ScriptFactory.groovy

public class ScriptFactory{
    private final Map<String, Script> cache = new HashMap<>()
    
    private static final GroovyClassLoader CLASS_LOADER = new GroovyClassLoader()
    private String template

    /**
      @param source is a dynamic expression to be evaluated: user.attr1 == 'x' || user.attr2 == 'y'
      @return instance of script
    */
    public Script create(String source) throws InstantiationException, IllegalAccessException, IOException{
        if (!cache.containsKey(source)) {
            cache.put(source, 
                      CLASS_LOADER.parseClass(String.format(loadTemplate(), source))newInstance()
                     )
        }
        return cache.get(source)
    }

    /**
        @return template used for dynamic expression execution
    */
    protected String loadTemplate() throws IOException
    {
        return """
          def evaluateExpression(Map context){
              def user =context.user 
              %s
          }
        """
    }
}

If a single instance of this is used in a highly concurrent app I'd recommend a ConcurrentHashMap to make sure all threads can see the puts.

private static final ConcurrentHashMap<String, Script> cache = new ConcurrentHashMap<>()

...
...
public Script create(String source) throws InstantiationException, IllegalAccessException, IOException {
    Script script = cache.get(source) // assume you'll get a hit after cache is warmed up
    if (script == null) {
        script = CLASS_LOADER...
        cache.put(source, script)
    }
    return script
}