public void exposeJavaObject() V8Object javaObject = new V8Object(runtime);// Add primitive properties javaObject.add("name", "MyJavaObject"); javaObject.add("version", 1.0); // Add function that Java implements javaObject.registerJavaMethod((receiver, parameters) -> String input = parameters.getString(0); return "Processed by Java: " + input.toUpperCase(); , "process"); // Register the object globally runtime.add("javaApi", javaObject); // Call from JavaScript String js = """ var result = javaApi.process('hello world'); print(result); """; runtime.executeVoidScript(js); javaObject.close();
V8 isolates are not thread-safe. Never share a V8 runtime across threads. Instead, use a pool of runtimes (one per thread) or serialize access via synchronized. Each runtime has its own native heap. Java Addon V8
You cannot simply drop v8.dll into a JVM. You need a JNI (Java Native Interface) bridge. Here are the major players.
Technically, this solution usually refers to libraries like J2V8. It is a set of Java Native Interface (JNI) bindings that allow a Java application to instantiate and interact with a real, native V8 runtime. V8 isolates are not thread-safe
Unlike Nashorn, which reimplemented JavaScript on the JVM, J2V8 wraps the actual C++ engine used by Chrome. This means you get:
Before diving into V8, we must acknowledge the elephant in the room: Java has supported scripting since Java 6 via the ScriptEngine API (javax.script). The core issue
The core issue? Nashorn and Rhino are interpreters compiling to JVM bytecode. They don't have the JIT (Just-In-Time) compiler magic of a true browser engine.
The V8 Advantage: Google’s V8 (Chrome, Node.js, Deno) compiles JavaScript directly to native machine code using TurboFan. By embedding V8, you get:
V8 is the engine behind Google Chrome and Node.js. It is aggressively optimized for speed. For computationally heavy tasks in JavaScript, V8 significantly outperforms older Java-based script engines like Nashorn or Rhino.