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mybatis basemapper 空指针 mybatis plus空指针

一、发现经历

事情是这样的,我今天本来要演示系统,就去前端同学的页面上点一点。不小心点到了其他同事编写的服务,然后界面就报错了。这给我吓得,这还能演示吗这。然后,我就去服务器查看了一下日志,发现了如下景象:

mybatis basemapper 空指针 mybatis plus空指针,mybatis basemapper 空指针 mybatis plus空指针_ide,第1张

 

 

看到这景象啊,我第一件事情就是查看堆栈,也没找到自己写的代码啊,好好的咋就报错了。

于是,我第一件事情,复制报错信息找到百度网站。复制粘贴,往上一怼!好家伙,竟然找不到一个和我症状一样的。

那我只能自己处理了。

 

二、问题定位

从堆栈信息定位一个问题的位置其实是很简单的,但是要明白为什么错误,还是得多看一会儿的。

我定睛看了一阵子,发现了

 at org.apache.ibatis.type.LocalDateTimeTypeHandler.getNullableResult(LocalDateTimeTypeHandler.java:38)

 

这一行报错,于是我就跟进源码查看。这个源码,写的也简单。

1 /**
 2  *    Copyright 2009-2019 the original author or authors.
 3  *
 4  *    Licensed under the Apache License, Version 2.0 (the "License");
 5  *    you may not use this file except in compliance with the License.
 6  *    You may obtain a copy of the License at
 7  *
 8  *       http://www.apache.org/licenses/LICENSE-2.0
 9  *
10  *    Unless required by applicable law or agreed to in writing, software
11  *    distributed under the License is distributed on an "AS IS" BASIS,
12  *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  *    See the License for the specific language governing permissions and
14  *    limitations under the License.
15  */
16 package org.apache.ibatis.type;
17 
18 import java.sql.CallableStatement;
19 import java.sql.PreparedStatement;
20 import java.sql.ResultSet;
21 import java.sql.SQLException;
22 import java.time.LocalDateTime;
23 
24 /**
25  * @since 3.4.5
26  * @author Tomas Rohovsky
27  */
28 public class LocalDateTimeTypeHandler extends BaseTypeHandler<LocalDateTime> {
29 
30   @Override
31   public void setNonNullParameter(PreparedStatement ps, int i, LocalDateTime parameter, JdbcType jdbcType)
32           throws SQLException {
33     ps.setObject(i, parameter);
34   }
35 
36   @Override
37   public LocalDateTime getNullableResult(ResultSet rs, String columnName) throws SQLException {
38     return rs.getObject(columnName, LocalDateTime.class);
39   }
40 
41   @Override
42   public LocalDateTime getNullableResult(ResultSet rs, int columnIndex) throws SQLException {
43     return rs.getObject(columnIndex, LocalDateTime.class);
44   }
45 
46   @Override
47   public LocalDateTime getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {
48     return cs.getObject(columnIndex, LocalDateTime.class);
49   }
50 }

一共也就这么几行。报错的是:

public LocalDateTime getNullableResult(ResultSet rs, String columnName) throws SQLException {
  return rs.getObject(columnName, LocalDateTime.class);
}
这个方法。这里面发生了空指针。

这时候,我发现还是最细的堆栈信息。于是,我到最细的那一层。

mybatis basemapper 空指针 mybatis plus空指针,mybatis basemapper 空指针 mybatis plus空指针_ide_02,第2张

 

 

 

也就是这一行。

 

看到这里,我明白了。实际上就是

getTimestamp(columnIndex)

这个获取时间的时候,数据库的submit_time字段没有值,然后cast的时候,发生了空指针。

 

三、问题解决

弄清了病症,也就好下药治疗了。我脑中浮现出两个想法:

1、让submit_time有值

这不简单吗,没值的时候有问题,我让你有值不就完事了。哈哈。开个玩笑,要结合业务处理的哈。这种方法明显不可取。

2、重写LocalDateTimeTypeHandler这个类,然后添加空指针判断。

这个方法不错,可以解决实际问题。

于是,我查看了其他类型的处理。

1 /**
 2  *    Copyright 2009-2018 the original author or authors.
 3  *
 4  *    Licensed under the Apache License, Version 2.0 (the "License");
 5  *    you may not use this file except in compliance with the License.
 6  *    You may obtain a copy of the License at
 7  *
 8  *       http://www.apache.org/licenses/LICENSE-2.0
 9  *
10  *    Unless required by applicable law or agreed to in writing, software
11  *    distributed under the License is distributed on an "AS IS" BASIS,
12  *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  *    See the License for the specific language governing permissions and
14  *    limitations under the License.
15  */
16 package org.apache.ibatis.type;
17 
18 import java.sql.CallableStatement;
19 import java.sql.PreparedStatement;
20 import java.sql.ResultSet;
21 import java.sql.SQLException;
22 
23 /**
24  * @author Clinton Begin
25  */
26 public class DoubleTypeHandler extends BaseTypeHandler<Double> {
27 
28   @Override
29   public void setNonNullParameter(PreparedStatement ps, int i, Double parameter, JdbcType jdbcType)
30       throws SQLException {
31     ps.setDouble(i, parameter);
32   }
33 
34   @Override
35   public Double getNullableResult(ResultSet rs, String columnName)
36       throws SQLException {
37     double result = rs.getDouble(columnName);
38     return result == 0 && rs.wasNull() ? null : result;
39   }
40 
41   @Override
42   public Double getNullableResult(ResultSet rs, int columnIndex)
43       throws SQLException {
44     double result = rs.getDouble(columnIndex);
45     return result == 0 && rs.wasNull() ? null : result;
46   }
47 
48   @Override
49   public Double getNullableResult(CallableStatement cs, int columnIndex)
50       throws SQLException {
51     double result = cs.getDouble(columnIndex);
52     return result == 0 && cs.wasNull() ? null : result;
53   }
54 
55 }

mybatis basemapper 空指针 mybatis plus空指针,mybatis basemapper 空指针 mybatis plus空指针_sql_03,第3张

 

 看了Double的类型处理【1、wasNull设置标志位 2、获取的外面通过标志位判空】,我又看了Integer的类型处理。。。

1  /**
 2  *    Copyright 2009-2018 the original author or authors.
 3  *
 4  *    Licensed under the Apache License, Version 2.0 (the "License");
 5  *    you may not use this file except in compliance with the License.
 6  *    You may obtain a copy of the License at
 7  *
 8  *       http://www.apache.org/licenses/LICENSE-2.0
 9  *
10  *    Unless required by applicable law or agreed to in writing, software
11  *    distributed under the License is distributed on an "AS IS" BASIS,
12  *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  *    See the License for the specific language governing permissions and
14  *    limitations under the License.
15  */
16 package org.apache.ibatis.type;
17 
18 import java.sql.CallableStatement;
19 import java.sql.PreparedStatement;
20 import java.sql.ResultSet;
21 import java.sql.SQLException;
22 
23 /**
24  * @author Clinton Begin
25  */
26 public class IntegerTypeHandler extends BaseTypeHandler<Integer> {
27 
28   @Override
29   public void setNonNullParameter(PreparedStatement ps, int i, Integer parameter, JdbcType jdbcType)
30       throws SQLException {
31     ps.setInt(i, parameter);
32   }
33 
34   @Override
35   public Integer getNullableResult(ResultSet rs, String columnName)
36       throws SQLException {
37     int result = rs.getInt(columnName);
38     return result == 0 && rs.wasNull() ? null : result;
39   }
40 
41   @Override
42   public Integer getNullableResult(ResultSet rs, int columnIndex)
43       throws SQLException {
44     int result = rs.getInt(columnIndex);
45     return result == 0 && rs.wasNull() ? null : result;
46   }
47 
48   @Override
49   public Integer getNullableResult(CallableStatement cs, int columnIndex)
50       throws SQLException {
51     int result = cs.getInt(columnIndex);
52     return result == 0 && cs.wasNull() ? null : result;
53   }
54 }

mybatis basemapper 空指针 mybatis plus空指针,mybatis basemapper 空指针 mybatis plus空指针_ide_04,第4张

 

 Integer的类型处理也是【1、wasNull设置标志位 2、获取的外面通过标志位判空】。

 

这真是好家伙,坐不住了。其他的类型都处理了,合着就我用的LocalDateTime没做空指针处理。这哪能行。重写,必须重写。

1 package com.vsofo;
 2 
 3 import org.apache.ibatis.type.LocalDateTimeTypeHandler;
 4 import org.springframework.stereotype.Component;
 5 
 6 import java.sql.ResultSet;
 7 import java.sql.SQLException;
 8 import java.time.LocalDateTime;
 9 
10 @Component
11 public class LocalDateTimeTypeHandlerPlus extends LocalDateTimeTypeHandler {
12 
13     @Override
14     public LocalDateTime getResult(ResultSet rs, String columnName) throws SQLException {
15         Object object = rs.getObject(columnName);
16         if(object==null){
17             return  null;
18         }
19         return super.getResult(rs, columnName);
20     }
21 }

我直接继承,然后重写获取逻辑。

1、先获取数据库的值

2、判空,如果值为空,直接返回。

3、如果,值不为空,进行原来的强转逻辑。

 

重写之后,问题完美解决了。

 

=============================================================================

2021-08-18 最近在做另外一个项目的时候,也发现了这个问题,然而一样的步骤失效了,原因了,没有使用到这个自定义的LocalDateTime处理器。后面,我使用类替换的形式代替,解决了该问题。复制出原来的LocalDateTimeTypeHandler放在同一个包下 ,依旧是重写getResult(ResultSet rs, String columnName)方法解决了该问题,这使用的方式是直接替换了源码中的类。特此记录!

1 /**
 2  *    Copyright 2009-2019 the original author or authors.
 3  *
 4  *    Licensed under the Apache License, Version 2.0 (the "License");
 5  *    you may not use this file except in compliance with the License.
 6  *    You may obtain a copy of the License at
 7  *
 8  *       http://www.apache.org/licenses/LICENSE-2.0
 9  *
10  *    Unless required by applicable law or agreed to in writing, software
11  *    distributed under the License is distributed on an "AS IS" BASIS,
12  *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  *    See the License for the specific language governing permissions and
14  *    limitations under the License.
15  */
16 package org.apache.ibatis.type;
17 
18 import java.sql.CallableStatement;
19 import java.sql.PreparedStatement;
20 import java.sql.ResultSet;
21 import java.sql.SQLException;
22 import java.time.LocalDateTime;
23 
24 /**
25  * @since 3.4.5
26  * @author Tomas Rohovsky
27  */
28 public class LocalDateTimeTypeHandler extends BaseTypeHandler<LocalDateTime> {
29   
30   @Override
31   public LocalDateTime getResult(ResultSet rs, String columnName) throws SQLException {
32     Object object = rs.getObject(columnName);
33     if(object==null){
34       return  null;
35     }
36     return super.getResult(rs, columnName);
37   }
38 
39   @Override
40   public void setNonNullParameter(PreparedStatement ps, int i, LocalDateTime parameter, JdbcType jdbcType)
41           throws SQLException {
42     ps.setObject(i, parameter);
43   }
44 
45   @Override
46   public LocalDateTime getNullableResult(ResultSet rs, String columnName) throws SQLException {
47     return rs.getObject(columnName, LocalDateTime.class);
48   }
49 
50   @Override
51   public LocalDateTime getNullableResult(ResultSet rs, int columnIndex) throws SQLException {
52     return rs.getObject(columnIndex, LocalDateTime.class);
53   }
54 
55   @Override
56   public LocalDateTime getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {
57     return cs.getObject(columnIndex, LocalDateTime.class);
58   }
59 }

 或者,是在字段上的注解@TableField设置该字段的类型转换器

/**
     * 下发时间
     */
    @TableField(value = "oper_time",typeHandler =LocalDateTimeTypeHandlerPlus.class) 
   private LocalDateTime operTime;

如果是xml的话,也有该配置

<resultMap id="myParam" type="com.base.slave.entity.UserStaticUserinfo" >
    <result column="plat_oper_time" property="platOperTime" typeHandler="cn.lxw.LocalDateTimeTypeHandlerPlus"/>
</resultMap>

 

最后,还有一种方式,那就是把对应映射的字段类型改成java.util.Date类型,因为Date类型的源码已经做了特殊处理,只是这样要动到一些涉及的代码而增加一些风险。

四、心得体会

我觉着吧,框架是个好东西,能让我们开发项目事半功倍。但是如果给你埋了一个大雷,也可能让你事倍功半。

所以,我们用框架开发的过程中,应该多用多测多实践。找出影响项目的问题,然后解决它。

分享结束,谢谢大家观看哈!




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