请教个问题。搞了半天也不知道怎么解决 org.apache.catalina.core.StandardWrapperValve invoke

[forgettable]

出现 这个样的错误该怎么样解决啊，网上说的不太明白是什么意思
org.apache.catalina.core.StandardWrapperValve invoke
我的连接数据库这样写的
package org.zjy.db;
import java.sql.*;
//该用来负责与数据库之间的连接，同时执行Sql语句
public class DBUtil {
private static Connection conn=null;
private static Statement st=null;
//该方法用来获取与数据之间的连接
public static Connection getConnection(){
if(conn==null){
try{
Class.forName("com.mysql.jdbc.Driver");
String username="root";
String password="rychel";
String url="jdbc:mysql://localhost:3306/blog";
conn=DriverManager.getConnection(url,username,password);
}catch(Exception ex){
ex.printStackTrace();
}
}
return conn;
}
//该方法用来获取执行Sql语句对象
public static Statement getStatement(){
if(st==null){
try{
Connection c=getConnection();
st=c.createStatement();
}catch(Exception ex){
ex.printStackTrace();
}
}
return st;
}
//如果Sql语句是Select语句,则外界可以调用该方法来执行
public static ResultSet executeQuery(String sql){
ResultSet set=null;
try{
Statement state=getStatement();
set=state.executeQuery(sql);
}catch(Exception ex){
ex.printStackTrace();
}
return set;
}
//如果Sql语句是insert,update,delete语句,则外界可以调用该方法来执行
public static int executeUpdateInsertDelete(String sql){
int i=0;
try{
Statement state=getStatement();
i=state.executeUpdate(sql);
}catch(Exception ex){
ex.printStackTrace();
}
return i;
}
//该方法用来获取外界所给定表中id列当前最的值
public static int getMaxId(String tableName){
StringBuffer sql=new StringBuffer();
sql.append("select id from "+tableName+" order by id desc;");
int i=0;
ResultSet set=executeQuery(sql.toString());
try{
while(set.next()){
i=set.getInt("id");
break;
}
}catch(Exception ex){
ex.printStackTrace();
}
return i;
}
}


下面是出现错误的信息。。


2011-3-14 0:10:40 org.apache.catalina.core.AprLifecycleListener init
信息: Loaded Apache Tomcat Native library 1.1.14.
2011-3-14 0:10:40 org.apache.catalina.core.AprLifecycleListener init
信息: APR capabilities: IPv6 [false], sendfile [true], accept filters [false], random [true].
2011-3-14 0:10:40 org.apache.coyote.http11.Http11AprProtocol init
信息: Initializing Coyote HTTP/1.1 on http-8090
2011-3-14 0:10:40 org.apache.coyote.ajp.AjpAprProtocol init
信息: Initializing Coyote AJP/1.3 on ajp-8009
2011-3-14 0:10:40 org.apache.catalina.startup.Catalina load
信息: Initialization processed in 1252 ms
2011-3-14 0:10:40 org.apache.catalina.core.StandardService start
信息: Starting service Catalina
2011-3-14 0:10:40 org.apache.catalina.core.StandardEngine start
信息: Starting Servlet Engine: Apache Tomcat/6.0.14
2011-3-14 0:10:41 org.apache.catalina.core.ApplicationContext log
信息: ContextListener: contextInitialized()
2011-3-14 0:10:41 org.apache.catalina.core.ApplicationContext log
信息: SessionListener: contextInitialized()
2011-3-14 0:10:42 org.apache.coyote.http11.Http11AprProtocol start
信息: Starting Coyote HTTP/1.1 on http-8090
2011-3-14 0:10:42 org.apache.coyote.ajp.AjpAprProtocol start
信息: Starting Coyote AJP/1.3 on ajp-8009
2011-3-14 0:10:42 org.apache.catalina.startup.Catalina start
信息: Server startup in 1642 ms
top.jsp的Blog对象为空
2011-3-14 0:10:53 org.apache.catalina.core.StandardWrapperValve invoke
严重: Servlet.service() for servlet jsp threw exception
java.lang.NullPointerException
at org.apache.jsp.left_jsp._jspService(left_jsp.java:108)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:393)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:320)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:263)
at org.apache.coyote.http11.Http11AprProcessor.process(Http11AprProcessor.java:852)
at org.apache.coyote.http11.Http11AprProtocol$Http11ConnectionHandler.process(Http11AprProtocol.java:584)
at org.apache.tomcat.util.net.AprEndpoint$Worker.run(AprEndpoint.java:1508)
at java.lang.Thread.run(Thread.java:619)
2011-3-14 0:10:53 org.apache.catalina.core.StandardWrapperValve invoke
严重: Servlet.service() for servlet jsp threw exception
java.lang.NullPointerException
at org.apache.jsp.top_jsp._jspService(top_jsp.java:91)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:393)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:320)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:263)
at org.apache.coyote.http11.Http11AprProcessor.process(Http11AprProcessor.java:852)
at org.apache.coyote.http11.Http11AprProtocol$Http11ConnectionHandler.process(Http11AprProtocol.java:584)
at org.apache.tomcat.util.net.AprEndpoint$Worker.run(AprEndpoint.java:1508)
at java.lang.Thread.run(Thread.java:619)
2011-3-14 0:10:53 org.apache.catalina.core.StandardWrapperValve invoke
严重: Servlet.service() for servlet jsp threw exception
java.lang.NullPointerException
at org.apache.jsp.main_jsp._jspService(main_jsp.java:66)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:393)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:320)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:263)
at org.apache.coyote.http11.Http11AprProcessor.process(Http11AprProcessor.java:852)
at org.apache.coyote.http11.Http11AprProtocol$Http11ConnectionHandler.process(Http11AprProtocol.java:584)
at org.apache.tomcat.util.net.AprEndpoint$Worker.run(AprEndpoint.java:1508)
at java.lang.Thread.run(Thread.java:619)

[forgettable]

[Quote=引用楼主 forgettable 的回复:]
出现 这个样的错误该怎么样解决啊，网上说的不太明白是什么意思
org.apache.catalina.core.StandardWrapperValve invoke
我的连接数据库这样写的
package org.zjy.db;
import java.sql.*;
//该用来负责与数据库之间的连接，同时执行Sql语句
public class DBUtil {
private s……
[/Quote]额，这是老师给的例子，让我们参考的

[wkcgy]

我看错误信息不是报了一个空指针错误吗？？你先改了那个再看一下错误！！！

[Pc498471249]

怎么还在用jdbc操作连接数据库? 你没有学习Hibernate吗??

[Pc498471249]

//该方法用来获取外界所给定表中id列当前最的值
public static int getMaxId(String tableName){
StringBuffer sql=new StringBuffer();
sql.append("select id from "+tableName+" order by id desc;");
int i=0;
ResultSet set=executeQuery(sql.toString());
try{
while(set.next()){
i=set.getInt("id");
break;
}
}catch(Exception ex){
ex.printStackTrace();
}
return i;
}
}

你这代码问题百出,你的sql语句查询出的是多条Id,但是你只用一个i来接收?? 你要查最大Id,sql里面应该用max()函数