怎样查询出数据库的帖子标题？遇到点问题，看下面具体代码，求大神赐教啊···

Question

这里涉及到两张表，一张帖子，一张用户表。下面主要是想查询出用户发的帖子的标题.数据库通过登录时session等到的userName来查询用户所发的帖子。下面是我写的查询代码。（帖子表中的PostSender和用户表中的UserName 是相等的）但是运行时会报错，错误代码在下面。我不知道怎么错的，请大家教教我啊···
public List<Poster> listpraPost(String userName) throws SQLException {
ArrayList<Poster> postList = new ArrayList<Poster>();
Connection conn = null;
PreparedStatement stat = null;
ResultSet rst = null;
Poster poster = new Poster();
User user=new User();
try {
conn = db.getConnection();
stat = conn.prepareStatement("select PostTitle from Bbs_Post,tbl_Assistant where Bbs_Post.PostSender=tbl_Assistant.UserName and UserName=? ");
stat.setString(1,poster.getPostTitle());
stat.setString(2,userName);
rst=stat.executeQuery();
while (rst.next()) {
poster.setPostTitle(rst.getString(1));
user.setUserName(rst.getString(2));
//poster.setPostSender(rst.getString(2));
postList.add(poster);
}
} finally {
DB.release(conn, stat, rst);
}
return postList;
}
JSP页面：
<%@ page language="java" contentType="text/html; charset=UTF-8" import="java.sql.*"
    pageEncoding="UTF-8"%>
    <%@page import="valuebean.User" %>
    <%@page import="dao.UsersDao" %>
   <%@page import="valuebean.Poster" %> 
    <%@page import="dao.PostDao" %>
    <jsp:useBean id="connBean" scope="page" class="db.connDB"/>
  <%--   <%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%> --%>
<%
String basePath = request.getScheme() + "://"
+ request.getServerName() + ":" + request.getServerPort()
+ request.getContextPath() + "/";
/* User user=new User();
Poster poster=new Poster(); */
%><%
String userName=(String)session.getAttribute("userName");
User user=new User();
UsersDao usersdao=new UsersDao();
user=usersdao.selectInfo(userName);
    String userName1=(String)user.getUserName();
    int grade=user.getGrade();
    Poster poster=new Poster();
    PostDao postdao=new PostDao();
    postdao.listpraPost(userName);
    String posttitle=poster.getPostTitle();
%>
下面的代码省略···
错与提示：org.apache.jasper.JasperException: An exception occurred processing JSP page /front/myplace.jsp at line 2623:     int grade=user.getGrade();
24:     Poster poster=new Poster();
25:     PostDao postdao=new PostDao();
26:     postdao.listpraPost(userName);
27:     String posttitle=poster.getPostTitle();
28: %>
29: 
Stacktrace:
at org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:567)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:456)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:389)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:333)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:304)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:684)
at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:471)
at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:402)
at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:329)
at servlet.placearea.doPost(placearea.java:97)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:641)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:304)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:224)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:164)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:929)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:405)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:279)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:515)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:302)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
Caused by: javax.servlet.ServletException: java.sql.SQLException: [Microsoft][SQLServer 2000 Driver for JDBC]Invalid parameter binding(s).
at org.apache.jasper.runtime.PageContextImpl.doHandlePageException(PageContextImpl.java:911)
at org.apache.jasper.runtime.PageContextImpl.handlePageException(PageContextImpl.java:840)
at org.apache.jsp.front.myplace_jsp._jspService(myplace_jsp.java:290)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:433)
... 28 more
Caused by: java.sql.SQLException: [Microsoft][SQLServer 2000 Driver for JDBC]Invalid parameter binding(s).
at com.microsoft.jdbc.base.BaseExceptions.createException(Unknown Source)
at com.microsoft.jdbc.base.BaseExceptions.getException(Unknown Source)
at com.microsoft.jdbc.base.BasePreparedStatement.validateParameterIndex(Unknown Source)
at com.microsoft.jdbc.base.BasePreparedStatement.setObjectInternal(Unknown Source)
at com.microsoft.jdbc.base.BasePreparedStatement.setString(Unknown Source)
at dao.PostDao.listpraPost(PostDao.java:54)
at org.apache.jsp.front.myplace_jsp._jspService(myplace_jsp.java:101)
... 31 more

Answer 1

select PostTitle from Bbs_Post,tbl_Assistant where Bbs_Post.PostSender=tbl_Assistant.UserName and UserName=? 
看看你的 Sql 语句是不是有问题 ，其他真看不出来 了

Answer 2

看了你的listpraPost类，发现几个问题
1. select PostTitle from Bbs_Post,tbl_Assistant where Bbs_Post.PostSender=tbl_Assistant.UserName and UserName=? 。。别名用错了。。
改为：
select PostTitle from Bbs_Post bp,tbl_Assistant ta where bp.PostSender=ta.UserName and ta.UserName=? 2. while (rst.next()) {
poster.setPostTitle(rst.getString(1));
user.setUserName(rst.getString(2));
//poster.setPostSender(rst.getString(2));
postList.add(poster);
} 查出的数据存入对象时每个都要实例化。。不然存入list中的始终只有一个
改为：
while (rst.next()) {
Poster poster = new Poster();
poster.setPostTitle(rst.getString(1));
user.setUserName(rst.getString(2));
//poster.setPostSender(rst.getString(2));
postList.add(poster);
}3. jsp中：
Poster poster=new Poster();  //这里new了一个Poster以后啥都没做。。
  PostDao postdao=new PostDao();
  postdao.listpraPost(userName);
  String posttitle=poster.getPostTitle();  // 上面posternew出来啥没做。这里何来值取？改为：
Poster poster=null;
ArrayList<Poster> postList =postdao.listpraPost(userName);
for(...) // 自己写一个循环取出Poster对象
// 自己写一个取出Poster对象为poster赋值
String posttitle=poster.getPostTitle();  // 这样取就有值了其他的LZ自己好好研究吧。。

Answer 3

stat = conn.prepareStatement("select PostTitle from Bbs_Post,tbl_Assistant where Bbs_Post.PostSender=tbl_Assistant.UserName and UserName=? ");
stat.setString(1,poster.getPostTitle());
stat.setString(2,userName);
根据异常信息
Caused by: java.sql.SQLException: [Microsoft][SQLServer 2000 Driver for JDBC]Invalid parameter binding(s).
查找以上代码发现sql指定一个参数却set两个参数，因此报错
楼上说的问题虽然可能不会导致抛异常，但也是很低级的错误，希望lz加把力。

Answer 4

首先你的sql就有问题：
select PostTitle from Bbs_Post,tbl_Assistant where Bbs_Post.PostSender=tbl_Assistant.User
应该是
select p.PostTitle from Bbs_Post p ,tbl_Assistant t where p.PostSender=t.User