Question

Are Java static variables shared across instances of the same web application?

class MyClass
{
    private static SomeClass myStaticObject = new SomeClass();
}

If a web application uses MyClass and multiple instances of that application is run on a web server, is myStaticObject initialized multiple times?

Answer 1

Typically, yes. Most containers will provide separate classloaders for each web application. This will result in the class being loaded multiple times when used by several applications, and thus resulting in multiple instances of the static variable.

Stating the Java Language Specification for reference:

At run time, several reference types
with the same binary name may be
loaded simultaneously by different
class loaders. These types may or may
not represent the same type
declaration. Even if two such types do
represent the same type declaration,
they are considered distinct.

By inference, multiple instances of static variables will exist, unless the classes are loaded only once by a parent class loader, and never loaded elsewhere by any other class loader.