package com.mycompany.app;
public class MyThing {
    private String a;
    private int b;
    public void setA(String a) { this.a = a; }
    public void setB(int b) { this.b = b; }
    public String getA() { return this.a; }
    public int getB() { return this.b; }
}

package com.mycompany.app;
import java.util.Map;
import org.mapstruct.Mapper;
import org.mapstruct.Mapping;
import com.mycompany.app.MyThing;

@Mapper
public interface MyMapper {
      // These mappings don't seem legal. What's the legal version? 
     // What I want in codegen is something like: 
     // target.setA(String.valueOf(map.get(1)))
     // target.setB(Integer.valueOf(map.get(2)))
    @Mapping(source = 1, target = "a")
    @Mapping(source = 2, target = "b") 
    MyThing map(Map<Integer, Object> dict);
}

package com.mycompany.app;
import com.mycompany.app.MyMapperImpl;
import com.mycompany.app.MyThing;
import java.util.Map;
import java.util.HashMap;

public class App
{
    public static void main( String[] args )
    {
        Map<Integer, Object> dict = new HashMap<Integer, Object>();
        dict.put(1, "here is your string");
        dict.put(2, 5555);

        // Map it 
        MyThing thing = new MyMapperImpl().map(dict);

        System.out.println("Hello A: "  + thing.getA()); // Expected:  Hello A: here is your string
        System.out.println("Hello B " + thing.getB()); // Expected:  Hello : 5555
    }
}