ServletConfig讲解

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: