从JDBC获取自动递增的ID

Question

Facing some exception without any clue message.

Here is my JDBC

            statement = con
                    .getConnection()
                    .prepareStatement(
                            "insert into  p3triplets set source_material= ? , process= ? ,target_material= ? , user_id = ?",
                            statement.RETURN_GENERATED_KEYS);
            statement.setString(1, pTriplet.getSource_Name());
            statement.setString(2, pTriplet.getProcessName());
            statement.setString(3, pTriplet.getTargetName());
            statement.setLong(4, user.getId());
            int i = statement.executeUpdate();
            generatedKeys=statement.getGeneratedKeys();
            long genId = generatedKeys.getLong(1);  //Exception
            for (p3TripleChild p3childTriple : childsDummyList) {
                if (p3childTriple.getId() == 0) {
                    p3childTriple.setId(genId);
                }
            }

And the exception is

java.sql.SQLException
    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.getLong(ResultSetImpl.java:2835)
    at com.mysql.jdbc.ResultSetImpl.getLong(ResultSetImpl.java:2830)
    at com.mtc.server.TripleServiceImpl.saveTriplet(TripleServiceImpl.java:161)
    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 com.google.gwt.user.server.rpc.RPC.invokeAndEncodeResponse(RPC.java:569)
    at com.google.gwt.user.server.rpc.RemoteServiceServlet.processCall(RemoteServiceServlet.java:208)
    at com.google.gwt.user.server.rpc.RemoteServiceServlet.processPost(RemoteServiceServlet.java:248)
    at com.google.gwt.user.server.rpc.AbstractRemoteServiceServlet.doPost(AbstractRemoteServiceServlet.java:62)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:487)
    at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:362)
    at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
    at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:181)
    at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:729)
    at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:405)
    at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
    at org.mortbay.jetty.handler.RequestLogHandler.handle(RequestLogHandler.java:49)
    at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
    at org.mortbay.jetty.Server.handle(Server.java:324)
    at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:505)
    at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:843)
    at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:647)
    at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:211)
    at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:380)
    at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:395)
    at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:488)

What I am missing ?

Id generated in database, but unable to get it back.

Answer 1

Your exception is occurring not when you call getGeneratedKeys() , but when you call getLong(1) . It is occurring because getGeneratedKeys return a ResultSet, and like any ResultSet, you need to call generatedKeys.next() to point to a row of the ResultSet before accessing data. That is why the exception is generated by the driver's internal checkRowPos method.

Answer 2

long genId = 0;
ResultSet keys = stmt.getGeneratedKeys();
if (keys.next()) {
    genId = keys.getLong(1);
}

JDBC returns a ResultSet as you could have inserted several records. And then you could have several generated keys per record.

So in the circumstantial tradition of JDBC, you need two steps further.