1 新建DispatcherServlet
1.2 在src目录下，新建applicationContext.xml
<?xml version="1.0" encoding="UTF-8"?>
<beans id="b1">
<bean id="emp" class="xxx.controller.EmpController"/>
<bean id="dept" class="xxx.controller.DeptController"/>
</beans>
1.3 在DispatcherServlet的构造方法中解析applicationContext.xml配置文件
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 o = Class.forName(className).newInstance();
map.put(id, o);
}
}
} 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
}
}
1.4 在DispatcherServlet的service方法中，通过ServletPath获取对应的Controller对象,优化反射的代码
@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
// 通过ServletPath获取对应的Controller对象
Object xxxController = map.get(servletPath);
String ac = request.getParameter("ac");
System.out.println("=======" + ac + "======");
if (StringUtil.isEmpty(ac))
ac = "index";
try {
// 这里只能try...catch异常，因为在重写的方法里，不能抛出比父类更大的异常
Method method = xxxController.getClass().getDeclaredMethod(ac, HttpServletRequest.class,HttpServletResponse.class);
if (method != null) {
method.invoke(xxxController, request, response);
} else {
throw new RuntimeException("ac值违法");
}
} catch (NoSuchMethodException | SecurityException | IllegalAccessException | IllegalArgumentException| InvocationTargetException e) {
e.printStackTrace();
}
}
1.5 写一个简单的EmpController
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class EmpController {
public void index(HttpServletRequest request,HttpServletResponse response) {
System.out.println("EmpController...index");
}
}
2. 第二次改进明天再写，每一个方法中都有获取参数的代码, 或者都有请求转发或是重定向的代码。解决跳转问题
（代码格式问题各位大佬别吐槽，复制过来的有时间改）