Page History

...

Another logging and tracing facility is available in Tuscany that gives the user a bit of flexibility in what gets logged , and requires no source code modifications to run. This is an Aspect Oriented Programming (AOP) approach that runs via a Java agent at runtime. Just like a debugger can start and stop and inspect a Tuscany Java program, so too can an AOP agent inspect and report on a Tuscany Java program. Tuscany employs the AspectJ implementation, and its runtime agent is contained in the aspectjweaver.jar file. The AOP agent is specified from a command line option or runtime options:

java -javaagent:"<path to aspectjweaver.jar>" calculator.CalculatorClient

The AOP logging and tracing agent can be run with any Tuscany program. No additional calls or log statements need be added to the Tuscany code. The results of running a timing for example, look like this:

Running org.apache.tuscany.sca.aspectj.TracingTestCase
Timing Around timedSection jp=call(void java.util.logging.Logger.info(String))
Oct 21, 2008 9:26:36 AM org.apache.tuscany.sca.aspectj.TracingTestCase info_aroundBody0
Timing Around timedSection Roundtrip is 32ms for jp.getSignature=void java.util.logging.Logger.info(String)

Full documentation on AspectJ is available at the AspectJ web site. Tuscany provides example usage in the module tracing-aspectj in the build tree and the released code.

Brief Apect Oriented Programming Introduction

In order to understand the aspect oriented approach to logging in Tuscany, one must understand a few basic concepts.

A join point is well defined point in the program flow. An example join point is the entry to a Java method. Another is after an exception is thrown. These join points contain useful information when running a program such as the argument list, the call stack, and the signature of the point that is executing.

A point cut is a subset of all the program join points. For instance, a point cut might be only the join points from exceptions thrown by the Tuscany runtime. Or only the set of calls to a Tuscany API org.apache.tuscany.sca.node.launcher.NodeLauncher.

Advice is the code that is run when a point cut is reached. For instance, your advice might want to print out all the arguments when entering a given method. Or your advice might show the call stack of an exception and print the original cause of the exception.

Finally, an aspect is a module that bundles up a particular set of point cuts and advice. Here is an example aspect that is marked with Java 5 annotations. The name of the aspect is LoggingAspect, there is a point cut defined at Tuscany calls to org.apache.tuscany.sca.* classes (but not inside of Aspect classes), and when the point cut is run, the advice for this point cut prints out the join point signature.

@Aspect
public class LoggingAspect {
    @Pointcut("call(* org.apache.tuscany.sca..*(..)) && (!within(org.apache.tuscany.sca.aspectj.*Aspect))")
    public void anyMethodCall() {
    }

    @Before("anyMethodCall()")
    public void before(JoinPoint jp) {
        System.out.println("Logging Before anyMethodCall jp.getSignature=" + jp.getSignature());
    }
}

Full explanation of these concepts are in the AspectJ documents. The purpose here is to provide enough information to allow a user to run or modify the Tuscany aspects to one's liking.

Logging and Tracing in Tuscany

...