一个救命问题啊 各位老大来帮帮忙啊

Question

请问各位老大 我这段代码为什么只能查找数据库里有的用户名 如果是数据库里没有的用户名就出错啊 
请各位老大给点提示
public String SelectName(String username){
this.work1_username = username;
System.out.println(work1_username);
try{
rst = stat.executeQuery("select work1_userpass from work1 where work1_userName = '"+work1_username+"'");
System.out.println("select work1_userpass from work1 where work1_userName = '"+work1_username+"'");
System.out.println(work1_userpass);
while(rst.next()){
work1_userpass = rst.getString("work1_userpass");
return work1_userpass;
}

}catch(SQLException e){
e.printStackTrace();
}catch(Exception e){
e.printStackTrace();
}
      
return null;
}

Answer 1

就是程序运行到while(rst.next()){
work1_userpass = rst.getString("work1_userpass");
return work1_userpass;
}
这个地方就不再运行了

Answer 2

006-8-3 14:39:43 org.apache.struts.action.RequestProcessor processException
警告: Unhandled Exception thrown: class java.lang.NullPointerException
2006-8-3 14:39:43 org.apache.catalina.core.StandardWrapperValve invoke
严重: Servlet.service() for servlet action threw exception
java.lang.NullPointerException
at com.item.struts.action.LoginAction.execute(LoginAction.java:66)
at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:484)
at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:274)
at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1482)
at org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:525)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:709)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:252)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:178)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:126)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:105)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:107)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:148)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:869)
at org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:664)
at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:527)
at org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:80)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:684)
at java.lang.Thread.run(Unknown Source)

Answer 3

LoginAction.java:66是哪一行啊？看看哪个可能是null。有了明确的目标再分析嘛

Answer 4

我猜,你在使用返回的String时没有对它检测,在使用它之前可以加条打印信息,来确保问题不是出在以上这段代码中.