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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：
1 1 package com.yyz.servletconfig; 2 2 3 3 import java.io.IOException; 4 4 import java.util.Enumeration; 5 5 6 6 import javax.servlet.ServletConfig; 7 7 import javax.servlet.ServletException; 8 8 import javax.servlet.http.HttpServlet; 9 9 import javax.servlet.http.HttpServletRequest;10 10 import javax.servlet.http.HttpServletResponse;11 11 12 12 public class ServletConfigDemo1 extends HttpServlet {13 13 14 14 15 15 16 16 ServletConfig config;17 17 public void doGet(HttpServletRequest request, HttpServletResponse response)18 18 throws ServletException, IOException {19 19 //获取指定的初始化参数20 20 String value = http://www.mamicode.com/config.getInitParameter("xxx");21 21 response.getOutputStream().write(value.getBytes());22 22 //获取所有的初始化参数23 23 Enumeration e = cofig.getInitParameterNames();24 24 while(e.hasMoreElements()){25 25 String name = (String) e.nextElement();26 26 value =http://www.mamicode.com/ config.getInitParameter(name);27 27 response.getOutputStream().write((name+"="+value+"<br/>").getBytes());28 28 }29 29 }30 30 31 31 32 32 public void doPost(HttpServletRequest request, HttpServletResponse response)33 33 throws ServletException, IOException {34 34 doGet(request,response);35 35 36 36 37 37 }38 38 39 39 40 40 @Override41 41 public void init(ServletConfig config) throws ServletException {42 42 this.config = config;43 43 }44 44 45 45 }
相应的web.xml如下：
1 <?xml version="1.0" encoding="UTF-8"?> 2 3 <web-app xmlns="http://java.sun.com/xml/ns/javaee" 4 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 5 xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" 6 version="2.5"> 7 <servlet> 8 9 <servlet-name>ServletConfigDemo1</servlet-name>10 <servlet-class>com.yyz.servletconfig.ServletConfigDemo1</servlet-class>11 <init-param>12 <param-name>xxx</param-name>13 <param-value>yyy</param-value>14 </init-param>15 <init-param>16 <param-name>name</param-name>17 <param-value>yyz</param-value>18 </init-param>19 <init-param>20 <param-name>password</param-name>21 <param-value>yyy</param-value>22 </init-param>23 </servlet>24 <servlet-mapping>25 <servlet-name>ServletConfigDemo1</servlet-name>26 <url-pattern>/servlet/ServletConfigDemo1</url-pattern>27 28 </servlet-mapping>29 </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：
1 public abstract class GenericServlet 2 implements Servlet, ServletConfig, java.io.Serializable3 {4 … …5 private transient ServletConfig config;6 public ServletConfig getServletConfig() {7 return config;8 }9 }
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:
1 1 package com.yyz.servletconfig; 2 2 3 3 import java.io.IOException; 4 4 import java.io.PrintWriter; 5 5 6 6 import javax.servlet.ServletException; 7 7 import javax.servlet.http.HttpServlet; 8 8 import javax.servlet.http.HttpServletRequest; 9 9 import javax.servlet.http.HttpServletResponse;10 10 11 11 public class ServletConfigDemo2 extends HttpServlet {12 12 13 13 public void doGet(HttpServletRequest request, HttpServletResponse response)14 14 throws ServletException, IOException {15 15 16 16 String value = http://www.mamicode.com/this.getServletConfig().getInitParameter("name");17 17 System.out.println(value);18 18 }19 19 20 20 public void doPost(HttpServletRequest request, HttpServletResponse response)21 21 throws ServletException, IOException {22 22 23 23 doGet(request, response);24 24 }25 25 26 26 }
web.xml文件：
<?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>
关于ServletConfig的小结
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