Computing OwnValueExtractionMethod

Computing With Own Value Extraction Method

import a2u.tn.utils.computer.calcobj.ObjCalcEngine;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;

public class Main2 {

  public static class ID {
    Object value;
    String sourceName;

    public ID(Object value, String sourceName) {
      this.value = value;
      this.sourceName = sourceName;
    }

    public Map<String, Object> loadObj() {
      //todo: Your implementation to load an object from a database or other source
      Map<String, Object> data = new LinkedHashMap<String, Object>();
      data.put("field01", "AAA");
      return data;
    }

    public String toString() {
      return value+"@"+sourceName;
    }
  }

  private static ObjCalcEngine engine = new ObjCalcEngine() {

    //We override this method to get values in our own way
    /**
     * Extract values from each object 'fromObjList' by code
     * @param byCode code for extracting values
     * @param fromObjList collection with objects for extracting values
     * @return Values
     */
    @Override
    protected Collection<Object> extractValues(String byCode, Collection<Object> fromObjList) {
      if (fromObjList == null) {
        return null;
      }

      List<Object> resultList = new ArrayList<Object>();

      for (Object obj : fromObjList) {
        if (obj instanceof ID) {
          //own way
          Map<String, Object> objData = ((ID)obj).loadObj();
          resultList.add(objData.get(byCode));
        }
        else {
          //standart way
          resultList.addAll(super.extractValues(byCode, Collections.singletonList(obj)));
        }
      }

      return resultList;
    }
  };


  public static void main(String[] args) {
    Map<String, Object> map = new LinkedHashMap<String, Object>();
    map.put("value01", new ID(12345, "table01"));
    map.put("value02", "BBB");
    System.out.println(engine.calc(".value01", map));
    System.out.println(engine.calc(".value01.field01", map));
    System.out.println(engine.calc(".value02", map));
    System.out.println(engine.calc(".value01.field01 + .value02", map));
  }

}

Output

12345@table01
AAA
BBB
AAABBB

The ID class is your own class that contains the data to retrieve the values ​​(value and sourceName). This class can retrieve values ​​using the loadObj() method.

You can override the extractValues method in the ObjCalcEngine class.

protected Collection<Object> extractValues(String byCode, Collection<Object> fromObjList)

where check instanceof to determine when you should call ID.loadObj().

if (obj instanceof ID) {
  //own way
  Map<String, Object> objData = ((ID)obj).loadObj();
  resultList.add(objData.get(byCode));
}