[heartofgold]

Here is an example to massage/manipulate CSV data.

Stolen from the README page for a clojure CSV parsing library (https://github.com/clojure/data.csv)

    (defn read-column [reader column-index]
      (let [data (read-csv reader)]
        (map #(nth % column-index) data)))
    
    (defn sum-second-column [filename]
      (with-open [reader (io/reader filename)]    ; Read in the CSV file (streaming / lazily)
        (->> (read-column reader 1)               ; Convert to just the first column of data.
             (drop 1)                             ; Drop the first row (the CSV header)
             (map #(Double/parseDouble %))        ; convert each string in this column into double
             (reduce + 0))))                      ; sum the result

Because it's lazy, this code should work regardless of how large the CSV file.

[heartofgold]

Using the clj-http library in clojure to fetch from a REST webservice:

    (client/get "http://example.com/resources/3" {:accept :json :query-params {"q" "foo, bar"}})

With the response, you can examine response headers, the body, etc.

[heartofgold]

What about JDBC?

Here's a few examples stolen from the doc page for the next.jdbc library (https://github.com/seancorfield/next-jdbc):

    > clj
    Clojure 1.10.1
    user=> (require '[next.jdbc :as jdbc])
    nil
    user=> (def db {:dbtype "h2" :dbname "example"})
    #'user/db
    user=> (def ds (jdbc/get-datasource db))
    #'user/ds
    user=> (jdbc/execute! ds ["
    create table address (
      id int auto_increment primary key,
      name varchar(32),
      email varchar(255)
    )"])
    [#:next.jdbc{:update-count 0}]
    user=> (jdbc/execute! ds ["
    insert into address(name,email)
      values('John Smith','[e-mail]')"])
    [#:next.jdbc{:update-count 1}]
    user=> (jdbc/execute! ds ["select * from address"])
    [#:ADDRESS{:ID 1, :NAME "John Smith", :EMAIL "[e-mail]"}]

That is an example REPL session to setup the library, setup a datasource, create a table, insert a row into the table, and then select from the table. The "user=>" part is the REPL command prompt. Essentially it's one statement for each SQL query executed, and 1 or 2 statements to setup the JDBC datasource. This is tight.

You can see the return from the select contains clojure native data-structures. It returns a list of rows, where each row is a map of fieldName to fieldValue. You can now go to town and manipulate lists and maps to your hearts content, convert the payload to HTML or JSON or whatever you like.