ServletConfig和ServletContext的应用

阳光穿透心脏的1/2处 2022-04-18 02:19 226阅读 0赞

1、ServletConfig的对象可以得到当前的servlet文件的配置信息，这些配置信息都写在web.xml文件当中，通过this.getServletConfig();方法就可以得到当前文件的ServletConfig对象，通过getInitParameterNames()方法可以得到当前

servlet文件中的所有配置信息的name，然后通过getInitParameter(name)方法就可以读出其中的value。

ServletConfig config = this.getServletConfig();
    		//得到当前存在于xml文件中的Servlet1的所有配置信息的名称
    		Enumeration<String> names = config.getInitParameterNames();
    		//输出所有配置信息的名称以及value值
    		while(names.hasMoreElements()) {
    			String name = names.nextElement();
    			String val = config.getInitParameter(name);
    			System.out.println(name);
    			System.out.println(val);
    		}

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" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">
      <display-name>firstWEB</display-name>
      <welcome-file-list>
        <welcome-file>index.html</welcome-file>
        <welcome-file>index.htm</welcome-file>
        <welcome-file>index.jsp</welcome-file>
        <welcome-file>default.html</welcome-file>
        <welcome-file>default.htm</welcome-file>
        <welcome-file>default.jsp</welcome-file>
      </welcome-file-list>
      <servlet>
        <description></description>
        <display-name>Servlet1</display-name>
        <servlet-name>Servlet1</servlet-name>
        <servlet-class>cn.horizonhui.Servlet1</servlet-class>
        <init-param>
          <param-name>Servlet1</param-name>
          <param-value>hello1</param-value>
        </init-param>
        <init-param>
          <param-name>Servlet1.1</param-name>
          <param-value>hello1.1</param-value>
        </init-param>
      </servlet>
      <servlet-mapping>
        <servlet-name>Servlet1</servlet-name>
        <url-pattern>/Servlet1</url-pattern>
      </servlet-mapping>
      <servlet>
        <description></description>
        <display-name>Servlet2</display-name>
        <servlet-name>Servlet2</servlet-name>
        <servlet-class>cn.horizonhui.Servlet2</servlet-class>
      </servlet>
      <servlet-mapping>
        <servlet-name>Servlet2</servlet-name>
        <url-pattern>/Servlet2</url-pattern>
      </servlet-mapping>
    </web-app>

2、ServletConfig的对象还维护了一个ServletContext对象，此对象中包含了当前网站的配置信息，ServletContext的对象是域对象，其中的信息是以键值对的形式存在的，通过setAttribute(key,value)与getAttribute(key)方法就可以设置与读取该对象的信息，由于ServletContext对象保存的是当前网站的信息，所以可以利用该对象实现信息的共享，两个或多个servlet文件都可以访问该对象，也就是实现了信息共享。

3、利用ServletContext对象读取\*.properties文件的内容，通过getRealPath(String path)方法可以得到文件的真实路径，其中传入的参数path是文件相对于该网站的相对路径。

a.properties

key=horizonhui
    value=https://mp.csdn.net/postedit/83578181

servlet1.java

package cn.horizonhui;
    
    import java.io.IOException;
    import java.util.Enumeration;
    
    import javax.servlet.ServletConfig;
    import javax.servlet.ServletContext;
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    
    /**
     * Servlet implementation class Servlet1
     */
    public class Servlet1 extends HttpServlet {
    	private static final long serialVersionUID = 1L;
           
        /**
         * @see HttpServlet#HttpServlet()
         */
        public Servlet1() {
            super();
            
            // TODO Auto-generated constructor stub
        }
    
    	/**
    	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
    	 */
    	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		// TODO Auto-generated method stub
    		//创建一个ServletConfig对象
    		ServletConfig config = this.getServletConfig();
    		//得到当前存在于xml文件中的Servlet1的所有配置信息的名称
    		Enumeration<String> names = config.getInitParameterNames();
    		//输出所有配置信息的名称以及value值
    		while(names.hasMoreElements()) {
    			String name = names.nextElement();
    			String val = config.getInitParameter(name);
    			System.out.println(name);
    			System.out.println(val);
    		}
    		
    		System.out.println("多个文件共享信息---------------------");
    		//创建一个ServletContext对象
    		ServletContext context = config.getServletContext();
    		//向当前网站的配置信息中写入键值对
    		context.setAttribute("name1", "123456");
    				
    		
    	}
    
    	/**
    	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
    	 */
    	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		// TODO Auto-generated method stub
    		doGet(request, response);
    	}
    
    }

Servlet2.java

package cn.horizonhui;
    
    import java.io.FileInputStream;
    import java.io.IOException;
    import java.util.Properties;
    
    import javax.servlet.ServletContext;
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    
    /**
     * Servlet implementation class Servlet2
     */
    public class Servlet2 extends HttpServlet {
    	private static final long serialVersionUID = 1L;
           
        /**
         * @see HttpServlet#HttpServlet()
         */
        public Servlet2() {
            super();
            // TODO Auto-generated constructor stub
        }
    
    	/**
    	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
    	 */
    	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		// TODO Auto-generated method stub
    		//创建一个ServletContext对象
    		ServletContext context1 = this.getServletConfig().getServletContext();
    		//读取共享的内容
    		System.out.println("servlet2------------");
    		String val = (String)context1.getAttribute("name1");
    		System.out.println("name1   "+val);
    		
    		//读取properties文件
    		String realPath = context1.getRealPath("/WEB-INF/a.properties");
    		Properties pros = new Properties();
    		pros.load(new FileInputStream(realPath));
    		System.out.println("key="+pros.getProperty("key"));
    		System.out.println("value="+pros.getProperty("value"));
    	}
    
    	/**
    	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
    	 */
    	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		// TODO Auto-generated method stub
    		doGet(request, response);
    	}
    
    }

输出现象

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