Springmvc+mybatis 问题总结（续ing）

约定不等于承诺〃 2022-08-08 17:42 10阅读 0赞

1、**java.lang.IllegalStateException: getWriter() has already been called for this response**

拦截器中相关代码
    @Override
        public boolean preHandle(HttpServletRequest request, HttpServletResponse response,
                Object arg2) throws Exception {
            response.setCharacterEncoding("UTF-8"); // 设置输出流格式为utf-8
            PrintWriter out = response.getWriter();  //获得输出流
        }
    
    controller相关代码
    
    @ResponseBody
        @RequestMapping(value="/back/updateadmin")
        public Json updateAdmin(UpdateAdmin admin,HttpServletResponse respose) {
            int result = 0;
            Json json = new Json();
            try {
                result = adminService.updateAdmin(admin);
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                if(result != 0) {
                    json.setMsg("更新管理员操作成功");
                    json.setSuccess(true);
                } else {
                    json.setMsg("更新管理员失败");
                    json.setSuccess(false);
                }
            }
            return json;    
        }

问题原因：  
在拦截器中 获得了PrintWriter对象  
而在Controller中@responseBody 返回json格式字符串时会自动调用getOutputStream方法。

解决方法：  
在拦截器中加上  
response.reset();即可

**2.SELECT top(1) \* FROM edition ORDER BY id DESC**  
在mysql 数据库下一直报  
\*\*You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ‘FROM edition  
ORDER BY id DESC’ at line 1\*\*

问题原因：  
并不是所有的数据库都支持top子句

解决方法:  
select \* from edition order by id limit 1