day54

servlet升級03

特點

當前設計又有一個問題，我們目前可以做到一個實體類用一個servlet，比如Student類的所有crud方法都可以在StudentServlet中的service方法中進行動態處理。假如又有User類，我們就要在UserServlet中設計service方法，在該service方法中再次進行動態方法的判斷處理

假如項目有幾百個實體類，可能對應幾百個Servlet，可能就要寫幾百個service方法的動態處理

通過分析，我們發現，可以將op的值特意設置為各個實體類的方 法名

使用反射動態獲取每一個servlet，通過發射得到每一個servlet后，動態獲取op的值，再來動態覺得調用各個op值所對應的方法

反射

“照妖鏡”，一個類中有四個訪問級別的成員，private只有自己能訪問，default自己和通過的類可以訪問，protected是自己，同包類和非同包子類可以訪問，public是當前項目所有類都可以訪問

反射可以在類的外部拿到任何訪問修飾基本的數據成員

反射功能強大，但是效率低

service方法的重構

使用反射來實現service方法的簡化

package com.saas.servlet;
?
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
?
public class BaseServlet extends HttpServlet {
?@Overrideprotected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {req.setCharacterEncoding("UTF-8");resp.setCharacterEncoding("UTF-8");resp.setContentType("text/html;charset=UTF-8");
?String op = req.getParameter("op");
?System.out.println(op);
?Class<? extends BaseServlet> clazz = getClass();
?try {Method method = clazz.getDeclaredMethod(op, HttpServletRequest.class, HttpServletResponse.class);
?//  設置方法可以被訪問method.setAccessible(true);
?//  使用反射調用對應的方法method.invoke(this, req, resp);} catch (NoSuchMethodException e) {throw new RuntimeException(e);} catch (IllegalAccessException e) {throw new RuntimeException(e);} catch (InvocationTargetException e) {throw new RuntimeException(e);}}
}

任何繼承自當前BaseServlet的servlet都會執行該BaseServlet的生命周期方法service方法

在service方法中，動態獲取用戶傳遞過來的op值

而該op值一定要設置為每個servlet中的方法名

運用反射得到op對應的方法對象，每個方法的參數列表都是HttpServletRequest和HttpServletResponse

得到每一個業務方法對象后，設置方法可以在外界被訪問

并調用invoke實現對于每個業務方法的調用

好處是當前項目只需要做一個op的判斷，無需再在每個servlet里面有關于op判斷的重復代碼

package com.saas.servlet;
?
import com.saas.entity.User;
import com.saas.service.IUserService;
import com.saas.service.impl.UserServiceImpl;
?
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.List;
?
@WebServlet("/User")
public class UserServlet extends BaseServlet{
?private IUserService userService = new UserServiceImpl();
?public void login(HttpServletRequest req, HttpServletResponse resp){System.out.println("UserServlet login");}public void register(HttpServletRequest req, HttpServletResponse resp){System.out.println("UserServlet register");}public void logout(HttpServletRequest req, HttpServletResponse resp){System.out.println("UserServlet logout");}
?protected void saveUser(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException{System.out.println("UserServlet saveUser");}
?protected void updateUser(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException{System.out.println("UserServlet updateUser");}
?protected void deleteUser(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException{System.out.println("UserServlet deleteUser");}
?protected void getUserByUid(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException{System.out.println("UserServlet getUserByUid");
?String suid = req.getParameter("uid");int uid = suid == null ? 0 : Integer.parseInt(suid);
?User u = userService.getUserByUid(uid);
?PrintWriter out = resp.getWriter();
?out.print("<form>");out.print("<input type='hidden' name='uid' value='" + u.getUid() + "' />");out.print("<input type='text' name='username' value='" + u.getUsername() + "' />");out.print("<input type='text' name='password' value='" + u.getPassword() + "' />");out.print("<input type='text' name='email' value='" + u.getEmail() + "' />");out.print("<input type='text' name='phone' value='" + u.getPhone() + "' />");out.print("<input type='text' name='address' value='" + u.getAddress() + "' />");out.print("<input type='submit' value='update' />");out.print("</form>");
?}
?protected void getAllUsers(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException{System.out.println("UserServlet getAllUsers");
?List<User> users = userService.getAllUsers();
?PrintWriter out = resp.getWriter();
?out.print("<table border=1 align='center' width='80%'>");out.print("<tr>");out.print("<th>uid</th>");out.print("<th>username</th>");out.print("<th>password</th>");out.print("<th>email</th>");out.print("<th>phone</th>");out.print("<th>address</th>");out.print("<th>manage</th>");out.print("</tr>");for (User user : users) {out.print("<tr>");out.print("<td>" + user.getUid() + "</td>");out.print("<td>" + user.getUsername() + "</td>");out.print("<td>" + user.getPassword() + "</td>");out.print("<td>" + user.getEmail() + "</td>");out.print("<td>" + user.getPhone() + "</td>");out.print("<td>" + user.getAddress() + "</td>");out.print("<td><a href='User?op=getUserByUid&uid=" + user.getUid() + "'>update</a></td>");out.print("</tr>");}out.print("</table>");}
}

package com.saas.servlet;
?
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
?
@WebServlet("/Student")
public class StudentServlet extends BaseServlet {
?private static final long serialVersionUID = 1L;
?public void getAllStudents(HttpServletRequest req, HttpServletResponse resp) {System.out.println("StudentServlet getAllStudents");}
?
?public void getStudentBySid(HttpServletRequest req, HttpServletResponse resp) {System.out.println("StudentServlet getStudentBySid");}
?
?public void getStudentsByPage(HttpServletRequest req, HttpServletResponse resp) {System.out.println("StudentServlet getStudentsByPage");}
?
?public void saveStudent(HttpServletRequest req, HttpServletResponse resp) {System.out.println("StudentServlet saveStudent");}
?
?public void updateStudent(HttpServletRequest req, HttpServletResponse resp) {System.out.println("StudentServlet updateStudent");}
?
?public void deleteStudent(HttpServletRequest req, HttpServletResponse resp) {System.out.println("StudentServlet deleteStudent");}
}

在UserServlet和StudentServlet中都將不會出現op的判斷處理，只需要在BaseServlet中實現一次即可，代碼大大簡化

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