我的第一个mybatis程序（含纠错）
编写一个mybatis程序的主要流程：
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搭建需要的环境
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导入相关jar包
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编写代码
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运行测试
搭建环境
使用MySQL数据库
创建一个表名为mybatis，写入几行数据，具体代码如下：
CREATE DATABASE `mybatis`; //新建数据库 USE `mybatis`; CREATE TABLE `user`( //创建表 `id` INT(20) NOT NULL, `name` VARCHAR(30) DEFAULT NULL, `pwd` VARCHAR(30) DEFAULT NULL, PRIMARY KEY(`id`) )ENGINE=INNODB DEFAULT CHARSET=utf8; INSERT INTO `user`(`id`,`name`,`pwd`) VALUES //写入数据 (1,'hayden','9918'), (2,'wong','8899'), (3,'jane','123456')
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新建一个普通的maven项目
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删除该项目下的src目录，使其成为一个父工程（方便之后进行在父工程下创建子工程）
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在pom.xml中导入依赖（MySQL驱动、mybatis、junit）
<!--导入依赖--> <dependencies> <!--mysql驱动--> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>5.1.46</version> </dependency> <!--mybatis--> <dependency> <groupId>org.mybatis</groupId> <artifactId>mybatis</artifactId> <version>3.5.5</version> </dependency> <!--junit--> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>4.12</version> <scope>test</scope> </dependency> </dependencies>
创建一个模块
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在之前的父工程下创建一个模块（本子模块就可以使用原来父工程的pom.xml中导入的jar包）
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配置核心配置：在新建的子工程目录下的src/main/resourses目录下新建文件：mybatis-config.xml，并写入下列核心配置文件
<?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核心配置文件--> <configuration> <environments default="development"> <environment id="development"> <transactionManager type="JDBC"/> <dataSource type="POOLED"> <property name="driver" value="${driver}"/> <property name="url" value="${url}"/> <property name="username" value="${username}"/> <property name="password" value="${password}"/> </dataSource> </environment> </environments> <!--每一个mapper.xml都需要在mybatis.xml的核心配置文件中注册--> <mappers> <mapper resource="com.wong.dao.UserMapper.xml"/> </mappers> </configuration>
将其中的value值修改为我们需要的：
<?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核心配置文件--> <configuration> <environments default="development"> <environment id="development"> <transactionManager type="JDBC"/> <dataSource type="POOLED"> <property name="driver" value="com.mysql.jdbc.Driver"/> <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=false&userUnicode=true&characterEncoding=UTF-8"/> <property name="username" value="root"/> <property name="password" value="123456"/> </dataSource> </environment> </environments> <!--每一个mapper.xml都需要在mybatis.xml的核心配置文件中注册--> <mappers> <mapper resource="com.wong.dao.UserMapper.xml"/> </mappers> </configuration>
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编写mybatis工具类（在java目录下创建包Utils，创建类MybatisUtils，使用sql语言时就需要用到这个工具类）
package com.wong.utils; 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 java.io.IOException; import java.io.InputStream; public class MybatisUtils { private static SqlSessionFactory sqlSessionFactory; static { try { String resource = "mybatis-config.xml"; InputStream inputStream = Resources.getResourceAsStream(resource); sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); } catch (IOException e) { e.printStackTrace(); } } //获取SqlSession连接 public static SqlSession getSession(){ return sqlSessionFactory.openSession(); } }
编写代码
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数据库相关实体类
package com.wong.pojo; public class User { private int id; private String name; private String pwd; public User() { } public User(int id, String name, String pwd) { this.id = id; this.name = name; this.pwd = pwd; } public int getId() { return id; } public void setId(int id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getPwd() { return pwd; } public void setPwd(String pwd) { this.pwd = pwd; } @Override public String toString() { return "User{" + "id=" + id + ", name='" + name + '\'' + ", pwd='" + pwd + '\'' + '}'; } }
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Dao接口
package com.wong.dao; import com.wong.pojo.User; import java.util.List; public interface UserMapper { List<User> selectUser(); }
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接口实现
<?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"> <!--namespace=绑定一个对应的Dao/Mapper接口--> <mapper namespace="com.wong.dao.UserMapper"> <select id="selectUser" resultType="com.wong.pojo.User"> select * from user </select> </mapper>
测试
package com.wong.dao; import com.wong.pojo.User; import com.wong.utils.MybatisUtils; import org.apache.ibatis.session.SqlSession; import org.junit.Test; import java.util.List; public class MyTest { @Test public void selectUser() { SqlSession session = MybatisUtils.getSession(); //方法一: //List<User> users = session.selectList("com.wong.mapper.UserMapper.selectUser"); //方法二: UserMapper mapper = session.getMapper(UserMapper.class); List<User> users = mapper.selectUser(); for (User user: users){ System.out.println(user); } session.close(); } }
得到结果：
User{id=1, name='hayden', pwd='9918'} User{id=2, name='wong', pwd='8899'} User{id=3, name='jane', pwd='123456'} Process finished with exit code 0
代码文件位置图
常见报错
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org.apache.ibatis.exceptions.PersistenceException: ### Error querying database. 异常解决
完整的url的value如下: jdbc:mysql://localhost:3306/mybatis?useSSL=false&useUnicode=true&characterEncoding=utf8
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org.apache.ibatis.binding.BindingException: Invalid bound statement (not found):
核心配置文件中缺少：
<mappers> <mapper resource="com.wong.dao.UserMapper.xml"/> </mappers>
或者名称错误！
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java.lang.ExceptionInInitializerError //初始化异常
在pom.xml中添加以下代码：
<!--防止资源导出失败的问题--> <build> <resources> <resource> <directory>src/main/java</directory> <includes> <include>**/*.properties</include> <include>**/*.xml</include> </includes> <filtering>false</filtering> </resource> <resource> <directory>src/main/resources</directory> <includes> <include>**/*.properties</include> <include>**/*.xml</include> </includes> <filtering>false</filtering> </resource> </resources> </build>
