java 使用策略模式操作JDBC数据库

java 使用策略模式操作JDBC数据库

1：构造一个操作数据库的工具类，可以获得连接和释放连接

public class DBUtil { 
  private static Connection conn = null; 
  static { //静态初始块 
      try { 
        Class.forName("com.mysql.jdbc.Driver"); 
        conn = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/test", "root", "064319"); //初始化获取连接 
      } catch (ClassNotFoundException e) { 
        e.printStackTrace(); 
      } catch (SQLException e) { 
        e.printStackTrace(); 
      } 
  } 
 
  /** 
   * 释放连接 
   * @param rs 
   * @param psmt 
   * @param conn 
   * @throws SQLException 
   */ 
  public static void closeAll(ResultSet rs, PreparedStatement psmt, Connection conn) throws SQLException { 
     
    if(rs != null) { 
      rs.close(); 
    }  
     
    if(psmt != null) { 
      psmt.close(); 
    } 
     
    if(conn != null) { 
      conn.close(); 
    } 
     
  } 
   
  /** 
   * 获取连接 
   * @return 
   */ 
  public static Connection getConnection() { 
    return conn; 
  } 
   
  /** 
   * 根据表的名字来获得表的列信息 
   * @param tableName 
   */ 
  public static void getTableColumnInfoByTableName(String tableName) { 
    Connection conn = getConnection(); 
    ResultSet rs = null; 
    PreparedStatement psmt = null; 
    String sql = "select * from " + tableName; 
    try { 
      psmt = conn.prepareStatement(sql); 
      rs = psmt.executeQuery(); 
       
      ResultSetMetaData resultSetMetaData = rs.getMetaData(); 
      for(int i = 1; i<= resultSetMetaData.getColumnCount(); i++) { 
        System.out.println(resultSetMetaData.getColumnName(i)); 
      } 
       
    } catch (SQLException e) { 
      e.printStackTrace(); 
    } finally { 
      try { 
        closeAll(rs, psmt, conn); 
      } catch (SQLException e) { 
        e.printStackTrace(); 
      } 
    } 
  } 
   
  /** 
   * 根据表的名字来获得表的信息 
   * @param tableName 
   */ 
  public static void getTableInfoByTableName(String tableName) { 
    Connection conn = getConnection(); 
    PreparedStatement psmt = null; 
    ResultSet rs = null; 
    String sql = "select * from " + tableName; 
    try { 
      psmt = conn.prepareStatement(sql); 
      rs = psmt.executeQuery(); 
       
      while(rs.next()) { 
        ResultSetMetaData resultSetMetaData = rs.getMetaData(); 
        for(int i = 1; i<= resultSetMetaData.getColumnCount(); i++) { 
          if(i < resultSetMetaData.getColumnCount()) { 
            System.out.print(rs.getObject(resultSetMetaData.getColumnName(i)) + ", "); 
          } else { 
            System.out.print(rs.getObject(resultSetMetaData.getColumnName(i))); 
          } 
        } 
        System.out.println(); 
      } 
     
    } catch (SQLException e) { 
      e.printStackTrace(); 
    } finally { 
      try { 
        closeAll(rs, psmt, conn); 
      } catch (SQLException e) { 
        e.printStackTrace(); 
      } 
    } 
  } 
} 

2：构造一个操作数据库的BaseDao类

public class BaseDao { 
   
  /** 
   * 根据一些参数来保存相应的对象 
   * @param sql 要执行的sql语句 
   * @param params 为sql语句中相应的参数赋值 
   * @return 
   */ 
  protected boolean saveOrUpdate(String sql, Object[] params) { 
    Connection conn = null; 
    PreparedStatement psmt = null; 
    boolean flag = false; 
     
    conn = DBUtil.getConnection(); 
    if(conn != null) { 
      try { 
        psmt = conn.prepareStatement(sql); 
        for(int i = 1; i <= params.length; i++) { 
          psmt.setObject(i, params[i-1]); 
        } 
        if(psmt.executeUpdate() > 0) { 
          flag = true; 
        } 
         
      } catch (SQLException e) { 
        e.printStackTrace(); 
      } finally { 
        try { 
          DBUtil.closeAll(null, psmt, conn); 
        } catch (SQLException e) { 
          e.printStackTrace(); 
        } 
      } 
    }  
    return flag; 
  } 
   
  /** 
   * 根据一定的参数获得某个具体的对象 
   * @param sql 要执行的sql语句 
   * @param params 为sql语句中相应的参数赋值 
   * @return 
   */ 
  public Object queryForObject(String sql, Object[] params, RowMapForObject rowMapForObject) { 
    Connection conn = null; 
    PreparedStatement psmt = null; 
     
    conn = DBUtil.getConnection(); 
    Object obj = null; 
    ResultSet rs = null; 
     
    if(conn != null) { 
      try { 
        psmt = conn.prepareStatement(sql); 
        if(params != null && params.length > 0) { 
          for(int i = 1; i <= params.length; i++) { 
             psmt.setObject(i, params[i - 1]); 
          } 
        } 
        rs = psmt.executeQuery(); 
        obj = rowMapForObject.rowMapForObject(rs); 
         
      } catch (SQLException e) { 
        e.printStackTrace(); 
      } finally { 
        try { 
          DBUtil.closeAll(null, psmt, conn); 
        } catch (SQLException e) { 
          e.printStackTrace(); 
        } 
      } 
    } 
     
    return obj; 
  } 
 
   
  /** 
   * 根据相应的参数获得查询的结果集 
   * @param sql 
   * @param params 
   * @return 
   */ 
  public List queryForList(String sql, Object[] params, RowMapForList rowMapForList) { 
    Connection conn = null; 
    PreparedStatement psmt = null; 
     
    conn = DBUtil.getConnection(); 
    List list = null; 
    ResultSet rs = null; 
     
    if(conn != null) { 
      try { 
        psmt = conn.prepareStatement(sql); 
        if(params != null && params.length > 0) { 
          for(int i = 1; i <= params.length; i++) { 
             psmt.setObject(i, params[i - 1]); 
          } 
        } 
        rs = psmt.executeQuery(sql); 
        list = new ArrayList(); 
        list = rowMapForList.rowMapForList(rs); 
         
      } catch (SQLException e) { 
        e.printStackTrace(); 
      } finally { 
        try { 
          DBUtil.closeAll(null, psmt, conn); 
        } catch (SQLException e) { 
          e.printStackTrace(); 
        } 
      } 
    } 
     
    return list; 
  } 
   
} 

3：新建一个StudentDao类，该类继承自BaseDao，实现对Student的管理

public class StudentDao extends BaseDao { 
 
  /** 
   * 保存一个Student的信息 
   */ 
  public boolean saveStudent(Student student) { 
    String sql = "insert into t_student(name, age) values(?, ?)"; 
    Object[] params = new Object[]{student.getName(), student.getAge()}; 
    return super.saveOrUpdate(sql, params); 
  } 
   
  /** 
   * 根据id获得一个Student的信息 
   * @param id 
   * @return 
   */ 
  public Student getStudentById(long id) { 
    String sql = "select * from t_student where id=?"; 
    Object[] params = new Object[]{id}; 
    return (Student)super.queryForObject(sql, params, new RowMapForObject() { 
       
      public Object rowMapForObject(ResultSet rs) { 
        Student student = null; 
         try { 
          if(rs != null && rs.next()) { 
             student = new Student(); 
             student.setAge(rs.getInt(Student.AGE)); 
             student.setId(rs.getLong(Student.ID)); 
             student.setName(rs.getString(Student.NAME)); 
           } 
        } catch (SQLException e) { 
          e.printStackTrace(); 
        } 
         return student; 
      } 
    }); 
  } 
 
  /** 
   * 获得所有Student的信息 
   * @return 
   */ 
  public List getStudentAll() { 
    String sql = "select * from t_student"; 
    List list = super.queryForList(sql, null, new RowMapForList() { 
 
      @Override 
      public List rowMapForList(ResultSet rs) { 
        List list = null; 
        try { 
          if(rs != null) { 
            list = new ArrayList(); 
            while(rs.next()) { 
              Student student = new Student(); 
              student.setId(rs.getLong("id")); 
              student.setAge(rs.getInt("age")); 
              student.setName(rs.getString("name")); 
              list.add(student); 
            } 
          } 
        } catch(SQLException e) { 
          e.printStackTrace(); 
        } 
        return list; 
      } 
    }); 
     
    return list; 
  }   
} 

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