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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