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JooFlux: a Java agent for dynamic aspect-oriented middlewares

JooFlux a JVM agent that allows both the dynamic replacement of method implementations and the application of aspect advices. Compared to existing approaches, JooFlux takes a novel route by taking advantage of the new invokedynamic instruction added in Java SE 7. The runtime overhead of JooFlux is marginal for method invocations, and fairly limited when aspects are being injected. In any case, JooFlux shows interesting performance compared to related approaches such as AOP tools or dynamic languages that rely on dynamic dispatch. More interestingly, JooFlux does not involve reloading whole classes on either method replacement or advice injection, which keeps a large range of just-in-time compilation optimizations valid.

JooFlux is being developed as part of a larger academic research group that focuses on the design and implementation of middlewares for dynamic environments.

Current status

The current iteration of the source code is only a proof-of-concept of leveraging invokedynamic for aspect-oriented programming and live code patching. It is not production-ready, and further developments need to be made to turn JooFlux into a usable product.

While it is our intention to turn it into something easier to use, we opted to release the initial developments source code to support the reproducibility and dissemination of our research results.

Please pardon the raw state of JooFlux, but the system we are in pushes us to publish research papers first before focusing on the technology transfer of prototypes :-)

Funding the JooFlux development

Our very own ability to progress on dynamic code replacement and aspect injection with JooFlux depends on funding.

We have no external funding for the JooFlux project at the moment, so if you feel like sustaining our research on this project, feel-free to contact us!


  • Julien Ponge and Frédéric Le Mouël. JooFlux : modification de code à chaud et injection d’aspects directement dans une JVM 7. In Proceedings of Conférence d’informatique en Parallélisme, Architecture et Système (ComPAS) - Conférence Française en Systèmes d’Exploitation (CFSE). Grenoble, January 2013. HAL INRIA entry.
  • Julien Ponge and Frédéric Le Mouël. JooFlux: Hijacking Java 7 InvokeDynamic To Support Live Code Modifications. 2012. Research report on arXiv
  • We demonstrated initial developments of JooFlux at the Devoxx France 2012 conference.


The initial work was conducted at INSA-Lyon in the CITI laboratory.

JooFlux is made available under the terms of the Mozilla Public License, v 2.0.

Header notice

Any source file must carry the following header:


Copyright (c) 2012 Institut National des Sciences Appliquées de Lyon (INSA-Lyon)
Copyright (c) 2012 Julien Ponge, INSA-Lyon
Copyright (c) 2012 Frédéric Le Mouël, INSA-Lyon

This Source Code Form is subject to the terms of the Mozilla Public
License, v. 2.0. If a copy of the MPL was not distributed with this
file, You can obtain one at

Third-party dependencies

JooFlux embeds the following libraries:


You may contact us using our INSA-Lyon email addresses (see the AUTHORS file).

If you would like to report issues, please do so with the issue tracker on GitHub.


We welcome contributions, see CONTRIBUTING.markdown for instructions.

Building and dependencies

JooFlux requires:

Building JooFlux is straightforward using Gradle :

gradle clean build

We also have a bunch of custom tasks for testing purposes, e.g.:

gradle test_fibonacci
gradle test_counterloop

To display the entire list, run gradle tasks.

Running JooFlux

JooFlux needs to be attached to a JVM like any other regular agent. JooFlux transforms bytecode in a way that sometimes breaks the bytecode verifier expectations. Nevertheless, the transformed bytecode remains correct at runtime, so it is best to run JooFlux while disabling the bytecode verifier (-noverify flag). Other JVM agents sometimes ask you to do the same, too.

Here is how you could run a Java application with JooFlux wired into the JVM:

java -noverify -javaagent:jooflux-{version}.jar -classpath lib1.jar:lib2.jar:lib3.jar some.Main

JooFlux uses Tinylog as its logging framework. You may tweak the configuration by passing flags as documented. For instance, -Dtinylog.level=ERROR filters most logs bar errors. You may also conveniently redirect the output to files.

Interactions with JooFlux currently happen through a JMX agent: fr.insalyon.telecom.jooflux.internal.jmx.JooFluxManagement. It offers methods to get metrics, update methods and apply aspects. While the interface is a bit raw at the moment, see the demoing/ folder for examples of valid parameters to perform demonstrations of JooFlux.

Backlog towards turning JooFlux into a product

Here are the items that need to be addressed.

Improving the code base

The source code went through scattered burst of interrupted developments. We had to show the feasibility of our approach first and foremost while having few allocatable time, hence we did not cover all corner cases and sometimes had to favor working code over cleaner code.

This is a general effort that any software project faces.

Corner cases

The bytecode transformations made by JooFlux are not trivial. We are well aware that it breaks some bytecode sequences, resulting in invalid stack frames (a fancy expression for "crash").

We would greatly appreciate if you could isolate pathological corner cases so that we can address those in subsequent releases, and eventually turn JooFlux into a tool usable on a larger set of JVM applications.

Of course if you can both isolate corner cases and offer a fix, feel-free to do so!

Thread safety

Our implementation is weak with respect to thread safety. More tests and fixes need to be made in multi-threading settings.

Memory leaks

We keep track of call sites in a registry. However, we keep references to the call sites forever, hence call sites cannot be garbage collected. This is problematic, and we need to turn to weak references and find the appropriate spot to occasionally remove expired entries from the registry.


JooFlux is currently manageable using JMX. This makes requesting operations such as patching a method tedious using tools such as jconsole.

Instead, we should design a (TCP?) protocol for external interactions with scripts / tools. Also, it should be possible to perform batches of operations (e.g., apply advice foo to all the classes implementing SomeInterface, update all methods of class Foo with those from Foo in foo-1.1.jar, etc).

Classpath injection

When one applies an advice or patches a method, the corresponding class needs to be visible from the JooFlux agent classpath. While this works fine for our demos, this is clearly not satisfying.

We need to be able to order the agent to resolve classes using dynamic classloaders.


Certain classes of applications may take advantage of JooFlux event notifications, for instance to react to a class being patched and perform various operations such as additional housekeeping.


JooFlux is a Java agent for dynamic aspect-oriented middlewares.







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