MyBatis 3+Spring3:选择返回空值

Question

我在MyBatis示例的基础上构建了一个项目(我还研究了JPetStore 6应用程序)。

问题是，我的getTrains()方法总是返回空对象。下面是源文件和配置文件：

TrainMapper.java

package org.example.mybatis.spring.persistence;

import java.util.List;
import org.example.mybatis.spring.domain.Train;

public interface TrainMapper {

    Train getTrain(int id);
    List<Train> getTrains();
    void insertTrain(Train train);
}

TrainService.java

package org.example.mybatis.spring.service;

import java.util.List;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;
import org.example.mybatis.spring.domain.Train;
import org.example.mybatis.spring.persistence.TrainMapper;

@Service("trainService")

public class TrainService {

@Autowired
private TrainMapper trainMapper;

public void setTrainMapper(TrainMapper trainMapper) {
    this.trainMapper = trainMapper;
}

public Train getTrain(int id) {
    return this.trainMapper.getTrain(id);
}

public List<Train> getTrains() {
    return this.trainMapper.getTrains();
}

@Transactional
public void insertTrain(Train train) {
    this.trainMapper.insertTrain(train);
}

}

TrainMapper.xml

   <?xml version="1.0" encoding="UTF-8" ?>
    <!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

    <mapper namespace="org.example.mybatis.spring.persistence.TrainMapper">
      <cache />
      <select id="getTrain" resultType="Train" parameterType="int">
        SELECT
          train_type
        FROM trains
        WHERE trains.train_id = #{id}
      </select>
      <select id="getTrains" resultType="org.example.mybatis.spring.domain.Train" parameterType="int">
        SELECT
          train_type
        FROM trains
      </select>
      <insert id="insertTrain" parameterType="Train">
        INSERT INTO trains (train_type)
        VALUES (#{type})
      </insert>
    </mapper>

applicationContext.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:jdbc="http://www.springframework.org/schema/jdbc"
       xmlns:tx="http://www.springframework.org/schema/tx"
       xsi:schemaLocation="
         http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.1.xsd
         http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.1.xsd
         http://www.springframework.org/schema/jdbc http://www.springframework.org/schema/jdbc/spring-jdbc-3.1.xsd
         http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.1.xsd">

  <context:property-placeholder location="classpath:mysql.jdbc.properties" />

  <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close">
    <property name="driverClassName" value="${jdbc.driverClassName}" />
    <property name="url" value="${jdbc.url}" />
    <property name="username" value="${jdbc.username}" />
    <property name="password" value="${jdbc.password}" />
  </bean>

  <bean id="transactionManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
    <property name="dataSource" ref="dataSource" />
  </bean>

  <context:component-scan base-package="org.example.mybatis.spring" />

  <tx:annotation-driven />

  <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
    <property name="dataSource" ref="dataSource" />
    <property name="typeAliasesPackage" value="org.example.mybatis.spring.domain" />
    <!--property name="configLocation" value="classpath:mybatis-config.xml"/-->
    <!--property name="mapperLocations" value="classpath:org/example/mybatis/spring/persistence/*.xml" /-->
  </bean>

  <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
    <property name="basePackage" value="org.example.mybatis.spring.persistence" />
  </bean>
</beans>

Train.java是一个简单的Java。

项目POM：

<project xmlns="http://maven.apache.org/POM/4.0.0" 
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>org.example</groupId>
  <artifactId>mybatis-spring-example</artifactId>
  <name>MyBatis-Spring Example</name>
  <version>0.0.1-SNAPSHOT</version>
  <packaging>jar</packaging>
  <description>Example of the MyBatis-Spring integration (within a Maven project)</description>

  <properties>
    <maven.compiler.plugin.version>2.5.1</maven.compiler.plugin.version>
    <log4j.version>1.2.17</log4j.version>
    <junit.version>4.10</junit.version>
    <mysql.connector.version>5.1.20</mysql.connector.version>
    <spring.version>3.1.2.RELEASE</spring.version>
    <mybatis.version>3.1.1</mybatis.version>
    <mybatis.spring.version>1.1.1</mybatis.spring.version>
    <hsqldb.version>2.2.8</hsqldb.version>
    <dbcp.version>1.4</dbcp.version>
    <cglib.version>2.2.2</cglib.version>
    <nexus.ip>x.y.w.z</nexus.ip>
    <nexus.port>xxxx</nexus.port>
    <nexus.public.group.url>http://${nexus.ip}:${nexus.port}/nexus/content/groups/public</nexus.public.group.url>
    <nexus.releases.url>http://${nexus.ip}:${nexus.port}/nexus/content/repositories/releases</nexus.releases.url>
    <nexus.snapshots.url>http://${nexus.ip}:${nexus.port}/nexus/content/repositories/snapshots</nexus.snapshots.url>
  </properties>

  <repositories>
    <repository>
      <id>nexus-internal-repo</id>
      <name>Sonatype Nexus Internal Repository</name>
      <url>${nexus.public.group.url}</url>
      <releases>
        <enabled>true</enabled>
        <updatePolicy>never</updatePolicy>
        <checksumPolicy>fail</checksumPolicy>
      </releases>
      <snapshots>
        <enabled>true</enabled>
        <updatePolicy>never</updatePolicy>
        <checksumPolicy>warn</checksumPolicy>
      </snapshots>
    </repository>
  </repositories>

  <dependencies>
<dependency>
  <groupId>org.mybatis</groupId>
  <artifactId>mybatis</artifactId>
  <version>${mybatis.version}</version>
</dependency>

<dependency>
  <groupId>org.mybatis</groupId>
  <artifactId>mybatis-spring</artifactId>
  <version>${mybatis.spring.version}</version>
</dependency>

<dependency>
  <groupId>log4j</groupId>
  <artifactId>log4j</artifactId>
  <version>${log4j.version}</version>
</dependency>

<dependency>
  <groupId>mysql</groupId>
  <artifactId>mysql-connector-java</artifactId>
  <version>${mysql.connector.version}</version>
</dependency>

<dependency>
  <groupId>commons-dbcp</groupId>
  <artifactId>commons-dbcp</artifactId>
  <version>${dbcp.version}</version>
</dependency>

<dependency>
  <groupId>cglib</groupId>
  <artifactId>cglib</artifactId>
  <version>${cglib.version}</version>
</dependency>

我以独立的方式运行应用程序：

package org.example.mybatis.spring;

import java.util.List;
import org.example.mybatis.spring.domain.Train;
import org.example.mybatis.spring.service.TrainService;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

    public class SelectTrainExample {

        public static void main(String[] args) {
            ApplicationContext context = new ClassPathXmlApplicationContext(
                    "applicationContext.xml");
            TrainService trainBean = (TrainService) context.getBean("trainService");

            List<Train> trains = trainBean.getTrains();
            System.out.println(trains.toString());

            Train train = trainBean.getTrain(1);
            System.out.println(train.toString());

            Train t = new Train();
            t.setType("Interregionale");
            trainBean.insertTrain(t);
        }
    }

数据库中的insert可以正常工作，而我无法从"trains“表中检索数据。下面是日志输出：

2012-01 15:25:03,400调试org.apache.ibatis.cache.decorators.LoggingCache - 2012-10-01 15:25:03,413调试org.mybatis.spring.SqlSessionUtils -2012-01 15:25:03,463调试org.mybatis.spring.transaction.SpringManagedTransaction - 2012-10-01 15:25:03,473调试org.mybatis.spring.transaction.SpringManagedTransaction-2012:10-01 15:03,474调试org.mybatis.spring.transaction.SpringManagedTransaction-2012-0115:25:03,479调试org.example.mybatis.spring.persistence.TrainMapper.getTrains -2012- 15: 25:25:03,497调试org.example.mybatis.spring.persistence.TrainMapper.getTrains - <==>准备:从trains中选择train_type >2012-01 15:25:03,578调试org.example.mybatis.spring.persistence.TrainMapper.getTrains - <==>参数：> 2012-10-01 15:25:03,660调试org.mybatis.spring.SqlSessionUtils -2012-01 15:15：25:03,661调试org.springframework.jdbc.datasource.DataSourceUtils -空，空，空，空，null 2012-10-01 15:25:03,664调试org.springframework.beans.factory.support.DefaultListableBeanFactory - 2012-10-01 15:25:03,668调试org.springframework.jdbc.datasource.DataSourceTransactionManager - 2012-10-01 15:25:03,669调试org.springframework.jdbc.datasource.DataSourceTransactionManager -2012-01 15:25:03,673调试org.springframework.jdbc.datasource.DataSourceTransactionManager -2012-01 15:03,674调试org.mybatis.spring。调试org.mybatis.spring.transaction.SpringManagedTransaction - 2012-10-01 15:25:03,674调试org.mybatis.spring.SqlSessionUtils -2012-01 15:25:03,679调试org.mybatis.spring.SqlSessionUtils- 2012-10-01 15:25:03，调试org.example.mybatis.spring.persistence.TrainMapper.insertTrain - <==>准备:插入trains (train_type)值(Train_type)值(?)>2012-01 15:25:03,680调试org.example.mybatis.spring.persistence.TrainMapper.insertTrain - <==>参数:区域间(字符串)> 2012-10-01 15:25:03,681调试org.mybatis.spring.SqlSessionUtils -2012-01 15:25:03,681调试org.mybatis.spring.SqlSessionUtils-2012-01 15:25:03,683调试org.springframework.jdbc.datasource.DataSourceTransactionManager - 2012-10-01 15:25:03,727调试组织调试org.springframework.jdbc.datasource.DataSourceTransactionManager - 2012-10-01 15:25:03,727调试org.mybatis.spring.SqlSessionUtils -2012-01 15:25:03,728调试.mybatis.spring.SqlSessionUtils -2012-01 15:25:03,728调试org.mybatis.spring.SqlSessionUtils-

请注意，我使用JDBC运行了同一个示例，它运行得很好。

库与环境:Spring3.1.2 MyBatis 3.1.1 MyBatis-Spring1.1.1 MySQL 5.5

提前谢谢。

Answer 1

您还没有发布您的“列车”java bean。但是在使用#{type}的Insert语句中，我认为您的bean属性名是"id“和"type”。但是在数据库表中，字段名是"id“和"train_type”。Mybatis不知道如何将表字段映射到java属性。在Mapper.xml中，您没有添加结果映射。有两种方法：

1. 在您的resultMap元素中添加mapper.xml元素，告诉mybiatis如何将数据库表字段名映射到java属性名。
2. 在select语句中使用"as“，如下所示 从列车中选择train_type作为类型