Dynamic properties and methods are used when the property/method name is not defined in advance, but can appear according to specific use cases. When they are dynamic, more readable and writable properties/methods names are provided.

In our script service a camera can have different settings depending on the model – brightness, contrast, saturation, zoom, etc. , so that we can handle dynamic get and set camera feature methods.

For example:

camera.setBrightness(6.0d);
camera.setZoom(3.2d);
double saturationValue = camera.saturation;
double constrastValue = camera.contrast;


Dynamic properties and methods are supported by a script service class when it implements:
•   com.prosyst.mprm.backend.rules.spi.PropertyMissing – handles dynamic properties.
•   com.prosyst.mprm.backend.rules.spi.MethodMissing – handles dynamic methods.

In our script service the Camera object will support dynamic properties and methods:

// extending the interfaces PropertyMissing and MethodMissing
public interface Camera extends PropertyMissing, MethodMissing, ScriptSerializable {
  …
}

And the implementation:

package com.prosyst.mprm.demos.rules.impl;
 
public class CameraImpl implements Camera {
  ...
  private static final String ASYNC_METHOD_PREFIX = "set";
  ...
  // executed when no static property was found
  public Object propertyMissing(String propertyName) throws Exception {
    Object propertyValue = getFeatureValue(propertyName);
    if (propertyValue == null) {
      throw new NoSuchFieldException("Feature '" + propertyName + "' not supported!");
    }
    return propertyValue;
  }
 
// executed when no static method was found
  public MethodMissingMetaData methodMissingMetaData(String methodName, Object arg) throws Exception {
    // there are only asynchornous dynamic methods
    return new MethodMissingMetaData(false, true);
  }
 
  // the dynamic synchronous method implementation
  public Object methodMissing(String methodName, Object args) throws Exception {
    throw new NoSuchMethodException("Synchronous dynamic methods are not supported!");
  }
 
  // the dynamic asynchronous method implementation
  public Object methodMissing(String methodName, Object args, AsyncResult asyncResult) throws Exception {
    if (methodName.startsWith(ASYNC_METHOD_PREFIX)) {
      String featureName =      methodName.substring(ASYNC_METHOD_PREFIX.length()).toLowerCase();    
      double featureValue = (Double)args;
      setFeature(featureName, featureValue, asyncResult);
      return null;
    } else {
      throw new NoSuchMethodException("Wrong dynamic asynchronous method prefix!");
    }
  }
  ...
}

When implementing PropertyMissing and MethodMissing interfaces these exceptions have to be thrown when needed:
•   java.lang.NoSuchFieldException – thrown when the object doesn't have a property with the specified name.
•   java.lang.NoSuchMethodException – thrown when the object doesn't have a method with the specified name.



The property missing method is called when no property of the object with the given static name is found.

For example, when script:

camera.saturation;

or

camera.getSaturation();

is called, then Object propertyMissing(String propertyName) throws Exception of the Camera object will be invoked.

When no method of the object with the given static name is found, for example:

camera.setBrightness(6.0d);


Then the MethodMissing interface methods are called in specific order:

  1. First one called is

    MethodMissingMetaData methodMissingMetaData(String methodName, Object arg) throws Exception

    After that we have to provide the value of the argument isAsync (true/false) depending on the script service logic and call the MethodMissingMetaData constructor with it

    MethodMissingMetaData(boolean reportResult, boolean isAsync)

  2. If the argument isAsync is true then the following method will be called:

    Object methodMissing(String methodName, Object args, AsyncResult asyncResult) throws Exception

    If false the called method will be:

    Object methodMissing(String methodName, Object args) throws Exception