JVM Usage

site.lempert:user-agent is the plain-JVM build of kmp-user-agent, published to Maven Central straight from the library's own Kotlin/JVM target -- the same detection/generation logic used by every other platform.

Install

Add the dependency to your module's build.gradle.kts (Maven Central is already in most projects' default repositories):

dependencies {
    implementation("site.lempert:user-agent:0.2.0")
}

The 0.2.0 above is a hand-pinned version, not something Gradle resolves for you -- bump it whenever you upgrade to a newer release, checking the Maven Central listing for the latest published version.

The bare site.lempert:user-agent coordinate above resolves correctly for any Gradle consumer (Gradle understands the Gradle Module Metadata that picks the right per-target artifact for you). A plain Maven (pom.xml) consumer -- common for Spring-based projects -- doesn't understand that metadata and needs the JVM target's own published artifact id instead:

<dependency>
    <groupId>site.lempert</groupId>
    <artifactId>user-agent-jvm</artifactId>
    <version>0.2.0</version>
</dependency>

The library's JVM target compiles against JVM_11 bytecode, so your project needs a Java 11+ runtime to use it. On an older runtime, loading it fails with java.lang.UnsupportedClassVersionError naming a class file version higher than your JVM supports (55 corresponds to Java 11) -- the fix is to upgrade the runtime, not the dependency.

Parse

Kotlin's vararg support means you call UserAgentParser/UserAgentGenerator directly with the packs you want -- no .get() or array-wrapping, unlike the JS bindings.

Unlike Android or a browser, a plain JVM process has no OS-provided "this device's User-Agent" to read -- System.getProperty("http.agent") returned null in a fresh run against this library's own JDK (Azul JDK 21), and is unset by default on most JVM distributions unless something (your own code, or a prior HttpURLConnection call) has already set it. If you're writing a JVM-based HTTP server (Ktor, Spring, Javalin, a plain servlet, ...), the User-Agent string you'll actually want to parse is the one on each incoming request -- e.g. call.request.headers["User-Agent"] in Ktor, or request.getHeader("User-Agent") in a servlet-based framework:

import site.lempert.useragent.UserAgentAllTypes
import site.lempert.useragent.UserAgentParser

// Substitute a real incoming request's header value in a server context.
val userAgent =
    "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) " +
        "Chrome/128.0.6613.120 Safari/537.36"

val info = UserAgentParser(UserAgentAllTypes)(userAgent)

println(info.browser) // Component(name=Chrome, version=128.0)
println(info.engine)
println(info.os)
println(info.device)
println(info.bot)
println(info.aiAgent)

The function returned by UserAgentParser(...) (and likewise UserAgentGenerator(...)) is cheap to construct, but it's still worth building once -- e.g. as a top-level val, or a singleton bean/property in whatever DI or application-lifecycle mechanism your server framework uses -- and reusing it across requests rather than rebuilding it per request. See Core Concepts' "Cost of calling the factories" for details. The returned function holds no mutable state of its own (only reads the library's precompiled, immutable rule tables), so it's safe to call concurrently from multiple request-handling threads without extra synchronization.

Generate

import site.lempert.useragent.Component
import site.lempert.useragent.UserAgentAllTypes
import site.lempert.useragent.UserAgentGenerator
import site.lempert.useragent.UserAgentInfo

val userAgentString = UserAgentGenerator(UserAgentAllTypes)(
    UserAgentInfo(
        browser = Component("Chrome", "128.0"),
        engine = Component("Blink", "128.0"),
        os = Component("Windows", "10"),
        device = null,
    ),
)

println(userAgentString)
// Mozilla/5.0 (Windows 10) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/128.0 Safari/537.36

Next steps

For the platform-agnostic UserAgentInfo model and the built-in type packs behind UserAgentAllTypes used above, see Core Concepts -- and the Type Reference for every name each pack recognizes.