相同的一个jsp文件，含有表达式的计算，为什么放在tomcat目录下的webapps目录下的任意应用程序目录下执行都可以得到正确的结果，如果应用程序目录不在tomcat目下的webapps下，执行就不会计算表达式，代码如下：
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<html>
<head>
<title> JSP 2.0 Expression Language - Basic Arithmetic </title>
</head>
<body>
<h1> JSP 2.0 Expression Language - Basic Arithmetic </h1>
<hr>
This example illustrates basic Expression Language arithmetic.
Addition (+), subtraction (-), multiplication (*), division (/ or div),
and modulus (% or mod) are all supported. Error conditions, like
division by zero, are handled gracefully.
<br>
<blockquote>
<code>
<table border= "1 ">
<thead>
<td> <b> EL Expression </b> </td>
<td> <b> Result </b> </td>
</thead>
<tr>
<td> \${1} </td>
<td> ${1} </td>
</tr>
<tr>
<td> \${1 + 2} </td>
<td> ${1 + 2} </td>
</tr>
<tr>
<td> \${1.2 + 2.3} </td>
<td> ${1.2 + 2.3} </td>
</tr>
<tr>
<td> \${1.2E4 + 1.4} </td>