Application Overview
Our client, a leading US mortgage company, had a legacy system for originating loans for its customers that was unable to cope with the rate of change required by the business and unable to handle neither the increasing volume of transactions nor the required 24-7 uptime.
Our solution, the Loan Origination System, consists of several service components (SC) like Loan Manager, Credit, Income, Appraisal, Title, and Stipulations, to name a few. All these service components' services are exposed by EJB Session bean interfaces, Web services, in some cases, and by JMS for asynchronous use cases.
Consider a typical use case of resolving a Credit Liability. The Credit Liability UI retrieves data from three service components: Loan Manager, Credit and Stipulations. It then uses this data to update two Service Components: Credit and Stipulations.
Typically all these services are deployed independently to make them easier to maintain. The deployment model for the above-mentioned service components is depicted in Figure 1 below.
Figure 1. Illustration of the Deployment Model
Use-Case Illustration
Figure 2 shows a typical use case in any Service Oriented Business Application (SOBA), but in particular shows the sequence diagram for a Credit Liability Rendering use case.
Figure 2. Illustration of the Use-Case Model
Looking at the use case, the user clicks on the credit liability link, and the request goes to WebDelegate, which is part of webWar deployed on host1. The call then goes to a different service component through LoanServiceBean, StipServiceBean, and CreditServiceBean. These are session beans that are part of the Loan Manager EAR, Stip Engine EAR, and Credit Engine EAR, respectively.
The Solution: Tracing Requests
Tracing is a special form of logging that allows you to log the entry and/or exit of selected methods. Additionally, you may also log key business events and critical business parameters. Tracing is particularly useful in helping to understand system behavior—especially when a debugger is not an option, either due to the speed at which the activities occur or the distributed nature of the application. The conventional approach would be to hand code the entry of the log statements and the exit of the method calls using logging kits like Log4j or the one ships with JDK 1.4. This solution uses Log4j for its logging framework and AspectJ to automate logging of the method entry and exit calls.
The following aspect could be used to log method entry and exit calls:
import org.aspectj.lang.*;
public aspect TraceAspect {
private Logger _logger = Logger.getLogger("trace");
pointcut traceMethods() : (execution(* *.*(..))
|| execution(*.new(..))) && !within(TraceAspect);
before() : traceMethods() {
if (_logger.isLoggable(Level.INFO)) {
Signature sig = thisJoinPointStaticPart.getSignature();
_logger.logp(Level.INFO,
sig.getDeclaringType().getName(),sig.getName() "Entering");
}
}
after() returning(Object retObj): traceMethods() {
if (_logger.isLoggable(Level.INFO)) {
Signature sig = thisJoinPointStaticPart.getSignature();
_logger.logp(Level.INFO,
sig.getDeclaringType().getName(),sig.getName() "Exiting");
}
}
}
You can restrict the methods in which you want to place the entry and exit calls to certain packages and you can also set the logging level. Additionally, you can also log the input and return arguments for selective methods, say at debug level. You can also use expanded logging only during development and testing, and minimal logging in production to ensure best performance.
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