JSP的变量

最新推荐文章于 2024-11-17 10:03:11 发布

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#jsp #null #application #servlet #import #session

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本文介绍了JSP中两种变量声明的方法及其区别。一种是在<%! %>中声明，这种声明方式使得变量成为servlet的类变量；另一种是在<% %>中声明，这种方式声明的变量为方法变量。通过示例代码展示了这两种声明方式的具体应用。

JSP的变量

jsp 的变量有两声明方法,

1, 写在 <%! %>里

2, 写在 <% %>里

注意它们一个有"!" , 另一个没有。它们的区别是：用第一种方法声明的变量将被翻译成 servlet 的类变量，用第二方法声明的变量将翻译成方法变量。如下边所示:

jsp文件：

<%@ page contentType="text/html;charset=GB2312" %>
<html>
<body>
<%! int i = 100 ; %>
<% int j = 1000 ; %>
<% out.print( " i=" + i + "; j=" + j ) ; %> </p>
</body>
</html>

生成的 servlet :

package org.apache.jsp;

import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.jsp.*;

public final class test_jsp extends org.apache.jasper.runtime.HttpJspBase
implements org.apache.jasper.runtime.JspSourceDependent {

int i = 100 ;
private static java.util.List _jspx_dependants;

public Object getDependants() {
return _jspx_dependants;
}

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

    JspFactory _jspxFactory = null;
    PageContext pageContext = null;
    HttpSession session = null;
    ServletContext application = null;
    ServletConfig config = null;
    JspWriter out = null;
    Object page = this;
    JspWriter _jspx_out = null;
    PageContext _jspx_page_context = null;

    try {
      _jspxFactory = JspFactory.getDefaultFactory();
      response.setContentType("text/html;charset=GB2312");
      pageContext = _jspxFactory.getPageContext(this, request, response,
         null, true, 8192, true);
      _jspx_page_context = pageContext;
      application = pageContext.getServletContext();
      config = pageContext.getServletConfig();
      session = pageContext.getSession();
      out = pageContext.getOut();
      _jspx_out = out;

      out.write("/r/n");
      out.write("/r/n");
      out.write("/r/n");
      out.write("<html>/r/n");
      out.write("<body>/r/n");
      out.write("/t");
      out.write('/r');
      out.write('/n');
      out.write(' ');
int j = 1000 ;
      out.write('/r');
      out.write('/n');
      out.write(' ');
out.print( " i=" + i + "; j=" + j ) ;
      out.write(" </p>/r/n");
      out.write("</body>/r/n");
      out.write("</html>");
    } catch (Throwable t) {
      if (!(t instanceof SkipPageException)){
        out = _jspx_out;
        if (out != null && out.getBufferSize() != 0)
          out.clearBuffer();
        if (_jspx_page_context != null) _jspx_page_context.handlePageException(t);
      }
    } finally {
      if (_jspxFactory != null) _jspxFactory.releasePageContext(_jspx_page_context);
    }
}
}　