模拟Spring的JdbcTemplate实现DAO

通常情况下，普—AO的实现大概是这样的：

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1、实体类：

public class Emp {private Integer id;private String name;private String sex;private Float sal;                //getter and setter methods...}

?2、DAO接口：

public interface EmpDAO {public int insert(Emp emp)throws SQLException;public int delete(Emp emp)throws SQLException;public int update(Emp emp)throws SQLException;public Emp findById(Emp emp)throws SQLException;public String findName(Emp emp)throws SQLException;}

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3、DAO实现类：

public class EmpDAOImpl implements EmpDAO {public int delete(Emp emp) throws SQLException {String sql = "delete from emp where id=?";Connection conn = null;PreparedStatement ps = null;try {conn = DBUtil.getConnection();ps = conn.prepareStatement(sql);ps.setInt(1, emp.getId());return ps.executeUpdate();} catch (SQLException e) {throw e;} finally {DBUtil.close(null, ps, conn);}}public Emp findById(Emp emp) throws SQLException {String sql = "select id,name,sal,sex from emp where id=?";Connection conn = null;PreparedStatement ps = null;ResultSet rs = null;Emp currEmp = null;try {conn = DBUtil.getConnection();ps = conn.prepareStatement(sql);ps.setInt(1, emp.getId());rs = ps.executeQuery();if (rs.next()) {currEmp = new Emp();currEmp.setId(rs.getInt("id"));currEmp.setName(rs.getString("name"));currEmp.setSal(rs.getFloat("sal"));currEmp.setSex(rs.getString("sex"));}} catch (SQLException e) {throw e;} finally {DBUtil.close(rs, ps, conn);}return currEmp;}public String findName(Emp emp) throws SQLException {String sql = "select name from emp where id=?";Connection conn = null;PreparedStatement ps = null;ResultSet rs = null;String name = null;try {conn = DBUtil.getConnection();ps = conn.prepareStatement(sql);ps.setInt(1, emp.getId());rs = ps.executeQuery();if (rs.next()) {name = rs.getString("name");}} catch (SQLException e) {throw e;} finally {DBUtil.close(rs, ps, conn);}return name;}public int insert(Emp emp) throws SQLException {String sql = "insert into emp(name,sal,sex) values(?,?,?)";Connection conn = null;PreparedStatement ps = null;try {conn = DBUtil.getConnection();ps = conn.prepareStatement(sql);ps.setString(1, emp.getName());ps.setFloat(2, emp.getSal());ps.setString(3, emp.getSex());return ps.executeUpdate();} catch (SQLException e) {throw e;} finally {DBUtil.close(null, ps, conn);}}public int update(Emp emp) throws SQLException {String sql = "update emp set name=?,sal=?,sex=? where id=?";Connection conn = null;PreparedStatement ps = null;try {conn = DBUtil.getConnection();ps = conn.prepareStatement(sql);ps.setString(1, emp.getName());ps.setFloat(2, emp.getSal());ps.setString(3, emp.getSex());ps.setInt(4, emp.getId());return ps.executeUpdate();} catch (SQLException e) {throw e;} finally {DBUtil.close(null, ps, conn);}}}

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以下是改造后的实现方式：

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1、实体类同上

2、接口同上

3、用于处理查询结果的接口：

public interface RowMapper {public Object mapperRow(ResultSet rs)throws SQLException;}

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4、模拟JdbcTemplate类

public class JdbcTemplate {public int update(String sql, Object[] args) throws SQLException {Connection conn = null;PreparedStatement ps = null;try {conn = DBUtil.getConnection();ps = conn.prepareStatement(sql);for (int i = 0; i < args.length; i++) {ps.setObject(i + 1, args[i]);}return ps.executeUpdate();} catch (SQLException e) {throw e;} finally {DBUtil.close(null, ps, conn);}}public Object find(String sql, Object[] args, RowMapper rowMapper)throws SQLException {Connection conn = null;PreparedStatement ps = null;ResultSet rs = null;Object obj = null;try {conn = DBUtil.getConnection();ps = conn.prepareStatement(sql);for (int i = 0; i < args.length; i++) {ps.setObject(i + 1, args[i]);}rs = ps.executeQuery();if (rs.next()) {obj = rowMapper.mapperRow(rs);}} catch (SQLException e) {throw e;} finally {DBUtil.close(rs, ps, conn);}return obj;}

?5、DAO实现类：

public class EmpDAOJdbcTemplateImpl implements EmpDAO {private JdbcTemplate jdbcTemplate = new JdbcTemplate();public int delete(Emp emp) throws SQLException {String sql = "delete from emp where id=?";Object[] args = new Object[] { emp.getId() };return jdbcTemplate.update(sql, args);}public Emp findById(Emp emp) throws SQLException {String sql = "select id,name,sal,sex from emp where id=?";Object[] args = new Object[] { emp.getId() };Object obj = jdbcTemplate.find(sql, args, new RowMapper() {@Overridepublic Object mapperRow(ResultSet rs) throws SQLException {Emp emp = new Emp();emp.setId(rs.getInt("id"));emp.setName(rs.getString("name"));emp.setSal(rs.getFloat("sal"));emp.setSex(rs.getString("sex"));return emp;}});return (Emp) obj;}public String findName(Emp emp) throws SQLException {String sql = "select name from emp where id=?";Object[] args = new Object[] { emp.getId() };Object obj = jdbcTemplate.find(sql, args, new RowMapper() {@Overridepublic Object mapperRow(ResultSet rs) throws SQLException {return rs.getString("name");}});return (String) obj;}public int insert(Emp emp) throws SQLException {String sql = "insert into emp(name,sal,sex) values(?,?,?)";Object[] args = new Object[] { emp.getName(), emp.getSal(),emp.getSex() };return jdbcTemplate.update(sql, args);}public int update(Emp emp) throws SQLException {String sql = "update emp set name=?,sal=?,sex=? where id=?";Object[] args = new Object[] { emp.getName(), emp.getSal(),emp.getSex(), emp.getId() };return jdbcTemplate.update(sql, args);}}

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