異常產生場景及異常信息
上週，由於在Mybatis的Mapper接口方法中使用實現了Map.Entry接口的泛型類，同時此方法對應的sql語句也使用了foreach標籤，導致出現了異常。如下為異常信息：
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
由於本人對Mybatis還不是非常的了解，導致用了很長的時間去debug找具體的異常原因。
接下來介紹我將重現異常並分析導致異常的原因。
異常重現
為了重現上面的異常，寫了demo。相關代碼如下：
數據庫表結構：
CREATE TABLE `goods_roomnight_30days` ( `goods_id` bigint(20) NOT NULL, `checkin_room_night_30days` int(11) NOT NULL DEFAULT '0' COMMENT '近30天消費間夜', PRIMARY KEY (`goods_id`)) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='goods的近30天消費間夜'
KeyValue.java 參數類：
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類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整合後environments配置將廢除,交給spring管理--> <environments default="development"> <environment id="development"> <!-- 使用jdbc事務管理--> <transactionManager type="JDBC" /> <!-- 數據庫連接池,整合後一般使用第三方的連接池--> <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文件的主要內容：
<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>以上為重現此異常的主要代碼，完整代碼可在Github查看：https://github.com/misterzhou/java-demo/tree/master/test-spring/spring-server
重現異常的測試代碼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(); } }}賣個關子，大家先不要往下看，想想導致異常的原因（熟練使用foreach標籤的同學應該能看出端倪）。
查找異常過程及異常分析
在項目中，由於DAO方法的參數類和返回結果類經常會包含一個鍵和鍵對應的值，為了避免重複定義類，我定義了一個實現了Map.Entry接口的KeyValue泛型類，具體請查看上節。
GoodsRoomnight30daysMapper.insertBatch()方法就使用了此泛型類。在運行之後就拋出了本文開始提到的異常信息。
看到異常信息後，就把重點放到了是不是Mybatis對泛型的支持不夠好上。問了下同事(@勝男)，同事在自己的機器上試了下，發現沒有異常。這就奇怪了。仔細看了下代碼，發現不同之處就是我的KeyValue泛型類實現了Map.Entry接口。 此時還不知道mybatis官網對於foreach標籤的說明：
可以將任何可迭代對象（如列表、集合等）和任何的字典或者數組對像傳遞給foreach作為集合參數。當使用可迭代對像或者數組時，index是當前迭代的次數，item的值是本次迭代獲取的元素。當使用字典（或者Map.Entry對象的集合）時，index是鍵，item是值。
接下來就是通過debug看看，異常產生的具體原因。於是就先用實現了Map.Entry接口的KeyValue類的代碼進行debug，通過異常日誌可以看到異常是在DefaultSqlSession.java:200 行拋出，那麼將斷點打到DefaultSqlSession.java:197行，然後一步步向下執行，當執行到ForEachSqlNode.java:73行時，終於煥然大悟。先看下debug調用鏈圖：
再看看具體的代碼ForEachSqlNode.java:73(此類就是foreach標籤對象的Node類):
此時具體的異常原因就很明顯了，此處的o 對象的所屬的類就是KeyValue類，由於KeyValue類實現了Map.Entry接口，所以o instance Map.Entry 為true，mybatis就把key值賦給了foreach的index屬性，而把value值賦給了item屬性，此處也就是把值為5的Integer對象賦給了item屬性。所以GoodsRoomnight30daysMapper.xml 中id為insertBatch 的select標籤的item屬性對應的對像也就沒有item.key 和item.value 屬性，這就是最終導致異常的原因。
<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>以上所述是小編給大家介紹的Mybatis foreach標籤使用不當導致異常的原因淺析，希望對大家有所幫助，如果大家有任何疑問請給我留言，小編會及時回復大家的。在此也非常感謝大家對武林網網站的支持！