自定义JSP标签查询数据报错问题

最新推荐文章于 2025-08-07 12:38:01 发布

原创最新推荐文章于 2025-08-07 12:38:01 发布 · 710 阅读

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本文分析了一起在JSP页面处理过程中出现的NullPointerException异常，该异常发生在使用EL表达式进行数据库查询操作时。通过代码审查发现，问题根源在于查询方法未声明为静态方法。本文详细介绍了异常产生的原因及解决方法。

错误信息

严重: Servlet.service() for servlet [jsp] in context with path [/Shopping] threw exception [An exception occurred processing JSP page /admin/product/add.jsp at line 69

66:                     </td>
67:                     <td class="ta_01" bgColor="#ffffff" colspan="3">
68:                         <select name="categorySecond.csid">
69:                             <c:forEach items="${myfn:findAllCategory() }" var="c">
70:                             <option value="${c.cid }">${c.cname }</option>
71:                             </c:forEach>
72:                         </select>


Stacktrace:] with root cause
java.lang.NullPointerException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.apache.el.parser.AstFunction.getValue(AstFunction.java:199)
    at org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:184)
    at org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate(PageContextImpl.java:944)
    at org.apache.jsp.admin.product.add_jsp._jspx_meth_c_005fforEach_005f0(add_jsp.java:262)
    at org.apache.jsp.admin.product.add_jsp._jspService(add_jsp.java:199)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:443)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:385)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:329)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:230)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:199)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:474)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:624)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:349)
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:495)
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:767)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1347)
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Unknown Source)

定义的查询方法

public  List<Category> findAllCategory() throws SQLException{
        String sql="select * from Category";
        QueryRunner qr=new QueryRunner(DataSourceUtils.getDataSource());
        return qr.query(sql,new BeanListHandler<Category>(Category.class));
        }