ServletConfig讲解

蔚落 2022-05-27 00:45 181阅读 0赞

### 配置Servlet初始化参数 ###

在Servlet的配置文件web.xml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。

例如：

<?xml version="1.0" encoding="UTF-8"?>
    <web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
             version="4.0">
        <servlet>
            <servlet-name>Demo1</servlet-name>
            <servlet-class>Java.Servlet.Demo1</servlet-class>
            <init-param>
                <param-name>name</param-name>
                <param-value>vina</param-value>
            </init-param>
            <init-param>
                <param-name>age</param-name>
                <param-value>20</param-value>
            </init-param>
            <init-param>
                <param-name>address</param-name>
                <param-value>wuhan</param-value>
            </init-param>
        </servlet>
        <servlet-mapping>
            <servlet-name>Demo1</servlet-name>
            <url-pattern>/demo1</url-pattern>
        </servlet-mapping>
    </web-app>

### 通过ServletConfig获取Servlet的初始化参数 ###

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，将ServletConfig对象传递给servlet。进而，我们通过ServletConfig对象就可以得到当前servlet的初始化参数信息。

例如：

package Java.Servlet;
    
    import javax.servlet.ServletConfig;
    import javax.servlet.ServletException;
    import javax.servlet.annotation.WebServlet;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import java.io.IOException;
    import java.io.PrintWriter;
    
    public class Demo1 extends HttpServlet {
        private ServletConfig config = null;
    
        @Override
        public void init() throws ServletException {
            super.init();
        }
    
        @Override
        public void init(ServletConfig config) throws ServletException {
            this.config = config;
        }
    
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            String name = config.getInitParameter("name");
            String age = config.getInitParameter("age");
            String address = config.getInitParameter("address");
            resp.setContentType("text/html");
            PrintWriter out = resp.getWriter();
            out.println("<h1>name:" + name);
            out.println("age:" + age);
            out.println("address:" + address + "</h1>");
        }
    }

运行结果如下:

![70][]

[70]: /images/20220527/b5cc35c91476434cbf836e506bd6a423.png