1、容器根据你所写的JSP生成一个类，
/* * Generated by the Jasper component of Apache Tomcat * Version: Apache Tomcat/7.0.77 * Generated at: 2017-06-11 15:47:28 UTC * Note: The last modified time of this file was set to * the last modified time of the source file after * generation to assist with modification tracking. */ package org.apache.jsp; import javax.servlet.*; import javax.servlet.http.*; import javax.servlet.jsp.*; public final class HelloWorld_jsp extends org.apache.jasper.runtime.HttpJspBase implements org.apache.jasper.runtime.JspSourceDependent { 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 org.apache.jasper.runtime.TagHandlerPool _005fjspx_005ftagPool_005fs_005fproperty_0026_005fvalue_005fnobody; private volatile javax.el.ExpressionFactory _el_expressionfactory; private volatile org.apache.tomcat.InstanceManager _jsp_instancemanager; public java.util.Map<java.lang.String,java.lang.Long> getDependants() { return _jspx_dependants; } public javax.el.ExpressionFactory _jsp_getExpressionFactory() { if (_el_expressionfactory == null) { synchronized (this) { if (_el_expressionfactory == null) { _el_expressionfactory = _jspxFactory.getJspApplicationContext(getServletConfig().getServletContext()).getExpressionFactory(); } } } return _el_expressionfactory; } public org.apache.tomcat.InstanceManager _jsp_getInstanceManager() { if (_jsp_instancemanager == null) { synchronized (this) { if (_jsp_instancemanager == null) { _jsp_instancemanager = org.apache.jasper.runtime.InstanceManagerFactory.getInstanceManager(getServletConfig()); } } } return _jsp_instancemanager; } public void _jspInit() { _005fjspx_005ftagPool_005fs_005fproperty_0026_005fvalue_005fnobody = org.apache.jasper.runtime.TagHandlerPool.getTagHandlerPool(getServletConfig()); } public void _jspDestroy() { _005fjspx_005ftagPool_005fs_005fproperty_0026_005fvalue_005fnobody.release(); } 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(" "); out.write(" "); out.write("<html> "); out.write("<head> "); out.write("<title>Hello World</title> "); out.write("</head> "); out.write("<body> "); out.write(" Hello World, "); if (_jspx_meth_s_005fproperty_005f0(_jspx_page_context)) return; out.write(" "); out.write("</body> "); 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 { if (response.isCommitted()) { out.flush(); } else { 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); } } private boolean _jspx_meth_s_005fproperty_005f0(javax.servlet.jsp.PageContext _jspx_page_context) throws java.lang.Throwable { javax.servlet.jsp.PageContext pageContext = _jspx_page_context; javax.servlet.jsp.JspWriter out = _jspx_page_context.getOut(); // s:property org.apache.struts2.views.jsp.PropertyTag _jspx_th_s_005fproperty_005f0 = (org.apache.struts2.views.jsp.PropertyTag) _005fjspx_005ftagPool_005fs_005fproperty_0026_005fvalue_005fnobody.get(org.apache.struts2.views.jsp.PropertyTag.class); boolean _jspx_th_s_005fproperty_005f0_reused = false; try { _jspx_th_s_005fproperty_005f0.setPageContext(_jspx_page_context); _jspx_th_s_005fproperty_005f0.setParent(null); // /HelloWorld.jsp(8,16) name = value type = java.lang.String reqTime = false required = false fragment = false deferredValue = false expectedTypeName = null deferredMethod = false methodSignature = null _jspx_th_s_005fproperty_005f0.setValue("name"); int _jspx_eval_s_005fproperty_005f0 = _jspx_th_s_005fproperty_005f0.doStartTag(); if (_jspx_th_s_005fproperty_005f0.doEndTag() == javax.servlet.jsp.tagext.Tag.SKIP_PAGE) { return true; } _005fjspx_005ftagPool_005fs_005fproperty_0026_005fvalue_005fnobody.reuse(_jspx_th_s_005fproperty_005f0); _jspx_th_s_005fproperty_005f0_reused = true; } finally { org.apache.jasper.runtime.JspRuntimeLibrary.releaseTag(_jspx_th_s_005fproperty_005f0, _jsp_getInstanceManager(), _jspx_th_s_005fproperty_005f0_reused); } return false; } }
2、需要知道的一些问题
对于问题1：JSP有一个内置对象叫config，它相当于servlet中的ServletConfig，在servlet中我们需要通过getServletConfig来获得它，然后再通过例如getInitParameter("name");获得参数，整个过程类似这样
而在JSP，由于它本身具有这样一个内置对象，因此只需要像下面这样就可以了
对于问题2：我猜想也是在web.xml中配置，因为JSP说到底不过是servlet的另外一种“书写方式”罢了。
事实证明这是正确的，
对于问题3：直接在<%!%>中进行覆盖就可以了
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