Clojure Q&A - Recent questions tagged wrapper

Consider including a built-in wrapper around `java.net.http.HttpClient` in future versions of Clojure

Mon, 08 Jun 2026 01:37:14 +0000

Java 9 introduced java.net.http.HttpClient[1] with support for HTTP/1.1, HTTP/2 as well as WebSocket along with other features. It was later standardized in Java 11[2] and has become one of the top picks for Java programs. The latest version of the HTTP client shipped with Java 26 also added support for HTTP/3.[3]

It would be nice for future versions of Clojure that are based on Java 11+ to include a new namespace with wrapper functions around java.net.http.HttpClient to make it easier (without all the OOP ceremonies) to work with HTTP in Clojure programs out of the box without relying on any 3rd-party libraries.

Examples of prior art:

[1] https://openjdk.org/jeps/110
[2] https://openjdk.org/jeps/321
[3] https://openjdk.org/jeps/517

Immutable wrapper around Java arrays?

Mon, 28 Aug 2023 11:20:27 +0000

Are there any immutable wrapper around Java arrays in Clojure, similar to Scala's ArraySeq?

What are your thoughts on introducing such a wrapper to Clojure's core?

How to invoke native C-functions in Clojure via JNR-FFI?

Fri, 04 Dec 2020 13:57:56 +0000

Hi Everyone,

I want to call native functions in a C-Library from Clojure via JNR-FFI without having to write Java code.

(defproject mypkg
	:dependencies [[org.clojure/clojure "1.10.1"]
				   [com.github.jnr/jnr-ffi "2.2.0"]])

Based on the jnr-ffi examples here and here a Java wrapper might look like

package blahblah;

public class BlahNative {
	private static int[] intDummy;
	private static double[] doubleDummy;

	public BlahNative() {
	}

	public static native void native_a(char var0, char var1, int var2, int var3, int var4, double[] var7, int var8, int var9);

	public static native void native_b(char var0, char var1, int var2, int var3, int var4, double[] var7, int var8, int var9);

	static {
		lib = LibraryLoader
            .create(LibSodium.class)
            .search("/usr/local/lib")
            .search("/opt/local/lib")
            .search("/usr/lib")
            .search("/lib")
            .load(LIBRARY_NAME);
        initializeLibrary(lib);
    }
}

I presume my Clojure namespace should use the gen-class feature for implementing Java classes.

(ns mypkg.native
	(:import [jnr.ffi LibraryLoader])
	(:import [jnr.ffi.annotations IgnoreError])
	(:import [jnr.ffi.provider FFIProvider])
    (:gen-class))

Then,

How do I write a native method in Clojure? In other words, do I even need to specify the method type (as native) when using Clojure's Java interop features?
After loading the native library I do not know how to access the C-functions in the library. How do I do it?
To avoid reloading the library for every Clojure wrapper function of each C-functions, can I write a method like

(defn lib (. LibraryLoader load LIBRARY_NAME))

and then access the native functions in it?

I am neither a C nor a Java expert so any guidance will be much appreciated.

Thanks.