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<K, V> implements Map.Entry<K, V> { 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<GoodsRoomnight30days> selectByExample(GoodsRoomnight30daysExample example); <K, V> int insertBatch(List<KeyValue<K, V>> records);}mybatis-config.xml文件：
<?xml version="1.0" encoding="UTF-8" ?><!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd"><configuration> <settings> <setting name="cacheEnabled" value="false"/> </settings> <!-- 和spring整合后 environments配置将废除,交给spring管理--> <environments default="development"> <environment id="development"> <!-- 使用jdbc事务管理--> <transactionManager type="JDBC" /> <!-- 数据库连接池,整合后一般使用第三方的连接池--> <dataSource type="POOLED"> <property name="driver" value="com.mysql.jdbc.Driver" /> <property name="url" value="jdbc:mysql://localhost:3306/hotel_report?characterEncoding=utf-8" /> <property name="username" value="test_user" /> <property name="password" value="user123" /> </dataSource> </environment> </environments> <mappers> <mapper resource="mybatis/GoodsRoomnight30daysMapper.xml"/> </mappers></configuration>
GoodsRoomnight30daysMapper.xml文件的主要内容：
<insert id="insertBatch" parameterType="list"> REPLACE INTO goods_roomnight_30days (goods_id, checkin_room_night_30days) VALUES <foreach collection="list" index="index" item="item" separator=","> (#{item.key}, #{item.value}) <!--<choose>--> <!--<when test="item.value == null">(#{item.key}, 0)</when>--> <!--<when test="item.value != null">(#{item.key}, #{item.value})</when>--> <!--</choose>--> </foreach> </insert>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
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<KeyValue<Long, Integer>> records = new ArrayList<>(); records.add(new KeyValue<Long, Integer>(1725L, 5)); records.add(new KeyValue<Long, Integer>(1728L, 3)); records.add(new KeyValue<Long, Integer>(1730L, null)); records.add(new KeyValue<Long, Integer>(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<GoodsRoomnight30days> 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，异常产生的具体原因。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：
再看看具体的代码 ForEachSqlNode.java:73(此类就是foreach标签对象的Node类):
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标签的item属性对应的对象也就没有 item.key 和 item.value 属性，这就是最终导致异常的原因。
<insert id="insertBatch" parameterType="list"> REPLACE INTO goods_roomnight_30days (goods_id, checkin_room_night_30days) VALUES <foreach collection="list" index="index" item="item" separator=","> (#{item.key}, #{item.value}) </foreach></insert>以上所述是小编给大家介绍的Mybatis foreach标签使用不当导致异常的原因浅析，希望对大家有所帮助，如果大家有任何疑问请给我留言，小编会及时回复大家的。在此也非常感谢大家对武林网网站的支持！