jdbc连接mysql首次成功，之后连接就报错

在系统中使用jdbc 连接mysql， 首次成功，之后连接就报错，驱动用的是mysql-connector-java-5.1.15-bin.jar
连接代码

 Connection conn = null; Statement stat = null; ResultSet rs = null; String url = "jdbc:mysql://*********:3306/*******?useUnicode=true&characterEncoding=GBK"; String sql = null; String tableName = "***"; List clock = new ArrayList(); sql = "select * from " + tableName + " where timevalue between '" + startTime + "' and '" + endTime + "' and doorName='" + doorName.substring(2) + "'"; System.out.println(sql); Class.forName("com.mysql.jdbc.Driver"); conn = DriverManager.getConnection(url, "root", "****"); stat = conn.createStatement(); rs = stat.executeQuery(sql); while (rs.next()) { ClockBO bo = new ClockBO(); ClockPKBO pkbo = new ClockPKBO(); pkbo.setCardNo1(rs.getString(1)); pkbo.setCardNo2(rs.getString(2)); pkbo.setTimeValue(ft.format(rs.getTimestamp(6))); bo.setPersonNo(rs.getString(3)); bo.setPersonName(rs.getString(4)); bo.setDepartment(rs.getString(5)); bo.setCtlIp(rs.getString(7)); bo.setDoorNo(rs.getString(8)); bo.setDoorName(rs.getString(9)); bo.setStateId(rs.getString(10)); bo.setRptState(rs.getString(11)); bo.setStateStr(rs.getString(12)); bo.setClockPK(pkbo); clock.add(bo); System.out.println(rs.getString(4)); System.out.println(bo.toString()); } } catch (Exception e) { e.printStackTrace(); }finally{ try{ if(null!=rs){ rs.close(); } if(null!=stat){ stat.close(); } if(null!=conn){ conn.commit(); conn.close(); } }catch(SQLException e){ e.printStackTrace(); } }

首次连接可以查出数据，再次调用就在连接的时候就抛出异常了，异常信息如下

java.sql.SQLException: ResultSet is from UPDATE. No Data.
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1078)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:989)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:975)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:920)
at com.mysql.jdbc.ResultSetImpl.next(ResultSetImpl.java:6999)
at com.mysql.jdbc.ConnectionImpl.loadServerVariables(ConnectionImpl.java:4184)
at com.mysql.jdbc.ConnectionImpl.initializePropsFromServer(ConnectionImpl.java:3585)
at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2534)
at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2304)
at com.mysql.jdbc.ConnectionImpl.(ConnectionImpl.java:834)
at com.mysql.jdbc.JDBC4Connection.(JDBC4Connection.java:47)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Unknown Source)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:416)
at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:346)

为什么会出现这种情况呢？