参考文献:https://blog.csdn.net/u013036274/article/details/55668317

原始dao方式

需要写dao接口和dao实现类。

• 创建dao接口：UserDao.java

package cn.itcast.mybatis.dao;
import cn.itcast.mybatis.po.Employee;
public interface UserDao {
    public Employee findUserById(int id) throws Exception;
    public void insertUser(Employee employee) throws Exception;
    public void deleteUser(int id) throws Exception;
}

• 创建dao实现类：UserDaoImpl.java

package cn.itcast.mybatis.dao;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import cn.itcast.mybatis.po.Employee;
public class UserDaoImpl implements UserDao{
    private SqlSessionFactory sqlSessionFactory;
    public  UserDaoImpl(SqlSessionFactory sqlSessionFactory) {
        this.sqlSessionFactory = sqlSessionFactory;
    }
    @Override
    public Employee findUserById(int id) throws Exception {
        SqlSession sqlSession =sqlSessionFactory.openSession();
        Employee employee = sqlSession.selectOne("test.findUserById",id);
        sqlSession.close();
        return employee;
    }
    @Override
    public void insertUser(Employee employee) throws Exception {
        SqlSession sqlSession =sqlSessionFactory.openSession();
        sqlSession.insert("test.insertUser",employee);
        sqlSession.commit();
        sqlSession.close(); 
    }
    @Override
    public void deleteUser(int id) throws Exception {
        SqlSession sqlSession =sqlSessionFactory.openSession();
        sqlSession.delete("test.deleteUser",id);
        sqlSession.commit();
        sqlSession.close(); 
    }
}

• 测试方法：

package cn.itcast.mybatis.dao;
import static org.junit.Assert.*;
import java.io.InputStream;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Before;
import org.junit.Test;
import cn.itcast.mybatis.po.Employee;
public class UserDaoImplTest {
    private SqlSessionFactory sqlSessionFactory;
    @Before
    public void setUp() throws Exception{
        String resource="SqlMapConfig.xml";
        InputStream inputStream= Resources.getResourceAsStream(resource);
        sqlSessionFactory =new SqlSessionFactoryBuilder().build(inputStream);
    }
    @Test
    public void test() throws Exception {
        UserDao userDao = new UserDaoImpl(sqlSessionFactory);
        Employee employee = userDao.findUserById(3);
        System.out.println(employee);
    }
}

缺点：

接口实现类方法中存在大量模板方法，设想能否将这些代码提取出来。
另外调用SqlSession方法时，将Statement的id硬编码了。
调用SqlSession方法时，传入的变量，由于SqlSession方法使用泛型，即使变量类型传入错误，在编译阶段也不报错，不利于开发。

mapper代理方法

• xml映射文件 (UserMapper.xml)
  ①在mapper.xml中namespace等于mapper接口地址
  ②mapper.java接口中的方法名和mapper.xml中的Statement的id一致
  ③mapper.java接口中的方法输入参数类型和mapper.xml中Statement的parameterType指定类型一致
  ④mapper.java接口中的方法返回值类型和mapper.xml中Statement的resultType指定的类型一致

<mapper namespace="cn.itcast.mybatis.mapper.UserMapper">
     <select id="findUserById" parameterType="int" resultType="cn.itcast.mybatis.po.Employee">
         select id,username,sex,address from users where id=#{id};
     </select>

• mapper接口，相当于dao接口(UserMapper.java)

package cn.itcast.mybatis.mapper;
import cn.itcast.mybatis.po.Employee;
public interface UserMapper {
    public Employee findUserById(int id) throws Exception;
        public java.util.List<Employee> findUserByName(String name) throws Exception;
    public void insertUser(Employee employee ) throws Exception;
    public void deleteUser(int id) throws Exception;

}

• 还需在SqlMapConfig.xml加载映射文件

<mapper resource="mapper/UserMapper.xml"/>

• 测试文件

package cn.itcast.mybatis.mapper;
import static org.junit.Assert.*;
import java.io.InputStream;
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 org.junit.Before;
import org.junit.Test;
import cn.itcast.mybatis.po.Employee;
public class UserMapperTest {
private SqlSessionFactory sqlSessionFactory;
    @Before
    public void setUp() throws Exception{
        String resource="SqlMapConfig.xml";
        InputStream inputStream= Resources.getResourceAsStream(resource);
        sqlSessionFactory =new SqlSessionFactoryBuilder().build(inputStream);
    }
    @Test
    public void test() throws Exception {
        SqlSession sqlSession =sqlSessionFactory.openSession();
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        Employee employee =userMapper.findUserById(2);
        System.out.println(employee);
    }
        @Test
    public void test1() throws Exception {
        SqlSession sqlSession =sqlSessionFactory.openSession();
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        java.util.List<Employee> list =userMapper.findUserByName("zhao");
        sqlSession.close();
        System.out.println(list);
    }
}

通过调用单独的文件连接数据库

• SqlMapConfig.xml

<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> 

• db.properties（和SqlMapConfig.xml在同一目录下）

jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/test?serverTimezone=GMT%2B8
jdbc.username=root
jdbc.password=

pojo包装类型实现

• UserMapper.xml（定义用户信息综合查询，查询条件复杂）

 <select id="findUserList" parameterType="cn.itcast.mybatis.po.UserQueryVo" resultType="cn.itcast.mybatis.po.EmployeeCustom">
         select id,username,sex,address from users where sex= #{employeeCustom.sex} and username like '%${employeeCustom.username}%';
     </select>

• UserQueryVo.java（包装对象）

package cn.itcast.mybatis.po;
public class UserQueryVo {
    private EmployeeCustom employeeCustom;
    public EmployeeCustom getEmployeeCustom() {
        return employeeCustom;
    }
    public void setEmployeeCustom(EmployeeCustom employeeCustom) {
        this.employeeCustom = employeeCustom;
    }
}

• EmployeeCustom.java

package cn.itcast.mybatis.po;
public class EmployeeCustom extends Employee{   
}

• 测试文件

@Test
    public void test1() throws Exception {
        SqlSession sqlSession =sqlSessionFactory.openSession();
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
                //创建包装对象，设置查询条件
        UserQueryVo userQueryVo= new UserQueryVo();
        EmployeeCustom employeeCustom=new EmployeeCustom();
        employeeCustom.setSex("nv");
        employeeCustom.setUsername("zhou");
        userQueryVo.setEmployeeCustom(employeeCustom);
               //调用userMapper的方法
        java.util.List<EmployeeCustom> list =userMapper.findUserList(userQueryVo);
        sqlSession.close(); 
        System.out.println(list);
    }

动态sql判断

• UserMapper.xml(判断传入的sex和username是否为空，若是空则不进行拼接)

 <select id="findUserList" parameterType="cn.itcast.mybatis.po.UserQueryVo" resultType="cn.itcast.mybatis.po.EmployeeCustom">
         select id,username,sex,address from users 
         <where>
              <if test="employeeCustom!=null">
                 <if test="employeeCustom.sex!=null and employeeCustom.sex!=''">
                      and sex= #{employeeCustom.sex}
                 </if>
                 <if test="employeeCustom.username!=null and employeeCustom.username!=''">
                       and username like '%${employeeCustom.username}%';
                 </if>
               </if>
         </where>  
          
     </select>

• 测试文件

@Test
    public void test1() throws Exception {
        SqlSession sqlSession =sqlSessionFactory.openSession();
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        UserQueryVo userQueryVo= new UserQueryVo();
        EmployeeCustom employeeCustom=new EmployeeCustom();
        //employeeCustom.setSex("nv");//注释此句后，查询语句中没有sex这个条件
        employeeCustom.setUsername("zhou");
        userQueryVo.setEmployeeCustom(employeeCustom);
        java.util.List<EmployeeCustom> list =userMapper.findUserList(userQueryVo);
        sqlSession.close(); 
        System.out.println(list);
    }

** 进行select * from users where id=1 or id=10 or id=11 ;**

• 在上面的UserMapper.xml中添加

<if test="ids!=null">
                 <!-- collection:指定输入对象中集合属性 item:每个遍历生成对象中 open:开始遍历时拼接串 
                 close:结束遍历时拼接的串 separator:遍历两个对象须拼接的串
                                实现拼接 AND (id=1 or id=10 or id=13) -->
                 <foreach collection="ids" item="user_id" open="AND (" close=")" separator="or">
                      id=#{user_id}
                 </foreach>

• 测试文件

@Test
    public void test1() throws Exception {
        SqlSession sqlSession =sqlSessionFactory.openSession();
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        UserQueryVo userQueryVo= new UserQueryVo();
        EmployeeCustom employeeCustom=new EmployeeCustom();
        //employeeCustom.setSex("nv");
        employeeCustom.setUsername("zhou");
        java.util.List<Integer> ids =new ArrayList<Integer>();
        ids.add(1);
        ids.add(10);
        ids.add(14);
        userQueryVo.setIds(ids);
        userQueryVo.setEmployeeCustom(employeeCustom);
        java.util.List<EmployeeCustom> list =userMapper.findUserList(userQueryVo);
        sqlSession.close(); 
        System.out.println(list);
    }