奇怪问题，请高手指点（Illegal operation on empty result set.）

Question

注：该问题不是所有的数据查询都发生，而是对部分数据，提示这样的错误
null
java.sql.SQLException: Illegal operation on empty result set.
        at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1055)
        at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:956)
        at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:926)
        at com.mysql.jdbc.ResultSetImpl.checkRowPos(ResultSetImpl.java:815)
        at com.mysql.jdbc.ResultSetImpl.getStringInternal(ResultSetImpl.java:552
8)
        at com.mysql.jdbc.ResultSetImpl.getString(ResultSetImpl.java:5448)
        at com.mysql.jdbc.ResultSetImpl.getString(ResultSetImpl.java:5488)
        at net.sf.odinms.client.MaplePet.loadFromDb(MaplePet.java:46)
        at net.sf.odinms.tools.MaplePacketCreator.addItemInfo(MaplePacketCreator
.java:1213)
        at net.sf.odinms.tools.MaplePacketCreator.addItemInfo(MaplePacketCreator
.java:1144)
        at net.sf.odinms.tools.MaplePacketCreator.getCharInfo(MaplePacketCreator
.java:866)
        at net.sf.odinms.net.channel.handler.PlayerLoggedinHandler.handlePacket(
PlayerLoggedinHandler.java:94)
        at net.sf.odinms.net.MapleServerHandler.messageReceived(MapleServerHandl
er.java:118)
        at org.apache.mina.common.support.AbstractIoFilterChain$TailFilter.messa
geReceived(AbstractIoFilterChain.java:570)
        at org.apache.mina.common.support.AbstractIoFilterChain.callNextMessageR
eceived(AbstractIoFilterChain.java:299)
        at org.apache.mina.common.support.AbstractIoFilterChain.access$1100(Abst
ractIoFilterChain.java:53)
        at org.apache.mina.common.support.AbstractIoFilterChain$EntryImpl$1.mess
ageReceived(AbstractIoFilterChain.java:648)
        at org.apache.mina.filter.codec.support.SimpleProtocolDecoderOutput.flus
h(SimpleProtocolDecoderOutput.java:58)
        at org.apache.mina.filter.codec.ProtocolCodecFilter.messageReceived(Prot
ocolCodecFilter.java:180)
        at org.apache.mina.common.support.AbstractIoFilterChain.callNextMessageR
eceived(AbstractIoFilterChain.java:299)
        at org.apache.mina.common.support.AbstractIoFilterChain.access$1100(Abst
ractIoFilterChain.java:53)
        at org.apache.mina.common.support.AbstractIoFilterChain$EntryImpl$1.mess
ageReceived(AbstractIoFilterChain.java:648)
        at org.apache.mina.filter.executor.ExecutorFilter.processEvent(ExecutorF
ilter.java:220)
        at org.apache.mina.filter.executor.ExecutorFilter$ProcessEventsRunnable.
run(ExecutorFilter.java:264)
        at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source
)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
        at org.apache.mina.util.NamePreservingRunnable.run(NamePreservingRunnabl
e.java:51)
        at java.lang.Thread.run(Unknown Source)

Answer 1

问题依旧，对应的源码如下：
源程序对应： 
  public static MaplePet loadFromDb(int itemid, byte position, int petid) { 
        try { 
            MaplePet ret = new MaplePet(itemid, position, petid); 
            Connection con = DatabaseConnection.getConnection(); // Get a connection to the database 
            PreparedStatement ps = con.prepareStatement("SELECT * FROM pets WHERE petid = ?"); // Get pet details.. 
            ps.setInt(1, petid); 
            ResultSet rs = ps.executeQuery(); 
            if(rs.next())
            { 
            ret.setName(rs.getString("name")); 
            ret.setCloseness(rs.getInt("closeness")); 
            ret.setLevel(rs.getInt("level")); 
            ret.setFullness(rs.getInt("fullness")); 
            } 
            rs.close(); 
            ps.close(); 
            return ret; 
        } catch (SQLException ex) { 
            Logger.getLogger(MaplePet.class.getName()).log(Level.SEVERE, null, ex); 
            return null; 
        } 
    }

Answer 2

public static MaplePet loadFromDb(int itemid, byte position, int petid) { 
        try { 
            MaplePet ret = new MaplePet(itemid, position, petid); 
            Connection con = DatabaseConnection.getConnection(); // Get a connection to the database 
            PreparedStatement ps = con.prepareStatement("SELECT * FROM pets WHERE petid = ?"); // Get pet details.. 
            ps.setInt(1, petid); 
            ResultSet rs = ps.executeQuery(); 
            if(rs.next()) 
            { 
            ret.setName(rs.getString("name")); 
            ret.setCloseness(rs.getInt("closeness")); 
            ret.setLevel(rs.getInt("level")); 
            ret.setFullness(rs.getInt("fullness")); 
            } 
            return ret; 
        } catch (SQLException ex) { 
            Logger.getLogger(MaplePet.class.getName()).log(Level.SEVERE, null, ex); 
            return null; 
        } 
finally{
try{
rs.close(); 
            ps.close(); 
con.close();}catch (SQLException e)
{
}
    }

Answer 3

if(rs.next()); 
        { 
        ret.setName(rs.getString("name")); 
        ret.setCloseness(rs.getInt("closeness")); 
        ret.setLevel(rs.getInt("level")); 
        ret.setFullness(rs.getInt("fullness")); 
        } else{ 
         return null; 
        }         return ret; 
    } catch (SQLException ex) { 
        Logger.getLogger(MaplePet.class.getName()).log(Level.SEVERE, null, ex); 
        return null; 
    }finally{ 
              rs.close(); 
              ps.close(); 
    } 

Answer 4

根据以上修改后，编译器会提示错误如下：
              rs.close(); 
            ps.close(); 
找不到符号，符号变量rs 及 ps

Answer 5

...老兄，遇到问题先思考一下了嘛
在try外面定义方法变量ResultSet rs =null;PreparedStatement ps=null;这个错误是变量作用域的范畴

Answer 6

ret.setCloseness(rs.getInt("closeness")); 
ret.setLevel(rs.getInt("level")); 
ret.setFullness(rs.getInt("fullness")); 你看看你的数据库的列值吧,可能是null的,转为int估计就出错了

Answer 7

。。
8楼的方式你先检查一下然后你的代码：
public static MaplePet loadFromDb(int itemid, byte position, int petid) { 
PreparedStatement ps =null;
ResultSet rs = null;
        try { 
            MaplePet ret = new MaplePet(itemid, position, petid); 
            Connection con = DatabaseConnection.getConnection(); // Get a connection to the database 
            ps = con.prepareStatement("SELECT * FROM pets WHERE petid = ?"); // Get pet details.. 
            ps.setInt(1, petid); 
            rs = ps.executeQuery(); 
            if(rs.next()); 
            { 
            ret.setName(rs.getString("name")); 
            ret.setCloseness(rs.getInt("closeness")); 
            ret.setLevel(rs.getInt("level")); 
            ret.setFullness(rs.getInt("fullness")); 
            } else{ 
                return null; 
            }             return ret; 
        } catch (SQLException ex) { 
            Logger.getLogger(MaplePet.class.getName()).log(Level.SEVERE, null, ex); 
            return null; 
        }finally{ 
                  rs.close(); 
                  ps.close(); 
        } 
    }

Answer 8

ret.setCloseness(rs.getInt("closeness")); 
ret.setLevel(rs.getInt("level")); 
ret.setFullness(rs.getInt("fullness")); 
看看是不是数据库里值为null，或列名写错了

Answer 9

定义后，编译器提示，try里面那2个已被定义过的错误

Answer 10

SELECT * FROM pets WHERE petid = ?
这个petid是唯一的吗？？

Answer 11

解决方法是：可以使用Integer row="select count(*) from hpibbs.firstcard where firstcard_id="+allcard_id;这时候，总会有返回的行，即使没有符合条件的数据

Answer 12

 ps = con.prepareStatement("SELECT * FROM pets WHERE petid = ?"); 
 ps.setInt(1, petid); 
好像是ps.setInt(0, petid);

Answer 13

后经反复测试和输出数据对比，发现错误的那个数据里面的petid=208,在数据库中没有208的这条数据，可我的数据库中所有的petid=0，怎么能出来208的数据呢，不知道哪里来的，真是晕啊！