zoukankan      html  css  js  c++  java
  • JAVAWEB学习总结 SERVLET开发(二)

    一、ServletConfig对象

    1.1、配置servlet初始化参数

      在servlet的配置文件中web.xml中,可以使用一个或多个<init-param>标签为servlet配置一些初始化参数。

      例如:

    <?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" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" 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">
      <servlet>
        <servlet-name>ServletDemo6</servlet-name>
        <servlet-class>my.servlet.demo.ServletDemo6</servlet-class>
        <!--配置ServletConfigDemo1的初始化参数 -->
        <init-param>
            <param-name>name</param-name>
            <param-value>my</param-value>
        </init-param>
         <init-param>
            <param-name>password</param-name>
            <param-value>123</param-value>
        </init-param>
        <init-param>
            <param-name>charset</param-name>
            <param-value>UTF-8</param-value>
        </init-param>
    </servlet>
     <servlet-mapping>
        <servlet-name>ServletDemo6</servlet-name>
        <url-pattern>/ServletDemo6</url-pattern>
        </servlet-mapping>
    </web-app>

    1.2、通过ServletConfig获取servlet初始化参数

      当servlet配置了初始化参数后,web容器在创建servlet实例对象时,会自动将这些初始化参数封装到ServletConfig对象中,并在调用servlet的init方法时,将ServletConfig对象传递给servlet。进而我们通过ServletConfig对象就可以得到当前servlet的初始化参数信息。

    例如:

    package my.servlet.demo;
    //导入必需的 java 库
    import java.io.*;
    import java.util.Enumeration;
    
    import javax.servlet.*;
    import javax.servlet.http.*;
    
    // 扩展 HttpServlet 类
    public class ServletDemo1 extends HttpServlet {
     
    /**
    * 定义ServletConfig对象来接收配置的初始化参数
    */
    
     private ServletConfig config;
    /**
    * 当servlet配置了初始化参数后,web容器在创建servlet实例对象时,
    * 会自动将这些初始化参数封装到ServletConfig对象中,并在调用servlet的init方法时,
    * 将ServletConfig对象传递给servlet。进而,程序员通过ServletConfig对象就可以
    * 得到当前servlet的初始化参数信息。
    */
    
      public void init(ServletConfig config) throws ServletException
      {
          // 执行必需的初始化
          this.config=config;
      }
      public void doGet(HttpServletRequest request,
                        HttpServletResponse response)
                throws ServletException, IOException
      {
      //获取在web.xml中配置的初始化参数 
       String paramVal=this.config.getInitParameter("name");//获取指定的初始化参数
       response.getWriter().print(paramVal);
       response.getWriter().print("<hr/>");
    //获取所有的初始化参数
       Enumeration<String> e =config.getInitParameterNames();
       while(e.hasMoreElements())
       {
           String name =e.nextElement();
           String value=config.getInitParameter(name);
           response.getWriter().print(name+"="+value+"<br/>");
       }
      }
      
      public void destroy()
      {
          // 什么也不做
      }
    }

      运行结果如下:

    二、ServletContext对象

    WEB容器在启动时,它会为每个WEB应用程序都创建一个对应的ServletContxt对象,它代表当前web应用。

    ServletConfig对象中维护了ServletContext对象的引用,开发人员在编写servlet时,可以通过ServletConfig.getServletContext方法获得ServletContext对象。

    由于一个WEB应用中的所有Servlet共享同一个ServletContext对象,因此Servlet对象之间可以通过ServletContext对象来实现通讯。ServletContext对象通常也被称为context域对象。

    2.1、多个servlet通过ServletContext对象实现数据共享

    例子:ServletDemo1和ServletDemo2通过ServletContext对象实现数据共享

    package my.servlet.demo;
    //导入必需的 java 库
    import java.io.*;
    import java.util.Enumeration;
    
    import javax.servlet.*;
    import javax.servlet.http.*;
    
    // 扩展 HttpServlet 类
    public class ServletDemo1 extends HttpServlet {
     
     private ServletConfig config;
    
      public void init(ServletConfig config) throws ServletException
      {
          // 执行必需的初始化
          this.config=config;
      }
      public void doGet(HttpServletRequest request,
                        HttpServletResponse response)
                throws ServletException, IOException
      {
    	 String data="itnnn";
    	 ServletContext context=config.getServletContext();
    	 context.setAttribute("data", data);
      }
      
      public void destroy()
      {
          // 什么也不做
      }
    }
    

      

    package my.servlet.demo;
    
    import java.io.IOException;
    
    import javax.servlet.ServletContext;
    import javax.servlet.ServletException;
    import javax.servlet.annotation.WebServlet;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    
    /**
     * Servlet implementation class ServletDemo2
     */
    @WebServlet("/ServletDemo2")
    public class ServletDemo2 extends HttpServlet {
    	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		// TODO Auto-generated method stub
    		ServletContext context =this.getServletContext();
    		String data=(String) context.getAttribute("data");
    		response.getWriter().print("data="+data);
    	}
    
    	/**
    	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
    	 */
    	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		// TODO Auto-generated method stub
    	}
    
    }
    

      先运行ServletDemo1,将数据data存储到ServletContext对象中,然后运行ServletDemo2就可以从ServletContext对象中取出数据了,这样就实现了数据共享,运行结果如下图所示:

    2.2、获取WEB应用的初始化参数

    在web.xml文件中使用<context-param>标签配置WEB应用的初始化参数,如下所示:

    <?xml version="1.0" encoding="UTF-8"?>
    <web-app version="3.0" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
        http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd">
        <display-name></display-name>
        <!-- 配置WEB应用的初始化参数 -->
        <context-param>
            <param-name>url</param-name>
            <param-value>jdbc:mysql://localhost:3306/test</param-value>
        </context-param>
    
        <welcome-file-list>
            <welcome-file>index.jsp</welcome-file>
        </welcome-file-list>
    </web-app>
    package my.servlet.demo;
    
    import java.io.IOException;
    
    import javax.servlet.ServletContext;
    import javax.servlet.ServletException;
    import javax.servlet.annotation.WebServlet;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    
    
    @WebServlet("/ServletDemo3")
    public class ServletDemo3 extends HttpServlet {
    
    
    	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		ServletContext context=this.getServletContext();
    		//获取整个web站点的初始化参数
    		String contextInitParam =context.getInitParameter("url");
    		response.getWriter().print(contextInitParam );
    	}
    	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		// TODO Auto-generated method stub
    	}
    
    }
    

      运行结果:

    2.3、用ServletContext实现请求转发

    ServletDemo4.java

    package my.servlet.demo;
    
    import java.io.IOException;
    
    import javax.servlet.RequestDispatcher;
    import javax.servlet.ServletContext;
    import javax.servlet.ServletException;
    import javax.servlet.annotation.WebServlet;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    
    public class ServletDemo4 extends HttpServlet {
     
    	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		// TODO Auto-generated method stub
    		String data="<h1><font color='red'>abc</font></h1>";
    		response.getOutputStream().write(data.getBytes());
    		ServletContext context=this.getServletContext();
    		RequestDispatcher rd =context.getRequestDispatcher("/ServletDemo5");
    		rd.forward(request, response);
    	}
    
    
    	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		// TODO Auto-generated method stub
    	}
    
    }
    

      ServletDemo5.java

    package my.servlet.demo;
    
    import java.io.IOException;
    import javax.servlet.ServletException;
    import javax.servlet.annotation.WebServlet;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    
    public class ServletDemo5 extends HttpServlet {
    
    
    
    	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		// TODO Auto-generated method stub
    		response.getOutputStream().write("servletDemo5".getBytes());
    	}
    
    
    	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		// TODO Auto-generated method stub
    	}
    
    }
    

      web.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" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" 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">
      <servlet>
        <description>This is the description of my J2EEcomponent</description>
        <display-name>This is the display of my J2EEcomponent</display-name>
        <servlet-name>ServletDemo4</servlet-name>
        <servlet-class>my.servlet.demo.ServletDemo4</servlet-class>
      </servlet>
      <servlet>
        <description>This is the description of my J2EEcomponent</description>
        <display-name>This is the display of my J2EEcomponent</display-name>
        <servlet-name>ServletDemo5</servlet-name>
        <servlet-class>my.servlet.demo.ServletDemo5</servlet-class>
      </servlet>
        <servlet-mapping>
        <servlet-name>ServletDemo4</servlet-name>
        <url-pattern>/ServletDemo4</url-pattern>
       </servlet-mapping>
      <servlet-mapping>
        <servlet-name>ServletDemo5</servlet-name>
        <url-pattern>/ServletDemo5</url-pattern>
        </servlet-mapping>
    </web-app>
    

      运行结果:

    访问的是ServletDemo4,浏览器显示的却是ServletDemo5的内容,这就是使用ServletContext实现了请求转发。

    2.4、利用ServletContext对象读取资源文件

     2.5、在客户端缓存servlet输出

  • 相关阅读:
    MVC 以内容字节数组形式 实现文件上传 下载
    iis+php+mysql 错误 Call to undefined function mysql_connect()的解决办法
    IIS环境下快速安装、配置和调试PHP5.2.0
    lineheight 在IE6 下失效的问题 解决办法(已经亲手验证)
    基于SOA的体系架构设计
    图片切割系统,这个比较完整了
    MS SQL Server中文版的預設日期datetime格式是yyyymmdd hh:mm:ss.mmm
    “应用程序或DLL C:\WINDOWS\system32\PNCRT.dll为无效的windows映像”的解决方法
    php操作MySQL数据库语句基础
    播放电影有声音没图像
  • 原文地址:https://www.cnblogs.com/tinmh/p/6187958.html
Copyright © 2011-2022 走看看