结果集：异常：集类型TYPE_FORWARD_ONLY -- 为什么？

java sql resultset jdbc-odbc

2022-09-01 16:24:47

我有非常简单的代码：

pstat=con.prepareStatement("select typeid from users where username=? and password=?");             
pstat.setString(1, username);
pstat.setString(2, password);
rs=pstat.executeQuery();
int rowCount=0;
while(rs.next())
{       
    rowCount++;         
}
rs.beforeFirst();
if(rowCount>=1)
{
while(rs.next())
{
    typeID=rs.getInt(1);
}

但是当执行此代码时，我得到...

java.sql.SQLException: Result set type is TYPE_FORWARD_ONLY
at sun.jdbc.odbc.JdbcOdbcResultSet.beforeFirst(Unknown Source)
at server.ClientImpl.login(ClientImpl.java:57)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at sun.rmi.server.UnicastServerRef.dispatch(Unknown Source)
at sun.rmi.transport.Transport$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at sun.rmi.transport.Transport.serviceCall(Unknown Source)
at sun.rmi.transport.tcp.TCPTransport.handleMessages(Unknown Source)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(Unknown Source)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)

导致此问题的原因是什么，我该如何解决？

答案 1

将第一个语句更改为此

pstat=con.prepareStatement("select typeid from users where username=? and password=?",
                            ResultSet.TYPE_SCROLL_SENSITIVE, 
                        ResultSet.CONCUR_UPDATABLE);

通过这种方式，您可以向前和向后移动，因此无需担心的事情更少

答案 2

类型 TYPE_FORWARD_ONLY 意味着您只能在结果集上前进，而不能向后移动，因此当您尝试使用返回时，您会收到异常。相反，您可以使用以下 prepareStatement（）（它将结果集类型作为参数接收），也可以执行以下操作：beforeFirst()

        pstat=con.prepareStatement("select typeid from users where username=? and password=?");             
        pstat.setString(1, username);
        pstat.setString(2, password);
        rs=pstat.executeQuery();
        int rowCount=0;

        while(rs.next())
        {
            rowCount++;
            typeID=rs.getInt(1);
        }