Mybatis foreach标签使用不当致使异常的缘由探究

时间 2019-11-11

标签 mybatis foreach 标签使用不当致使异常缘由探究栏目 MyBatis 繁體版

原文原文链接

Mybatis foreach标签使用不当致使异常的缘由探究

异常产生场景及异常信息

上周，因为Mybatis的Mapper接口方法参数使用实现了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，致使出现了异常。以下为异常信息：html

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

因为本人对Mybatis还不是很是的了解，本能的怀疑是Mybatis对泛型的支持不够好致使。java

接下来介绍我是如何重现异常并分析致使异常的缘由。mysql

异常重现

为了重现上面的异常，写了demo。相关代码以下：git

数据库表结构：github

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：spring

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.javasql

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：数据库

<?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" />
            <!-- 数据库链接池,整合后通常使用第三方的链接池-->
            <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：apache

<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数组

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，你们先不要往下看，想一想致使异常的缘由（熟练使用foreach标签的同窗应该能看出端倪）。

查找异常过程及异常分析

在项目中，常常会出现DAO方法的参数类和返回结果类只包含一个键和键对应的值，为了不重复定义类，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()方法参数就使用了此泛型类，运行代码以后就抛出了本文开始提到的异常信息。

看到异常信息后，就把重点放到了是否是Mybatis对泛型的支持不够好上，因而问了下同事(@胜南)，同事写了个Demo在本身的机器上试了下，发现没有异常。这就奇怪了，仔细看了下代码，不一样之处就是个人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(连接地址：http://www.mybatis.org/mybatis-3/zh/dynamic-sql.html#foreach)：

能够将任何可迭代对象（如列表、集合等）和任何的字典或者数组对象传递给foreach做为集合参数。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。

接下来就是经过debug看看，异常产生的具体缘由：

先用实现了Map.Entry接口的KeyValue类的代码进行debug，经过异常日志能够看到异常是在 DefaultSqlSession.java:200 行抛出，那么将断点打到 DefaultSqlSession.java:197行。
而后一步步向下执行，当执行到 ForEachSqlNode.java:73行时，焕然大悟了。
先看下debug时的方法调用链图：
再看看具体的代码 ForEachSqlNode.java:73(此类就是foreach标签对应的Node类):

此时具体的异常缘由就很明显了，此处 o 对象所属的类就是KeyValue类，因为KeyValue类实现了Map.Entry接口，因此表达式 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。因此 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，这就是最终致使异常的缘由。

<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>