load jar in repl

I have been studying clojure for a few days, but I need to write test code in files before using lein run to test it, which is definitely productiveless.
One way to load a jar in repl

(require '[clojure.data.json :as json])

New version of clojure deprecated the use to make it more consistant to import a package.
Since loading all functions into current namespace will result into a bunch of confliction problems.
So it is recommended to use require.

By using require with :refer and :all options, you could achieve the same work in a more flexible and consistant way.

;Also write some tips for loading `.clj` files manully.
;; file located at src/address_book/core.clj
(load "address_book/core") ;just need class name with slash
(load-file "src/address_book/core.clj");need canonical name and full clj extention
;remove namespace from current one
(remove-ns 'my-new-namespace)