public class Source {
    private String sourceField;

    public Source() {
        // no-op
    }

    public String getSourceField() {
        return sourceField;
    }

    public void setSourceField(String sourceField) {
        this.sourceField = sourceField;
    }
}

public class Target {
    private final Map<String, String> attributes = new HashMap<>();
    private String targetField;

    public Target() {
        // no-op
    }

    public Map<String, String> getAttributes() {
        return attributes;
    }

    public String getTargetField() {
        return targetField;
    }

    public void setTargetField(String targetField) {
        this.targetField = targetField;
    }
}

@Mapper
public interface S2TMapper {
    @Mapping(target = "targetField", source = "sourceField")
    Target map(Source source);
}