936~939 分类数据展示功能，实现前后台代码

分类实现展示功能

　　效果

后台代码

CategoryDao

public interface CategoryDao {
    public List<Category> findAll();//查询所有
}

CategoryDaoImpl

public class CategoryDaoImpl implements CategoryDao {

    private JdbcTemplate template = new JdbcTemplate(JDBCUtils.getDataSource());

    @Override//查询所有
    public List<Category> findAll() {
        String sql = "select * from tab_category ";
        return template.query(sql,new BeanPropertyRowMapper<Category>(Category.class));
    }
}

CategoryService

public interface CategoryService {

    public List<Category> findAll();
}

CategoryServiceImpl

public class CategoryServiceImpl implements CategoryService {

    private CategoryDao categoryDao = new CategoryDaoImpl();

    @Override
    public List<Category> findAll() {
        return categoryDao.findAll();
    }
}

CategoryServlet

@WebServlet("/category/*")
public class CategoryServlet extends BaseServlet {

    private CategoryService service = new CategoryServiceImpl();

   //查询所有
    public void findAll(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //1.调用service查询所有
        List<Category> cs = service.findAll();
        //2.序列化json返回
        /*
        ObjectMapper mapper = new ObjectMapper();
        response.setContentType("application/json;charset=utf-8");
        mapper.writeValue(response.getOutputStream(),cs);
         */
        writeValue(cs,response);
    }
}

BaseServlet也可以在UserServlet编写

  //直接将传入的对象序列化为json，并且写回客户端
    public void writeValue(Object obj, HttpServletResponse response) throws IOException {
        ObjectMapper mapper = new ObjectMapper();
        response.setContentType("application/json;charset=utf-8");
        mapper.writeValue(response.getOutputStream(), obj);
    }

   //将传入的对象序列化为json，返回
    public String writeValueAsString(Object obj) throws JsonProcessingException {
        ObjectMapper mapper = new ObjectMapper();
        return mapper.writeValueAsString(obj);
    }