在Java中，可以使用ResultMap来实现复杂的映射关系。以下是一个示例代码，演示如何实现复杂的映射关系：
@Results({
@Result(property = "id", column = "id"),
@Result(property = "name", column = "name"),
@Result(property = "age", column = "age"),
@Result(property = "address", column = "address"),
@Result(property = "department.id", column = "department_id"),
@Result(property = "department.name", column = "department_name")
})
@Select("SELECT e.id, e.name, e.age, e.address, d.id as department_id, d.name as department_name " +
"FROM employee e " +
"JOIN department d ON e.department_id = d.id")
List<Employee> getEmployeesWithDepartments();
在上面的示例中，我们使用@Results注解来指定每个属性和对应的数据库列之间的映射关系。其中，department.id和department.name表示Employee对象中的department属性下的id和name属性。
然后，在@Select注解中编写SQL查询语句，通过JOIN操作将employee表和department表关联起来，并查询出需要的字段。最终，通过getEmployeesWithDepartments方法获取查询结果，返回包含Employee对象的列表。
通过上述示例，可以看到Java中使用ResultMap可以很方便地实现复杂的映射关系。
