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Conversion SPI

Connecting "non-connectable" components using conversions.

Concept

This example demonstrates the use of the OMS ConversionProvider SPI to provide generic conversion of objects exchanged by components. Without this conversion support, the OMS @In and @Out connect of incompatible types would fail.

Implementation

The 'Point' class is used (as in the First Class Object example) to instantiate a pointer object as a parameter. 

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package ex03;

/**
 *
 * @author od
 */
public class Point {

    int x;
    int y;

    public void setX(int x) {
        this.x = x;
    }

    public void setY(int y) {
        this.y = y;
    }

    public int getX() {
        return x;
    }

    public int getY() {
        return y;
    }

}

The 'Comp' component consumes variable x and y integer values and incorporates them into a pointer object, which is output as a parameter object. 

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package ex03;

import oms3.annotations.*;

public class Comp {

    @Out public Point point;

    @Role(Role.PARAMETER)
    @In public int x;

    @Role(Role.PARAMETER)
    @In public int y;

    @Execute
    public void run() {
        point = new Point();
        point.setX(x);
        point.setY(y);
    }
}

The parameter object 'c.point' contains integer values and must be converted by 'PointWKTConversion' (a class that implements the OMS API 'ConversionProvider') to string values (WKT = well known text). Some formatting is incorporated into the converted object. 

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package ex03;

import oms3.ConversionProvider;
import oms3.Converter;

/** A Converter example
 *   ... converting from Point to String(WKT) 
 *
 * @author od
 */
public class PointWKTConversion implements ConversionProvider {

    @Override
    public Converter getConverter(Class from, Class to) {
        if (from == Point.class && to == String.class) {
            return new Converter<Point, String>() {
                @Override
                public String convert(Point src, Object arg) {
                    return "POINT ("+ src.x + " " + src.y + ")";
                }
            };
        }
        return null;
    }
}

'Comp1' simply consumes the converted parameter object and prints to output. 

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package ex03;

import oms3.annotations.*;

public class Comp1 {

    @In public String wkt_point;

    @Execute
    public void run() {
        System.out.println(wkt_point);
    }
}

In the simulation, the model has two connected components 'Comp' and 'Comp1'. Parameter integer values 20 and 30 are consumed by 'Comp' to produce a parameter object, which is converted from integer to string values, including formatting for output. The converted parameter object is consumed by 'Comp2' which prints the contents of the object. 

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import static oms3.SimBuilder.instance as OMS3

OMS3.sim {

    model {
       parameter {
          // pass in the coordinated as native integer to the 
          // first component. 
          'c.x'  30
          'c.y'  20
       }

       components {
          'c'  'ex03.Comp'
          'c2' 'ex03.Comp1'
       }

       connect {
          // this connect would fail without the PointWKTConversion class as
          // specified via the generic ConversionProvider SPI
          //    see META-INF.services/oms3.ConversionProvider
          //    
          // @Out 'Point'  ->  @In 'WKT String'
          // both are describing a point, just with two different types. 
          'c.point' 'c2.wkt_point'
       }
    }
}

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Contact Us:
Jack Carlson
Coordinator, OMS Laboratory
OMS Laboratory
Jack.Carlson@colostate.edu
(970) 492-7323

Olaf David
Director, OMS Laboratory
odavid (at) colostate.edu
(970) 491-8026