JAVA ScriptEngine 引擎

Java虚拟机能支持JavaScript、Scala、JRuby、Jython和Groovy等脚本语言.

Java虚拟机支持脚本的意义在于实现函数式编程, 即脚本中最重要的便是方法.

根据引擎名称,文件后缀,MIME或取脚本引擎, 并执行输出语句.

代码语言：javascript复制

@Test
public void hello() throws ScriptException {
  ScriptEngineManager manager = new ScriptEngineManager();
  ScriptEngine engine = manager.getEngineByName("JavaScript");
  //ScriptEngine engine = manager.getEngineByExtension("js");
  //ScriptEngine engine = manager.getEngineByMimeType("text/javascript");
  engine.eval("print('Hello World!');");
}

将参数传入脚本并执行

代码语言：javascript复制

@Test
public void testBinding() throws ScriptException {
  ScriptEngineManager manager = new ScriptEngineManager();
  ScriptEngine engine = manager.getEngineByName("JavaScript");
  Bindings bindings = new SimpleBindings();
  bindings.put("param", "playing games");
  engine.eval("print('I like '   param);", bindings);
File file = new File("test.txt");
engine.put("files", file);
engine.eval("print(files.getAbsolutePath());print(files.getName());");
}

通过脚本上下文修改输出重定向到文件并执行脚本

代码语言：javascript复制

@Test
public void scriptToFile() throws IOException, ScriptException {
  ScriptEngineManager manager = new ScriptEngineManager();
  ScriptEngine engine = manager.getEngineByName("JavaScript");
  ScriptContext context = engine.getContext();
  context.setWriter(new FileWriter("output.txt"));
  engine.eval("print('Hello World!');");
}

调用脚本中函数, 并传参执行. 一些脚本引擎允许使用者单独调用脚本中的某个方法, 支持此操作的脚本引擎可以通过实现javax.script.Invocable接口, JavaSE中的JavaScript引擎已实现了Invocable接口.

代码语言：javascript复制

@Test
public void invokeFunction() throws ScriptException, NoSuchMethodException {
  ScriptEngineManager manager = new ScriptEngineManager();
  ScriptEngine engine = manager.getEngineByName("JavaScript");
  String scriptText = "function greet(name) { print('Hello, '   name); } ";
  engine.eval(scriptText);
  Invocable invocable = (Invocable) engine;
  invocable.invokeFunction("greet", "Alex");
}

在脚本语言中,调用JDK中类和方法.

Packages是脚本语言里的一个全局变量,专用于访问JDK的package.

Invocable 接口允许java平台调用脚本程序中的函数或方法.

代码语言：javascript复制

@Test
public void testInvocable() throws ScriptException, NoSuchMethodException, InterruptedException {
  ScriptEngineManager manager = new ScriptEngineManager();
  ScriptEngine engine = manager.getEngineByName("javascript");
  String js = "function doSwing(t){var f=new Packages.javax.swing.JFrame(t);f.setSize(400,300);f.setVisible(true);}";
  engine.eval(js);
  Invocable inv = (Invocable) engine;
  inv.invokeFunction("doSwing", "Scripting Swing");
  Thread.currentThread().join();
}

对于在文件中的脚本也可以利用FileReader读入JDK并执行.

代码语言：javascript复制

public static void testScript() {
  try (FileReader fr = new FileReader("test.js")) {
    ScriptEngineManager manager = new ScriptEngineManager();
    ScriptEngine engine = manager.getEngineByName("javascript");
    engine.eval(fr);
  } catch (Exception ex) {
    ex.printStackTrace();
  }
}

除了JS文件可以解析外, 其他类别脚本也可以解析执行, 执行需要额外的jar做为支撑.

例如执行Python脚本, 需要额外jython-standalone.jar.

代码语言：javascript复制

<dependency>
    <groupId>org.python</groupId>
    <artifactId>jython-standalone</artifactId>
    <version>2.7.2</version>
</dependency>

jdk java javascript

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