public interface Callback {

   String callBack();
 }

public class Another {
  private Callback callback;
  //调用实现类的方法
  public void setCallback(Callback callback) {
    this.callback = callback;
  }
    //业务需要的时候，通过委派，来调用实现类的具体方法
  public void doCallback(){
    System.out.println(callback.callBack());
  }
}

public class TestCallcack {
  public static void main(String[] args) {
    //创建调用者的实现类
    Another another = new Another();
    //将回掉接口注册到实现类中
    another.setCallback(new Callback() {  
      @Override
      public String callBack() {
        return "you are a pig";
      }
    });
    //执行回调函数
    another.doCallback();
  }
}

public abstract class AbstractSup {
    //需要子类实现的方法
  public abstract void print();
    //模板方法
  public void doPrint(){
    System.out.println("执行模板方法");
    for (int i = 0; i < 3; i++) {
      print();
    }
  }
}

public class SubClass extends AbstractSup{
  @Override
  public void print() {
    System.out.println("子类的实现方法");
  }

}

public class TempleteTest {
  public static void main(String[] args) {
    SubClass subClass = new SubClass();
    subClass.print();
    subClass.doPrint();
  }
}

public List<User> query() { 
 
  List<User> userList = new ArrayList<User>(); 
  String sql = "select * from User"; 
 
  Connection con = null; 
  PreparedStatement pst = null; 
  ResultSet rs = null; 
  try { 
    con = HsqldbUtil.getConnection(); 
    pst = con.prepareStatement(sql); 
    rs = pst.executeQuery(); 
 
    User user = null; 
    while (rs.next()) { 
 
      user = new User(); 
      user.setId(rs.getInt("id")); 
      user.setUserName(rs.getString("user_name")); 
      user.setBirth(rs.getDate("birth")); 
      user.setCreateDate(rs.getDate("create_date")); 
      userList.add(user); 
    } 
 
 
  } catch (SQLException e) { 
    e.printStackTrace(); 
  }finally{ 
    if(rs != null){ 
      try { 
        rs.close(); 
      } catch (SQLException e) { 
        e.printStackTrace(); 
      } 
    } 
    try { 
      pst.close(); 
    } catch (SQLException e) { 
      e.printStackTrace(); 
    } 
    try { 
      if(!con.isClosed()){ 
        try { 
          con.close(); 
       } catch (SQLException e) { 
          e.printStackTrace(); 
        } 
      } 
    } catch (SQLException e) { 
      e.printStackTrace(); 
    } 
     
  } 
  return userList; 
}

public abstract class JdbcTemplate { 
 
  //模板方法
  public final Object execute(String sql) throws SQLException{
   
    Connection con = HsqldbUtil.getConnection(); 
    Statement stmt = null; 
    try { 
  
      stmt = con.createStatement(); 
      ResultSet rs = stmt.executeQuery(sql); 
      Object result = doInStatement(rs);//抽象方法（定制方法，需要子类实现）  
      return result; 
    } 
    catch (SQLException ex) { 
       ex.printStackTrace(); 
       throw ex; 
    } 
    finally { 
  
      try { 
        stmt.close(); 
      } catch (SQLException e) { 
        e.printStackTrace(); 
      } 
      try { 
        if(!con.isClosed()){ 
          try { 
            con.close(); 
          } catch (SQLException e) { 
            e.printStackTrace(); 
          } 
        } 
      } catch (SQLException e) { 
        e.printStackTrace(); 
      } 
       
    } 
  } 
   
  //抽象方法（定制方法）
  protected abstract Object doInStatement(ResultSet rs); 
}

public class JdbcTemplateUserImpl extends JdbcTemplate { 
 
  @Override 
  protected Object doInStatement(ResultSet rs) { 
    List<User> userList = new ArrayList<User>(); 
     
    try { 
      User user = null; 
      while (rs.next()) { 
 
        user = new User(); 
        user.setId(rs.getInt("id")); 
        user.setUserName(rs.getString("user_name")); 
        user.setBirth(rs.getDate("birth")); 
        user.setCreateDate(rs.getDate("create_date")); 
        userList.add(user); 
      } 
      return userList; 
    } catch (SQLException e) { 
      e.printStackTrace(); 
      return null; 
    } 
  } 
 
}

String sql = "select * from User"; 
JdbcTemplate jt = new JdbcTemplateUserImpl(); 
List<User> userList = (List<User>) jt.execute(sql); 

public interface StatementCallback { 
  Object doInStatement(Statement stmt) throws SQLException; 
 } 

public class JdbcTemplate { 
 
  //模板方法
  public final Object execute(StatementCallback action) throws SQLException{ 
     
    Connection con = HsqldbUtil.getConnection(); 
    Statement stmt = null; 
    try { 
  
      stmt = con.createStatement(); 
      Object result = action.doInStatement(rs);//回调方法
      return result; 
    } 
    catch (SQLException ex) { 
       ex.printStackTrace(); 
       throw ex; 
    } 
    finally { 
  
      try { 
        stmt.close(); 
      } catch (SQLException e) { 
        e.printStackTrace(); 
      } 
      try { 
        if(!con.isClosed()){ 
          try { 
            con.close(); 
          } catch (SQLException e) { 
            e.printStackTrace(); 
          } 
        } 
      } catch (SQLException e) { 
        e.printStackTrace(); 
      } 
       
    } 
  }     
  }
  public Object query(StatementCallback stmt) throws SQLException{ 
    return execute(stmt); 
  } 
}

public Object query(final String sql) throws SQLException { 
    class QueryStatementCallback implements StatementCallback { 
 
      public Object doInStatement(Statement stmt) throws SQLException { 
        ResultSet rs = stmt.executeQuery(sql); 
        List<User> userList = new ArrayList<User>(); 
 
        User user = null; 
        while (rs.next()) { 
 
          user = new User(); 
          user.setId(rs.getInt("id")); 
          user.setUserName(rs.getString("user_name")); 
          user.setBirth(rs.getDate("birth")); 
          user.setCreateDate(rs.getDate("create_date")); 
          userList.add(user); 
        } 
        return userList; 
 
      } 
 
    } 
 
    JdbcTemplate jt = new JdbcTemplate(); 
    return jt.query(new QueryStatementCallback()); 
  }