jsp中<%! %>

 1 <body>  
 2 <%!  
 3   
 4 //1、可定义方法  
 5 public String outMethod(){  
 6     return "outMethod";  
 7 }  
 8 //2、可定义static方法  
 9 public static String outStaticMethod(){  
10     return "outStaticMethod";  
11 }  
12 //3、可定义static属性  
13 public static int count = 0;  
14   
15 //4、不可以使用out对象  
16 %>  
17   
18 <%  
19 //1、不可定义方法  
20 //2、不可定义static方法  
21 //3、不可定义static属性  
22   
23 //可以使用out对象  
24 out.print(outMethod());  
25 out.print("<br>");  
26 out.print(outStaticMethod());  
27 out.print("<br>");  
28 out.print(count);  
29 %>  
30 </body>

经Tomcat编译后，生成的java文件如下：

  1 package org.apache.jsp;  
  2   
  3 import javax.servlet.*;  
  4 import javax.servlet.http.*;  
  5 import javax.servlet.jsp.*;  
  6   
  7 public final class test_jsp extends org.apache.jasper.runtime.HttpJspBase  
  8     implements org.apache.jasper.runtime.JspSourceDependent {  
  9   
 10   
 11   
 12 //1、可定义方法  
 13 public String outMethod(){  
 14     return "outMethod";  
 15 }  
 16 //2、可定义static方法  
 17 public static String outStaticMethod(){  
 18     return "outStaticMethod";  
 19 }  
 20 //3、可定义static属性  
 21 public static int count = 0;  
 22   
 23 //4、不可以使用out对象  
 24   
 25   private static final JspFactory _jspxFactory = JspFactory.getDefaultFactory();  
 26   
 27   private static java.util.List _jspx_dependants;  
 28   
 29   private javax.el.ExpressionFactory _el_expressionfactory;  
 30   private org.apache.AnnotationProcessor _jsp_annotationprocessor;  
 31   
 32   public Object getDependants() {  
 33     return _jspx_dependants;  
 34   }  
 35   
 36   public void _jspInit() {  
 37     _el_expressionfactory = _jspxFactory.getJspApplicationContext(getServletConfig().getServletContext()).getExpressionFactory();  
 38     _jsp_annotationprocessor = (org.apache.AnnotationProcessor) getServletConfig().getServletContext().getAttribute(org.apache.AnnotationProcessor.class.getName());  
 39   }  
 40   
 41   public void _jspDestroy() {  
 42   }  
 43   
 44   public void _jspService(HttpServletRequest request, HttpServletResponse response)  
 45         throws java.io.IOException, ServletException {  
 46   
 47     PageContext pageContext = null;  
 48     HttpSession session = null;  
 49     ServletContext application = null;  
 50     ServletConfig config = null;  
 51     JspWriter out = null;  
 52     Object page = this;  
 53     JspWriter _jspx_out = null;  
 54     PageContext _jspx_page_context = null;  
 55   
 56   
 57     try {  
 58       response.setContentType("text/html; charset=utf-8");  
 59       pageContext = _jspxFactory.getPageContext(this, request, response,  
 60                 null, true, 8192, true);  
 61       _jspx_page_context = pageContext;  
 62       application = pageContext.getServletContext();  
 63       config = pageContext.getServletConfig();  
 64       session = pageContext.getSession();  
 65       out = pageContext.getOut();  
 66       _jspx_out = out;  
 67   
 68       out.write("
");  
 69       out.write("<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
");  
 70       out.write("<html>
");  
 71       out.write("<head>
");  
 72       out.write("<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
");  
 73       out.write("<title>Insert title here</title>
");  
 74       out.write("</head>
");  
 75       out.write("<body>
");  
 76       out.write("
");  
 77       out.write("
");  
 78   
 79 //1、不可定义方法  
 80 //2、不可定义static方法  
 81 //3、不可定义static属性  
 82   
 83 //可以使用out对象  
 84 out.print(outMethod());  
 85 out.print("<br>");  
 86 out.print(outStaticMethod());  
 87 out.print("<br>");  
 88 out.print(count);  
 89   
 90       out.write("
");  
 91       out.write("</body>
");  
 92       out.write("</html>");  
 93     } catch (Throwable t) {  
 94       if (!(t instanceof SkipPageException)){  
 95         out = _jspx_out;  
 96         if (out != null && out.getBufferSize() != 0)  
 97           try { out.clearBuffer(); } catch (java.io.IOException e) {}  
 98         if (_jspx_page_context != null) _jspx_page_context.handlePageException(t);  
 99       }  
100     } finally {  
101       _jspxFactory.releasePageContext(_jspx_page_context);  
102     }  
103   }  
104 }

在生成的java文件中，我们可以看到，<%! %>中的代码对应于java类文件的成员方法、静态方法，静态变量，而<% %>中的代码对应于java类文件的_jspService方法中的代码（_jspService对应于servlet中的service方法），这也就是为什么在<% %>中不能声明方法、静态变量的原因了（方法中是不可以再创建方法的）