Proxyで遊んだ。 出力 3.0 ab

main_java_demo_Main.java

package demo;

import net.orekyuu.JavaScriptBinder;

import javax.script.ScriptException;

public class Main {
    public static void main(String[] args) throws ScriptException {
        TestJs testJs = JavaScriptBinder.create(TestJs.class);

        double sumInt = testJs.sum(1, 2);
        System.out.println(sumInt);
        
        String sumStr = testJs.sum("a", "b");
        System.out.println(sumStr);
    }
}

main_java_demo_TestJs.java

package demo;

import net.orekyuu.annotation.Function;
import net.orekyuu.annotation.ScriptFile;

@ScriptFile("/test.js") // resources/test.jsを使用する
public interface TestJs {

    @Function("sum") //アノテーションで指定したtest.jsにある関数を呼び出す
    String sum(String a, String b);

    //アノテーションがなければメソッド名と同じ関数を呼び出し
    double sum(int a, int b);

    @Function("hello")
    String hello();

    @Function("append")
    String append();
}

main_java_net_orekyuu_annotation_Function.java

package net.orekyuu.annotation;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface Function {
    /**
     * @return 呼び出す関数名
     */
    String value();
}

main_java_net_orekyuu_annotation_ScriptFile.java

package net.orekyuu.annotation;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
public @interface ScriptFile {
    /**
     * @return ロードするスクリプトファイル
     */
    String value();
}

main_java_net_orekyuu_JavaScriptBinder.java

package net.orekyuu;

import net.orekyuu.annotation.ScriptFile;
import net.orekyuu.script.ScriptRunner;

import javax.script.*;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.lang.reflect.Proxy;
import java.util.Objects;

public class JavaScriptBinder {

    private JavaScriptBinder() {
        throw new UnsupportedOperationException();
    }

    public static <T> T create(Class<T> t, InputStream stream) throws ScriptException {
        Objects.requireNonNull(stream, "inputStream is null");

        ScriptEngineManager manager = new ScriptEngineManager();
        ScriptEngine js = manager.getEngineByName("js");
        if (js instanceof Compilable) {
            CompiledScript compile = ((Compilable) js).compile(new InputStreamReader(stream));
            compile.eval();
            js = compile.getEngine();
        } else {
            js.eval(new InputStreamReader(stream));
        }
        return create(t, js);
    }

    public static <T> T create(Class<T> t) throws ScriptException {
        ScriptFile annotation = t.getAnnotation(ScriptFile.class);
        if (annotation == null) {
            throw new IllegalArgumentException("ScriptFileアノテーションが見つかりません");
        }
        String value = annotation.value();
        if (value == null) {
            throw new IllegalArgumentException("ファイルを指定してください");
        }
        return create(t, t.getResourceAsStream(value));
    }

    @SuppressWarnings("unchecked")
    private static <T> T create(Class<T> t, ScriptEngine engine) {
        return (T) Proxy.newProxyInstance(t.getClassLoader(), new Class[]{t}, new ScriptRunner(engine));
    }
}

main_java_net_orekyuu_script_ScriptRunner.java

package net.orekyuu.script;

import net.orekyuu.annotation.Function;

import javax.script.*;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;

public class ScriptRunner implements InvocationHandler {

    private ScriptEngine engine;
    public ScriptRunner(ScriptEngine engine) {
        this.engine = engine;
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        Function annotation = method.getDeclaredAnnotation(Function.class);
        String functionName = method.getName();
        if (annotation != null) {
            functionName = annotation.value();
        }

        if (engine instanceof Invocable) {
            return ((Invocable) engine).invokeFunction(functionName, args);
        }
        return null;
    }
}

main_resources_test.js

/**
 * Created by orekyuu on 2016/04/09.
 */
function sum(a, b) {
    return a + b;
}

function hello() {
    return "hello";
}

function append(str) {
    return str + 'a';
}