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【Head First Servlets and JSP】笔记17：JSP所生成的servlet相关问题

2017-06-15 16:06 691 查看
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("\r\n");
out.write("\r\n");
out.write("<html>\r\n");
out.write("<head>\r\n");
out.write("<title>Hello World</title>\r\n");
out.write("</head>\r\n");
out.write("<body>\r\n");
out.write("   Hello World, ");
if (_jspx_meth_s_005fproperty_005f0(_jspx_page_context))
return;
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 {
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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