MyBatis入门

MyBatis 入门

入门学习小目标：结合官方的说明文档，实现基本的增删改查的操作。

初识 MyBatis

简介

MyBatis 是一款持久层框架
支持自定义SQL、存储过程、高级映射
MyBatis 免除了几乎所有JDBC代码以及设置参数和获取结果集的工作
MyBatis本是apache的一个开源项目iBatis，2010年这个项目由apache software foundation迁移到了google code，并且改名为MyBatis。

特征

①、简单易学：本身就很小且简单。没有任何第三方依赖，最简单安装只要两个jar文件+配置几个sql映射文件。易于学习，易于使用。通过文档和源代码，可以比较完全的掌握它的设计思路和实现。
②、灵活：mybatis不会对应用程序或者数据库的现有设计强加任何影响。 sql写在xml里，便于统一管理和优化。通过sql语句可以满足操作数据库的所有需求。
③、解除sql与程序代码的耦合：通过提供DAO层，将业务逻辑和数据访问逻辑分离，使系统的设计更清晰，更易维护，更易单元测试。sql和代码的分离，提高了可维护性。
④、提供映射标签，支持对象与数据库的orm字段关系映射。（Object Relational Mapping，简称ORM 对象关系映射）
⑤、提供对象关系映射标签，支持对象关系组建维护。
⑥、提供xml标签，支持编写动态sql。

入门安装

删除src目录，新建Module: mybatis_01，新建包

整体项目结构图：

导入依赖包

配置pom.xml文件

<?xml version="1.0" encoding="UTF-8"?>
<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>com.rucoding</groupId>
    <artifactId>MyBatis_Study</artifactId>
    <packaging>pom</packaging>
    <version>1.0-SNAPSHOT</version>
    <modules>
        <module>mybatis_01</module>
    </modules>

    <dependencies>
        <!--mybatis的jar包-->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.2</version>
        </dependency>
        <!--Mysql驱动包-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.47</version>
        </dependency>
        <!--单元测试包-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>
    </dependencies>

</project>

创建SqlMapConfig文件

resources目录下新建文件：mybatis-config.xml

<?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>
    <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:13306/mybatis?useSSL=false&amp;useUnicode=true&amp;characterEncoding=UTF-8"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>
</configuration>

编写工具类

package com.rucoding.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 = null;
    static {
        try {
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static SqlSession getSqlSession() {
        return sqlSessionFactory.openSession();
    }

}

编写实体类

package com.rucoding.pojo;

public class User {
    private Integer id;
    private String name;
    private String pwd;

    public User(Integer id) {
        this.id = id;
    }

    public User(Integer id, String name, String pwd) {
        this.id = id;
        this.name = name;
        this.pwd = pwd;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer 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 + '\'' +
                '}';
    }
}

编写Dao层和SqlMap.xml

UserDao:

package com.rucoding.dao;

import com.rucoding.pojo.User;

import java.util.List;

public interface UserDao {
    /**
     * 获取所有用户信息
     * @return
     */
    List<User> getAllUser();
}

UserDaoMapper.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="com.rucoding.dao.UserDao">
    <select id="getAllUser" resultType="User">
        select * from user
    </select>
</mapper>

新建测试类

package com.rucoding.demo;

import com.rucoding.dao.UserDao;
import com.rucoding.pojo.User;
import com.rucoding.utils.MyBatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import java.util.List;

public class MyBatisDemo {

    @Test
    public void testQuery() {
        SqlSession sqlSession = MyBatisUtils.getSqlSession();
        UserDao userMapper = sqlSession.getMapper(UserDao.class);
        List<User> allUser = userMapper.getAllUser();
        for (User user : allUser) {
            System.out.println(user);
        }

    }
}

启动运行：

报错①

报错如下：

org.apache.ibatis.binding.BindingException: Type interface com.rucoding.dao.UserDao is not known to the MapperRegistry.

理解报错信息：

MapperRegistry:在核心配置文件中注册Mappers
每一个Mapper.xml都需要在MyBatis核心配置文件中注册!
mybatis-config.xml中配置

完善配置文件 mybatis-config.xml：

<?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>
    <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&amp;useUnicode=true&amp;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核心配置文件中注册!-->
    <mappers>
        <mapper resource="com/rucoding/dao/UserDaoMapper.xml"/>
    </mappers>
</configuration>

再次运行：

报错②

### Cause: org.apache.ibatis.builder.BuilderException: Error parsing SQL Mapper Configuration. Cause: java.io.IOException: Could not find resource com/rucoding/dao/UserDaoMapper.xml

理解报错信息：

Could not find resource com/rucoding/dao/UserDaoMapper.xml

此时展开target目录：

target是用来存放项目构建后的文件和目录、jar包、war包、编译的class文件的。

发现target目录没有对应编辑后的文件，完善配置pom.xml文件

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<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>com.rucoding</groupId>
    <artifactId>MyBatis_Study</artifactId>
    <packaging>pom</packaging>
    <version>1.0-SNAPSHOT</version>
    <modules>
        <module>mybatis_01</module>
    </modules>

    <dependencies>
        <!--mybatis的jar包-->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.2</version>
        </dependency>
        <!--Mysql驱动包-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.47</version>
        </dependency>
        <!--单元测试包-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>
    </dependencies>
    <!--在build中配置resources，来防止我们资源导出失败的问题-->
    <!--maven由于他的约定大于配置，我们之后可以能遇到我们写的配置文件，无法被导出或者生效的问题，-->
    <build>
        <resources>
            <resource>
                <directory>src/main/resources</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>true</filtering>
            </resource>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>true</filtering>
            </resource>
        </resources>
    </build>

</project>

报错③

### Cause: org.apache.ibatis.builder.BuilderException: Error parsing SQL Mapper Configuration. Cause: org.apache.ibatis.builder.BuilderException: Error parsing Mapper XML. The XML location is 'com/rucoding/dao/UserDaoMapper.xml'. Cause: org.apache.ibatis.builder.BuilderException: Error resolving class. Cause: org.apache.ibatis.type.TypeException: Could not resolve type alias 'User'.  Cause: java.lang.ClassNotFoundException: Cannot find class: User

理解报错信息：

Could not resolve type alias 'User'.无法解析User
resultType="com.rucoding.pojo.User"> 配置有误

修改UserDaoMapper.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="com.rucoding.dao.UserDao">
    <select id="getAllUser" resultType="com.rucoding.pojo.User">
        select * from user
    </select>
</mapper>

报错④

org.apache.ibatis.exceptions.PersistenceException: 
### Error querying database.  Cause: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

The last packet successfully received from the server was 1,793 milliseconds ago.  The last packet sent successfully to the server was 1,781 milliseconds ago.
### The error may exist in com/rucoding/dao/UserDaoMapper.xml
### The error may involve com.rucoding.dao.UserDao.getAllUser
### The error occurred while executing a query
### Cause: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

The last packet successfully received from the server was 1,793 milliseconds ago.  The last packet sent successfully to the server was 1,781 milliseconds ago.

报错信息：

这是连接Mysql数据库参数配置问题:
useSSL=true 修改为 useSSL=false
& 表示的就是 &

 <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=true&amp;useUnicode=true&amp;characterEncoding=UTF-8"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
</dataSource>

拓展：mybatis的特殊符号：&amp；&lt；&gt；&quot；&apos；

	  特殊字符   		      替代符号
	
	     &            		 &
	
	     <            		 &lt;
	
	     >                   &gt;
	
	     "                   &quot;
	
	     '                   &apos;
	    小于等于    a<=b      a &lt;= b           a <![CDATA[<= ]]>b

		大于等于    a>=b      a &gt;= b           a <![CDATA[>= ]]>b

		不等于     a!=b       a <![CDATA[ <> ]]>b      a <![CDATA[!= ]]>b	

运行成功：

入门文档官方地址

MyBatis官方地址文档说明