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<chapter id="messages" xreflabel="Messages">
<title>Messages</title>
<sect1 id="messages-introduction">
<title>Introduction</title>
<para>
Messages point out potential problems in the input program; some
are clearly problems (errors), but many more may depend on what
the programmer intends. To keep the noise down, the latter are treated
as warnings that can be ignored by the programmer or information
hidden from the programmer. However, when investigating
unexpected behavior, it's helpful to show them. This describes how
to configure messages, presents some problem scenarios when
compiling or doing load-time weaving, and summarizes some of the
more relevant messages.
</para>
<sect2 id="messages-introduction-config"
xreflabel="messages-configuration">
<title>Configuring Messages</title>
<para>
The compiler offers <literal>-verbose</literal>,
<literal>-warning</literal>, and <literal>-XLint</literal> options
when invoked using the command-line, Ant, or embedded in an IDE.
All options are listed in the AspectJ Development Environment Guide
sections for
<ulink url="../devguide/ajc-ref.html">Ajc</ulink> and
<ulink url="../devguide/antTasks-iajc.html">Ant Tasks</ulink>.
The <ulink url="../devguide/ltw.html">Load-time Weaving</ulink>
section describes how to use XML configuration files and
system properties to pass options to the weaver. (You can also
pass options to the weaver using system properties in build-
time weaving.)
The <literal>-verbose</literal> option has the effect of including
messages level "info", which are normally ignored.
Both <literal>warning</literal> and <literal>XLint</literal>
enable you to identify specific messages to emit, but warning
messages tend to be the same provided by the underlying Eclipse
JDT (Java) compiler, while XLint messages are emitted by the
AspectJ compiler or weaver. Obviously, during load-time weaving
only weaver messages will be emitted. Similarly, if aspects
are compiled but not woven, then only compiler messages will be
emitted. However, the usual case for the compiler/weaver working
at build time is to emit both compiler and weaver messages.
</para>
<para> The table below lists some options used to control AspectJ messages. The method
of configuration depends on your environment so refer to the relevant
documentation for
<ulink url="../devguide/ajc-ref.html">ajc</ulink>,
<ulink url="../devguide/.html#antTasks-iajc-options">Ant</ulink> or
<ulink url="../devguide/ltw-configuration.html#weaver-options">LTW</ulink>.
</para>
<informaltable>
<tgroup cols="2">
<thead>
<row>
<entry>Option</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry>
<literal>-verbose</literal>
</entry>
<entry>
Show informational messages including AspectJ version
and build date.
</entry>
</row>
<row>
<entry>
<literal>-debug</literal>
</entry>
<entry>
(Load-time weaving only). Show debugging messages such as
which classes are being woven or those that are excluded.
(This is not related to the compiler -g option to
include debug information in the output .class files.)
</entry>
</row>
<row>
<entry>
<literal>-showWeaveInfo</literal>
</entry>
<entry>
Show weaving messages.
</entry>
</row>
<row>
<entry>
<literal>-Xlint</literal>
</entry>
<entry>
Control level of lint messages.
</entry>
</row>
<row>
<entry>
<literal>messageHolderClass</literal>
</entry>
<entry>
In Ant tasks, specify the class to receive all messages.
See
<ulink url="../devguide/antTasks-iajc.html#antTasks-iajc-options">
iajc task options</ulink>.
</entry>
</row>
<row>
<entry>
<literal>rg.aspectj.tools.Main.setMessageHolder(..)</literal>
</entry>
<entry>
Programmatic access for setting the message holder
outside of Ant.
</entry>
</row>
<row>
<entry>
<literal>org.aspectj.weaving.messages</literal>
</entry>
<entry>
Set this system property to redirect compiler/weaver
messages to logging facilities, as described in
<xref linkend="trace-configuration"/>.
</entry>
</row>
<row>
<entry>
<literal>@SuppressAjWarnings</literal>
</entry>
<entry>
Include this is Java 5 code to suppress AspectJ
warnings associated with the next line of code.
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</sect2>
</sect1>
<sect1 id="messages-scenarios">
<title>Message scenarios</title>
<sect2 id="messages-scenarios-ct">
<title>Compile-time weaving scenarios</title>
<sect3 id="messages-scenarios-ct-adviceNotWoven">
<title>Advice not woven</title>
<para>This means that the pointcut for the advice did not match,
and it should be debugged as described in
<xref linkend="pointcuts"/>.</para>
</sect3>
</sect2>
<sect2 id="messages-scenarios-ltw">
<title>Load-time weaving scenarios</title>
<para> You can use <literal>META-INF/aop.xml</literal> to control which
messages are produced during LTW. The following example will produce
basic informational messages about the lifecyle of the weaver in
addition to any warning or error messages. </para>
<programlisting><![CDATA[
<aspectj>
<weaver options="-verbose">
</weaver>
</aspectj>
]]></programlisting>
<para>The messages indicate which <literal>META-INF/aop.xml</literal>
configurations file(s) are being used. Each message is also preceeded by the
name of the defining class loader associated with weaver. You can use this
information in a large system to distinguish between different applications each
of which will typically have its own class loader. </para>
<programlisting><![CDATA[
[AppClassLoader@92e78c] info AspectJ Weaver Version 1.5.3 built on Thursday Oct 26, 2006 at 17:22:31 GMT
[AppClassLoader@92e78c] info register classloader sun.misc.Launcher$AppClassLoader@92e78c
[AppClassLoader@92e78c] info using configuration /C:/temp/META-INF/aop.xml
[AppClassLoader@92e78c] info using configuration /C:/temp/META-INF/aop-ajc.xml
[AppClassLoader@92e78c] info register aspect ExceptionHandler
[AppClassLoader@92e78c] info processing reweavable type ExceptionHandler: ExceptionHandler.aj
]]></programlisting>
<sect3 id="messages-scenarios-ltw-adviceNotWoven">
<title>Advice not woven</title>
<para> It is often difficult to determine, especially when using load-time weaving (LTW),
why advice has not been woven. Here is a quick guide to the messages to
look for. Firstly if you use the <literal>-verbose</literal> option you
should see the following message when your aspect is registered: </para>
<programlisting><![CDATA[
info register aspect MyAspect
]]></programlisting>
<para> Secondly if you use the <literal>-debug</literal> option you should
see a message indicating that you class is being woven: </para>
<programlisting><![CDATA[
debug weaving 'HelloWorld'
]]></programlisting>
<para> However this does not mean that advice has actually been woven into
your class; it says that the class has been passed to the weaver. To determine
whether your pointcuts match you can use the <literal>-showWeaveInfo</literal>
option which will cause a message to be issued each time a join point is woven: </para>
<programlisting><![CDATA[
weaveinfo Join point 'method-execution(void HelloWorld.main(java.lang.String[]))' ...
]]></programlisting>
<para>If advice should be woven at this join point, you should get a
corresponding message.</para>
</sect3>
</sect2>
</sect1>
<sect1 id="messages-xlint">
<title>Lint messages</title>
<para>
The table below lists some useful <literal>-Xlint</literal> messages. </para>
<informaltable>
<tgroup cols="3">
<thead>
<row>
<entry>Message</entry>
<entry>Default</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry>
<literal>aspectExcludedByConfiguration</literal>
</entry>
<entry>
<literal>ignore</literal>
</entry>
<entry>
If an aspect is not being woven, despite being
registered, it could be that it has been excluded
by either an <literal>include</literal> or <literal>exclude</literal>
element in the
<literal>aspects</literal> section of <literal>META-INF/aop.xml</literal>.
Enable this message to determine whether an aspect has
been excluded.
</entry>
</row>
<row>
<entry>
<literal>adviceDidNotMatch</literal>
</entry>
<entry>
<literal>warning</literal>
</entry>
<entry>
Issued when advice did not potentially affect any join points.
This means the corresponding pointcut did not match any join
points in the program. This may be valid e.g., in library
aspects or code picking up error conditions, but often the
programmer simply made a mistake in the pointcut. The best
approach is to debug the pointcut.
</entry>
</row>
<row>
<entry>
<literal>invalidAbsoluteTypeName</literal>
</entry>
<entry>
<literal>warning</literal>
</entry>
<entry>
Issued when an exact type in a pointcut does not match any type
in the system. Note that this can interact with the rules for
resolving simple types, which permit unqualified names if they
are imported.
</entry>
</row>
<row>
<entry>
<literal>typeNotExposedToWeaver</literal>
</entry>
<entry>
<literal>warning</literal>
</entry>
<entry>
This means that a type which could be affected by an aspect
is not available for weaving. This happens when a class on
the classpath should be woven.
</entry>
</row>
<row>
<entry>
<literal>runtimeExceptionNotSoftened</literal>
</entry>
<entry>
<literal>warning</literal>
</entry>
<entry>
Before AspectJ 5, declare soft used to soften runtime exceptions
(unnecessarily). Since then, it does not but does issue this
warning in case the programmer did intend for the exception
to be wrapped.
</entry>
</row>
<row>
<entry>
<literal>unmatchedSuperTypeInCall</literal>
</entry>
<entry>
<literal>warning</literal>
</entry>
<entry>
Issued when a call pointcut specifies a defining type which
is not matched at the call site (where the declared type of
the reference is used, not the actual runtime type). Most
people should use
'target(Foo) && call(void foo())'
instead.
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</sect1>
</chapter>
|
