ServletConfig使用说明

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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。

Servlet：

public class ConfigServlet extends HttpServlet {    ServletConfig config;    public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {        //获取指定的初始化参数        String donwloadPath  = config.getInitParameter("donwloadPath");        System.out.println("donwloadPath="+donwloadPath);        response.getOutputStream().write(donwloadPath.getBytes());        //循环获取所有初始化参数        Enumeration<String> list = config.getInitParameterNames();        while(list.hasMoreElements()){            String name = list.nextElement();            String value = config.getInitParameter(name);            System.out.println(name+"="+value);            String str = name+"="+value;            response.getOutputStream().write(str.getBytes());        }    }    public void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException {        doGet(request,response);    }    public void init(ServletConfig config) {        this.config = config;    }}

web.xml：

    <!-- 测试servletConfig的使用 这里的init-param要放在servlet中-->    <servlet>        <servlet-name>ConfigServlet</servlet-name>        <servlet-class>com.learn.servletconfig.ConfigServlet</servlet-class>        <init-param>            <param-name>donwloadPath</param-name>            <param-value>/user/downloadPath</param-value>        </init-param>        <init-param>            <param-name>name</param-name>            <param-value>root</param-value>        </init-param>        <init-param>            <param-name>password</param-name>            <param-value>111111111</param-value>        </init-param>           </servlet>    <servlet-mapping>        <servlet-name>ConfigServlet</servlet-name>        <url-pattern>/config.action</url-pattern>    </servlet-mapping>

运行结果:

donwloadPath=/user/downloadPathpassword=111111111donwloadPath=/user/downloadPathname=root

ConfigServlet对象中有一个ServletConfig对象，其实这是不必要的。因为ConfigServlet继承了HttpServlet，HttpServlet又继承了GenericServlet 。GenericServlet 已经在内部维护了一个ServletConfig对象

GenericServlet源码如下：

public abstract class GenericServlet     implements Servlet, ServletConfig, java.io.Serializable{    private static final String LSTRING_FILE = "javax.servlet.LocalStrings";    private static ResourceBundle lStrings =        ResourceBundle.getBundle(LSTRING_FILE);    private transient ServletConfig config;    public GenericServlet() { }}

直接使用this.getServletConfig()方法：

    public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {        //获取指定的初始化参数                String donwloadPath  = this.getServletConfig().getInitParameter("donwloadPath");        System.out.println("donwloadPath="+donwloadPath);        response.getOutputStream().write(donwloadPath.getBytes());        //循环获取所有初始化参数        Enumeration<String> list = this.getServletConfig().getInitParameterNames();        while(list.hasMoreElements()){            String name = list.nextElement();            String value = this.getServletConfig().getInitParameter(name);            System.out.println(name+"="+value);            String str = name+"="+value;            response.getOutputStream().write(str.getBytes());        }    }

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