convert list of strings to list of java type objects in clojure

Question

I am using mongo java driver along with clojure for mongo connection, to establish connection in java I am using following code snippet

import com.mongodb.MongoClient;
import com.mongodb.MongoClientURI;
import com.mongodb.ServerAddress;

MongoClientURI uri = new MongoClientURI("mongodb://xxx:***@url:27017/test?readPreference=primary");
List<String> hosts = uri.getHosts();
List<ServerAddress> serverList = new LinkedList<>();

for(String host:hosts) {
    serverList.add(new ServerAddress(host)); //updated
}

I want to get this same functionality in clojure so I tried this

(def uri (MongoClientURI. uri))
(def hosts (.getHosts uri))

Now I have List of hosts which are String, how do I convert them to list of type ServerAddress ?

Sean Corfield · Accepted Answer · 2021-10-16 02:01:55Z

2

What's perhaps a little hard to spot in the Java code is that because serverList is a List<ServerAddress>, when you add String objects to that, they are implicitly converted to ServerAddress objects via the latter's constructor.

Something like the following should get you what you want:

(def host (map #(ServerAddress. %) (.getHosts uri)))

Note that you'll have a Clojure sequence at that point -- if you are passing it into Java methods, you may need to type hint it or even pour it into a (mutable) Java List.

answered Oct 16, 2021 at 2:01

Sean Corfield

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3 Comments

amalloy Over a year ago

No, the Java code is just wrong. It does not implicitly do any conversion, it just fails to compile.

Sean Corfield Over a year ago

There wasn't enough information in the OP's post for me to easily try out the Java code (what dependencies? what versions?) and the OP accepted my answer so... shrug

amalloy Over a year ago

Sure, your answer is totally right, they just need a specific way to convert a String to a Foo. It's just that Java never does any implicit conversions except for upcasts, and ServerAddress is clearly not a supertype of String, so we can easily tell that the Java code also doesn't compile.

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