Jsp代码加感叹号与不加感叹号的区别

最新推荐文章于 2021-11-05 13:05:59 发布

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最新推荐文章于 2021-11-05 13:05:59 发布

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文章标签： jsp null import application string session

本文链接：https://blog.youkuaiyun.com/tzgj2007/article/details/6492179

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本文探讨了在JSP中使用<%! %>和<% %>的区别。通过分析Jsp生成的Java文件，可以发现<%! %>声明的变量成为类的属性，而<% %>声明的变量仅存在于_jspService方法内部，不能声明方法。

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用Jsp编写代码时，有时候用<%! %>，有时候用<% %>，加不加感叹号，到底有什么不同吗？

这个问题，可以从Jsp生成的Java文件里，得到答案。

在Tomcat5.5中

hello.jsp
=========
<%@ page contentType="text/html; charset=gb2312" %>
<HTML>
<HEAD>
<TITLE></TITLE>
</HEAD>
<BODY>
<%! String hello = "hello"; %>
<%
String world = "world";
%>
</BODY>
</HTML>

所生成对应的java文件(E:/Tomcat4.1/work/Standalone/localhost/test/)

hello_jsp.java
==============
package org.apache.jsp;

import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.jsp.*;
import org.apache.jasper.runtime.*;

public class hello_jsp extends HttpJspBase {

    String hello = "hello";

      private static java.util.Vector _jspx_includes;

public java.util.List getIncludes() {
return _jspx_includes;
}

public void _jspService(HttpServletRequest request, HttpServletResponse response)
throws java.io.IOException, ServletException {

JspFactory _jspxFactory = null;
javax.servlet.jsp.PageContext pageContext = null;
HttpSession session = null;
ServletContext application = null;
ServletConfig config = null;
JspWriter out = null;
Object page = this;
JspWriter _jspx_out = null;

try {
_jspxFactory = JspFactory.getDefaultFactory();
response.setContentType("text/html; charset=gb2312");
pageContext = _jspxFactory.getPageContext(this, request, response,
null, true, 8192, true);
application = pageContext.getServletContext();
config = pageContext.getServletConfig();
session = pageContext.getSession();
out = pageContext.getOut();
_jspx_out = out;

out.write("/r/n");
out.write("<HTML>/r/n");
out.write("<HEAD>/r/n");
out.write("<TITLE>");
out.write("</TITLE>/r/n");
out.write("</HEAD>/r/n");
out.write("<BODY>/r/n");
out.write("/r/n");

              String world = "world";

              out.write("/r/n");
out.write("</BODY>/r/n");
out.write("</HTML>");
} catch (Throwable t) {
out = _jspx_out;
if (out != null && out.getBufferSize() != 0)
out.clearBuffer();
if (pageContext != null) pageContext.handlePageException(t);
} finally {
if (_jspxFactory != null) _jspxFactory.releasePageContext(pageContext);
}
}
}