如何从 JSP <%!...％>堵塞? [英] How to output HTML from JSP <%! ... %> block?
问题描述
我刚开始学习 JSP 技术，遇到了一堵墙.
I just started learning JSP technology, and came across a wall.
如何从 <%! 中的方法输出 HTML！... %> JSP 声明块?
这不起作用:
<%!
void someOutput() {
out.println("Some Output");
}
%>
...
<% someOutput(); %>
服务器说没有出局".
U: 我知道如何使用返回字符串的方法重写代码，但是有没有办法在 <%!无效(){}％>?虽然它可能不是最佳的，但它仍然很有趣.
U: I do know how to rewrite code with this method returning a string, but is there a way to do this inside <%! void () { } %> ? Though it may be non-optimal, it's still interesting.
推荐答案
您不能在指令中使用 'out' 变量(也不能使用任何其他预先声明的"scriptlet 变量).
You can't use the 'out' variable (nor any of the other "predeclared" scriptlet variables) inside directives.
JSP 页面由您的网络服务器转换为 Java servlet.例如，在 tomcats 中，scriptlet 中的所有内容(以<%"开头)以及所有静态 HTML 都被转换为一个巨大的 Java 方法，该方法将您的页面一行一行地写入一个名为out"的 JspWriter 实例.这就是您可以直接在 scriptlet 中使用out"参数的原因.另一方面，指令(以<%!"开头)被翻译为单独的 Java 方法.
The JSP page gets translated by your webserver into a Java servlet. Inside tomcats, for instance, everything inside scriptlets (which start "<%"), along with all the static HTML, gets translated into one giant Java method which writes your page, line by line, to a JspWriter instance called "out". This is why you can use the "out" parameter directly in scriptlets. Directives, on the other hand (which start with "<%!") get translated as separate Java methods.
举个例子，一个非常简单的页面(我们称之为 foo.jsp):
As an example, a very simple page (let's call it foo.jsp):
<html>
<head/>
<body>
<%!
String someOutput() {
return "Some output";
}
%>
<% someOutput(); %>
</body>
</html>
最终看起来像这样(为了清晰起见，忽略了很多细节):
would end up looking something like this (with a lot of the detail ignored for clarity):
public final class foo_jsp
{
// This is where the request comes in
public void _jspService(HttpServletRequest request, HttpServletResponse response)
throws IOException, ServletException
{
// JspWriter instance is gotten from a factory
// This is why you can use 'out' directly in scriptlets
JspWriter out = ...;
// Snip
out.write("<html>");
out.write("<head/>");
out.write("<body>");
out.write(someOutput()); // i.e. write the results of the method call
out.write("</body>");
out.write("</html>");
}
// Directive gets translated as separate method - note
// there is no 'out' variable declared in scope
private String someOutput()
{
return "Some output";
}
}
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