jsp <%! %> 与 <% %> 区别
<body>
<%!
//1、可定义方法
public String outMethod(){
return "outMethod";
}
//2、可定义static方法
public static String outStaticMethod(){
return "outStaticMethod";
}
//3、可定义static属性
public static int count = 0;
//4、不可以使用out对象
%>
<%
//1、不可定义方法
//2、不可定义static方法
//3、不可定义static属性
//可以使用out对象
out.print(outMethod());
out.print("<br>");
out.print(outStaticMethod());
out.print("<br>");
out.print(count);
%>
</body>
经Tomcat编译后，生成的java文件如下：
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 {
//1、可定义方法
public String outMethod(){
return "outMethod";
}
//2、可定义static方法
public static String outStaticMethod(){
return "outStaticMethod";
}
//3、可定义static属性
public static int count = 0;
//4、不可以使用out对象
private static final JspFactory _jspxFactory = JspFactory.getDefaultFactory();
private static java.util.List _jspx_dependants;
private javax.el.ExpressionFactory _el_expressionfactory;
private org.apache.AnnotationProcessor _jsp_annotationprocessor;
public Object getDependants() {
return _jspx_dependants;
}
public void _jspInit() {
_el_expressionfactory = _jspxFactory.getJspApplicationContext(getServletConfig().getServletContext()).getExpressionFactory();
_jsp_annotationprocessor = (org.apache.AnnotationProcessor) getServletConfig().getServletContext().getAttribute(org.apache.AnnotationProcessor.class.getName());
}
public void _jspDestroy() {
}
public void _jspService(HttpServletRequest request, HttpServletResponse response)
throws java.io.IOException, ServletException {
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 {
response.setContentType("text/html; charset=utf-8");
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("<!DOCTYPE html PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\" \"http://www.w3.org/TR/html4/loose.dtd\">\r\n");
out.write("<html>\r\n");
out.write("<head>\r\n");
out.write("<meta http-equiv=\"Content-Type\" content=\"text/html; charset=utf-8\">\r\n");
out.write("<title>Insert title here</title>\r\n");
out.write("</head>\r\n");
out.write("<body>\r\n");
out.write("\r\n");
out.write("\r\n");
//1、不可定义方法
//2、不可定义static方法
//3、不可定义static属性
//可以使用out对象
out.print(outMethod());
out.print("<br>");
out.print(outStaticMethod());
out.print("<br>");
out.print(count);
out.write("\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)
try { out.clearBuffer(); } catch (java.io.IOException e) {}
if (_jspx_page_context != null) _jspx_page_context.handlePageException(t);
}
} finally {
_jspxFactory.releasePageContext(_jspx_page_context);
}
}
}
小结：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）。
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