第一个Mybatis程序

傷城~ 2023-02-19 11:29 123阅读 0赞

1、创建数据库

  1. # 创建数据库
  2. create database `mybatis`;
  4. # 使用数据库
  5. use `mybatis`;
  7. # 创建用户表
  8. create table `user`(
  9.     `id` INT(20) NOT NULL PRIMARY KEY,
  10.     `name` VARCHAR(30) DEFAULT NULL,
  11.     `pwd` VARCHAR(30) DEFAULT NULL
  12. )ENGINE=INNODB DEFAULT CHARSET=utf8;
  14. # 插入数据
  15. INSERT INTO `user`(`id`,`name`,`pwd`)
  16. VALUES (1,'小明',12345),(2,'张三',12345),(3,'李四',12345);

2、创建项目

创建一个普通的Maven项目
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修改Maven地址
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导入Maven依赖

  1. <?xml version="1.0" encoding="UTF-8"?>
  2. <project xmlns="http://maven.apache.org/POM/4.0.0"
  3.          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  4.          xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  5.     <modelVersion>4.0.0</modelVersion>
  7.     <!-- 父工程-->
  8.     <groupId>com.study</groupId>
  9.     <artifactId>Mybatis-study</artifactId>
  10.     <version>1.0-SNAPSHOT</version>
  12.     <dependencies>
  13.         <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
  14.         <dependency>
  15.             <groupId>mysql</groupId>
  16.             <artifactId>mysql-connector-java</artifactId>
  17.             <version>5.1.47</version>
  18.         </dependency>
  20.         <dependency>
  21.             <groupId>org.mybatis</groupId>
  22.             <artifactId>mybatis</artifactId>
  23.             <version>3.5.2</version>
  24.         </dependency>
  26.         <!-- https://mvnrepository.com/artifact/junit/junit -->
  27.         <dependency>
  28.             <groupId>junit</groupId>
  29.             <artifactId>junit</artifactId>
  30.             <version>4.12</version>
  31.             <scope>test</scope>
  32.         </dependency>
  33.     </dependencies>
  34. </project>

删除主目录src，并新建module。这样做的好处是自动继承父工程的依赖
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我们可以看到父工程的POM.xml文件中出现了一下内容。
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3、编写mybatis配置文件

3.1 编写xml文件

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从Mybatis官网复制配置内容

  1. <?xml version="1.0" encoding="UTF-8" ?>
  2. <!DOCTYPE configuration
  3.   PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
  4.   "http://mybatis.org/dtd/mybatis-3-config.dtd">
  6. <!--核心配置文件-->
  7. <configuration>
  8.   <environments default="development">
  9.     <environment id="development">
  10.       <transactionManager type="JDBC"/>
  11.       <dataSource type="POOLED">
  12.         <property name="driver" value="${driver}"/>
  13.         <property name="url" value="${url}"/>
  14.         <property name="username" value="${username}"/>
  15.         <property name="password" value="${password}"/>
  16.       </dataSource>
  17.     </environment>
  18.   </environments>
  20. </configuration>

3.2 编写工具类获取sqlSession

编写获取sqlSession的工具类

快速创建三级目录
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间隔使用/，如果使用.则只有一级目录。
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  1. import org.apache.ibatis.session.SqlSessionFactory;
  2. import org.apache.ibatis.session.SqlSessionFactoryBuilder;
  4. import java.io.IOException;
  5. import java.io.InputStream;
  7. public class MybatisUtils {
  10.     private static SqlSessionFactory sqlSessionFactory;
  12.     static {
  14.         try {
  16.             //使用Mybatis第一步：获取sqlSessionFactory对象
  17.             String resource = "mybatis-config.xml";
  18.             InputStream inputStream = Resources.getResourceAsStream(resource);
  19.             sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
  20.         } catch (IOException e) {
  22.             e.printStackTrace();
  23.         }
  24.     }
  26.     //既然有了 SqlSessionFactory，顾名思义，我们可以从中获得 SqlSession 的实例。SqlSession 提供了在数据库执行 SQL 命令所需的所有方法。
  27.     public static SqlSession getSqlSession(){
  29.         return sqlSessionFactory.openSession();
  30.     }
  32. }

4、编写实体类

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  1. package com.study.pojo;
  3. public class User {
  5.     private int id;
  6.     private String name;
  7.     private String pwd;
  9.     public User() {
  11.     }
  13.     public User(int id, String name, String pwd) {
  15.         this.id = id;
  16.         this.name = name;
  17.         this.pwd = pwd;
  18.     }
  20.     public int getId() {
  22.         return id;
  23.     }
  25.     public void setId(int id) {
  27.         this.id = id;
  28.     }
  30.     public String getName() {
  32.         return name;
  33.     }
  35.     public void setName(String name) {
  37.         this.name = name;
  38.     }
  40.     public String getPwd() {
  42.         return pwd;
  43.     }
  45.     public void setPwd(String pwd) {
  47.         this.pwd = pwd;
  48.     }
  50.     @Override
  51.     public String toString() {
  53.         return "User{" +
  54.                 "id='" + id + '\'' +
  55.                 ", name='" + name + '\'' +
  56.                 ", pwd='" + pwd + '\'' +
  57.                 '}';
  58.     }
  59. }

5、Dao接口及Mapper配置文件

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5.1 Dao接口

  1. package com.study.dao;
  3. import com.study.pojo.User;
  5. import java.util.List;
  7. public interface UserMapper {
  9.     List<User> getUserList();
  10. }

5.2 接口实现类由原来的UserDaoImpl转变为Mapper配置文件

  1. <?xml version="1.0" encoding="UTF-8" ?>
  2. <!DOCTYPE mapper
  3.         PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  4.         "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  6. <!--绑定UserMapper-->
  7. <mapper namespace="com.study.dao.UserMapper">
  8.     <!--id和方法名一致-->
  9.     <select id="getUserList" resultType="com.study.pojo.User">
  10.         select * from user
  11.     </select>
  12. </mapper>

注意：namespace对应Mapper接口，id属性对应方法名，resultType对应返回值类型

5.3 在Mybatis配置文件中注册

  1. <?xml version="1.0" encoding="UTF-8" ?>
  2. <!DOCTYPE configuration
  3.         PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
  4.         "http://mybatis.org/dtd/mybatis-3-config.dtd">
  6. <!--核心配置文件-->
  7. <configuration>
  8.     <environments default="development">
  9.         <environment id="development">
  10.             <transactionManager type="JDBC"/>
  11.             <dataSource type="POOLED">
  12.                 <property name="driver" value="com.mysql.jdbc.Driver"/>
  13.                 <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=true&useUnicode=true&characterEncoding=UTF-8"/>
  14.                 <property name="username" value="root"/>
  15.                 <property name="password" value="123456"/>
  16.             </dataSource>
  17.         </environment>
  18.     </environments>
  20.     <!--注册位置-->
  21.     <mappers>
  22.         <mapper resource="com/study/dao/UserMapper.xml"/>
  23.     </mappers>
  25. </configuration>

mappers标签内为注册内容。

6、编写测试

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  1. package com.study.dao;
  3. import com.study.pojo.User;
  4. import com.study.utils.MybatisUtils;
  5. import org.apache.ibatis.session.SqlSession;
  6. import org.junit.Test;
  8. import java.util.List;
  10. public class UserDaoTest {
  13.     @Test
  14.     public void test(){
  16.         //第一步：获取sqlSession对象
  17.         SqlSession sqlSession = MybatisUtils.getSqlSession();
  19.         //方式一：
  20.         UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
  21.         List<User> userList = userMapper.getUserList();
  23.         for(User user : userList){
  25.             System.out.println(user);
  26.         }
  28.         //关闭sqlSession
  29.         sqlSession.close();
  31.     }
  32. }

运行抛出异常（maper注册了，依然出现问题）

原因是mapper.xml没有导出

  1. java.lang.ExceptionInInitializerError
  2.     at com.study.dao.UserDaoTest.test(UserDaoTest.java:15)
  3.     at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
  4.     at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
  5.     at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
  6.     at java.lang.reflect.Method.invoke(Method.java:498)
  7.     at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
  8.     at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
  9.     at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
  10.     at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
  11.     at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
  12.     at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
  13.     at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
  14.     at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
  15.     at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
  16.     at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
  17.     at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
  18.     at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
  19.     at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
  20.     at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
  21.     at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
  22.     at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
  23.     at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
  24.     at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)
  25. Caused by: org.apache.ibatis.exceptions.PersistenceException: 
  26. ### Error building SqlSession.
  27. ### The error may exist in com/study/dao/UserMapper.xml
  28. ### Cause: org.apache.ibatis.builder.BuilderException: Error parsing SQL Mapper Configuration. Cause: java.io.IOException: Could not find resource com/study/dao/UserMapper.xml
  29.     at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:30)
  30.     at org.apache.ibatis.session.SqlSessionFactoryBuilder.build(SqlSessionFactoryBuilder.java:80)
  31.     at org.apache.ibatis.session.SqlSessionFactoryBuilder.build(SqlSessionFactoryBuilder.java:64)
  32.     at com.study.utils.MybatisUtils.<clinit>(MybatisUtils.java:20)
  33.     ... 23 more
  34. Caused by: org.apache.ibatis.builder.BuilderException: Error parsing SQL Mapper Configuration. Cause: java.io.IOException: Could not find resource com/study/dao/UserMapper.xml
  35.     at org.apache.ibatis.builder.xml.XMLConfigBuilder.parseConfiguration(XMLConfigBuilder.java:121)
  36.     at org.apache.ibatis.builder.xml.XMLConfigBuilder.parse(XMLConfigBuilder.java:98)
  37.     at org.apache.ibatis.session.SqlSessionFactoryBuilder.build(SqlSessionFactoryBuilder.java:78)
  38.     ... 25 more
  39. Caused by: java.io.IOException: Could not find resource com/study/dao/UserMapper.xml
  40.     at org.apache.ibatis.io.Resources.getResourceAsStream(Resources.java:114)
  41.     at org.apache.ibatis.io.Resources.getResourceAsStream(Resources.java:100)
  42.     at org.apache.ibatis.builder.xml.XMLConfigBuilder.mapperElement(XMLConfigBuilder.java:372)
  43.     at org.apache.ibatis.builder.xml.XMLConfigBuilder.parseConfiguration(XMLConfigBuilder.java:119)
  44.     ... 27 more

解决方法：

maven由于它的约定大于配置，我们之后可能遇到编写的配置文件，无法被导出或者生效的问题，解决方案

  1. <!--在build中配置resources，来防止我们资源导出失败-->
  2. <build>
  3.         <resources>
  4.             <resource>
  5.                 <directory>src/main/resources</directory>
  6.                 <includes>
  7.                     <include>**/*.properties</include>
  8.                     <include>**/*.xml</include>
  9.                 </includes>
  10.                 <filtering>true</filtering>
  11.             </resource>
  13.             <resource>
  14.                 <directory>src/main/java</directory>
  15.                 <includes>
  16.                     <include>**/*.properties</include>
  17.                     <include>**/*.xml</include>
  18.                 </includes>
  19.                 <filtering>true</filtering>
  20.             </resource>
  21.         </resources>
  22. </build>

完整的pom.xml文件

  1. <?xml version="1.0" encoding="UTF-8"?>
  2. <project xmlns="http://maven.apache.org/POM/4.0.0"
  3.          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  4.          xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  5.     <modelVersion>4.0.0</modelVersion>
  7.     <!-- 父工程-->
  8.     <groupId>com.study</groupId>
  9.     <artifactId>Mybatis-study</artifactId>
  10.     <packaging>pom</packaging>
  11.     <version>1.0-SNAPSHOT</version>
  12.     <modules>
  13.         <module>study-01</module>
  14.     </modules>
  16.     <dependencies>
  17.         <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
  18.         <dependency>
  19.             <groupId>mysql</groupId>
  20.             <artifactId>mysql-connector-java</artifactId>
  21.             <version>5.1.47</version>
  22.         </dependency>
  24.         <dependency>
  25.             <groupId>org.mybatis</groupId>
  26.             <artifactId>mybatis</artifactId>
  27.             <version>3.5.2</version>
  28.         </dependency>
  30.         <!-- https://mvnrepository.com/artifact/junit/junit -->
  31.         <dependency>
  32.             <groupId>junit</groupId>
  33.             <artifactId>junit</artifactId>
  34.             <version>4.12</version>
  35.             <scope>test</scope>
  36.         </dependency>
  39.     </dependencies>
  41.     <build>
  42.         <resources>
  43.             <resource>
  44.                 <directory>src/main/resources</directory>
  45.                 <includes>
  46.                     <include>**/*.properties</include>
  47.                     <include>**/*.xml</include>
  48.                 </includes>
  49.                 <filtering>true</filtering>
  50.             </resource>
  52.             <resource>
  53.                 <directory>src/main/java</directory>
  54.                 <includes>
  55.                     <include>**/*.properties</include>
  56.                     <include>**/*.xml</include>
  57.                 </includes>
  58.                 <filtering>true</filtering>
  59.             </resource>
  60.         </resources>
  61.     </build>
  63. </project>

运行结果

  1. User{
  2.     id='1', name='小明', pwd='12345'}
  3. User{
  4.     id='2', name='张三', pwd='12345'}
  5. User{
  6.     id='3', name='李四', pwd='12345'}
  8. Process finished with exit code 0

可能会遇到的问题

  1. 配置文件没有注册
  2. 绑定接口错误
  3. 方法名不对
  4. 返回类型不对
  5. Maven导出资源问题

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