------------------------------------- JDBC封装DBUtil和DAO模式----------------------------------------------
JdbcUtils工具类
1 JdbcUtils的作用
你也看到了，连接数据库的四大参数是：驱动类、url、用户名，以及密码。这些参数都与特定数据库关联，如果将来想更改数据库，那么就要去修改这四大参数，那么为了不去修改代码，我们写一个JdbcUtils类，让它从配置文件中读取配置参数，然后创建连接对象。
2 JdbcUtils代码
JdbcUtils.java
publicclass JdbcUtils { privatestaticfinal String dbconfig = "dbconfig.properties"; privatestatic Properties prop = new Properties(); static { try { InputStream in = Thread.currentThread().getContextClassLoader().getResourceAsStream(dbconfig); prop.load(in); Class.forName(prop.getProperty("driverClassName")); } catch(IOException e) { thrownew RuntimeException(e); } }
publicstatic Connection getConnection() { try { return DriverManager.getConnection(prop.getProperty("url"), prop.getProperty("username"), prop.getProperty("password")); } catch (Exception e) { thrownew RuntimeException(e); } } } |
dbconfig.properties
driverClassName=oracle.jdbc.OracleDriver url= jdbc:oracle:thin:@127.0.0.1:1521:orcl username=scott password=tiger |
3 UserDao
1 DAO模式
DAO（Data Access Object）模式就是写一个类，把访问数据库的代码封装起来。DAO在数据库与业务逻辑（Service）之间。
l 实体域（JavaBean），即操作的对象，例如我们操作的表是user表，那么就需要先写一个User类；
l DAO模式需要先提供一个DAO接口；
l 然后再提供一个DAO接口的实现类；
l 再编写一个DAO工厂，Service通过工厂来获取DAO实现。
2 代码
User.java
publicclass User { private String uid; private String username; private String password; … } |
UserDao.java
publicinterface UserDao { publicvoid add(User user); publicvoid mod(User user); publicvoid del(String uid); public User find(String uid); public List<User> findAll(); } |
UserDaoImpl.java
publicclass UserDaoImpl implements UserDao { publicvoid add(User user) { Connection con = null; PreparedStatement pstmt = null; try { con = JdbcUtils.getConnection(); String sql = "insert into user value(?,?,?)"; pstmt = con.prepareStatement(sql); pstmt.setString(1, user.getUid()); pstmt.setString(2, user.getUsername()); pstmt.setString(3, user.getPassword()); pstmt.executeUpdate(); } catch(Exception e) { thrownew RuntimeException(e); } finally { try { if(pstmt != null) pstmt.close(); if(con != null) con.close(); } catch(SQLException e) {} } }
publicvoid mod(User user) { Connection con = null; PreparedStatement pstmt = null; try { con = JdbcUtils.getConnection(); String sql = "update user set username=?, password=? where uid=?"; pstmt = con.prepareStatement(sql); pstmt.setString(1, user.getUsername()); pstmt.setString(2, user.getPassword()); pstmt.setString(3, user.getUid()); pstmt.executeUpdate(); } catch(Exception e) { thrownew RuntimeException(e); } finally { try { if(pstmt != null) pstmt.close(); if(con != null) con.close(); } catch(SQLException e) {} } }
publicvoid del(String uid) { Connection con = null; PreparedStatement pstmt = null; try { con = JdbcUtils.getConnection(); String sql = "delete from user where uid=?"; pstmt = con.prepareStatement(sql); pstmt.setString(1, uid); pstmt.executeUpdate(); } catch(Exception e) { thrownew RuntimeException(e); } finally { try { if(pstmt != null) pstmt.close(); if(con != null) con.close(); } catch(SQLException e) {} } }
public User load(String uid) { Connection con = null; PreparedStatement pstmt = null; ResultSet rs = null; try { con = JdbcUtils.getConnection(); String sql = "select * from user where uid=?"; pstmt = con.prepareStatement(sql); pstmt.setString(1, uid); rs = pstmt.executeQuery(); if(rs.next()) { returnnew User(rs.getString(1), rs.getString(2), rs.getString(3)); } returnnull; } catch(Exception e) { thrownew RuntimeException(e); } finally { try { if(pstmt != null) pstmt.close(); if(con != null) con.close(); } catch(SQLException e) {} } }
public List<User> findAll() { Connection con = null; PreparedStatement pstmt = null; ResultSet rs = null; try { con = JdbcUtils.getConnection(); String sql = "select * from user"; pstmt = con.prepareStatement(sql); rs = pstmt.executeQuery(); List<User> userList = new ArrayList<User>(); while(rs.next()) { userList.add(new User(rs.getString(1), rs.getString(2), rs.getString(3))); } return userList; } catch(Exception e) { thrownew RuntimeException(e); } finally { try { if(pstmt != null) pstmt.close(); if(con != null) con.close(); } catch(SQLException e) {} } } } |
UserDaoFactory.java
publicclass UserDaoFactory { privatestatic UserDao userDao; static { try { InputStream in = Thread.currentThread().getContextClassLoader() .getResourceAsStream("dao.properties"); Properties prop = new Properties(); prop.load(in); String className = prop.getProperty("com.rl.jdbc.UserDao"); Class clazz = Class.forName(className); userDao = (UserDao) clazz.newInstance(); } catch (Exception e) { thrownew RuntimeException(e); } }
publicstatic UserDao getUserDao() { returnuserDao; } } |
dao.properties
com.rl.jdbc.UserDao=com.rl.jdbc.UserDaoImpl |
