运行时错误：

index.jsp(12,8) PWC6038: "${sqlStatement == null}" contains invalid expression(s):
javax.el.ELException: Unable to find ExpressionFactory of type:
    org.apache.el.ExpressionFactoryImpl
    org.apache.jasper.JasperException: : javax.el.ELException: Unable to find ExpressionFactory of type: org.apache.el.ExpressionFactoryImpl

问题：

1. 我将如何调试呢？
2. 找不到类型为org.apache.el.E​​xpressionFactoryImpl <-的ExpressionFactory，这是什么意思？

这就是我所拥有的

• NetBeans IDE 7.3
• Tomcat 7.0
• MySql连接

这是Murach书中的简单sql网关

index.jsp

<%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>

    <c:if test="${sqlStatement == null}">
        <c:set var="sqlStatment" value="select * from User" />
    </c:if>

    <h1>The SQL Gateway</h1>
    <p>Enter an SQL statement and click the execute button. Then, information about the<br/>
    statement will appear at the bottom of this page.
    </p>

    <p><b>SQL Statement:</b></p>

    <form action="SqlGateway" method="POST">

        <textarea name="sqlStatement" cols="60" rows="8">${sqlStatement}</textarea>
        <br/><br/>
        <input type="submit" value="Execute">

    </form>

    <p><b>SQL result:</b></p>
    <p>${sqlResult}</p>

web.xml

    <servlet>
    <servlet-name>SqlGatewayServlet</servlet-name>
    <servlet-class>sql.SqlGatewayServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>SqlGatewayServlet</servlet-name>
    <url-pattern>/SqlGateway</url-pattern>
</servlet-mapping>

我认为servlet没什么问题，但是如果您需要我发布它，请告诉我。