I have JSON data in the following format:
{"load":{"meta": 12345}}
{"load":{"meta": 54321}}
...
When I attempt to load the data with Cheshire I get back only the first line of data translated into edn:
(def read-json-data (parse-string (slurp "data/json_data") true))
=> {:load {:meta 12345}}
If anybody has come accross this and can help show how to read the whole file would be much appreciated.
This is correct behaviour - cheshire/parse-string parses the first JSON object it can find.
If you want the whole file to be parsed as a single JSON object you should make an array:
[{"load": {"meta": 12345}},
{"load": {"meta": 54321}},
...]
Alternatively, if you want to parse each line separately you can do something like this:
(map #(cheshire/parse-string % true)
(line-seq (clojure.java.io/reader "data/json_data")))
(Also, notice the colons in the JSON.)
Related
I have a following EDN file
:abc #request/builder/abc {
"def" #request/builder/def {
"someVector" ["sample1", "sample2"]
}
}
I have defined custom tag reader in Clojure, which internally calls java code
(defn custom-readers []
{
#request/builder/def defBuilder
#request/builder/abc abcBuilder
}
)
(defn defBuilder [params]
(.defBuilder (someJavaUtilityClass.) params)
)
(defn abcBuilder [params]
(.abcBuilder (someJavaUtilityClass.) params)
)
When I read EDN using edn/read-string, defBuilder executes first and its value gets passed to abcBuilder.
I want to reverse the order of execution without modifying EDN. I want to modify abcBuilder code such that if java call in abcBuilder returns some value then only execute defBuilder. How can I achieve this.
I tried by modifying code as below
(defn defBuilder [params]
'(.defBuilder (someJavaUtilityClass.) params)
)
(defn abcBuilder [params]
if((.abcBuilder (someJavaUtilityClass.) params)
(eval (get params "def"))
)
)
But this throws error like it "Unable to resolve someJavaUtilityClass and params". Is there a better way to solve this?
I'm afraid that's not possible. That isn't how EDN's tagged literals work. The tag handler is called after reading the form, which includes calling the tag handlers for any tagged literals in the form. In other words, the tag handlers are called inside-out.
If this weren't the case, then what a tag means will depend on where that tagged literal is situated, which is needlessly context dependent.
Check out: https://github.com/edn-format/edn#tagged-elements
Here's the relevant part:
Upon encountering a tag, the reader will first read the next element (which may itself be or comprise other tagged elements), then pass the result to the corresponding handler for further interpretation, and the result of the handler will be the data value yielded by the tag + tagged element, i.e. reading a tag and tagged element yields one value.
Also check out: https://clojure.org/reference/reader#tagged_literals
This is about the Clojure reader. And again, here is the relevant bit:
by invoking the Var #'my.project.foo/bar on the vector [1 2 3]. The data reader function is invoked on the form AFTER it has been read as a normal Clojure data structure by the reader.
Also, symbols can only contain one /, delimiting the namespace and the name. Check out: https://github.com/edn-format/edn#symbols
I'm trying to create a simple input loop in Clojure. The idea is to read in a line of text like so:
> look
You see nothing, as this game hasn't actually been written.
The method I'm using to attempt this is below:
(defn get-input []
(print "> ")
(string/trim-newline (read-line)))
However, the input loop instead looks like this:
look
> You see nothing, as this game hasn't actually been written.
How would one go about getting the angle quote to print before user input rather than after it?
This is a buffering issue. "> " is only a small amount of text, and doesn't contain a newline (and one isn't automatically added since you aren't using println), so it gets stuck in the outstream buffer. You just need to do a flush after printing.
When I need a print/flush combo like this in multiple places, I usually create a little helper function to neaten things up:
(defn print-fl [& messages]
(apply print messages) ; Pass the strings to print to be printed
(flush)) ; Then flush the buffer manually so small strings don't get stuck
(defn get-input []
(print-fl "> ")
(string/trim-newline (read-line)))
(get-input)
> look
"look"
tl;dr
How can I derive a keyword from a number in ClojureScript:
(keyword 22)
;;=> :22 but in fact returns nil.
Background
In my ClojureScript/Hoplon application I make HTTP requests via cljs-http. Parts of the response I receive look like this:
{:companies
{:22 {:description ... } ; A company.
:64 {:description ... }
... }
{:offers
[{:description ... } ; An offer.
{:description ... }
... ]
Each offer within the vector behind :offers has a :companyId which represents a key in :companies. As soon as I receive the response, I reset! a cell (similar to an atom) query.
Now, I'd like to iterate over each offer and call a function offer-tpl that creates the corresponding HTML. In order to do so, offer-tpl needs the offer itself as well as the related company:
(for [offer (:offers #query)]
(offer-tpl offer (get-in #query [:companies (keyword (:companyId offer))]))))))
Despite the fact that this surely can be done more elegant (suggestions very appreciated), the get-in doesn't work. (:companyId offer) returns a number (e.g. 22) but (keyword (:companyId offer)) returns nil. Calling (keyword (str (:companyId offer))) does the trick, but aren't there any other ways to do this?
(keyword "22") or (keyword (str 22)) returns :22
The reason you are getting :22 is likely because of the keywordize-keys option of a JSON translation. For example:
cljs-http defaults to keywordize-keys for jsonp:
https://github.com/r0man/cljs-http/blob/1fb899d3f9c5728521786432b5f6c36d1d7a1452/src/cljs_http/core.cljs#L115
But you can (and should) in this case pass in a flag to disable keywordization.
Not all keys in JSON are appropriate for Clojure keywordization. For example spaces in a JSON key are valid, but not in Clojure.
Please be aware that numeric keywords are probably incorrect.
https://clojuredocs.org/clojure.core/keyword#example-542692cec026201cdc326d70
It seems like that caveat has been removed from the current Clojure website, so perhaps that means something but I'm not sure what.
http://clojure.org/reference/reader Currently states that
Keywords - Keywords are like symbols, except: They can and must begin
with a colon, e.g. :fred. They cannot contain '.' or name classes.
Like symbols, they can contain a namespace, :person/name A keyword
that begins with two colons is resolved in the current namespace: In
the user namespace, ::rect is read as :user/rect
and that
Symbols begin with a non-numeric character and can contain
alphanumeric.
This definition of a keyword excludes :22 and :with spaces
The keyword function returns a result for invalid input, but this is not an endorsement, it is simply because checking for incorrect input would be a performance overhead in a core part of Clojure.
In short, not all JSON keys translate to keywords, so you should avoid keywordize-keys unless you know the keyspace and/or doing so provides some conveniences.
I know there are a lot of questions out there with this headline, but I can't glean my answer from them, so here goes.
I'm an experienced programmer, but fairly new to Clojure. I'm trying to parse a RTF file by converting it to a HTML file then calling the html parser.
The converter I'm using (unrtf) always prints to stdout, so I need to capture the output and write the file myself.
(defn parse-rtf
"Use unrtf to parse a rtf file"
[#^java.io.InputStream istream charset]
(let [rtffile (File/createTempFile "parse" ".rtf" (File. "/vault/tmp/"))
htmlfile (File/createTempFile "parse" ".ohtml" (File. "/vault/tmp/"))
command (str "/usr/bin/unrtf "
(.getPath rtffile)
)
]
(try
(with-open [rtfout (FileOutputStream. rtffile)]
(IOUtils/copy istream rtfout))
(let [ proc (.exec (Runtime/getRuntime) command)
ostream (.getInputStream proc)
result (.waitFor proc)]
(if (> result 0)
(
(println "unrtf failed" command result)
; throwing an exception causes a parse failure to be logged
(throw (Exception. (str "RTF to HTML conversion failed")))
)
(
(with-open [htmlout (FileOutputStream. htmlfile)]
(IOUtils/copy ostream htmlout))
; since we now have html, run it through the html parser
(parse-html (FileInputStream. htmlfile) charset)
)
)
)
(finally
(.delete rtffile)
(.delete htmlfile)
)
)))
The exception points to the line with
(IOUtils/copy ostream htmlout))
which really confuses me, since I used that form earlier (just after the try:) and it seems to be OK there. I can't see the difference.
Thanks for any help you can give.
As others have correctly pointed out, you can't just add extra parentheses for code organization to group forms together. Parentheses in a Clojure file are tokens that delimit a list in the corresponding code; lists are evaluated as s-expressions - that is, the first form is evaluated and the result is invoked as a function (unless it names a special form such as if or let).
In this case you have the following:
(
(with-open [htmlout (FileOutputStream. htmlfile)]
(IOUtils/copy ostream htmlout))
; since we now have html, run it through the html parser
(parse-html (FileInputStream. htmlfile) charset)
)
The IOUtils/copy function has an integer return value (the number of bytes copied). This value is then returned when the surrounding with-open macro is evaluated. Since the with-open form is the first in a list, Clojure will then try to invoke the integer return value from IOUtils/copy as a function, resulting in the exception that you see.
To evaluate multiple forms for side-effects without invoking the result from the first one, wrap them in a do form; this is a special form that evaluates each expression and returns the result of the final expression, discarding the result from all others. Many core macros and special forms such as let, when, and with-open (among many others) accept multiple expressions and evaluate them in an implicit do.
I didnt try to run your code, just had a look at it, and after the if (> result 0) you have ((println ...)(throw ...)) without a do. Having an extra parens causes the returned value from the inner parens to be treated as a function and get executed.
try to include it, like this (do (println ...) (throw ...))
I am trying use Clojure and Enlive to extract content of p html tag under condition that one of attributes has values I designated. Something like this
<p itemprop="description"> Some content I want to extract </p>
So I want to get Some content I want to extract if itemprop="description".
I am very new to Clojure so help would be great.
To get the text content of any node with the specific attribute, the selector would look something like the following:
(require '[net.cgrand.enlive-html :as e])
[(e/attr= :itemprop "description") e/text-node]
If the contents contain a mix of text and tags, and you wanted to keep both of them, you should use net.cgrand.enlive-html/any-node instead of net.cgrand.enlive-html/text-node.
You can test it with the following:
(require '[net.cgrand.enlive-html :as e])
(def data "<p itemprop=\"description\"> Some content I want to extract </p>")
(e/select-nodes* (e/html-snippet data)
[(e/attr= :itemprop "description") e/text-node])
;=> (" Some content I want to extract ")