📄 jsp-directives.xtp
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<document> <header> <product>resin</product> <title>Directives</title> <description> <p> JSP Directives control the processing of an entire page. Directive examples include setting a scripting language, setting an error page, including other sections, and setting a character encoding. </p> </description> </header> <body> <summary/> <s1 name="jsp" title="JSP Directives"> <s2 name="language" title="<%@ page language="lang" %>" index="language" type="defun"> <p>Sets the JSP script language to <var>lang</var>. Defaults to Java. All JSP 1.0 implementations must support Java. Some implementations, like Resin, may support other scripting languages, e.g. JavaScript.</p> </s2> <s2 name="import" title="<%@ page import="package" %>" index="import" type="defun"> <p>Adds to the Java package import list for the generated Java file.</p> <note>Only relevant when using Java.</note> </s2> <s2 name="errorPage" title="<%@ page errorPage="path" %>" index="errorPage" type="defun"> <p>Defines a page to display if an error occurs in the JSP page.</p> <p>Robust applications can return informative error pages when something goes wrong in a file, for example if a database is overloaded. <var>path</var> is returned as the response file. The error page can use the additional implicit variable <a href="#exception">exception</a> containing the thrown exception.</p> <p><var>path</var> is relative to the current page. Its root is relative to the application root.</p> <p>The error page itself can be a JSP page. If the error page is a JSP page, it can use the implicit variable <code>exception</code> to get information about the thrown exception.</p> </s2> <s2 name="isErrorPage" title="<%@ page isErrorPage="true" %>" index="error page" type="defun"> <p>Gives an error page access to the <code>exception</code> implicit variable. Default to false.</p> <example title="errorpage.jsp"> &lt%@ page isErrorPage="true" %> <h1>Received error <%= exception.message %></h1> </example> </s2> <s2 name="include" title="<%@ include file="path" %>" index="include, at translation" type="defun"> <p>Includes the raw file <var>path</var> at translation time.</p> <p>The include directive is a replacement for an SSI include (or the C '#include'). It includes the contents of the file at <var>path</var> into the JSP file. The included file is parsed as JSP, so it can have active elements like expressions, declarations and scriptlets.</p> <p><var>path</var> is relative to the current page, and its root is the application root.</p> <example title="header.jsp"> <html><head> <title>&lt%= title %></title> </head> <body color=white> </example> <example title="page.jsp"> <% var title = "Hello, World"; %> <%@ include file='header.jsp' %> <h1><%= title %></h1> </example> </s2> <s2 name="buffer" index="page buffer" title="<%@ page buffer=sizekb %>" type="defun"> <p>Gives the <var>size</var> of the page buffer in kb or <var>none</var> for no buffer. Default 8kb. If <code>buffer</code> is <var>none</var>, all output is immediately flushed. </p> <p>JSP 1.0 gives page writers flexibility by buffering its output before sending the response to HTTP. The buffering allows <a href="#errorpage">error recovery</a> and forwarding, even after generating some content. Once the buffer has filled, it will be flushed. So applications must still detect their errors early.</p> <p>The following example generates an XML section (for variety). If the form's query is missing the 'name' parameter, it will redirect the results.</p> <example> <?xml version='1.0'?> <form> <% if (request.form["name"] == null) pageContext.forward("redo-form.jsp"); for (var name in request.form) { out.print("<" + name + ">"); out.print(request.form[name]); out.println("</" + name + ">"); } %> </form> </example> </s2> <s2 name="autoFlush" index="page buffer" title="<%@ page autoFlush="true" %>" type="defun"> <p>Tells JSP to flush the page buffer when it fills. Default is true.</p> <p>If autoFlush is false, the JSP engine will throw an exception if the buffer overflows.</p> </s2> <s2 name="pagesession" index="session" title="<%@ page session="true" %>" type="defun"> <p>Tells JSP that the page participates in a session. Defaults to true.</p> <p>The session declaration makes the session implicit variable available to a JSP page.</p> <p>If the page doesn't use sessions, it should set <code>session</code> to false. </p> <example> <%@ page session="true" %> <% session.value.count++; %> <h1>Welcome, visitor <%= count %></h1;> </example> </s2> <s2 name="isThreadSafe" index="synchronization" title="<%@ page isThreadSafe="true" %>" type="defun"> <p>Tells the JSP that multiple pages can execute in parallel. Defaults to true.</p> <p>JSP pages are always responsible for synchronization of shared variables, such as the <code>session</code> and <code>application</code> variables. In some rare cases, a page may use servlet variables (created with a declaration), and be too lazy to handle the synchronization.</p> <p>Even with <code>isThreadSafe=false</code>, the JSP engine may create multiple instances of the JSP servlet. So the page author can never absolve herself of synchronization issues.</p> <p>In the following example, a JSP engine might create 3 servlet instances of the page. So three calls to the same page may return counts of 17, 3 and 398. In addition, the JSP engine is free to destroy and recreate the servlet at any time, essentially resetting the counter to 0.</p> <example> <%@ page isThreadSafe="false" %> <%! var count = 0; %> <h1>Welcome, visitor <%= count++ %> </example> </s2> <s2 name="info" title="<%@ page info="description" %>" type="defun"> <p>Gives a brief description for the page.</p> </s2> <s2 name="contentType" title="<%@ page contentType="description" %>" type="defun"> <p>Sets the content type and character encoding of the page.</p> <p><code>contentType</code> can also set the character encoding, for example to utf-8. </p> <example> <%@ page contentType="text/plain; charset=utf-8" %> <%! var count = 0; %> <h1>Welcome, visitor <%= count++ %> </example> </s2> <s2 name="extends" title="<%@ page extends="Java class" %>" type="defun"> <p>Changes the generated servlet's class.</p> <p>In general, a filter is a better solution than using the extends directive.</p> </s2> <s2 name="taglib" title="<%@ taglib prefix="x" uri="foo" %>" type="defun"> <p>Configures tags with prefix <var>x</var> to use the tag library <var>foo</var>.</p> <example> <%@ taglib prefix='x' uri='http://www.caucho.com/mytag/test' %> <x:mytag/> </example> </s2> </s1> </body></document>⌨️ 快捷键说明
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