Mule 1.x

Mule 1.x is currently developed and thoroughly tested against Java SE 1.4.2.

A conscious decision has been made to avoid any use of JDK 5-dependent functionality (generics, annotations, autoboxing, etc.) in the code base so as to support the "lowest common denominator" of our corporate users. In the few cases where Mule uses a 3rd party library which makes use of JDK 5 functionality, that library is retrotranslated to be runnable in JDK 1.4.2

Having said that, Mule will generally run without issues in JDK 5 since the JRE itself is backwards-compatible.

Although we certainly welcome issues to be filed against running Mule in JDK 5 or even JDK 6, they will be of lower priority if they are not reproducible in JDK 1.4.2

Mule 2.x

As of Mule 2.0.0-RC2 we switched to building Mule primarily using JDK 5. This means that Mule 2.0 will not run on JDK 1.4 out of the box but you're still able to compile the source yourself.

While we maintain compatability with JDK 1.4 for Mule's core and most of its transports, newer transports and modules will use language features and API only available in JDK 5 and above.

Have a look at [the build instructions ] for details.