Java 处理JSP页面时发生异常

我试图返回mysql行数。我在运行.jsp文件时遇到以下错误：

org.apache.jasper.jaspereException:处理时发生异常 第54行的JSP页面/index.JSP

这是哪一行代码：

// count posts in category 1
catCount = conn.countCategoryPosts(1);

我知道数据库连接设置良好。 这是

countCategoryPosts

方法

public int countCategoryPosts(int ncatID) throws Exception{
    int catID = ncatID;
    try{
        sql = "SELECT COUNT(*) FROM crm_posts WHERE cat_id = ?";
        prep = conn.prepareStatement(sql);
        prep.setInt(1, catID);
        rs = prep.executeQuery();
    }catch(Exception e){
        e.printStackTrace();
    }
    return rs.getInt(1);
}

是什么导致了错误

编辑：根据请求，完整堆栈跟踪：

type Exception report

message An exception occurred processing JSP page /index.jsp at line 54

description The server encountered an internal error that prevented it from fulfilling this request.

exception

org.apache.jasper.JasperException: An exception occurred processing JSP page /index.jsp at line 54

51:                         id = Integer.parseInt(catAttributes[1]);
52:                         
53:                         // count posts in this category
54:                         catCount = conn.countCategoryPosts(1);
55:                         
56:                         // get posts in this category
57:                         postList = conn.getCategoryPosts(id);


Stacktrace:
    org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:568)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:455)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    org.tuckey.web.filters.urlrewrite.RuleChain.handleRewrite(RuleChain.java:176)
    org.tuckey.web.filters.urlrewrite.RuleChain.doRules(RuleChain.java:145)
    org.tuckey.web.filters.urlrewrite.UrlRewriter.processRequest(UrlRewriter.java:92)
    org.tuckey.web.filters.urlrewrite.UrlRewriteFilter.doFilter(UrlRewriteFilter.java:394)
root cause

javax.servlet.ServletException: java.sql.SQLException: Before start of result set
    org.apache.jasper.runtime.PageContextImpl.doHandlePageException(PageContextImpl.java:916)
    org.apache.jasper.runtime.PageContextImpl.handlePageException(PageContextImpl.java:845)
    org.apache.jsp.index_jsp._jspService(index_jsp.java:208)
    org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    org.tuckey.web.filters.urlrewrite.RuleChain.handleRewrite(RuleChain.java:176)
    org.tuckey.web.filters.urlrewrite.RuleChain.doRules(RuleChain.java:145)
    org.tuckey.web.filters.urlrewrite.UrlRewriter.processRequest(UrlRewriter.java:92)
    org.tuckey.web.filters.urlrewrite.UrlRewriteFilter.doFilter(UrlRewriteFilter.java:394)
root cause

java.sql.SQLException: Before start of result set
    com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1084)
    com.mysql.jdbc.SQLError.createSQLException(SQLError.java:987)
    com.mysql.jdbc.SQLError.createSQLException(SQLError.java:973)
    com.mysql.jdbc.SQLError.createSQLException(SQLError.java:918)
    com.mysql.jdbc.ResultSetImpl.checkRowPos(ResultSetImpl.java:850)
    com.mysql.jdbc.ResultSetImpl.getInt(ResultSetImpl.java:2705)
    com.servlet.explore.dbCon.countCategoryPosts(dbCon.java:103)
    org.apache.jsp.index_jsp._jspService(index_jsp.java:145)
    org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    org.tuckey.web.filters.urlrewrite.RuleChain.handleRewrite(RuleChain.java:176)
    org.tuckey.web.filters.urlrewrite.RuleChain.doRules(RuleChain.java:145)
    org.tuckey.web.filters.urlrewrite.UrlRewriter.processRequest(UrlRewriter.java:92)
    org.tuckey.web.filters.urlrewrite.UrlRewriteFilter.doFilter(UrlRewriteFilter.java:394)

你不能打电话

rs.getInt(1)

如果您没有用鼠标移动光标

rs.next() // for example

这应该起作用：

public int countCategoryPosts(int ncatID) throws Exception{
    int catID = ncatID;
    int result = 0;
    try{
        sql = "SELECT COUNT(*) FROM crm_posts WHERE cat_id = ?";
        prep = conn.prepareStatement(sql);
        prep.setInt(1, catID);
        rs = prep.executeQuery();
        if (rs.next()) {
           result = rs.getInt(1);
        }
    }catch(Exception e){
        e.printStackTrace();
    }
    return result;
}

---

请显示完整的stacktrace。好的，我把它添加到了问题中。为什么要使用Scriptlet？请参阅从JSP调用存储时不尊重MVC模式。您最好遵循MVC模式，添加将管理数据上升到视图的层。考虑到计数只返回一行，是否有更合适的方法来执行此操作？您可以使用

rs.first（）

而不是

rs.next（）

。