According to the practice, what do I do to call dynamic language script
If there is such a situation: it is necessary to judge the size of a variable a, but the judgment rule is uncertain, which may be a < 1, a > 1, a == 1, etc.

• The following is the implementation without calling dynamic script:

public boolean compare(double a, String expression) {
  int n = Integer.parseInt(expression.replaceAll("\\D", ""));
  if(expression.contains(">=")) {
    return a >= n;
  } else if(expression.contains("<=")) {
    return a < n;
  } else if(expression.contains("==")) {
    return a == n;
  } else if(expression.contains(">")) {
    return a > n;
  } else {
    ...
  }
}

It's a lot of trouble to realize. It's just a bunch of judgments. But for a < 1 & & a > 0, this kind of complex expression is more difficult to implement.

• The following is the implementation of calling js script:

public boolean compare(double a, String expression) throws Exception{
  expression = expression.replace("a", a)
  ScriptEngineManager sem = new ScriptEngineManager();
  ScriptEngine scriptEngine = sem.getEngineByName("js");
  return scriptEngine.eval(expression);
}

In this way, it is very simple and can deal with complex expressions.

The following is a comparison between executing js script and lua script:

• Execute js script

Test code

        int size = 10000;
        ScriptEngineManager sem = new ScriptEngineManager();
        ScriptEngine scriptEngine = sem.getEngineByName("js");
        long start = System.currentTimeMillis();
        for (int i = 0; i < size; i++) {
            String jsStr = String.format("%d > %d", i, i+1);
            try{
                scriptEngine.eval(jsStr);
            }catch (Exception e) {
                e.printStackTrace();
            }
        }
        long end = System.currentTimeMillis();
        System.out.printf("js: %d ms\n" ,end - start);

• Execute lua script

Luaj is a lua interpreter based on lua version 5.2. X, which considers the following objectives:

• The Java centric lua vm implementation aims to take advantage of standard Java functions.
• Lightweight, high-performance lua execution.
• Multiple platforms that can run in JME, JSE, or JEE environments.
• A complete library and toolset for integration into the actual project.
• Due to the sufficient unit test of vm and library functions, it is reliable.

Test code

        int size = 100000;

        Globals globals = JsePlatform.standardGlobals();
        long start = System.currentTimeMillis();
        for (int i = 0; i < size; i++) {
            String luaStr = String.format("return %d > %d", i, i+1);
            LuaValue chunk = globals.load(luaStr);
            chunk.call().toboolean();
        }
        long end = System.currentTimeMillis();
        System.out.printf("lua: %d ms\n", end - start);

Average execution time

lua: 900 ms
javascript: 60000 ms
The execution efficiency of lua script is much higher than that of js script.