Spring 3.x + SimpleJdbcTemplate：返回多列

Question

我在Spring 3.x使用SimpleJdbcTemplate 。 為了獲得單列，我使用下面的代碼，它可以正常工作：

public String selectSingleColumn(int deptId){
    return jdbcTemplate.queryForObject("SELECT DEPT_NAME FROM DEPT WHERE DEPT_ID = ?", String.class, deptId);
}

問題：

我想從上面的表中獲取多個列，例如DEPT_NAME和DEPT_CODE （但不是所有屬於該表的列），如何修改上面的代碼來完成？ 在這種情況下，我對queryForObject的second parameter感到困惑； 理想情況下，我認為應該是Object[]但stilll感到困惑。 請指導我。

Answer 1

我只需要查詢整個域對象，而不必為不同的列編寫不同的查詢。 首先，它使dao更可重用。

例如：

部門域對象

public class Department {
    private long id;
    private String deptName;
    private String deptCode;
    // other fields

    // getters and setters
}

DepartmentDao

public class DepartmentDaoImpl extends JdbcTemplate implements DepartmentDao {

    private static final String DEPT_BY_ID 
                          = "select * from DEPARTMENT where DEPT_ID = ?";

    @Override
    public Department getDepartmentById(long id) {
        return (Department) queryForObject(
             DEPT_BY_ID, 
             new Object[] { id },
             new RowMapper<Department>() {
                 @Override
                 public Department mapRow(ResultSet rs, int rowNumber) {
                     Department dept = new Department();
                     dept.setId(rs.getLong("DEPT_ID");
                     dept.setDeptName(rs.getString("DEPT_NAME");
                     dept.setDeptCode(rs.getString("DEPT_CODE");
                     // set other properties

                     return dept;
                 }
             });
    }
}

如果確實只需要兩列，則可以使用queryForMap

public class TestCustomerDao extends JdbcTemplate implements DepartmentDao {

    private static final String FOR_MAP 
                = "select DEPT_NAME,DEPT_CODE from DEPARTMENT where DEPT_ID = ?";

    @Override
    public Map<String, Object> getCoupleColumnsById(long id) {
        return (Map<String, Object>)queryForMap(FOR_MAP, new Object[] {id});
    }
}

地圖將返回為

   key        value
DEPT_NAME  =  value
DEPT_CODE  =  value

Answer 2

以下是執行此操作的步驟-

（1）為部門創建域對象

public class Department{
    private String departmentName;
    private String departmentCode;
    //getters and setters omitted for brevity
}

（2）創建一個RowMapper類以將結果集映射到Department Object

public class DepartmentRowMapper implements RowMapper<Department>
{
    public Department mapRow(ResultSet rs, int rowNum) throws SQLException {
        Department department= new Department ();
        department.setDepartmentName(rs.getString("DEPT_NAME"));
        department.setDepartmentCode(rs.getString("DEPT_CODE"));
        return department;
    }

}

（3）創建Dao類

public class DepartmentDao
   private JdbcTemplate jdbcTemplate; 
   //getters and setters omitted for brevity 
   public Department getDepartment(int deptId){
    return (Department)jdbcTemplate.queryForObject("SELECT DEPT_NAME FROM DEPT WHERE DEPT_ID = ?",new Object[] {deptId}, new DepartmentRowMapper ());
   }
}