JavaEE中关于ServletConfig的小结

     在servlet的配置文件中，可以使用一个或多个<init-param>标签为servlet配置一些初始化参数。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，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。
示例代码如下：

 package com.yyz.servletconfig;
 import java.io.ioexception;
 import java.util.enumeration;
 import javax.servlet.servletconfig;
 import javax.servlet.servletexception;
 import javax.servlet.http.httpservlet;
 import javax.servlet.http.httpservletrequest;
 import javax.servlet.http.httpservletresponse;
 public class servletconfigdemo1 extends httpservlet {
     servletconfig config;
     public void doget(httpservletrequest request, httpservletresponse response)
             throws servletexception, ioexception {
       //获取指定的初始化参数
         string value = config.getinitparameter("xxx");
         response.getoutputstream().write(value.getbytes());
         //获取所有的初始化参数
         enumeration e = cofig.getinitparameternames();
         while(e.hasmoreelements()){
             string name = (string) e.nextelement();
             value = config.getinitparameter(name);
             response.getoutputstream().write((name+"="+value+"<br/>").getbytes());
         }
     }
     public void dopost(httpservletrequest request, httpservletresponse response)
             throws servletexception, ioexception {
         doget(request,response);
     }
     @override
     public void init(servletconfig config) throws servletexception {
         this.config = config;
     }
 }

相应的web.xml如下：

 <?xml version="1.0" encoding="utf-8"?>
 
 <web-app xmlns=""
     xmlns:xsi="http://www.w3.org/2001/xmlschema-instance"
     xsi:schemalocation=" "
     version="2.5">
   <servlet>
   
     <servlet-name>servletconfigdemo1</servlet-name>
     <servlet-class>com.yyz.servletconfig.servletconfigdemo1</servlet-class>
     <init-param>
                <param-name>xxx</param-name>
                <param-value>yyy</param-value>
     </init-param>
       <init-param>
                <param-name>name</param-name>
                <param-value>yyz</param-value>
     </init-param>
       <init-param>
                <param-name>password</param-name>
                <param-value>yyy</param-value>
     </init-param>
   </servlet>
  <servlet-mapping>
     <servlet-name>servletconfigdemo1</servlet-name>
     <url-pattern>/servlet/servletconfigdemo1</url-pattern>
  
   </servlet-mapping>
 </web-app>

测试结果如下：

 在上面的代码中，servletconfigdemo1对象中有一个servletconfig对象，其实这是不必要的。因为servletconfigdemo1继承了httpservlet，httpservlet又继承了genericservlet 。genericservlet 已经在内部维护了一个servletconfig对象。相关实现如下：

 public abstract class genericservlet
     implements servlet, servletconfig, java.io.serializable
 {
     …    …
 private transient servletconfig config;
 public servletconfig getservletconfig() {
           return config;
     }
 }

因而我们可以通过我们写的servlet对象的getservletconfig()方法直接拿到servletconfig对象，示例代码如下:

 package com.yyz.servletconfig;
 
 import java.io.ioexception;
 import java.io.printwriter;
 
 import javax.servlet.servletexception;
 import javax.servlet.http.httpservlet;
 import javax.servlet.http.httpservletrequest;
 import javax.servlet.http.httpservletresponse;
 
 public class servletconfigdemo2 extends httpservlet {
 
     public void doget(httpservletrequest request, httpservletresponse response)
             throws servletexception, ioexception {
 
         string value = this.getservletconfig().getinitparameter("name");
         system.out.println(value);
 }
 
     public void dopost(httpservletrequest request, httpservletresponse response)
             throws servletexception, ioexception {
 
         doget(request, response);
     }
 
 }

web.xml文件：

<?xml version="1.0" encoding="utf-8"?>

<web-app xmlns=""
    xmlns:xsi="http://www.w3.org/2001/xmlschema-instance"
    xsi:schemalocation=" "
    version="2.5">
 <servlet>
    <servlet-name>servletconfigdemo2</servlet-name>
    <servlet-class>com.yyz.servletconfig.servletconfigdemo2</servlet-class>
     <init-param>
               <param-name>name</param-name>
               <param-value>yyz</param-value>
    </init-param>
  </servlet>
 <servlet-mapping>
    <servlet-name>servletconfigdemo2</servlet-name>
    <url-pattern>/servlet/servletconfigdemo2</url-pattern>
  </servlet-mapping>
</web-app>