?? error.html
字號:
<HTML>
<HEAD>
<META http-equiv="Content-Type" content="text/html; charset=UTF-8">
<TITLE>Handling Unhandled Exceptions in a JSP Page
(Java Developers Almanac Example)
</TITLE>
<META CONTENT="Patrick Chan" NAME="AUTHOR">
<META CONTENT="Code Examples from The Java Developers Almanac 1.4" NAME="DESCRIPTION">
<META CONTENT="Addison-Wesley/Patrick Chan" NAME="OWNER">
<META CONTENT="3/20/02" NAME="revision">
<STYLE TYPE="text/css">
<!-- BODY CODE {font-family: Courier, Monospace; font-size: 11pt} TABLE, BODY {font-family: Verdana, Arial, Helvetica, sans-serif; font-size: 10pt} PRE {font-family: Courier, Monospace; font-size: 10pt} H3 {font-family: Verdana, Arial, Helvetica, sans-serif; font-size: 11pt} A.eglink {text-decoration: none} A:hover.eglink {text-decoration: underline} -->
</STYLE>
</HEAD>
<BODY>
<TABLE CELLSPACING="0" CELLPADDING="0" BORDER="0">
<TR>
<TD rowspan="3"><A HREF="/?l=ex"><IMG BORDER="0" ALIGN="BOTTOM" HSPACE="10" SRC="/egs/almanac14a.jpg"></A></TD><TD VALIGN="top"><font face="Times" size="6"><b>The Java Developers Almanac 1.4</b></font>
<br>
Order this book from <a href="/cgi-bin/scripts/redirect.pl?l=ex&url=http://www.amazon.com/exec/obidos/ASIN/0201752808/xeo">Amazon</a>.
</TD>
</TR>
<TR>
<TD align="right" valign="bottom">
<FORM method="get" action="/cgi-bin/search/find.pl">
<INPUT size="25" name="words" type="text"><INPUT value="Search" type="submit">
</FORM>
</TD>
</TR>
</TABLE>
<HR color="#6666cc">
<DIV ALIGN="LEFT">
<A HREF="/">Home</A>
>
<A HREF="../index.html">List of Packages</A>
>
<B><A HREF="../javax.servlet.jsp/pkg.html">javax.servlet.jsp</A></B><font color="#666666" SIZE="-2">
[18 examples]
</font>
>
<B><A HREF="../javax.servlet.jsp/pkg.html#Java%20Server%20Pages%20Output">Java Server Pages Output</A></B><font color="#666666" SIZE="-2">
[4 examples]
</font>
</DIV><P>
<h3>
e1059.
Handling Unhandled Exceptions in a JSP Page</h3>
A JSP page should handle any exceptions that might arise from the use
of scriptlets, expressions, or other JSP elements. However, there is
always a chance that something unexpected happens and an unhandled
exception is thrown. A JSP page can specify a specific page to be
included when an unhandled exception is thrown. This error page would
typically show an error message to the user, log the error message,
and possibly notify an administrator of the problem.
<P> Author's note: Some developers design their pages to throw an
exception (e.g. <code>NumberFormatException</code>) if the user's input is
invalid and then have the error page handle the exception. However,
if an unhandled exception does arise, the error page can become
confused. I prefer to handle input errors by explicitly checking for
them and then including (see <a href="../javax.servlet.jsp/include.jsp.html" class="eglink"><font size="-1"><b>e1053</b> Including a File in a JSP Page</font></a>) the
appropriate error page if necessary.
<P> A JSP page specifies the error page with the <code>page</code>
directive and <code>errorPage</code> attribute. When an unhandled exception
occurs, any unflushed output in the output stream is discarded and the
error page is immediately executed. Here is an example of JSP page
specifying <code>erropage.jsp</code> to be the error page:
<pre>
<%@ page errorPage="errorpage.jsp" %>
<%
if (request.getParameter("param").equals("value")) {
// ...
}
// The test above will throw a NullPointerException if param is
// not part of the query string. A better implementation would be:
if ("value".equals(request.getParameter("param"))) {
// ...
}
%>
</pre>
The error page indicates that it is an error page with the <code>page</code>
directive and <code>isErrorPage</code> attribute. This makes the unhandled
exception available in a variable called <code>exception</code>. Here is an
example of an error page that simply prints the name of the unhandled
exception:
<pre>
<%@ page isErrorPage="true" %>
An unexcepted error occurred. The name of the exception is:
<%= exception %>
</pre>
<P><table width="600" CELLSPACING="0" CELLPADDING="2" BORDER="0">
<tr>
<td bgcolor="#6666cc" align="center"><font color="#ffffff">
Related Examples
</font></td>
</tr>
</table>
e1056. <a class="eglink" href="comment.html?l=rel">
Commenting a JSP Page
</a>
<br>
e1057. <a class="eglink" href="expr.html?l=rel">
Generating Dynamic Content on a JSP Page
</a>
<br>
e1058. <a class="eglink" href="if.html?l=rel">
Implementing Conditional Content on a JSP Page
</a>
<br>
<table width="600" CELLSPACING="0" CELLPADDING="2" BORDER="0">
<tr>
<td align="left">
<br>
See also:
<a class="eglink" href="/egs/javax.servlet.jsp/pkg.html?l=rel#Java%20Server%20Pages">
Java Server Pages
</a>
<a class="eglink" href="/egs/javax.servlet.jsp/pkg.html?l=rel#Java%20Server%20Pages%20Headers">
Java Server Pages Headers
</a>
<a class="eglink" href="/egs/javax.servlet.jsp/pkg.html?l=rel#Java%20Server%20Pages%20Input">
Java Server Pages Input
</a>
</td>
</tr>
</table>
<br>
<br>
<FONT FACE="Verdana, Arial, Helvetica, sans-serif" SIZE="0">
© 2002 Addison-Wesley.
</FONT>
</BODY>
</HTML>
?? 快捷鍵說明
復制代碼
Ctrl + C
搜索代碼
Ctrl + F
全屏模式
F11
切換主題
Ctrl + Shift + D
顯示快捷鍵
?
增大字號
Ctrl + =
減小字號
Ctrl + -