuleSession(ruleURL, null, RuleRuntime.STTELESS_SESSION_TYPE);

List inputRules = new ArrayList();
inputRules.add(new String(“Rule 1”));
inputRules.add(new Integer(1));

List resultRules = ruleSession.executeRules(inputRules);

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