ajc — compiler and bytecode weaver for the AspectJ and Java languages


ajc [Options] [file... | @file... | -argfile file...]


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 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 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.)


-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.


Generate aop xml file for load-time weaving with default name (META-INF/aop-ajc.xml).

-outxmlfile filename

Generate aop.xml file for load-time weaving with custom name.


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.


Generate a build .ajsym file into the output directory. Used for viewing crosscutting references by tools like the AspectJ Browser.


Generate .ajesym symbol files for emacs support (deprecated).


Same as -Xlint:warning (enabled by default)


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.


Emit information on compiler options and usage


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)


Set compliance level to 1.3 This implies -source 1.3 and -target 1.1.


Set compliance level to 1.4 (default) This implies -source 1.4 and -target 1.2.


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.


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'):

    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.


Same as -warn:deprecation


Emit no errors for unresolved imports


Keep compiling after error, dumping class files with problem methods


debug attributes level, that may take three forms:

    -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.,


Preserve all local variables during code generation (to facilitate debugging).


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]'.


Emit messages about accessed/processed compilation units


Emit messages about weaving

-log file

Specify a log file for compiler messages.


Show progress (requires -log mode).


Display speed information.


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).


Causes compiler to terminate before weaving


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.


(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.


(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.


(Experimental) Normally it is an error to declare aspects Serializable. This option removes that restriction.


(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.


AspectJ is a compatible extension to the Java programming language. The AspectJ compiler adheres to the The Java Language Specfication, Second Edition and to the 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 AspectJ Version Compatibility.


Example 2.1. A simple example

Compile two files:

        ajc HelloWorld.java Trace.java

Example 2.2. An example using -argfile/@

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:


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

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.

Example 2.3. An example using -inpath and -aspectpath

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:


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:

    cd examples 
    export ajrt=../lib/aspectjrt.jar 
    export CLASSPATH="$ajrt" 
    export PATH="../bin:$PATH" 

Build a read-only tracing library:

    ajc -argfile tracing/tracelib.lst -outjar tracelib.jar 

Build the application with tracing in one step:

    ajc -aspectpath tracelib.jar -argfile tracing/notrace.lst -outjar tracedapp.jar 

Run the application with tracing:

    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):

        mkdir classes 
        javac -d classes tracing/*.java 
        jar cfM app.jar -C classes . 
  • (b) Build the application with tracing:

        ajc -inpath app.jar -aspectpath tracelib.jar -outjar tracedapp.jar 

Run the application with tracing (same as above):

    java -classpath "$ajrt;tracedapp.jar;tracelib.jar" tracing.ExampleMain 

Run the application without tracing:

    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

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:

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

  at Main.new$constructor_call37(Main.java;SynchAspect.java[1k]:1030)

where instead of the usual


format, you see

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.