Mybatis foreach标签使用不当导致异常的原因探究

2016-12-28 10:11:44来源:oschina作者:Gen_zhou人点击

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# Mybatis foreach标签使用不当导致异常的原因探究
## 异常产生场景及异常信息
上周,由于在Mybatis的Mapper接口方法中使用实现了Map.Entry接口的泛型类,同时此方法对应的sql语句也使用了foreach标签,导致出现了异常。如下为异常信息:
```
org.apache.ibatis.exceptions.PersistenceException:
### Error updating database.Cause: org.apache.ibatis.reflection.ReflectionException: There is no getter for property named 'key' in 'class java.lang.Integer'
### The error may involve org.guojing.test.spring.server.GoodsRoomnight30daysMapper.insertBatch-Inline
### The error occurred while setting parameters
### SQL: REPLACE INTO goods_roomnight_30days (goods_id, checkin_room_night_30days) VALUES (?, ?) , (?, ?), (?, ?), (?, ?)
### Cause: org.apache.ibatis.reflection.ReflectionException: There is no getter for property named 'key' in 'class java.lang.Integer'
at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:30)
at org.apache.ibatis.session.defaults.DefaultSqlSession.update(DefaultSqlSession.java:200)
at org.apache.ibatis.session.defaults.DefaultSqlSession.insert(DefaultSqlSession.java:185)
at org.apache.ibatis.binding.MapperMethod.execute(MapperMethod.java:57)
at org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:53)
at com.sun.proxy.$Proxy4.insertBatch(Unknown Source)
at org.guojing.test.spring.server.GoodsRoomnight30daysTest.test(GoodsRoomnight30daysTest.java:47)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:271)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:70)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)
at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
at org.junit.runner.JUnitCore.run(JUnitCore.java:160)
at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:51)
at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:237)
at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)
Caused by: org.apache.ibatis.reflection.ReflectionException: There is no getter for property named 'key' in 'class java.lang.Integer'
at org.apache.ibatis.reflection.Reflector.getGetInvoker(Reflector.java:409)
at org.apache.ibatis.reflection.MetaClass.getGetInvoker(MetaClass.java:164)
at org.apache.ibatis.reflection.wrapper.BeanWrapper.getBeanProperty(BeanWrapper.java:162)
at org.apache.ibatis.reflection.wrapper.BeanWrapper.get(BeanWrapper.java:49)
at org.apache.ibatis.reflection.MetaObject.getValue(MetaObject.java:122)
at org.apache.ibatis.reflection.MetaObject.getValue(MetaObject.java:119)
at org.apache.ibatis.mapping.BoundSql.getAdditionalParameter(BoundSql.java:75)
at org.apache.ibatis.scripting.defaults.DefaultParameterHandler.setParameters(DefaultParameterHandler.java:72)
at org.apache.ibatis.executor.statement.PreparedStatementHandler.parameterize(PreparedStatementHandler.java:93)
at org.apache.ibatis.executor.statement.RoutingStatementHandler.parameterize(RoutingStatementHandler.java:64)
at org.apache.ibatis.executor.SimpleExecutor.prepareStatement(SimpleExecutor.java:86)
at org.apache.ibatis.executor.SimpleExecutor.doUpdate(SimpleExecutor.java:49)
at org.apache.ibatis.executor.BaseExecutor.update(BaseExecutor.java:117)
at org.apache.ibatis.session.defaults.DefaultSqlSession.update(DefaultSqlSession.java:198)
... 29 more
```
由于本人对Mybatis还不是非常的了解,导致用了很长的时间去debug找具体的异常原因。
接下来介绍我将重现异常并分析导致异常的原因。
## 异常重现
为了重现上面的异常,写了demo。相关代码如下:
数据库表结构:
```
CREATE TABLE `goods_roomnight_30days` (
`goods_id` bigint(20) NOT NULL,
`checkin_room_night_30days` int(11) NOT NULL DEFAULT '0' COMMENT '近30天消费间夜',
PRIMARY KEY (`goods_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='goods的近30天消费间夜'
```
KeyValue.java 参数类:
```
public class KeyValue implements Map.Entry {
private K key;
private V value;
public KeyValue() {
}
public KeyValue(K key, V value) {
this.key = key;
this.value = value;
}
@Override
public K getKey() {
return key;
}
@Override
public V getValue() {
return value;
}
@Override
public V setValue(V value) {
V oldValue = this.value;
this.value = value;
return oldValue;
}
public JSONObject toJSONObject() {
return ReportJSONObject.newObject().append(String.valueOf(key), value);
}
@Override
public String toString() {
return toJSONObject().toJSONString();
}
}
```
DAO类GoodsRoomnight30daysMapper.java
```
public interface GoodsRoomnight30daysMapper {
int deleteByExample(GoodsRoomnight30daysExample example);List selectByExample(GoodsRoomnight30daysExample example);
int insertBatch(List> records);
}
```
mybatis-config.xml文件:
```
<?xml version="1.0" encoding="UTF-8" ?>
"http://mybatis.org/dtd/mybatis-3-config.dtd">






















```
GoodsRoomnight30daysMapper.xml文件的主要内容:
```

REPLACE INTO goods_roomnight_30days (goods_id, checkin_room_night_30days)
VALUES

(#{item.key}, #{item.value})






```
以上为重现此异常的主要代码,完整代码可在Github查看:[https://github.com/misterzhou/java-demo/tree/master/test-spring/spring-server](https://github.com/misterzhou/java-demo/tree/master/test-spring/spring-server)
重现异常的测试代码 GoodsRoomnight30daysTest.java:
```
package org.guojing.test.spring.server;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.guojing.spring.commons.KeyValue;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.List;
/**
* Created at: 2016-12-24
*
* @author guojing
*/
public class GoodsRoomnight30daysTest {
SqlSessionFactory sqlSessionFactory;
SqlSession sqlSession;
GoodsRoomnight30daysMapper goodsRoomnight30daysMapper;
@Before
public void init() throws IOException {
String resource = "mybatis/mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
sqlSession = sqlSessionFactory.openSession(true);
goodsRoomnight30daysMapper = sqlSession.getMapper(GoodsRoomnight30daysMapper.class);
}
@Test
public void test() {
List> records = new ArrayList<>();
records.add(new KeyValue(1725L, 5));
records.add(new KeyValue(1728L, 3));
records.add(new KeyValue(1730L, null));
records.add(new KeyValue(1758L, null));
int deleted = goodsRoomnight30daysMapper.deleteByExample(new GoodsRoomnight30daysExample());
System.out.println("----- deleted row size: " + deleted);
int row = goodsRoomnight30daysMapper.insertBatch(records);
System.out.println("----- affected row: " + row);
List result = goodsRoomnight30daysMapper.selectByExample(new GoodsRoomnight30daysExample());
for (GoodsRoomnight30days item : result) {
System.out.println(item.toString());
}
}
@After
public void after() {
if (sqlSession != null) {
sqlSession.close();
}
}
}
```
卖个关子,大家先不要往下看,想想导致异常的原因(熟练使用foreach标签的同学应该能看出端倪)。
## 查找异常过程及异常分析
在项目中,由于DAO方法的参数类和返回结果类经常会包含一个键和键对应的值,为了避免重复定义类,我定义了一个实现了Map.Entry接口的KeyValue泛型类,具体请查看上节。
GoodsRoomnight30daysMapper.insertBatch()方法就使用了此泛型类。在运行之后就抛出了本文开始提到的异常信息。
看到异常信息后,就把重点放到了是不是Mybatis对泛型的支持不够好上。问了下同事(@胜男),同事在自己的机器上试了下,发现没有异常。这就奇奇怪了。仔细看了下代码,发现不同之处就是我的KeyValue泛型类实现了Map.Entry接口。
此时还不知道mybatis官网对于foreach标签的说明:
> 可以将任何可迭代对象(如列表、集合等)和任何的字典或者数组对象传递给foreach作为集合参数。当使用可迭代对象或者数组时,index是当前迭代的次数,item的值是本次迭代获取的元素。当使用字典(或者Map.Entry对象的集合)时,index是键,item是值。
接下来就是通过debug看看,这种情况的具体原因。于是就先用实现了Map.Entry接口的KeyValue类的代码进行debug,通过异常日志可以看到异常是在 DefaultSqlSession.java:200 行抛出,那么将断点打到 DefaultSqlSession.java:197行,然后一步步向下执行,当执行到 ForEachSqlNode.java:73行时,终于焕然大悟。先看下debug调用链图:
![调用链](/2014th7cj/d/file/p/20161228/lvdeotzw0zb.png)
再看看具体的代码 ForEachSqlNode.java:73(此类就是foreach标签对象的Node类):
![ForEachSqlNode.java:73](/2014th7cj/d/file/p/20161228/japg55lbszq.png)
此时具体的异常原因就很明显了,此处的 o 对象的所属的类就是KeyValue类,由于KeyValue类实现了Map.Entry接口,所以 `o instance Map.Entry` 为true,mybatis就把key值赋给了foreach的index属性,而把value值赋给了item属性,此处也就是把值为5的Integer对象赋给了item属性。所以 GoodsRoomnight30daysMapper.xml 中id为 insertBatch 的select标签内部:
```

(#{item.key}, #{item.value})

```
item也就没有key和value属性。这就是最终导致异常的原因。
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