ServletConfig对象

在Servlet的配置文件中，可以使用一个或者多个<init-param>标签为servlet配置一些初始化参数。

当servlet配置了初始化常熟后，web容器在常见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，程序员通过servletconfig对象就可以得到当前servlet的初始化参数信息。

阅读ServletConfig API，并举例说明该对象的作用：

获得字符集编码

获得数据库连接信息

获得配置文件，查看structs案例的web.xml文件

package cn.itcast.servlet;

import java.io.IOException;
import java.util.Enumeration;

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;


public class ConfigServletDemo1 extends HttpServlet {
    private static final long serialVersionUID = 1L;
    private ServletConfig config;
    
    

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //获取指定的初始化参数
        String value = config.getInitParameter("xxx");
        resp.getOutputStream().write(value.getBytes());
        
        //获取所有初始化参数
        Enumeration e = config.getInitParameterNames();
        while(e.hasMoreElements()){
            String name = (String) e.nextElement();
            value = config.getInitParameter(name);
            resp.getOutputStream().write((name + "=" + value + "<br />").getBytes());
        }
    }
    
    /**
     * 这个方法有什么用？
     * 1.配置初始化参数，配置字符集
     * <init-param>
          <param-name>charset</param-name>
          <param-value>utf-8</param-value>
      </init-param>
     * 2.配置数据库连接设置
     * <init-param>
     *     <param-name>url</param-name>
     *     <param-value>jdbc:mysql://localhost:3306/test</param-value>
     * </init-param>
     * <init-param>
     *     <param-name>username</param-name>
     *     <param-value>root</param-value>
     * </init-param>
     * <init-param>
     *     <param-name>password</param-name>
     *     <param-value>root</param-value>
     * </init-param>
     * 3.
     */
    



    @Override
    public void init(ServletConfig config) throws ServletException {
        this.config = config;
    }
       
    

}

下面的方法更简洁，在以后的开发过程中使用下面的方法

package cn.itcast.servlet;

import java.io.IOException;

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;

/**
 * Servlet implementation class ConfigServletDemo2
 */

public class ConfigServletDemo2 extends HttpServlet {
    private static final long serialVersionUID = 1L;
       
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        ServletConfig config = this.getServletConfig();
        String value = config.getInitParameter("xxx");
        response.getOutputStream().write(value.getBytes());
    }

    
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}