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我想在 servlet 中执行 JavaScript。是否可以在所有 servlet 调用中重用相同的脚本引擎？ Servlet 实例由多个线程共享。这是否需要为每个请求创建一个新的脚本引擎？那将是 Not Acceptable 性能损失。举个例子，下面的代码保存了吗？
public class MyServlet extends HttpServlet {
private ScriptEngineManager factory;
private ScriptEngine engine;
@Override
public void init() throws ServletException {
factory = new ScriptEngineManager();
engine = factory.getEngineByName("nashorn");
}
@Override
public void doGet(HttpServletRequest req, HttpServletResponse res) throws IOException {
try (PrintWriter writer = res.getWriter()) {
ScriptContext newContext = new SimpleScriptContext();
newContext.setBindings(engine.createBindings(), ScriptContext.ENGINE_SCOPE);
Bindings engineScope = newContext.getBindings(ScriptContext.ENGINE_SCOPE);
engineScope.put("writer", writer);
Object value = engine.eval("writer.print('Hello, World!');", engineScope);
writer.close();
} catch (IOException | ScriptException ex) {
Logger.getLogger(AsyncServlet.class.getName()).log(Level.SEVERE, null, ex);
}
}
如果这不安全，避免为每个请求创建引擎的最佳方法是什么？使用引擎池？
编辑: 是否可以为所有 servlet 请求重用一个相同的引擎和一个相同的 JavaScriptObject，它作为 JS 函数的评估结果，如果该函数不更改任何共享对象而仅使用给定的参数称呼？请看上面示例的以下改编:
public class MyServlet extends HttpServlet {
private ScriptEngineManager factory;
private ScriptEngine engine;
private ScriptObjectMirror script;
@Override
public void init() throws ServletException {
try {
factory = new ScriptEngineManager();
engine = factory.getEngineByName("nashorn");
script = (ScriptObjectMirror)engine.eval("function(writer) {writer.print('Hello, World!');}");
} catch (ScriptException ex) {
Logger.getLogger(MyServlet.class.getName()).log(Level.SEVERE, null, ex);
}
}
@Override
public void doGet(HttpServletRequest req, HttpServletResponse res) throws IOException {
try (PrintWriter writer = res.getWriter()) {
script.call(null, writer);
writer.close();
} catch (IOException ex) {
Logger.getLogger(MyServlet.class.getName()).log(Level.SEVERE, null, ex);
}
}
这样安全吗？