JSP 初始化参数

JSP 初始化参数：

tomcat启动的时候就会执行那个函数；

xml：

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
    http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID"
    version="3.0">
    <display-name>TestBootWeb</display-name>
    <servlet>
        <servlet-name>index007</servlet-name>
        <jsp-file>/index007.jsp</jsp-file>
        <init-param>
            <param-name>email</param-name>
            <param-value>s@s.com</param-value>
        </init-param>
    </servlet>
    <servlet-mapping>
        <servlet-name>index007</servlet-name>
        <url-pattern>/index007.jsp</url-pattern>
        <!-- 写成/index007.jsp的话，竟然index007.jsp和index0071.jsp都可以访问，而且是两个实例，但是获取初始化参数的时候有问题 -->
    </servlet-mapping>
    <jsp-config>
        <jsp-property-group>
            <url-pattern>/index006.jsp</url-pattern>
            <scripting-invalid>true</scripting-invalid>
        </jsp-property-group>
    </jsp-config>
    <welcome-file-list>
        <welcome-file>index.jsp</welcome-file>
    </welcome-file-list>
</web-app>

jsp：

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
    String path = request.getContextPath();
    String basePath = request.getScheme() + "://" + request.getServerName() + ":" + request.getServerPort() + path + "/";
%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>007index</title>
</head>
<body>
    cnt is :<%=++cnt%>
    <hr>
    <%!int cnt = 0;%>
    <%!
        public void jspInit(){
        ServletConfig config = getServletConfig();
        String s = config.getInitParameter("email");
        System.out.println("s is :"+s);
    }
    %>
</body>
</html>

生成的java：

/*
 * Generated by the Jasper component of Apache Tomcat
 * Version: Apache Tomcat/7.0.35
 * Generated at: 2015-10-20 01:19:21 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.*;
import java.util.*;

public final class index007_jsp extends org.apache.jasper.runtime.HttpJspBase
    implements org.apache.jasper.runtime.JspSourceDependent {

int cnt = 0;

        public void jspInit(){
        ServletConfig config = getServletConfig();
        String s = config.getInitParameter("email");
        System.out.println("s is :"+s);
    }
    
  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('
');
      out.write('
');

    String path = request.getContextPath();
    String basePath = request.getScheme() + "://" + request.getServerName() + ":" + request.getServerPort() + path + "/";

      out.write("
");
      out.write("<!DOCTYPE html>
");
      out.write("<html>
");
      out.write("<head>
");
      out.write("<meta charset="UTF-8">
");
      out.write("<title>007index</title>
");
      out.write("</head>
");
      out.write("<body>
");
      out.write("	cnt is :");
      out.print(++cnt);
      out.write("
");
      out.write("	<hr>
");
      out.write("	");
      out.write('
');
      out.write('
');
      out.write('    ');
      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 { 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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原文地址：https://www.cnblogs.com/stono/p/4893768.html