<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Test</title>
</head>
<body>
<%! String test1 = "定义一些成员变量或者方法"; %>
<% String test2 = "定义局部变量或者一些逻辑操作"; %>
<%="test" %>
equals
<% out.println("test"); %>
</body>
</html>
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这里列举了三个标签<%%>、<%! %>、<%= %>。这里kk从编译成的Servlet来PK下这三者的区别。
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<% ?%>: 用来放入一些逻辑操作和局部变量，其中的一些逻辑将会放入到_jspService(final javax.servlet.http.HttpServletRequest request, final javax.servlet.http.HttpServletResponse response)方法中(如下图)，上面的jsp中<% String test1 = "定义局部变量或者一些逻辑操作"; %>就是方法中的局部变量。
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<%! ?%>: 用来定义成员变量或者成员方法，<%! String test2 = "定义一些成员变量或者方法"; %>将会最终编译成Servlet中的成员变量（如下图）。
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<%=123 ? %> 相当于 <% out.println("123");%>,会在前台页面输出指定的内容。
注：在使用<%= %>时其后不能有封号。
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令附上jsp在tomcat中编译成的Servlet（jsp页面在程序tomcat启动后并访问该页面，会在tomcat path\work\Catalina\localhost\KKWebTest\org\apache\jsp中编译成Servlet）如下：?
package org.apache.jsp;
import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.jsp.*;
public final class index_jsp extends org.apache.jasper.runtime.HttpJspBase
implements org.apache.jasper.runtime.JspSourceDependent {
String test1 = "定义一些成员变量或者方法";
private static final javax.servlet.jsp.JspFactory _jspxFactory =
javax.servlet.jsp.JspFactory.getDefaultFactory();
private static java.util.Map<java.lang.String,java.lang.Long> _jspx_dependants;
private javax.el.ExpressionFactory _el_expressionfactory;
private org.apache.tomcat.InstanceManager _jsp_instancemanager;
public java.util.Map<java.lang.String,java.lang.Long> getDependants() {
return _jspx_dependants;
}
public void _jspInit() {
_el_expressionfactory = _jspxFactory.getJspApplicationContext(getServletConfig().getServletContext()).getExpressionFactory();
_jsp_instancemanager = org.apache.jasper.runtime.InstanceManagerFactory.getInstanceManager(getServletConfig());
}
public void _jspDestroy() {
}
public void _jspService(final javax.servlet.http.HttpServletRequest request, final javax.servlet.http.HttpServletResponse response)
throws java.io.IOException, javax.servlet.ServletException {
final javax.servlet.jsp.PageContext pageContext;
javax.servlet.http.HttpSession session = null;
final javax.servlet.ServletContext application;
final javax.servlet.ServletConfig config;
javax.servlet.jsp.JspWriter out = null;
final java.lang.Object page = this;
javax.servlet.jsp.JspWriter _jspx_out = null;
javax.servlet.jsp.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>Test</title>\r\n");
out.write("</head>\r\n");
out.write("<body>\r\n");
out.write(" ");
out.write("\r\n");
out.write(" ");
String test2 = "定义局部变量或者一些逻辑操作";
out.write("\r\n");
out.write(" \r\n");
out.write(" ");
out.print("test" );
out.write(" \r\n");
out.write(" equals\r\n");
out.write(" ");
out.println("test");
out.write("\r\n");
out.write("</body>\r\n");
out.write("</html>");
} catch (java.lang.Throwable t) {
if (!(t instanceof javax.servlet.jsp.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);
else throw new ServletException(t);
}
} finally {
_jspxFactory.releasePageContext(_jspx_page_context);
}
}
}
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原文：http://kk-liang.iteye.com/blog/2272350