检测是否在servlet容器中运行或独立运行

Question

I have a simple problem: I want to configure an object differently based on whether the object is instantiated within a servlet container, or whether it is instantiated in a stand alone app.

The object is a database connection, and I care about setting query timeouts.

The first solution that I can come up with is:

if (insideServletContainer(this.getClass().getClassLoader()) { 
  /// do some servlet specific config
}
else {
 /// do some standalone config
}

The question is, of course, can I write a reliable method of telling whether the class was loaded within a servlet container. It feels like a hack at best.

The second option is to assume that the default case is a stand alone instantiation, set defaults based on stand-alone configuration, and override them within the servlet context.

So, to sum up my question is : Do you know of a good/reliable mechanism if the class was loaded from within a servlet container? If not, I will have to take the second route.

Nick

Answer 1

This seems like a really bad idea. Instead, why don't you allow the class to take parameters, then let the container or app configure it appropriately?

Answer 2

Setting aside whether or not this is a good idea, I'd suggest looking up java:comp/env, which is only going to be available in an EE server:

try {
  new InitialContext().lookup("java:comp/env");
  /// do some servlet specific config
} catch (NamingException ex) {
  /// do some standalone config
}

Answer 3

An alternate way to do this sort of thing is to have the configuration injected into this class by some sort of bootstrap loader.

In a standalone version, this would be done by the main() method (or something called from it).

In a webapp version, this would be done by a listener or filter invoked configured within the web.xml .

Dependency injection is useful here as it removes the need for your application to check these sorts of things; instead the application is given what it needs.

Answer 4

I would recommend Dependency Injection like @matt b.

As a second option, if it is only the simple case you described and you don't want to add or learn a DI framework to support this feature. You can accomplish the same thing as your current code by using a properties file to load different value based on the environment. You can simply use a different file for each environment and supply a VM arg to indicate which environment you are running.

db_prop.dev
db_prop.stalone
dp_prop.int
db_prop.prod

Then you can load by resource

"db_prop." + System.getProperty("runtime.env")