Estimated time: 10 minutes.
Let’s add JavaScript to the example project we created before.
Copy the project to have a clean state:
cp -R primes-web primes-js
cd primes-js
Edit the src/main/java/primes/web/PrimesController.java
file to look like the following.
package primes.web;
import io.micronaut.http.annotation.Controller;
import io.micronaut.http.annotation.*;
import java.io.*;
import java.util.*;
import java.util.stream.*;
import org.graalvm.polyglot.*;
@Controller("/primes")
public class PrimesController {
private final Engine sharedEngine = Engine.newBuilder().build();
private ThreadLocal<Value> isPrimes = ThreadLocal.withInitial(() -> {
Map<String, String> options = new HashMap<>();
options.put("js.commonjs-require", "true");
options.put("js.commonjs-require-cwd", new File(".").getAbsolutePath());
Context cx = Context.newBuilder("js")
.allowAllAccess(true)
.allowHostAccess(HostAccess.ALL)
.allowPolyglotAccess(PolyglotAccess.ALL)
.allowExperimentalOptions(true)
.options(options)
.engine(sharedEngine)
.build();
return cx.eval("js",
"(function isPrime(num) {\n" +
" for(var i = 2; i < num; i++)\n" +
" if(num % i === 0) return false;\n" +
" return num > 1;\n" +
"})"
);
});
private Random r = new Random(41);
@Get("/random/{upperbound}")
public List<Long> random(int upperbound) {
int to = 2 + r.nextInt(upperbound - 2);
int from = 1 + r.nextInt(to - 1);
return primeSequence(from, to);
}
@Get("/{from}/{to}")
public List<Long> primes(@PathVariable int from, @PathVariable int to) {
return primeSequence(from, to);
}
public boolean isPrime(long n) {
return isPrimes.get().execute(n).asBoolean();
}
public List<Long> primeSequence(long min, long max) {
return LongStream.range(min, max)
.filter(this::isPrime)
.boxed()
.collect(Collectors.toList());
}
}
This code defines a GraalVM Engine and a polyglot Context per thread in our Micronaut application.
Then we evaluate a snippet of JavaScript code, given as a String for simplicity, that contains the definition of the isPrime
function.
The Java method can consume it then as if it was a normal Java object. We could even convert it to a java.util.Function
function.
We have the project built normally with ./gradlew build
and can run it with the normally like this:
java -jar build/libs/primes-web-0.1-all.jar