获取spring mvc projetc的json格式数据

Question

您好我想以JSON格式选择所有数据。我怎么能这样做？

此泛型类包含我用于查找，添加，更新和删除的方法。我应该在selectAll方法中添加一些东西以使其有效吗？

public class GenericDaoImpl<E> implements IGenericDao<E>{
    @PersistenceContext
    EntityManager em;

    private Class<E> type;

    public Class<E> getType() {
        return type;
    }

    public GenericDaoImpl() {
        Type t = getClass().getGenericSuperclass();
        ParameterizedType pt = (ParameterizedType) t;
        type = (Class<E>) pt.getActualTypeArguments()[0];
    }

    @Override
    public E add(E entity) {
         em.persist(entity);
         return entity;
    }

    @Override
    public E update(E entity) {
        return em.merge(entity);
    }

    @Override
    public List<E> selectAll() {
        Query query = em.createQuery("select t from " + type.getSimpleName() + " t ");
        return (List<E>) query.getResultList();
    }

    @Override
    public List<E> selectAll(String sortField, String sort) {
        Query query = em.createQuery("select t from"+type.getSimpleName()+ " t order by " + sortField + " " + sort);
        return query.getResultList();
    }

    @Override
    public E getById(Long id) {
        return em.find(type, id);
    }

    @Override
    public void remove(Long id) {
        E tab = em.getReference(type, id);
        em.remove(tab); 
    }

    @Override
    public E findOne(String paramName, Object paramValue) {
        Query query = em.createQuery("select t from"+type.getSimpleName()+ " t where " + paramName + " = :x");
        query.setParameter(paramName, paramValue);
        return query.getResultList().size()>0 ? (E) query.getResultList().get(0):null;
    }

    @Override
    public E findOne(String[] paramName, Object[] paramValue) {
        if (paramName.length != paramValue.length) {
            return null;
        }
        String queryString = "select e from " + type.getSimpleName() + " e where ";
        int len = paramName.length;
        for (int i = 0; i < len; i++) {
            queryString += " e." + paramName[i] + "= :x" + i;
            if ((i + 1) < len) {
                queryString += " and ";
            }
        }
        Query query = em.createQuery(queryString);
        for (int i = 0; i < paramValue.length; i++) {
            query.setParameter("x" + i, paramValue[i]);
        }
        return query.getResultList().size() > 0 ? (E) query.getResultList().get(0) : null;
    }

    @Override
    public int findCountBy(String paramName, Object paramValue) {
        Query query = em.createQuery("select t from"+type.getSimpleName()+ " t where " + paramName + " = :x");
        query.setParameter(paramName, paramValue);
        return query.getResultList().size() > 0 ?((Long)query.getSingleResult()).intValue():0;
    }

    @Override
    public E getByLogin(String login) {
        return em.find(type, login);
    }

    @Override
    public E getByIdAdmin(Integer id) {
        return em.find(type, id);
    }

    @Override
    public void removeByLogin(String login) {
        E tab = em.getReference(type, login);
        em.remove(tab);
    }

    @Override
    public void removeByIdAdmin(Integer id) {
        E tab = em.getReference(type, id);
        em.remove(tab);
    }
}