2.3 在DispatcherServlet的构造方法中解析applicationContext.xml配置文件

package com.hy.servlet;

import java.io.IOException;
import java.io.InputStream;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
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 javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;

import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.xml.sax.SAXException;

@WebServlet("*.do")
public class DispatcherServlet extends HttpServlet {
    private Map<String, Object> map = new ConcurrentHashMap<>();

    public DispatcherServlet() {
        try {
            InputStream inputStream = this.getClass().getClassLoader().getResourceAsStream("applicationContext.xml");
            // 1,通过工厂模式，创建documentBuilderFactory工厂对象
            DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();

            // 2,创建DocumentBuilder对象
            DocumentBuilder documentBuilder = documentBuilderFactory.newDocumentBuilder();

            // 3,得到Document对象( 注意导入org.w3c.dom包中的)
            Document document = documentBuilder.parse(inputStream);

            // 4,获得所有的bean标签
            NodeList nodeList = document.getElementsByTagName("bean");
            for (int i = 0; i < nodeList.getLength(); i++) {
                Node node = nodeList.item(i);

                if (node.getNodeType() == Node.ELEMENT_NODE) {
                    //(注意导入org.w3c.dom包中的)
                    //强转成Element类的对象，里面有比Node类更方便的方法
                    Element element = (Element) node;

                    String id = element.getAttribute("id");
                    String className = element.getAttribute("class");
                    boolean flag = map.containsKey(id);
                    if (flag == true)
                        return;
                    Object xxxController = Class.forName(className).newInstance();
                    map.put(id, xxxController);
                }
            }
        } catch (ParserConfigurationException | SAXException | IOException | ClassNotFoundException | InstantiationException | IllegalAccessException e) {
            e.printStackTrace();
        }
    }

    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // 设置编码
        request.setCharacterEncoding("UTF-8");
        response.setCharacterEncoding("UTF-8");
        response.setContentType("text/html;charset=UTF-8");

        // 假设url是： http://localhost:8080/mymvc2/hello.do
        // ServletPath是Servlet的访问路径： /hello.do
        // 思路是：
        // 第1步： /hello.do -> hello 或者 /book.do -> book
        // 第2步： hello -> HelloController 或者 book -> BookController
        String servletPath = request.getServletPath(); // /hello.do
        int lastDotIndex = servletPath.lastIndexOf(".do");
        servletPath = servletPath.substring(1, lastDotIndex); // hello
    }
}