Example analysis of how Java uses strategy mode to operate JDBC database

This article mainly introduces the relevant information about java using the strategy mode to operate the JDBC database. Here is an example to implement the function of adding, deleting, modifying and checking the JDBC database. Friends in need can refer to it

java uses strategy mode to operate JDBC database

1: Construct a tool class to operate the database to obtain and release connections

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: Construct a BaseDao class that operates the database

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: Create a new StudentDao class, which inherits from BaseDao to realize the management of Students

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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