JavaWeb学习-Servlet优化（MVC思想）

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1. 把多个Servlet变成一个Servlet

（1）访问不同的servlet处理不同的业务

（2）整合Servlet，访问同一个servlet，重写servlet方法处理不同的业务

（3）代码实现

A.fruit.do

package com.fruits.servelet;

import com.fruits.dao.FruitDAO;
import com.fruits.dao.Impl.FruitDAOImpl;
import com.fruits.pojo.Fruit;
import com.fruits.util.StringUtil;
import com.myssm.myspringmvc.ViewBaseServlet;

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.servlet.http.HttpSession;
import java.io.IOException;
import java.util.List;

@WebServlet("/fruit.do")
public class FruitServlet extends ViewBaseServlet {
    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        request.setCharacterEncoding("utf-8");
        String operate = request.getParameter("operate");
        if(StringUtil.isEmpty(operate)){
            operate = "index"; //如果operate为空，则设置为index
        }
        switch (operate){
            case "index":
                Index(request,response);
                break;
            case "add":
                Add(request,response);
                break;
            case "delete":
                Delete(request,response);
                break;
            case  "edit":
                Edit(request,response);
                break;
            case "update":
                Update(request,response);
                break;
            default:
                throw new RuntimeException("operate不合法！");
        }

    }

    private void Index(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        HttpSession session=request.getSession();
        int pageNo = 1;
        String oper = request.getParameter("oper");
        //如果oper不是空的，则是通过表单的查询按钮点击过来的，
        //如果oper是空的，说明不是通过表单的查询按钮点击过来的，
        // 因为index文件可以通过点击分页按钮进入，增删改后也可以进入。
        String keyword = null;
        if(StringUtil.isNotEmpty(oper)&&"search".equals(oper)){
            //是通过表单的查询按钮点击过来的，
            //此时，pageNo应该还原为 1 ， keyword应该从请求参数中获取
            pageNo=1;
            keyword = request.getParameter("keyword");
            if(StringUtil.isEmpty(keyword)){
                keyword = "";
            }
            session.setAttribute("keyword",keyword);
        }else{
            //说明不是通过表单的查询按钮点击过来的，（比如点击上一页下一页或者直接在地址栏中输入网址 ）
            //此时keyword应该从session作用域中获取
            String pageNoStr = request.getParameter("pageNo");
            if(StringUtil.isNotEmpty(pageNoStr)){
                pageNo = Integer.parseInt(pageNoStr);
            }
            Object keywordobj = session.getAttribute("keyword");
            if(keywordobj!=null){
                keyword = (String)keywordobj;
            }else{
                keyword="";
            }
        }
        session.setAttribute("pageNo",pageNo);

        FruitDAO fruitDAO=new FruitDAOImpl();
        //List<Fruit> fruitList = fruitDAO.getFruitList();
        //List<Fruit> fruitList = fruitDAO.getFruitListbypageNo(pageNo);
        List<Fruit> fruitList = fruitDAO.getListbypageNo(keyword, pageNo);
        session.setAttribute("fruitList", fruitList);

        //总记录条数
        // int count = fruitDAO.getFruitCount();
        int count = fruitDAO.getCount(keyword);
        //总页数
        int pageCount = count/5+1;
        session.setAttribute("pageCount", pageCount);
        //此处的视图名称是index，
        //那么thymeleaf会将这个 逻辑视图名称 对应到 物理视图 名称上去
        //逻辑视图名称：index
        //物理视图名称： view-prefix+逻辑视图名称+view-suffix
        //所以真是的视图名称为   /   index.    html
        super.processTemplate("index",request,response);
    }
    private void Add(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        String fidstr = request.getParameter("fid");
        int fid = Integer.parseInt(fidstr);
        String fname = request.getParameter("fname");
        String fpricestr = request.getParameter("price");
        int price =Integer.parseInt(fpricestr);
        String fcountstr = request.getParameter("fcount");
        int fcount =Integer.parseInt(fcountstr);
        String remark = request.getParameter("remark");

        System.out.println(fid+" "+fname+" "+price+" "+fcount+" "+remark);

        FruitDAO fruitDAO = new FruitDAOImpl();
        boolean b = fruitDAO.addFruits(new Fruit(fid,fname,price,fcount,remark));
        if(b){
            System.out.println("添加成功");
        }
        else{
            System.out.println("添加失败");
        }
        response.sendRedirect("fruit.do");
    }
    private void Delete(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String fidstr = request.getParameter("fid");
        int fid = Integer.parseInt(fidstr);
        FruitDAO fruitDAO = new FruitDAOImpl();
        boolean b = fruitDAO.deleteFruitById(fid);
        if(b){
            System.out.println("删除成功！");
        }
        else{
            System.out.println("删除失败！");
        }
        response.sendRedirect("fruit.do");
    }

    private void Edit(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String fidstr = request.getParameter("fid");
        int fid = Integer.parseInt(fidstr);
        FruitDAO fruitDAO1=new FruitDAOImpl();
        Fruit fruit1 = new Fruit();
        fruit1= fruitDAO1.getFruitById(fid);
        request.setAttribute("fruit",fruit1);
        super.processTemplate("edit",request,response);
    }
    private void Update(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        request.setCharacterEncoding("utf-8");

        String fidstr = request.getParameter("fid");
        int fid = Integer.parseInt(fidstr);
        String fname = request.getParameter("fname");
        String fpricestr = request.getParameter("price");
        int price =Integer.parseInt(fpricestr);
        String fcountstr = request.getParameter("fcount");
        int fcount =Integer.parseInt(fcountstr);
        String remark = request.getParameter("remark");

        FruitDAO fruitDAO=new FruitDAOImpl();

        boolean b = fruitDAO.updateFruitById(new Fruit(fid, fname, price, fcount, remark));
        if(b){
            System.out.println("修改成功");
        }
        else{
            System.out.println("修改失败");
        }
        /*super.processTemplate("index",request,response);
        相当于
        request.getRequestDispatcher("index").forward(request,response); 获得的数据还是更新之前的数据
        此处需要重定向，目的是重新给IndexServlet发请求，
        重新获取fruitList，然后覆盖到session中，这样index.html页面上显示的session中的数据才是最新的。
        */
        response.sendRedirect("fruit.do");
    }
}

B. 界面代码修改

th:href="@{/fruit.do(fid=${fruit.fid},operate='edit')}"

//js
function delFruit( fid ) {
    if(confirm("是否确认删除？")){
        window.location.href="fruit.do?fid="+fid+"&operate=delete";
    }
}
function page(pageNo) {
    window.location.href="fruit.do?pageNo="+pageNo;
}
//add
<input type="hidden" name="operate" value="update">

2. 用反射技术代替switch

fruit.do

protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    //设置编码
    request.setCharacterEncoding("utf-8");

    String operate = request.getParameter("operate");

    if(StringUtil.isEmpty(operate)){
        operate = "index";
    }

    //获取当前类中所有的方法
    Method[] methods = this.getClass().getDeclaredMethods();
    for(Method m : methods){
        String name = m.getName();
        if(operate.equals(name)){
            try {
                m.invoke(this,request,response);
                return;
            } catch (IllegalAccessException e) {
                e.printStackTrace();
            } catch (InvocationTargetException e) {
                e.printStackTrace();
            }
        }
        throw new RuntimeException("operate不合法！");
    }
}

3. 引入DispatcherServlet

  DispatcherServlet中央控制器，客户端的请求都交给DispatcherServlet，DispatcherServlet根据用户的请求不同对应不同的Servlet。

DispatcherServlet.java

package com.springmvc;

import com.fruits.util.StringUtil;
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.*;
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("*.do")
public class DispatcherServlet extends HttpServlet {

    private Map<String,Object> beanMap = new HashMap<>();

    public DispatcherServlet(){
    }

    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() ;
                    Method setServletContextMethod = controllerBeanClass.getDeclaredMethod("setServletContext",ServletContext.class);
                    setServletContextMethod.invoke(beanObj , this.getServletContext());

                    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();
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            e.printStackTrace();
        }
    }

    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //设置编码
        request.setCharacterEncoding("UTF-8");
        //假设url是：  http://localhost:8080/pro15/hello.do
        //那么servletPath是：    /hello.do
        // 我的思路是：
        // 第1步： /hello.do ->   hello   或者  /fruit.do  -> fruit
        // 第2步： hello -> HelloController 或者 fruit -> FruitController
        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("operate");
        if(StringUtil.isEmpty(operate)){
            operate = "index" ;
        }

        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();
        }
    }
}

applicationContext.xml

<?xml version="1.0" encoding="utf-8" ?>

<beans>
    <!-- bean标签的作用是：servletPath中涉及的名字是fruit，那么就要FruitController这个类来处理 -->
    <bean id="fruit" class="com.fruits.controller.FruitController"></bean>
</beans>

<!--
xml文档包含三个部分
1）XML声明，放在xml文件的第一行
2）DTD 文档类型定义
3）XML 正文
-->

 

文章来源:https://www.cnblogs.com/Joyce-mi7/p/16497130.html
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