《servlet进化史》

ゝ一世哀愁。 2023-09-30 21:42 5阅读 0赞

## 《servlet进化史》 ##

#### servlet注册方法 ####

*  xml注册

<?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>TestServlet</servlet-name>
            <servlet-class>TestServlet</servlet-class>
        </servlet>
        <servlet-mapping>
            <servlet-name>TestServlet</servlet-name>
            <url-pattern>/testServlet</url-pattern>
        </servlet-mapping>
    
    </web-app>

*  注解注册

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;
    @WebServlet(urlPatterns = "/test", loadOnStartup = 1)
    public class TestServlet extends HttpServlet {
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            super.doGet(req, resp);
        }
    }

#### 一代servlet ####

import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import java.io.IOException;
    public class TestServlet extends HttpServlet {
        
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        
            super.doGet(req, resp);
        }
    }

#### 二代servlet（switch） ####

import javax.servlet.ServletException;
    import javax.servlet.ServletRequest;
    import javax.servlet.ServletResponse;
    import javax.servlet.annotation.WebServlet;
    import javax.servlet.http.HttpServlet;
    import java.io.IOException;
    
    @WebServlet(urlPatterns = "/test", loadOnStartup = 1)
    public class TestServletSwitch extends HttpServlet {
        @Override
        public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException {
            System.out.println("init-service");
            String operation = req.getParameter("operation");
            switch (operation){
                case "add":
                    add(req,res);
                    break;
                case "delete":
                    delete(req,res);
                    break;
                case "update":
                    update(req,res);
                    break;
                case "query":
                    query(req,res);
                    break;
            }
        }
    
        private void query(ServletRequest req, ServletResponse res) throws IOException{
            res.getWriter().write("query");
        }
    
        private void update(ServletRequest req, ServletResponse res) throws IOException{
            res.getWriter().write("update");
        }
    
        private void delete(ServletRequest req, ServletResponse res) throws IOException{
            res.getWriter().write("delete");
        }
    
        private void add(ServletRequest req, ServletResponse res) throws IOException {
            res.getWriter().write("add");
        }
    
        @Override
        public void destroy() {
            super.destroy();
            System.out.println("init-destroy");
        }
    
        @Override
        public void init() throws ServletException {
            super.init();
            System.out.println("init-servlet");
        }
    
    }

#### 三代servlet（reflex） ####

import javax.servlet.ServletException;
    import javax.servlet.ServletRequest;
    import javax.servlet.ServletResponse;
    import javax.servlet.annotation.WebServlet;
    import javax.servlet.http.HttpServlet;
    import java.io.IOException;
    import java.lang.reflect.Method;
    
    @WebServlet(urlPatterns = "/test2", loadOnStartup = 1)
    public class TestServletReflex extends HttpServlet {
        @Override
        public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException {
            System.out.println("init-service");
            String operation = req.getParameter("operation");
            Method[] methods = this.getClass().getDeclaredMethods();
            for (Method method : methods) {
                if (method.getName().equals(operation)) {
                    try {
                        method.invoke(this, req, res);
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            }
        }
    
        private void query(ServletRequest req, ServletResponse res) throws IOException{
            res.getWriter().write("query");
        }
    
        private void update(ServletRequest req, ServletResponse res) throws IOException{
            res.getWriter().write("update");
        }
    
        private void delete(ServletRequest req, ServletResponse res) throws IOException{
            res.getWriter().write("delete");
        }
    
        private void add(ServletRequest req, ServletResponse res) throws IOException {
            res.getWriter().write("add");
        }
    
        @Override
        public void destroy() {
            super.destroy();
            System.out.println("init-destroy");
        }
    
        @Override
        public void init() throws ServletException {
            super.init();
            System.out.println("init-servlet");
        }
    
    }

#### 四代servlet（springmvc） ####

*  dispatchServlet

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;
    
    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 java.io.IOException;
    import java.io.InputStream;
    import java.lang.reflect.InvocationTargetException;
    import java.lang.reflect.Method;
    import java.util.HashMap;
    import java.util.Map;
    
    @WebServlet(value = "*.do",loadOnStartup = 1)
    public class DispatchServlet extends HttpServlet {
        private Map<String, Object> beanMap = new HashMap<>();
    
        @Override
        protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
            request.setCharacterEncoding("UTF-8");
            String servletPath = request.getServletPath();
            servletPath = servletPath.substring(1);
            int lastDotIndex = servletPath.lastIndexOf(".do");
            servletPath = servletPath.substring(0, lastDotIndex);
    
            Object controllerBeanObj = beanMap.get(servletPath);
            String operate = request.getParameter("operation");
            try {
                Method method = controllerBeanObj.getClass().getDeclaredMethod(operate, HttpServletRequest.class, HttpServletResponse.class);
                if (method != null) {
                    method.setAccessible(true);
                    method.invoke(controllerBeanObj, request, response);
                } else {
                    throw new RuntimeException("operate值非法!");
                }
            } catch (NoSuchMethodException e) {
                e.printStackTrace();
            } catch (IllegalAccessException e) {
                e.printStackTrace();
            } catch (InvocationTargetException e) {
                e.printStackTrace();
            }
    
        }
    
        public void init() {
            try {
                InputStream inputStream = getClass().getClassLoader().getResourceAsStream("applicationContext.xml");
                //1.创建DocumentBuilderFactory
                DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
                //2.创建DocumentBuilder对象
                DocumentBuilder documentBuilder = documentBuilderFactory.newDocumentBuilder();
                //3.创建Document对象
                Document document = documentBuilder.parse(inputStream);
    
                //4.获取所有的bean节点
                NodeList beanNodeList = document.getElementsByTagName("bean");
                for (int i = 0; i < beanNodeList.getLength(); i++) {
                    Node beanNode = beanNodeList.item(i);
                    if (beanNode.getNodeType() == Node.ELEMENT_NODE) {
                        Element beanElement = (Element) beanNode;
                        String beanId = beanElement.getAttribute("id");
                        String className = beanElement.getAttribute("class");
                        Class controllerBeanClass = Class.forName(className);
                        Object beanObj = controllerBeanClass.newInstance();
                        beanMap.put(beanId, beanObj);
                    }
                }
            } catch (ParserConfigurationException e) {
                e.printStackTrace();
            } catch (SAXException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            } catch (IllegalAccessException e) {
                e.printStackTrace();
            } catch (InstantiationException e) {
                e.printStackTrace();
            } catch (ClassNotFoundException e) {
                e.printStackTrace();
            }
    
        }
    
    }

*  resource目录下的xml文件

<?xml version="1.0" encoding="utf-8"?>
    
    <beans>
        
        <bean id="test" class="test.TestController"/>
        <bean id="test2" class="test.Test2Controller"/>
    </beans>

*  servlet1

import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import java.io.IOException;
    
    public class TestController extends HttpServlet {
        
    
        public void add(HttpServletRequest req, HttpServletResponse res) throws IOException {
        
            res.getWriter().write("add");
        }
        public void delete(HttpServletRequest req, HttpServletResponse res) throws IOException {
        
            res.getWriter().write("delete");
        }
        public void update(HttpServletRequest req, HttpServletResponse res) throws IOException {
        
            res.getWriter().write("update");
        }
        public void query(HttpServletRequest req, HttpServletResponse res) throws IOException {
        
            res.getWriter().write("query");
        }
    }

*  servlet2

import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import java.io.IOException;
    
    public class Test2Controller extends HttpServlet {
    
        public void add(HttpServletRequest req, HttpServletResponse res) throws IOException {
            res.getWriter().write("add22222");
        }
        public void delete(HttpServletRequest req, HttpServletResponse res) throws IOException {
            res.getWriter().write("delete2222");
        }
        public void update(HttpServletRequest req, HttpServletResponse res) throws IOException {
            res.getWriter().write("update222");
        }
        public void query(HttpServletRequest req, HttpServletResponse res) throws IOException {
            res.getWriter().write("query2222");
        }
    }

*  项目结构  
    ![在这里插入图片描述][3ec75fd88738445e8ab2cb3bdf42d289.png]

[3ec75fd88738445e8ab2cb3bdf42d289.png]: https://img-blog.csdnimg.cn/3ec75fd88738445e8ab2cb3bdf42d289.png