使用JavaScript调用Java方法是否可行？

Question

Java有一个脚本管理器，可以让Java调用JavaScript，例如：

import javax.script.*;
public class ExecuteScript {
 public static void main(String[] args) throws Exception {
 // create a script engine manager
 ScriptEngineManager factory = new ScriptEngineManager();
 // create a JavaScript engine
 ScriptEngine engine = factory.getEngineByName("JavaScript");
 // evaluate JavaScript code from String
 engine.eval("print('Welocme to java world')");
 }

 public static void sayHi(){
   System.out.println("hihi");
 }
}

我的问题是，如果我有一个 sayHi() 函数，我能否通过脚本引擎使用 JavaScript 调用 Java 函数？谢谢。

- DNB5brims

Answer 1

以下��码片段：

package org.test.script;
import javax.script.*;

public class ExecuteScript {
    public static void main(String[] args) throws Exception {
        // create a script engine manager
        ScriptEngineManager factory = new ScriptEngineManager();
        // create a JavaScript engine
        ScriptEngine engine = factory.getEngineByName("JavaScript");
        // evaluate JavaScript code from String
        engine.eval("" +
            "importPackage(org.test.script);\n" +
            "print('Welocme to java world\\n');\n" +
            "ExecuteScript.sayHi();");
    }

    public static void sayHi() {
        System.out.println("hihi");
    }
}

输出

Welocme to java world
hihi

- szhem

---

引擎.put(.. 似乎是多余的。同意。答案已被修改。 - szhem

提醒大家一下，importPackage 在 Java 8 中需要在前面加上一行代码才能正常工作：load("nashorn:mozilla_compat.js"); - jfdoming

Answer 2

快速从JavaDocs中拼凑而成。

import javax.script.*;

public class ExecuteScript {

    public static void main(String[] args) throws Exception {
        // create a Java object
        ExecuteScript es = new ExecuteScript();

        // create a script engine manager
        ScriptEngineManager factory = new ScriptEngineManager();
        // create a JavaScript engine
        ScriptEngine engine = factory.getEngineByName("JavaScript");
        // evaluate JavaScript code from String
        engine.eval("println('Welcome to Java world')");

        // add the Java object into the engine.
        engine.put("es",es);

        ScriptEngineFactory sef = engine.getFactory();
        String s = sef.getMethodCallSyntax("es", "sayHi", new String[0]);
        // show the correct way to call the Java method
        System.out.println(s);
        engine.eval(s);
    }

    public static void sayHi(){
        System.out.println("hihi");
    }
}

输出

Welcome to Java world
es.sayHi()
hihi
Press any key to continue . . .

- Andrew Thompson

Answer 3

我不确定您使用的脚本管理器是什么，但是使用Rhino，您可以做出以下操作：

var date = new java.util.Date();
print(date);

所以根据你的例子，你应该能够像静态方法一样调用它：

ExecuteScript.sayHi();

- Daff

Answer 4

这是一个使用Java 8 Nashorn的微小示例，它作为独立脚本而不需要任何包：

import javax.script.*;
import java.util.LinkedList;

public class RunJavaFromJs {
  public static void main(String[] args) throws Exception {
    LinkedList<Integer> jList = new LinkedList<>();
    jList.add((Integer)42);

    ScriptEngine engine = 
      (new ScriptEngineManager())
      .getEngineByName("nashorn");
    Bindings bindings = engine.getBindings(ScriptContext.ENGINE_SCOPE);
    bindings.put("jList", jList);
    engine.eval("" + 
      "load('nashorn:mozilla_compat.js');\n" +
      "// call static method\n" + 
      "var i = Packages.RunJavaFromJs.helloWorld(42);\n" + 
      "// perform side effect\n" + 
      "print('Result was: ' + i + '(printed from JS)');\n" + 
      "// call method on `jList` instance passed in bindings \n" +
      "jList.add(12345);\n" +
      "print(jList.toString());"
    );
  }
  public static int helloWorld(int x) {
    System.out.println("Hello, world! (printed from Java in static method)");
    return x * x;
  }
}

如果您只是将其保存在RunJavaFromJs.java中，然后使用以下方式进行编译和运行

javac RunJavaFromJs.java && java RunJavaFromJs

然后你会得到：

Hello, world! (printed from Java in static method)
Result was: 1764(printed from JS)
[42, 12345]

- Andrey Tyukin