path: root/docs/devguide/ajc.adoc

[[ajc]]
= `ajc`, the AspectJ compiler/weaver

== Name

`ajc` - compiler and bytecode weaver for the AspectJ and Java languages

== Synopsis

[subs=+quotes]
 ajc [_option_...] [_file_... | @_file_... | -argfile _file_...]

== Description

The `ajc` command compiles and weaves AspectJ and Java source and .class
files, producing .class files compliant with any Java VM (1.1 or later).
It combines compilation and bytecode weaving and supports incremental
builds; you can also weave bytecode at run-time using xref:ltw.adoc#ltw[Load-Time Weaving].

The arguments after the options specify the source file(s) to compile.
To specify source classes, use `-inpath` (below). Files may be listed
directly on the command line or in a file. The `-argfile file` and
`@file` forms are equivalent, and are interpreted as meaning all the
arguments listed in the specified file.

`Note:` You must explicitly pass `ajc` all necessary sources. Be sure to
include the source not only for the aspects or pointcuts but also for
any affected types. Specifying all sources is necessary because, unlike
javac, ajc does not search the sourcepath for classes. (For a discussion
of what affected types might be required, see
xref:../progguide/implementation.adoc[The AspectJ Programming Guide,
Implementation Appendix].)

To specify sources, you can list source files as arguments or use the
options `-sourceroots` or `-inpath`. If there are multiple sources for
any type, the result is undefined since ajc has no way to determine
which source is correct. (This happens most often when users include the
destination directory on the inpath and rebuild.)

[[ajc_options]]
=== Options

`-injars <JarList>`::
  deprecated: since 1.2, use -inpath, which also takes directories.
`-inpath <Path>`::
  Accept as source bytecode any .class files in the .jar files or
  directories on Path. The output will include these classes, possibly
  as woven with any applicable aspects. Path is a single argument
  containing a list of paths to zip files or directories, delimited by
  the platform-specific path delimiter.
`-aspectpath <Path>`::
  Weave binary aspects from jar files and directories on path into all
  sources. The aspects should have been output by the same version of
  the compiler. When running the output classes, the run classpath
  should contain all aspectpath entries. Path, like classpath, is a
  single argument containing a list of paths to jar files, delimited by
  the platform- specific classpath delimiter.
`-argfile <File>`::
  The file contains a line-delimited list of arguments. Each line in the
  file should contain one option, filename, or argument string (e.g., a
  classpath or inpath). Arguments read from the file are inserted into
  the argument list for the command. Relative paths in the file are
  calculated from the directory containing the file (not the current
  working directory). Comments, as in Java, start with `//` and extend
  to the end of the line. Options specified in argument files may
  override rather than extending existing option values, so avoid
  specifying options like <-classpath> in argument files unlike the
  argument file is the only build specification. The form <@file> is the
  same as specifying <-argfile file>.
`-outjar <output.jar>`::
  Put output classes in zip file output.jar.
`-outxml`::
  Generate aop.xml file for load-time weaving with default name.
`-outxmlfile <custom/aop.xml>`::
  Generate aop.xml file for load-time weaving with custom name.
`-incremental`::
  Run the compiler continuously. After the initial compilation, the
  compiler will wait to recompile until it reads a newline from the
  standard input, and will quit when it reads a 'q'. It will only
  recompile necessary components, so a recompile should be much faster
  than doing a second compile. This requires -sourceroots.
`-sourceroots <DirPaths>`::
  Find and build all .java or .aj source files under any directory
  listed in DirPaths. DirPaths, like classpath, is a single argument
  containing a list of paths to directories, delimited by the platform-
  specific classpath delimiter. Required by -incremental.
`-crossrefs`::
  Generate a build .ajsym file into the output directory. Used for
  viewing crosscutting references by tools like the AspectJ Browser.
`-emacssym`::
  Generate .ajesym symbol files for emacs support (deprecated).
`-Xlint`::
  Same as -Xlint:warning (enabled by default)
`-Xlint:\{level}`::
  Set default level for messages about potential programming mistakes in
  crosscutting code. \{level} may be ignore, warning, or error. This
  overrides entries in org/aspectj/weaver/XlintDefault.properties from
  aspectjtools.jar, but does not override levels set using the
  -Xlintfile option.
`-Xlintfile <PropertyFile>`::
  Specify properties file to set levels for specific crosscutting
  messages. PropertyFile is a path to a Java .properties file that takes
  the same property names and values as
  org/aspectj/weaver/XlintDefault.properties from aspectjtools.jar,
  which it also overrides.
`-help`::
  Emit information on compiler options and usage
`-version`::
  Emit the version of the AspectJ compiler
`-classpath <Path>`::
  Specify where to find user class files. Path is a single argument
  containing a list of paths to zip files or directories, delimited by
  the platform-specific path delimiter.
`-bootclasspath <Path>`::
  Override location of VM's bootclasspath for purposes of evaluating
  types when compiling. Path is a single argument containing a list of
  paths to zip files or directories, delimited by the platform-specific
  path delimiter.
`-extdirs <Path>`::
  Override location of VM's extension directories for purposes of
  evaluating types when compiling. Path is a single argument containing
  a list of paths to directories, delimited by the platform-specific
  path delimiter.
`-d <Directory>`::
  Specify where to place generated .class files. If not specified,
  <Directory> defaults to the current working dir.
`-target <[1.1 to 1.5]>`::
  Specify classfile target setting (1.1 to 1.5, default is 1.2)
`-1.3`::
  Set compliance level to 1.3 This implies -source 1.3 and -target 1.1.
`-1.4`::
  Set compliance level to 1.4 (default) This implies -source 1.4 and
  -target 1.2.
`-1.5`::
  Set compliance level to 1.5. This implies -source 1.5 and -target 1.5.
`-source <[1.3|1.4|1.5]>`::
  Toggle assertions (1.3, 1.4, or 1.5 - default is 1.4). When using
  -source 1.3, an assert() statement valid under Java 1.4 will result in
  a compiler error. When using -source 1.4, treat `assert` as a keyword
  and implement assertions according to the 1.4 language spec. When
  using -source 1.5, Java 5 language features are permitted.
`-nowarn`::
  Emit no warnings (equivalent to '-warn:none') This does not suppress
  messages generated by `declare warning` or `Xlint`.
`-warn: <items>`::
  Emit warnings for any instances of the comma-delimited list of
  questionable code (eg '-warn:unusedLocals,deprecation'):
+
[source, text]
....
constructorName        method with constructor name
packageDefaultMethod   attempt to override package-default method
deprecation            usage of deprecated type or member
maskedCatchBlocks      hidden catch block
unusedLocals           local variable never read
unusedArguments        method argument never read
unusedImports          import statement not used by code in file
none                   suppress all compiler warnings
....
+
`-warn:none` does not suppress messages generated by `declare warning`
  or `Xlint`.
`-deprecation`::
  Same as -warn:deprecation
`-noImportError`::
  Emit no errors for unresolved imports
`-proceedOnError`::
  Keep compiling after error, dumping class files with problem methods
`-g<:[lines,vars,source]>`::
  debug attributes level, that may take three forms:
+
[source, text]
....
-g         all debug info ('-g:lines,vars,source')
-g:none    no debug info
-g:{items} debug info for any/all of [lines, vars, source], e.g.,
           -g:lines,source
....
`-preserveAllLocals`::
  Preserve all local variables during code generation (to facilitate
  debugging).
`-referenceInfo`::
  Compute reference information.
`-encoding <format>`::
  Specify default source encoding format. Specify custom encoding on a
  per file basis by suffixing each input source file/folder name with
  '[encoding]'.
`-verbose`::
  Emit messages about accessed/processed compilation units
`-showWeaveInfo`::
  Emit messages about weaving
`-log <file>`::
  Specify a log file for compiler messages.
`-progress`::
  Show progress (requires -log mode).
`-time`::
  Display speed information.
`-noExit`::
  Do not call System.exit(n) at end of compilation (n=0 if no error)
`-repeat <N>`::
  Repeat compilation process N times (typically to do performance
  analysis).
`-XterminateAfterCompilation`::
  Causes compiler to terminate before weaving
`-XaddSerialVersionUID`::
  Causes the compiler to calculate and add the SerialVersionUID field to
  any type implementing Serializable that is affected by an aspect. The
  field is calculated based on the class before weaving has taken place.
`-Xreweavable[:compress]`::
  (Experimental - deprecated as now default) Runs weaver in reweavable
  mode which causes it to create woven classes that can be rewoven,
  subject to the restriction that on attempting a reweave all the types
  that advised the woven type must be accessible.
`-XnoInline`::
  (Experimental) do not inline around advice
`-XincrementalFile <file>`::
  (Experimental) This works like incremental mode, but using a file
  rather than standard input to control the compiler. It will recompile
  each time file is changed and and halt when file is deleted.
`-XserializableAspects`::
  (Experimental) Normally it is an error to declare aspects
  Serializable. This option removes that restriction.
`-XnotReweavable`::
  (Experimental) Create class files that can't be subsequently rewoven
  by AspectJ.
`-Xajruntimelevel:1.2, ajruntimelevel:1.5`::
  (Experimental) Allows code to be generated that targets a 1.2 or a 1.5
  level AspectJ runtime (default 1.5)

=== File names

ajc accepts source files with either the `.java` extension or the `.aj`
extension. We normally use `.java` for all of our files in an AspectJ
system -- files that contain aspects as well as files that contain
classes. However, if you have a need to mechanically distinguish files
that use AspectJ's additional functionality from those that are pure
Java we recommend using the `.aj` extension for those files.

We'd like to discourage other means of mechanical distinction such as
naming conventions or sub-packages in favor of the `.aj` extension.

* Filename conventions are hard to enforce and lead to awkward names for
your aspects. Instead of `TracingAspect.java` we recommend using
`Tracing.aj` (or just `Tracing.java`) instead.
* Sub-packages move aspects out of their natural place in a system and
can create an artificial need for privileged aspects. Instead of adding
a sub-package like `aspects` we recommend using the `.aj` extension and
including these files in your existing packages instead.

=== Compatibility

AspectJ is a compatible extension to the Java programming language. The
AspectJ compiler adheres to the
https://java.sun.com/docs/books/jls/index.html[The Java Language
Specification, Second Edition] and to the
https://java.sun.com/docs/books/vmspec/index.html[The Java Virtual
Machine Specification, Second Edition] and runs on any Java 2 compatible
platform. The code it generates runs on any Java 1.1 or later compatible
platform. For more information on compatibility with Java and with
previous releases of AspectJ, see xref:compatibility.adoc#versionCompatibility[Version Compatibility].

=== Examples

Compile two files:

[source, text]
....
ajc HelloWorld.java Trace.java
....

To avoid specifying file names on the command line, list source files in
a line-delimited text argfile. Source file paths may be absolute or
relative to the argfile, and may include other argfiles by @-reference.
The following file `sources.lst` contains absolute and relative files
and @-references:

[source, text]
....
Gui.java
/home/user/src/Library.java
data/Repository.java
data/Access.java
@../../common/common.lst
@/home/user/src/lib.lst
view/body/ArrayView.java
....

Compile the files using either the -argfile or @ form:

[source, text]
....
ajc -argfile sources.lst
ajc @sources.lst
....

Argfiles are also supported by jikes and javac, so you can use the files
in hybrid builds. However, the support varies:

* Only ajc accepts command-line options
* Jikes and Javac do not accept internal @argfile references.
* Jikes and Javac only accept the @file form on the command line.

Bytecode weaving using -inpath: AspectJ 1.2 supports weaving .class
files in input zip/jar files and directories. Using input jars is like
compiling the corresponding source files, and all binaries are emitted
to output. Although Java-compliant compilers may differ in their output,
ajc should take as input any class files produced by javac, jikes,
eclipse, and, of course, ajc. Aspects included in -inpath will be woven
into like other .class files, and they will affect other types as usual.

Aspect libraries using -aspectpath: AspectJ 1.1 supports weaving from
read-only libraries containing aspects. Like input jars, they affect all
input; unlike input jars, they themselves are not affected or emitted as
output. Sources compiled with aspect libraries must be run with the same
aspect libraries on their classpath.

The following example builds the tracing example in a command-line
environment; it creates a read-only aspect library, compiles some
classes for use as input bytecode, and compiles the classes and other
sources with the aspect library.

The tracing example is in the AspectJ distribution
(\{aspectj}/doc/examples/tracing). This uses the following files:

[source, text]
....
aspectj1.1/
  bin/
    ajc
  lib/
    aspectjrt.jar
  examples/
    tracing/
      Circle.java
      ExampleMain.java
      lib/
        AbstractTrace.java
        TraceMyClasses.java
      notrace.lst
      Square.java
      tracelib.lst
      tracev3.lst
      TwoDShape.java
      version3/
        Trace.java
        TraceMyClasses.java
....

Below, the path separator is taken as ";", but file separators are "/".
All commands are on one line. Adjust paths and commands to your
environment as needed.

Setup the path, classpath, and current directory:

[source, text]
....
cd examples
export ajrt=../lib/aspectjrt.jar
export CLASSPATH="$ajrt"
export PATH="../bin:$PATH"
....

Build a read-only tracing library:

[source, text]
....
ajc -argfile tracing/tracelib.lst -outjar tracelib.jar
....

Build the application with tracing in one step:

[source, text]
....
ajc -aspectpath tracelib.jar -argfile tracing/notrace.lst -outjar tracedapp.jar
....

Run the application with tracing:

[source, text]
....
java -classpath "$ajrt;tracedapp.jar;tracelib.jar" tracing.ExampleMain
....

Build the application with tracing from binaries in two steps:

* (a) Build the application classes (using javac for
demonstration's sake):
+
[source, text]
....
mkdir classes
javac -d classes tracing/*.java
jar cfM app.jar -C classes .
....
* (b) Build the application with tracing:
+
[source, text]
....
ajc -inpath app.jar -aspectpath tracelib.jar -outjar tracedapp.jar
....

Run the application with tracing (same as above):

[source, text]
....
java -classpath "$ajrt;tracedapp.jar;tracelib.jar" tracing.ExampleMain
....

Run the application without tracing:

[source, text]
....
java -classpath "app.jar" tracing.ExampleMain
....

=== The AspectJ compiler API

The AspectJ compiler is implemented completely in Java and can be called
as a Java class. The only interface that should be considered public are
the public methods in `org.aspectj.tools.ajc.Main`. E.g.,
`main(String[] args)` takes the the standard `ajc` command line
arguments. This means that an alternative way to run the compiler is

[subs=+quotes]
 java org.aspectj.tools.ajc.Main [_option_...] [_file_...]

To access compiler messages programmatically, use the methods
`setHolder(IMessageHolder holder)` and/or
`run(String[] args, IMessageHolder holder)`. `ajc` reports each message
to the holder using `IMessageHolder.handleMessage(..)`. If you just want
to collect the messages, use `MessageHandler` as your `IMessageHolder`.
For example, compile and run the following with `aspectjtools.jar` on
the classpath:

[source, java]
....
import org.aspectj.bridge.*;
import org.aspectj.tools.ajc.Main;
import java.util.Arrays;

public class WrapAjc {
  public static void main(String[] args) {
    Main compiler = new Main();
    MessageHandler m = new MessageHandler();
    compiler.run(args, m);
    IMessage[] ms = m.getMessages(null, true);
    System.out.println("messages: " + Arrays.asList(ms));
  }
}
....

=== Stack Traces and the SourceFile attribute

Unlike traditional java compilers, the AspectJ compiler may in certain
cases generate classfiles from multiple source files. Unfortunately, the
original Java class file format does not support multiple SourceFile
attributes. In order to make sure all source file information is
available, the AspectJ compiler may in some cases encode multiple
filenames in the SourceFile attribute. When the Java VM generates stack
traces, it uses this attribute to specify the source file.

(The AspectJ 1.0 compiler also supports the .class file extensions of
JSR-45. These permit compliant debuggers (such as jdb in Java 1.4.1) to
identify the right file and line even given many source files for a
single class. JSR-45 support is planned for ajc in AspectJ 1.1, but is
not in the initial release. To get fully debuggable .class files, use
the -XnoInline option.)

Probably the only time you may see this format is when you view stack
traces, where you may encounter traces of the format

[source, text]
....
java.lang.NullPointerException
  at Main.new$constructor_call37(Main.java;SynchAspect.java[1k]:1030)
....

where instead of the usual

[source, text]
....
File:LineNumber
....

format, you see

[source, text]
....
File0;File1[Number1];File2[Number2] ... :LineNumber
....

In this case, LineNumber is the usual offset in lines plus the "start
line" of the actual source file. That means you use LineNumber both to
identify the source file and to find the line at issue. The number in
[brackets] after each file tells you the virtual "start line" for that
file (the first file has a start of 0).

In our example from the null pointer exception trace, the virtual start
line is 1030. Since the file SynchAspect.java "starts" at line 1000
[1k], the LineNumber points to line 30 of SynchAspect.java.

So, when faced with such stack traces, the way to find the actual source
location is to look through the list of "start line" numbers to find the
one just under the shown line number. That is the file where the source
location can actually be found. Then, subtract that "start line" from
the shown line number to find the actual line number within that file.

In a class file that comes from only a single source file, the AspectJ
compiler generates SourceFile attributes consistent with traditional
Java compilers.