Chapter 4. Tracing
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## Chapter 4. Tracing

## Introduction

The AspectJ developers have instrumented the compiler/weaver with many "trace" messages for their own debugging use. These remain in the production releases because tracing helps when it is hard to isolate the problem in a test case. This sections describes how to enable tracing so you can provide trace information on bug reports.

The usual approach to opening a report on Bugzilla is to describe the symptoms of the problem and attach a simple testcase. This allows the AspectJ team to try and reproduce the problem in an attempt to fix it as well as improve the test suite. Unfortunately it may not be possible to produce such a testcase either because your program is too large or is commercially sensitive. Alternatively the problem may relate to your specific environment where AspectJ is being used and will not be reproducible by the AspectJ team. In each of these situations you can produce a trace of the compiler when the problem occurs instead. This can then be attached to the bug report.

### Configuring Tracing

When available (Java 5 or later) AspectJ will use the java.util.logging infrastructure configured using a `logging.properties` file. By default only error and fatal events will be logged but less severe warnings as well as fine-grained method entry and exit events can be obtained using the appropriate configuration. All regular compiler messages can also be logged through the infrastructure by setting the `org.aspectj.weaving.messages` System property.

If you are running the AspectJ compiler/weaver under JDK 1.4 or earlier, AspectJ will use a simple built-in trace infrastructure that logs to stderr. This is enabled by setting the `org.aspectj.weaving.tracing.enabled` System property. You may also override the default behaviour or provide your own trace implementation using the `org.aspectj.weaving.tracing.factory` System property.

The table below lists the System properties that can be used to configure tracing.

Property | Description
--- | ---
`org.aspectj.tracing.debug` | Enable simple debugging of the trace infrastructure itself. Default: `false`.
`org.aspectj.tracing.enabled` | Enable the built-in AspectJ trace infrastructure. Default: `false`.
`org.aspectj.tracing.factory` | Select trace infrastructure. Specify the fully qualified class name of the `org.aspectj.weaver.tools.TraceFactory` interface to use a custom infrastructure. Specify a value of `default` to force AspectJ to use it's built-in infrastructure.
`org.aspectj.tracing.messages` | Enable tracing of compiler messages. The kind of messages logged is determined by the selected trace infrastructure not the message configuration. Default: `false`.

### Examples

Using `-Dorg.aspectj.tracing.factory=default` to force AspectJ to use its internal infrastructure, `-Dorg.aspectj.tracing.enabled=true` to turn it on and `-Dorg.aspectj.tracing.messages=true` to include messages running a simple HelloWorld with LTW will generate tracing to stderr. Below is an extract from that trace with method arguments removed. You will notice the millisecond time stamp, thread id and indication of entry/exit/event or message type for each line of trace.

    15:44:18.630 main > org.aspectj.weaver.loadtime.Aj.<init>
    15:44:18.660 main < org.aspectj.weaver.loadtime.Aj.<init>
    15:44:18.660 main > org.aspectj.weaver.loadtime.Aj.preProcess
    15:44:18.660 main - org.aspectj.weaver.loadtime.Aj.preProcess
    15:44:18.730 main > org.aspectj.weaver.loadtime.ClassLoaderWeavingAdaptor.<init>
    15:44:18.730 main < org.aspectj.weaver.loadtime.ClassLoaderWeavingAdaptor.<init>
    15:44:18.730 main > org.aspectj.weaver.loadtime.ClassLoaderWeavingAdaptor.initialize
    15:44:18.821 main I [AppClassLoader@92e78c] info AspectJ Weaver Version DEVELOPMENT ...
    15:44:18.821 main > org.aspectj.weaver.loadtime.ClassLoaderWeavingAdaptor.parseDefinitions
    15:44:18.821 main I [AppClassLoader@92e78c] info register classloader ...
    15:44:18.821 main - org.aspectj.weaver.loadtime.ClassLoaderWeavingAdaptor.parseDefinitions
    15:44:18.841 main - org.aspectj.weaver.loadtime.ClassLoaderWeavingAdaptor.parseDefinitions
    15:44:18.841 main I [AppClassLoader@92e78c] info using configuration ...
    15:44:18.891 main < org.aspectj.weaver.loadtime.ClassLoaderWeavingAdaptor.parseDefinitions
    15:44:19.021 main > org.aspectj.weaver.World$TypeMap.<init>
    15:44:19.021 main < org.aspectj.weaver.World$TypeMap.<init>
    15:44:19.021 main > org.aspectj.weaver.CrosscuttingMembersSet.<init>
    15:44:19.021 main < org.aspectj.weaver.CrosscuttingMembersSet.<init>
    15:44:19.021 main > org.aspectj.weaver.Lint.<init>
    15:44:19.021 main < org.aspectj.weaver.Lint.<init>
    15:44:19.021 main > org.aspectj.weaver.World.<init>
    15:44:19.111 main < org.aspectj.weaver.World.<init>
    15:44:19.201 main > org.aspectj.weaver.bcel.BcelWeaver.<init>
    15:44:19.201 main < org.aspectj.weaver.bcel.BcelWeaver.<init>
    15:44:19.201 main > org.aspectj.weaver.loadtime.ClassLoaderWeavingAdaptor.registerDefinitions
    15:44:19.211 main > org.aspectj.weaver.bcel.BcelWeaver.setReweavableMode
    15:44:19.351 main < org.aspectj.weaver.bcel.BcelWeaver.setReweavableMode
    15:44:19.351 main > org.aspectj.weaver.loadtime.ClassLoaderWeavingAdaptor.registerAspects
    15:44:19.351 main I [AppClassLoader@92e78c] info register aspect Aspect
    15:44:19.351 main > org.aspectj.weaver.bcel.BcelWeaver.addLibraryAspect
    15:44:19.501 main - org.aspectj.weaver.bcel.BcelWorld.lookupJavaClass
    15:44:19.632 main > org.aspectj.weaver.CrosscuttingMembersSet.addOrReplaceAspect
    15:44:19.792 main < org.aspectj.weaver.CrosscuttingMembersSet.addOrReplaceAspect
    15:44:19.792 main < org.aspectj.weaver.bcel.BcelWeaver.addLibraryAspect
    15:44:19.792 main < org.aspectj.weaver.loadtime.ClassLoaderWeavingAdaptor.registerAspects
    15:44:19.792 main < org.aspectj.weaver.loadtime.ClassLoaderWeavingAdaptor.registerDefinitions
    15:44:19.792 main > org.aspectj.weaver.bcel.BcelWeaver.prepareForWeave
    15:44:19.822 main < org.aspectj.weaver.bcel.BcelWeaver.prepareForWeave
    15:44:19.822 main > org.aspectj.weaver.loadtime.ClassLoaderWeavingAdaptor.weaveAndDefineConcete...
    15:44:19.822 main < org.aspectj.weaver.loadtime.ClassLoaderWeavingAdaptor.weaveAndDefineConcete...
    15:44:19.822 main < org.aspectj.weaver.loadtime.ClassLoaderWeavingAdaptor.initialize
    15:44:19.822 main > org.aspectj.weaver.tools.WeavingAdaptor.weaveClass
    ...

Alternatively when running under Java 5 the `logging.properties` file below could be used to configure Java Logging. The resulting file, just containing trace for the `org.aspectj.weaver.loadtime` package, will be written to `java0.log` in your `user.home` directory.

    handlers= java.util.logging.FileHandler

    .level= INFO

    java.util.logging.FileHandler.pattern = %h/java%u.log
    java.util.logging.FileHandler.count = 1
    java.util.logging.FileHandler.formatter = java.util.logging.SimpleFormatter
    java.util.logging.FileHandler.level = FINER

    org.aspectj.weaver.loadtime.level = FINER

By setting the System property `-Dorg.aspectj.tracing.debug=true` you should see a message confirming which trace infrastructure is being used.

    	TraceFactory.instance=org.aspectj.weaver.tools.Jdk14TraceFactory@12dacd1

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