JavaEE中关于ServletConfig的小结

时间：2020-10-08 13:27:16|栏目：JAVA代码|点击：次

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：

复制代码代码如下:

 
  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：

复制代码代码如下:

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

<web-app 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_2_5.xsd"
     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：

复制代码代码如下:

 
  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:

复制代码代码如下:

 
  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：

复制代码代码如下:

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

<web-app 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_2_5.xsd"
    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>

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