Setting up a QoS interceptor to meet the usecase in https://github.com/betfair/cougar/issues/19

RejectCalls.java

public class RejectCalls implements ExecutionPreProcessor {
  
    private Set<String> toReject = new HashSet<String>();
    
    public void setToReject(String s) {
        for (String r : s.split(",")) {
            toReject.add(r.trim());
        }
    }
    
    @Override
    public ExecutionRequirement getExecutionRequirement() {
        // won't get called
        return ExecutionRequirement.EVERY_OPPORTUNITY;
    }

    @Override
    public InterceptorResult invoke(ExecutionContext ctx, OperationKey key, Object[] args) {
        if (toReject.contains(key.getOperationName())) {
            return new InterceptorResult(InterceptorState.FORCE_ON_EXCEPTION, new CougarServiceException(ServerFaultCode.FrameworkError, "Execution rejected");
        }
        return new InterceptorResult(InterceptorState.CONTINUE);
    }

    @Override
    public String getName() {
        return "RejectCalls";
    }
}

spring-context.xml

<!-- Define the inner processor bean -->
<bean name="rejectCalls" class="RejectCalls">
  <property name="toReject" value="unimportantCall" />
</bean>

<!-- Define the status source -->
<!-- TODO -->

<!-- Define the QoS processor -->
<bean name="highLoadAverageRejectUnimportantCalls" class="com.betfair.cougar.core.impl.ev.QoSProcessor">
  <constructor-arg index="0" ref="loadAverageMonitor"/>
  <constructor-arg index="1" value="WARN"/>
  <constructor-arg index="2" ref="rejectCalls"/>
</bean>

<!-- register the qos processor -->
<bean parent="preProcessorInterceptorRegistrationHelper">
  <property name="interceptor" ref="highLoadAverageRejectUnimportantCalls"/>
</bean>

The upshot of this would be to reject all calls to any operation of the name "unimportantCall" when the given load average monitor is in either a WARN or a FAIL state.