如何用struts返回一个json数组？

Here is my struts action

这是我的struts动作

@Action("/trylogin")
@ParentPackage("json-default")
@Result(type = "json", params = { "includeProperties", "msg, productsList" })
public class Login extends ActionSupport {

    private static final long serialVersionUID = 1L;
    private String utilisateur;
    private String motdepasse;
    private String msg;
    private ArrayList<Article> productsList = new ArrayList<Article>();

    @Autowired
    private Dao dao;

    public String execute() {

        if (dao.validCredentials(utilisateur, motdepasse)) {
            System.out.println("USER FOUND");
            productsList = dao.fetchProducts();
            msg = "success";
        } else {
            System.out.println("ERREUR");
            msg = "error";
        }
        return ActionSupport.SUCCESS;
    }

public ArrayList<Article> getProductsList() {
    return productsList;
}

public String getMsg() {
    return msg;
}
@Acti