2019-04-03 搭建Mybatis环境

1. 配置pom.xml依赖

　　　　<dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.0</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.15</version>
        </dependency>

2. 增加db.properties进行记录JDBC相关信息

jdbc.driver=com.mysql.cj.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/mybatis?serverTimezone=UTC
jdbc.username=root
jdbc.password=x5

这里需要注意的是url中需要增加参数serverTimezone=UTC，否则会报错

Exception in thread "main" org.apache.ibatis.exceptions.PersistenceException: 
### Error querying database.  Cause: java.sql.SQLException: The server time zone value 'Öйú±ê׼ʱ¼ä' is unrecognized or represents more than one time zone. You must configure either the server or JDBC driver (via the serverTimezone configuration property) to use a more specifc time zone value if you want to utilize time zone support.
### The error may exist in com/hugh/mybatis/mapper/EmployeesMapper.xml
### The error may involve com.hugh.mybatis.dao.EmployeesMapper.selectByEmployeeID
### The error occurred while executing a query
### Cause: java.sql.SQLException: The server time zone value 'Öйú±ê׼ʱ¼ä' is unrecognized or represents more than one time zone. You must configure either the server or JDBC driver (via the serverTimezone configuration property) to use a more specifc time zone value if you want to utilize time zone support.
    at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:30)
    at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:150)
    at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:141)
    at org.apache.ibatis.session.defaults.DefaultSqlSession.selectOne(DefaultSqlSession.java:77)
    at org.apache.ibatis.binding.MapperMethod.execute(MapperMethod.java:84)
    at org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:58)
    at com.sun.proxy.$Proxy0.selectByEmployeeID(Unknown Source)
    at com.hugh.mybatis.App.main(App.java:28)
Caused by: java.sql.SQLException: The server time zone value 'Öйú±ê׼ʱ¼ä' is unrecognized or represents more than one time zone. You must configure either the server or JDBC driver (via the serverTimezone configuration property) to use a more specifc time zone value if you want to utilize time zone support.
    at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:129)
    at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:97)
    at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:89)
    at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:63)
    at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:73)
    at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:76)
    at com.mysql.cj.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:835)
    at com.mysql.cj.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:455)
    at com.mysql.cj.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:240)
    at com.mysql.cj.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:199)
    at java.sql.DriverManager.getConnection(DriverManager.java:664)
    at java.sql.DriverManager.getConnection(DriverManager.java:208)
    at org.apache.ibatis.datasource.unpooled.UnpooledDataSource.doGetConnection(UnpooledDataSource.java:201)
    at org.apache.ibatis.datasource.unpooled.UnpooledDataSource.doGetConnection(UnpooledDataSource.java:196)
    at org.apache.ibatis.datasource.unpooled.UnpooledDataSource.getConnection(UnpooledDataSource.java:93)
    at org.apache.ibatis.datasource.pooled.PooledDataSource.popConnection(PooledDataSource.java:403)
    at org.apache.ibatis.datasource.pooled.PooledDataSource.getConnection(PooledDataSource.java:89)
    at org.apache.ibatis.transaction.jdbc.JdbcTransaction.openConnection(JdbcTransaction.java:138)
    at org.apache.ibatis.transaction.jdbc.JdbcTransaction.getConnection(JdbcTransaction.java:60)
    at org.apache.ibatis.executor.BaseExecutor.getConnection(BaseExecutor.java:336)
    at org.apache.ibatis.executor.SimpleExecutor.prepareStatement(SimpleExecutor.java:85)
    at org.apache.ibatis.executor.SimpleExecutor.doQuery(SimpleExecutor.java:62)
    at org.apache.ibatis.executor.BaseExecutor.queryFromDatabase(BaseExecutor.java:324)
    at org.apache.ibatis.executor.BaseExecutor.query(BaseExecutor.java:156)
    at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:109)
    at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:83)
    at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:148)
    ... 6 more
Caused by: com.mysql.cj.exceptions.InvalidConnectionAttributeException: The server time zone value 'Öйú±ê׼ʱ¼ä' is unrecognized or represents more than one time zone. You must configure either the server or JDBC driver (via the serverTimezone configuration property) to use a more specifc time zone value if you want to utilize time zone support.
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
    at com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:61)
    at com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:85)
    at com.mysql.cj.util.TimeUtil.getCanonicalTimezone(TimeUtil.java:132)
    at com.mysql.cj.protocol.a.NativeProtocol.configureTimezone(NativeProtocol.java:2241)
    at com.mysql.cj.protocol.a.NativeProtocol.initServerSession(NativeProtocol.java:2265)
    at com.mysql.cj.jdbc.ConnectionImpl.initializePropsFromServer(ConnectionImpl.java:1319)
    at com.mysql.cj.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:966)
    at com.mysql.cj.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:825)
    ... 26 more

3. 增加Mybatis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>
    <properties resource="db.properties"></properties>

    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC" />
            <dataSource type="POOLED">
                <property name="driver" value="${jdbc.driver}" />
                <property name="url" value="${jdbc.url}" />
                <property name="username" value="${jdbc.username}" />
                <property name="password" value="${jdbc.password}" />
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="com/hugh/mybatis/mapper/EmployeesMapper.xml"/>
    </mappers>
</configuration>

这里需要注意的是，假如Mapper类不是和映射文件放在同一个包下，是不能使用<package name=""/>来进行配置的，只有当配置文件和mapper接口同名且在同一包内才可以使用包配置（这个没有进行测试）

4. 配置映射文件

<?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.hugh.mybatis.dao.EmployeesMapper" >
  
  <select id="selectByEmployeeID"  resultMap="employee">
    select 
        EMPLOYEE_ID, FIRST_NAME, LAST_NAME, EMAIL, SALARY
        from EMPLOYEES
        where EMPLOYEE_ID = 100
  </select>
  
  <resultMap type="com.hugh.mybatis.domain.Employee" id="employee">
      <result property="employeeId" column="EMPLOYEE_ID"/>
      <result property="firstName" column="FIRST_NAME"/>
      <result property="lastName" column="LAST_NAME"/>
      <result property="email" column="EMAIL"/>
      <result property="salary" column="SALARY"/>
  </resultMap>
</mapper>

5. 增加Mapper接口，对应上面配置文件的接口名和方法

package com.hugh.mybatis.dao;

import com.hugh.mybatis.domain.Employee;

public interface EmployeesMapper {
    
    Employee selectByEmployeeID();
}

6. 使用API

　　　　  SqlSessionFactory sf = null;
        String resource = "mybatis-config.xml";
        InputStream inputStream = null;
        try {
            inputStream = Resources.getResourceAsStream(resource);
        } catch (IOException e) {  
            e.printStackTrace();
        }
        sf= new SqlSessionFactoryBuilder().build(inputStream);
        
        SqlSession session = sf.openSession();
        // 方式1
        EmployeesMapper mapper = session.getMapper(EmployeesMapper.class);
        System.out.println(mapper.selectByEmployeeID());
        
        // 方式2
        System.out.println(session.selectOne("com.hugh.mybatis.dao.EmployeesMapper.selectByEmployeeID"));
        
        session.close();

总结：

1.Mybatis框架在使用API时，会先根据Mybatis配置进行加载Configuration对象，从而创建sessionFactory

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2.调用API时，可以理解为通过Configuration对象获取对应xml配置进行反射生成Mapper代理类

3.采用方式2进行生成代理类时，并不一定要有对应的接口，也就是采用方式2执行statement时，不需要提供Mapper接口类，只要通过namespace和id定位到statement即可