DAO

电玩女神 2022-03-27 10:48 187阅读 0赞

优化JDBC代码(模板模式)

优化查询操作，区分开变化和不变的部分：

sql和ResultSet的处理是变化部分，创建和释放资源部分是不变部分。

l提取超类，将不变部分放入超类，变化部分留给子类实现。

l超类的主要代码：

public Object find(String sql, Object\[\] args) \{

…

rs = ps.executeQuery();

if (rs.next()) return rowMapper(rs);

…

protected abstract Object rowMapper(ResultSet rs);

public abstract class AbstractDao \{  
protected abstract Object rowMapper(ResultSet rs)throws SQLException;  
public Object find(String sql,Object\[\] args) \{  
Object obj=null;  
Connection conn=null;  
PreparedStatement ps=null;  
ResultSet rs=null;  
try \{  
// 建立连接  
// conn=JdbcUtils.getConnection();  
conn=JdbcUtilsSing.getInstance().getConnection();//使用单例  
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(rs);  
\}  
\} catch (Exception e) \{  
//对于异常，能处理就处理，不能处理就抛出，不能隐藏  
//在不污染接口的情况下通知上一层，给上层选择处理的权力  
throw new DaoException(e.getMessage(),e);  
\}finally\{  
// 释放资源  
JdbcUtils.free(rs, ps, conn);  
\}  
return obj;  
\}  
public void update(String sql,Object\[\] args) \{  
Connection conn = null;  
PreparedStatement ps = null;  
ResultSet rs = null;  
try \{  
// 建立连接  
// conn=JdbcUtils.getConnection();  
conn = JdbcUtilsSing.getInstance().getConnection();// 使用单例  
ps = conn.prepareStatement(sql);  
for(int i=0;i<args.length;i++)\{  
ps.setObject(i+1, args\[i\]);  
\}  
ps.executeUpdate();  
\} catch (Exception e) \{  
e.printStackTrace();  
\} finally \{  
// 释放资源  
JdbcUtils.free(rs, ps, conn);  
\}  
\}  
\}

\------------------------------------------------------------------------

public class UserDaoImpl extends AbstractDao \{  
public void delete(User user) \{  
String sql="delete from user where id=?";  
Object\[\] args=new Object\[\]\{user.getId()\};  
super.update(sql, args);  
\}  
public void update(User user) \{  
String sql = "update user set name=?,birthday=?,money=? where id=?";  
Object\[\] args = new Object\[\] \{ user.getName(), user.getBirthday(),  
user.getMoney(), user.getId() \};  
super.update(sql, args);  
\}  
@Override  
protected Object rowMapper(ResultSet rs) throws SQLException \{  
User user;  
user=new User();  
user.setId(rs.getInt("id"));  
user.setName(rs.getString("name"));  
user.setMoney(rs.getFloat("money"));  
user.setBirthday(rs.getDate("birthday"));  
return user;  
\}  
public User finUser(String loginName, String password) \{  
String sql="select id,name,birthday,money from user where name=?";  
Object\[\] args=new Object\[\]\{loginName\};  
Object user=super.find(sql,args);  
return (User)user;  
\}  
\}

\------------------------------------------------------------------------------------------------------

策略模式（Strategy)：定义一系列的算法，将每个算法封装到具有共同接口的独立类中，以便使得算法可以相互替换，而不影响客户端。

组合优化JDBC代码(策略模式)

优化查询操作，区分开变化和不变的部分：

sql和ResultSet的处理是变化部分，创建和释放资源部分是不变部分。

提取接口封装变化部分。

JDBC操作主要代码：

public Object find(String sql, Object\[\] args, RowMapper rowMapper) \{

…

rs = ps.executeQuery();

if (rs.next())return rowMapper.mapRow(rs);

…

回调接口：

public interface RowMapper \{

public Object mapRow(ResultSet rs) throws SQLException;

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

\-----------------------------------------------------------------------------------------

public class MyDaoTemplate \{  
protected Object rowMapper(ResultSet rs) throws SQLException \{  
return null;  
\}  
public Object find(String sql, Object\[\] args, RowMapper rowMapper) \{  
Object obj = null;  
Connection conn = null;  
PreparedStatement ps = null;  
ResultSet rs = null;  
try \{  
// 建立连接  
// conn=JdbcUtils.getConnection();  
conn = JdbcUtilsSing.getInstance().getConnection();// 使用单例  
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.mapRow(rs);  
\}  
\} catch (Exception e) \{  
// 对于异常，能处理就处理，不能处理就抛出，不能隐藏  
// 在不污染接口的情况下通知上一层，给上层选择处理的权力  
throw new DaoException(e.getMessage(), e);  
\} finally \{  
// 释放资源  
JdbcUtils.free(rs, ps, conn);  
\}  
return obj;  
\}  
public void update(String sql, Object\[\] args) \{  
Connection conn = null;  
PreparedStatement ps = null;  
ResultSet rs = null;  
try \{  
// 建立连接  
// conn=JdbcUtils.getConnection();  
conn = JdbcUtilsSing.getInstance().getConnection();// 使用单例  
ps = conn.prepareStatement(sql);  
for (int i = 0; i < args.length; i++) \{  
ps.setObject(i + 1, args\[i\]);  
\}  
ps.executeUpdate();  
\} catch (Exception e) \{  
e.printStackTrace();  
\} finally \{  
// 释放资源  
JdbcUtils.free(rs, ps, conn);  
\}  
\}  
\}

\------------------------------------------------------------------------------------------------------

public class UserDaoImpl2\{  
MyDaoTemplate template=new MyDaoTemplate();  
public User findUser(String loginName, String password) \{  
String sql="select id,name,birthday,money from user where name=?";  
Object\[\] args=new Object\[\]\{loginName\};  
Object user=this.template.find(sql, args, new UserRowMapper());  
return (User) user;  
\}  
public String finderUserName(int id)\{  
String sql="select name from user when id=?";  
Object\[\] args=new Object\[\]\{id\};  
Object name=this.template.find(sql, args, new RowMapper()\{  
public Object mapRow(ResultSet rs) throws SQLException\{  
return rs.getString("name");  
\}\});  
return (String)name;  
\}  
class UserRowMapper implements RowMapper\{  
@Override  
public Object mapRow(ResultSet rs) throws SQLException \{  
User user;  
user=new User();  
user.setId(rs.getInt("id"));  
user.setName(rs.getString("name"));  
user.setMoney(rs.getFloat("money"));  
user.setBirthday(rs.getDate("birthday"));  
return user;  
\}  
\}  
\}