Question

Possible Duplicate:
Why does require in the ns form behave different from the require function

I am dabbling in clojure and have run into a problem with importing. From the REPL

clojure.core=>(import '(java.io FileReader))
clojure.core=>(import 'java.io.FileReader)
clojure.core=>(import java.io FileReader)

each work perfectly, but from file only the following works:

(ns project.core
  (import java.io.FileReader))

These each fail

(ns project.core
  (import 'java.io.FileReader)) 

(ns project.core
  (import '(java.io FileReader))

with the following errors:

ClassNotFoundException quote.java.io.FileReader  java.net.URLClassLoader$1.run (URLClassLoader.java:366)

ClassNotFoundException quote.(java.io FileReader)  java.net.URLClassLoader$1.run (URLClassLoader.java:366)

respectively.

In reality I need to import more than just java.io.FileReader, but this is a distilled version of the problem.

Any ideas what might be going wrong? I can’t seem to find the problem anywhere else

Answer 1

The solution is:

(ns project.core
  (:import [java.io FileReader BufferedReader FooBar]))

As to why this is necessary, the ns macro accepts several directives, including :import. Due to the way the macro is implemented, it expects arguments to the import directive to be in a list-like form – hence, [java.io ...]. Incidentally, a list such as (java.io ...) would work just as well.

For a complete rundown of how to use ns, please take a look at the ClojureDocs page: http://clojuredocs.org/clojure_core/clojure.core/ns. ClojureDocs is an invaluable resource for these sorts of problems.