java-context-param简明教程

java-context-param简明教程

1.加载顺序

分别对应方法：

contextInitialized(ServletContextEvent sce) -》init(FilterConfig config) -》init() throws ServletException

都是在tomcat容器启动之前完成的

必须充分理解这一句话：

2.相关源码

SysListener.java

package com;

import javax.servlet.ServletContextEvent;

import javax.servlet.ServletContextListener;

public class SysListener implements ServletContextListener {

public void contextDestroyed(ServletContextEvent sce) {

//用于在容器关闭时,操作

System.out.println("SysListener contextDestroyed");

}

//用于在容器开启时,操作

public void contextInitialized(ServletContextEvent sce) {

String rootpath = sce.getServletContext().getRealPath("/");

System.out.println("-------------rootPath:"+rootpath);

if (rootpath != null) {

rootpath = rootpath.replaceAll("\\\\", "/");

} else {

rootpath = "/";

}

if (!rootpath.endsWith("/")) {

rootpath = rootpath + "/";

}

System.out.println("Application Run Path:"+rootpath);

String urlrewrtie = sce.getServletContext().getInitParameter("urlrewrite");

boolean burlrewrtie = false;

if (urlrewrtie != null) {

burlrewrtie = Boolean.parseBoolean(urlrewrtie);

}

System.out.println("Use cluster:"+sce.getServletContext().getInitParameter("cluster"));

System.out.println("Use

servletmapping:"+sce.getServletContext().getInitParameter("servletmapping"));

System.out.println("Use

poststoragemode:"+sce.getServletContext().getInitParameter("poststoragemode"));

System.out.println("Use Urlrewrite:"+urlrewrtie);

}

}

Testcontextparam.java

package com;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.ServletRequest;

import javax.servlet.ServletResponse;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import javax.servlet.ServletConfig;

import java.io.IOException;

/**

* Created by liuswk on 2015/8/19.

*/

public class Testcontextparam extends HttpServlet {

public void init() throws ServletException{

System.out.println("下面的两个参数param1是在servlet中存放的");

System.out.println(this.getInitParameter("param1"));

ServletConfig config = getServletConfig();

System.out.println("另外一种获取servlet init-param方法"+config.getInitParameter("param1"));

System.out.println("下面的参数是存放在servletcontext中的");

System.out.println(getServletContext().getInitParameter("urlrewrite"));

System.out.println("另外一种获取servletcontext方法"+config.getServletContext().getInitParameter("urlrewrite"));

}

@Override

protected void doGet(HttpServletRequest req, HttpServletResponse resp)

throws ServletException, IOException {

System.out.println("Testcontextparam doget...");

System.out.println("doGet中得到context-param "+getServletContext().getInitParameter("urlrewrite"));

doPost(req, resp);

}

@Override

protected void doPost(HttpServletRequest req, HttpServletResponse resp)

throws ServletException, IOException {

System.out.println("Testcontextparam dopost...");

}

}

login.jsp:

<%@ page contentType="text/html; charset=GBK" %>

<%@ page import="java.util.Enumeration"%>

some test page ! A 请登录先,跳转到login.jsp

<%

out.println( "
");

Enumeration enema=application.getInitParameterNames(); while(enema.hasMoreElements()){

String name=(String)enema.nextElement();

String value=application.getInitParameter(name);

out.println("name="+name+" value="+value+"
");

}

//String aa="";

//for(int i=10;i<1000;i++){

// aa+="user"+i+",";

//}

// out.println(aa);

out.println( "
");

out.println( "
");

ServletContext sc=getServletContext ();

Enumeration enema1=sc.getInitParameterNames();

while(enema1.hasMoreElements()){

String name=(String)enema1.nextElement();

String value=sc.getInitParameter(name);

out.println("name="+name+" value="+value+"
");

}

%>

3.web.xml配置

Testcontextparam

com.Testcontextparam

param1

avalible in servlet init()

0

Testcontextparam

/testcontextparam

urlrewrite

false

cluster

false

servletmapping

*.bbscs

poststoragemode

1

com.SysListener

4.在监听中使用context-prarm

在监听中得到context-param参数，首先实现ServletContextListener接口，这个接口有2个方法

源码在2.相关源码中，可以看到SysListener

在启动web应用的过程中就执行初始方法了，如下

5.在jsp中使用context-prarm

具体见2相关源码中的login.jsp

源码中使用了jsp内置对象application或者getServletContext 都ok 得到结果：

6.在servlet中使用context-param 见2相关源码：Testcontextparam.java

分别取得servlet中的init-param

和context-param中的参数

7.servlet的init方法加载时间

具体源码查看2.相关源码：Testcontextparam.java

是在加载webapp的时候初始化的，在容器完成启动前

如下图：

补充：查看网上的

8.context-param的说明及作用

验证3、4、5的顺序

具体源码查看2.相关源码中的SysListener.java

在tomcat发布filter项目的时候，接着就调用了监听的contextInitialized方法了，而这个方法能获取到值，说明context-param的参数读取先以SysListener

9.参考

https://www.360docs.net/doc/979677436.html,/sxbjffsg163/article/details/9955479