Question

求救求救！！！jsp调用javabean为什么resultset返回空值？

javabean直接运行可以连接到数据库！
package conn;
import java.sql.*;
public class JDBConnection{
private static Connection conn=null;
private static Statement st=null;
private static ResultSet rs=null;
public static void main(String[] args){
String driverName="com.microsoft.sqlserver.jdbc.SQLServerDriver";
String dbURL="jdbc:sqlserver://localhost:1433;DatabaseName=TICKETING";
String userName="sa";
String userPwd="123";
try{
Class.forName(driverName);
conn=DriverManager.getConnection(dbURL, userName, userPwd);
String sql="select * from userInfo";
st=conn.createStatement();
rs=st.executeQuery(sql);
while(rs.next()){
System.out.println(rs.getString(1));
}
System.out.println("连接成功！");
rs.close();
}catch(Exception e){
System.out.println("连接失败！");
}
}
public ResultSet executeQuery(String sql){
try{
Statement stm=conn.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,ResultSet.CONCUR_READ_ONLY);
rs=stm.executeQuery(sql);
return rs;
}catch(Exception e){
return null;
下面是调用部分
<jsp:useBean id="connection" scope="page" class="conn.JDBConnection"/>
<%
ResultSet rs=null;
request.setCharacterEncoding("UTF-8");
String sql="select * from userInfo";
rs=connection.executeQuery(sql);
if(rs.next()){%> <-----这边就不行了！如果这边写成if(rs==null)就直接跳到index.jsp了
<script language="javascript">
window.location.href="index.jsp";
</script>
<% }
错误：
严重: Servlet.service() for servlet [jsp] in context with path [/TICKETING] threw exception [An exception occurred processing JSP page /longin_1.jsp at line 39
37: String sql="select * from userInfo";
38: rs=connection.executeQuery(sql);
39: if(rs.next()){%>
40: <script language="javascript">
Stacktrace:] with root cause
java.lang.NullPointerException
at org.apache.jsp.longin_005f1_jsp._jspService(longin_005f1_jsp.java:105)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
。。。

Answer 1

直接运行能成功是你有main函数 有连接到数据库
<jsp:useBean id="connection" scope="page" class="conn.JDBConnection"/>
<%
ResultSet rs=null;
request.setCharacterEncoding("UTF-8");
String sql="select * from userInfo";
rs=connection.executeQuery(sql);
if(rs.next()){%> <-----这边就不行了！如果这边写成if(rs==null)就直接跳到index.jsp了
<script language="javascript">
window.location.href="index.jsp";
</script>
<% } 而你的这代码里面是没有连接数据库的，所以操作返回的结果就是null。

Answer 2

Servlet.service() for servlet [jsp] in context with path [/TICKETING] threw exception [An exception occurred processing JSP page /longin_1.jsp at line 39
这个问题~！

追问

这个问题怎么解决啊，大侠！

Answer 3

可能executeQuery()方法中的conn=null,
Statement stm=conn.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,ResultSet.CONCUR_READ_ONLY);
//这句话就出错了

Answer 4

你这边前面直接 ResultSet rs=null;
这么写 rs肯定没值了 你这边可以通过new JDBConnection（）来操作