DAO模式

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今天在写数据库层的时候用到了DAO模式，发现这样就可以将实现类完全的分隔开来，并且把实现类的类名保存在配置文件中，这样的话即使我下次需要改变实现类，那么也只用将配置文件中实现类的信息修改即可。例如，我刚开始数据库用的是XML来存储，实现类也是对于XML的操作，当我不想用XML的时候，将它替换成Mysql,那么我只需添加一个关于mysql的实现类，并在配置文件中添加该类的信息。

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。

具体步骤如下：

· 实体域，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；

·DAO模式需要先提供一个DAO接口；

· 然后再提供一个DAO接口的实现类；

·再编写一个DAO工厂，Service通过工厂来获取DAO实现。

User.java

public class User {private String uid;private String username;private String password;…}

UserDao.java

public interface UserDao {public void add(User user);public void mod(User user);public void del(String uid);public User load(String uid);public List<User> findAll();}

UserDaoImpl.java

public class UserDaoImpl implements UserDao {public void 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) {throw new RuntimeException(e);} finally {try {if(pstmt != null) pstmt.close();if(con != null) con.close();} catch(SQLException e) {}}}public void 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) {throw new RuntimeException(e);} finally {try {if(pstmt != null) pstmt.close();if(con != null) con.close();} catch(SQLException e) {}}}public void 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) {throw new 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()) {return new User(rs.getString(1), rs.getString(2), rs.getString(3));}return null;} catch(Exception e) {throw new 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) {throw new RuntimeException(e);} finally {try {if(pstmt != null) pstmt.close();if(con != null) con.close();} catch(SQLException e) {}}}}

UserDaoFactory.java

public class UserDaoFactory {private static UserDao userDao;static {try {InputStream in = Thread.currentThread().getContextClassLoader().getResourceAsStream("dao.properties");Properties prop = new Properties();prop.load(in);String className = prop.getProperty("cn.dyf.jdbc.UserDao");Class clazz = Class.forName(className);userDao = (UserDao) clazz.newInstance();} catch (Exception e) {throw new RuntimeException(e);}}public static UserDao getUserDao() {return userDao;}}

配置文件dao.properties

cn.dyf.jdbc.UserDao=cn.dyf.jdbc.UserDaoImpl

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