SQLException：结果集开始之前

Question

我在其他文章中检查过这个问题，它说要指向表中的第一行，我需要执行“result.next（）”。 但我仍然遇到这个问题，我检查了函数的输入，没关系，并且匹配数据库中的信息。 它不执行“while”循环，就像表格的内容是空的一样... 我使用GWT，所以调试很痛苦！

表：picId（primary_key），书，fromChapter，toChapter ....（重要的）

内容：书= 1，章= 6 和数据库中包含这样的行。 我希望我不会像往常一样在这里失去一些愚蠢的东西！ :)

public List<PicAsset> getPicture(int book, int chapter) throws Exception 

    { 

    System.out.print("getPicture ok " + book +"," + chapter); 
    Connection conn = null; 
    PreparedStatement pstmt = null; 
    ResultSet result = null; 
    List<PicAsset> relevantAssets = new ArrayList<PicAsset>(); 
    PicAsset relAsset; 


    try { 
     conn = getConnection(); 
     pstmt = conn.prepareStatement("SELECT * FROM picasset WHERE book = ? AND fromChapter = ?"); 

     //System.out.print("connection" + conn); 
     pstmt.setInt(1, book); 
     pstmt.setInt(2, chapter); 
     // pstmt.setInt(3, chapter); 
     // pstmt.setInt(4, chapter); 
     result = pstmt.executeQuery(); 


     while (result.next()) { 

      System.out.print(result.next()); 
      relAsset = new PicAsset(result.getInt("picId"),result.getInt("book"), result.getInt("fromChapter"), result.getInt("toChapter"),result.getInt("fromVerse"),result.getInt("toVerse"),result.getString("creator"),result.getString("discription"),result.getString("source"),result.getString("title"),result.getString("duration"),result.getString("url")); 
      relevantAssets.add(relAsset); 

     } 
    } 

     catch (SQLException sqle) 
     { 
      sqle.printStackTrace(); 
     } 
     finally 
     { 
      // Cleanup 
      result.close(); 
      pstmt.close(); 
      conn.close(); 
     } 

    return relevantAssets; 


    } 
} 

堆栈跟踪：

getPicture ok 1,6connectioncom.mysql.jdbc.Connection@18e476fajava.sql.SQLException: Before start of result set 
    at com.mysql.jdbc.ResultSet.checkRowPos(ResultSet.java:700) 
    at com.mysql.jdbc.ResultSet.getNativeString(ResultSet.java:3747) 
    at com.mysql.jdbc.ResultSet.getStringInternal(ResultSet.java:4979) 
    at com.mysql.jdbc.ResultSet.getString(ResultSet.java:4810) 
    at com.biblereader.server.MySQLConnection.getPicture(MySQLConnection.java:151) 
    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:561) 
    at com.google.gwt.user.server.rpc.RemoteServiceServlet.processCall(RemoteServiceServlet.java:265) 
    at com.google.gwt.user.server.rpc.RemoteServiceServlet.processPost(RemoteServiceServlet.java:305) 
    at com.google.gwt.user.server.rpc.AbstractRemoteServiceServlet.doPost(AbstractRemoteServiceServlet.java:62) 
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:755) 
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:848) 
    at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:686) 
    at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:501) 
    at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:137) 
    at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:557) 
    at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:231) 
    at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1086) 
    at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:428) 
    at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:193) 
    at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1020) 
    at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:135) 
    at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:116) 
    at org.eclipse.jetty.server.handler.RequestLogHandler.handle(RequestLogHandler.java:68) 
    at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:116) 
    at org.eclipse.jetty.server.Server.handle(Server.java:370) 
    at org.eclipse.jetty.server.AbstractHttpConnection.handleRequest(AbstractHttpConnection.java:489) 
    at org.eclipse.jetty.server.AbstractHttpConnection.content(AbstractHttpConnection.java:960) 
    at org.eclipse.jetty.server.AbstractHttpConnection$RequestHandler.content(AbstractHttpConnection.java:1021) 
    at org.eclipse.jetty.http.HttpParser.parseNext(HttpParser.java:865) 
    at org.eclipse.jetty.http.HttpParser.parseAvailable(HttpParser.java:240) 
    at org.eclipse.jetty.server.AsyncHttpConnection.handle(AsyncHttpConnection.java:82) 
    at org.eclipse.jetty.io.nio.SelectChannelEndPoint.handle(SelectChannelEndPoint.java:668) 
    at org.eclipse.jetty.io.nio.SelectChannelEndPoint$1.run(SelectChannelEndPoint.java:52) 
    at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:608) 
    at org.eclipse.jetty.util.thread.QueuedThreadPool$3.run(QueuedThreadPool.java:543) 
    at java.lang.Thread.run(Unknown Source) 

Answer 1

的问题似乎是在这里;

while (result.next()) { 

    System.out.print(result.next()); 

    ... 

在while循环中第一次调用result.next()会将光标移至第一个结果。打印中的第二个将其推进到第二个结果（可能不存在）。

如果查询中只有一个结果，则在第二次调用next（）后游标无效，从下一行的游标获取数据将失败。