Define an interface that declares the query method.

package com.example.mapper;
import com.example.model.Employee;
import java.util.Collection;

public interface EmployeeMapper {
    Collection<Employee> retrieveAllEmployees();
}

Create a XML mapping file that links the interface method to an SQL statement.

<?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.example.mapper.EmployeeMapper">
    <select id="retrieveAllEmployees" resultType="employee">
        SELECT id, name, department, salary FROM employees
    </select>
</mapper>

Configure MyBatis to scan for mapper interfaces in the main configuration file.

<mappers>
    <mapper class="com.example.mapper.EmployeeMapper"/>
</mappers>

Write a test to execute the query using the mapper proxy.

package com.example.test;
import com.example.mapper.EmployeeMapper;
import com.example.model.Employee;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.*;
import java.io.Reader;
import java.util.List;

public class EmployeeQueryTest {
    private SqlSession session;

    @Before
    public void setup() throws Exception {
        try (Reader configReader = Resources.getResourceAsReader("mybatis-config.xml")) {
            SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(configReader);
            session = factory.openSession();
        }
    }

    @Test
    public void testRetrieveAllEmployees() {
        EmployeeMapper mapper = session.getMapper(EmployeeMapper.class);
        List<Employee> employees = mapper.retrieveAllEmployees();
        employees.forEach(emp -> System.out.println(emp.toString()));
    }

    @After
    public void cleanup() {
        if (session != null) {
            session.close();
        }
    }
}

MyBatis employs dynamic proxy generation to create a concrete implementation of the mapper interface at runtime. The getMapper method returns a proxy object that intercepts method calls, maps them to corresponding SQL statements defined in the XML, and executes the database operations. This eliminates the need for manually coding implementation classes.