番禺网站设计,做移动类网站的书推荐,一个完整的网站 技术,莱芜十大首富一、 Servlet的自动加载
默认情况下#xff0c;第一次访问servlet的时候#xff0c;创建servlet对象。如果servlet构造函数里面的代码或者init方法里面的代码比较多#xff0c;就会导致用户第一次访问servlet的时候比较慢。这个时候#xff0c;我们可以改变servlet对象的创…一、 Servlet的自动加载
默认情况下第一次访问servlet的时候创建servlet对象。如果servlet构造函数里面的代码或者init方法里面的代码比较多就会导致用户第一次访问servlet的时候比较慢。这个时候我们可以改变servlet对象的创建时机提前到加载web应用的时候。在servlet的配置信息中加上一个load-on-startup标签即可。
servletservlet-nameloadOnStartup/servlet-nameservlet-classcom.by.servlet.LoadOnStartupServlet/servlet-class!--容器是否在启动时加载该servlet,数字越小优先级越高越高--load-on-startup1/load-on-startup
/servlet
servlet实例:
public class LoadOnStartupServlet implements HttpServlet {public LoadOnStartupServlet(){System.out.println(LoadOnStartupServlet constructor method has run....);}
}
这样配置之后servlet的构造函数和init方法就会在web应用加载的时候就会执行。
二、ServletConfig对象 是什么 ServletConfig是javax.servlet.包下的一个接口ServletConfig它是Servlet的一个配置对象 ServletConfig是由tomcat容器创建通过init方法传入给Servlet ServletConfig对象如何获取? 在GenericServlet里面定义了
public ServletConfig getServletConfig() {return this.config;
} 常用方法
getInitParameter(String parameterName); //根据参数名称获取指定的参数值
getInitParameterNames(); //获取所有的参数名称 需求
获取servlet里面定义的参数
servletservlet-namedemo2/servlet-nameservlet-classcom.by.servlet.ServletConfigServlet/servlet-class!--Servlet的初始化参数--init-paramparam-nameusername/param-nameparam-valueroot/param-value/init-paraminit-paramparam-namepassword/param-nameparam-valueroot123/param-value/init-param/servletservlet-mappingservlet-namedemo2/servlet-nameurl-pattern/demo2/url-pattern/servlet-mapping ServletConfigServlet
package com.by.servlet;import javax.servlet.*;
import javax.servlet.http.HttpServlet;public class ServletConfigServlet extends HttpServlet {Overridepublic void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException {//1.获取ServletConfig对象ServletConfig servletConfig getServletConfig();//2.获取Servlet中的初始化参数String username servletConfig.getInitParameter(username);System.out.println(username);String password servletConfig.getInitParameter(password);System.out.println(password);//3.获取ServletContext对象(域对象)ServletContext servletContext servletConfig.getServletContext();}
}
思考param参数可不可以在另外的Servlet中获取? 不能
public class ServletConfigServlet2 extends HttpServlet {Overridepublic void goGet(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException {//1.获取ServletConfig对象ServletConfig servletConfig getServletConfig();//2.获取Servlet中的初始化参数String username servletConfig.getInitParameter(username);//不能获取System.out.println(username);String password servletConfig.getInitParameter(password);//不能获取System.out.println(password);//3.获取ServletContext对象(域对象)ServletContext servletContext servletConfig.getServletContext();}
}
三、ServletContext对象 是什么 ServletContext是javax.servlet包下的一个接口又称上下文对象是配置对象也是一个域对象 当服务器启动时会为服务器中的每一个web应用程序创建一个ServletContext对象 在web应用中的servlet要想实现资源的共享可以通过ServletContext来完成 如何获取这个对象:
public ServletContext getServletContext() {//获取ServletContext对象return this.getServletConfig().getServletContext();
} 这个对象里面也有很多方法
getInitParameter() //获取指定参数名称的全局参数值
getRealPath(String path) //获得当前项目的服务器磁盘路径
getContextPath() //获取项目的根路径
getAttribute(String parameterName) //获取ServletContext域中指定名称的参数值
setAttribute(String paramterName,Object parameterValue) //存储参数到ServletContext域中
removeAttribute(String parameterNam) //将ServletContext域中指定名称的参数移除 需求
获取servlet里面定义的参数 context-paramparam-nameusername/param-nameparam-valueroot/param-value/context-paramcontext-paramparam-namepassword/param-nameparam-valueroot456/param-value/context-param package com.by.servlet;import javax.servlet.*;
import javax.servlet.http.HttpServlet;public class ServletContextServlet extends HttpServlet {Overridepublic void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException {//获取ServletContext对象ServletContext servletContext getServletContext();//1.获取全局初始化参数String username servletContext.getInitParameter(username);System.out.println(username);String password servletContext.getInitParameter(password);System.out.println(password);//2.获取服务器真实路径String upload servletContext.getRealPath();System.out.println(upload);//3.获取项目的根路径String contextPath servletContext.getContextPath();System.out.println(contextPath);//4.往ServletContext域中存储一个名称为msg的属性值为helloString str hello;servletContext.setAttribute(msg,str);}
}
思考param参数可不可以在另外的Servlet中获取? 不能
package com.by.servlet;import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServlet;public class ServletContextServlet2 extends HttpServlet {Overridepublic void doGet(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException {//从ServletContext域中取出msg的值ServletContext servletContext getServletContext();//1.获取全局初始化参数String username servletContext.getInitParameter(username);System.out.println(username);String password servletContext.getInitParameter(password);System.out.println(password);//2.获得msg属性Object msg servletContext.getAttribute(msg);//能获取System.out.println(msg);}
}
package com.by.servlet;import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServlet;public class ServletContextServlet3 extends HttpServlet {Overridepublic void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException {//1.获取ServletContext对象ServletContext servletContext getServletContext();//将ServletContext域中的msg参数移除servletContext.removeAttribute(msg);}
} servletservlet-namecontext3/servlet-nameservlet-classcom.by.servlet.ServletContextServlet/servlet-class/servletservlet-mappingservlet-namecontext3/servlet-nameurl-pattern/context/url-pattern/servlet-mappingservletservlet-namecontext2/servlet-nameservlet-classcom.by.servlet.ServletContextServlet2/servlet-class/servletservlet-mappingservlet-namecontext2/servlet-nameurl-pattern/context2/url-pattern/servlet-mappingservletservlet-namecontext3/servlet-nameservlet-classcom.by.servlet.ServletContextServlet3/servlet-class/servletservlet-mappingservlet-namecontext3/servlet-nameurl-pattern/context3/url-pattern/servlet-mapping
