Ajax 案例之三级联动

　　每次在博客园网站写博客，格式真的好难搞，还望好心人告知更好的编辑工具。接下来进入正题：三级联动（其效果演示可看我的博文 Ajax 学习总结 末尾）。

1. 数据表设计（Oracle）
   1. 新建数据表 Employees（员工信息）、Locations（城市信息）、Departments（部门信息），其中 Departments 表的外键为 locations 表的 location_id ，Employees 表的外键为 Departments 表Department_id

      

2. DAO 层设计（c3p0 数据库连接池、JDBCUtils）

   a. 获取释放数据库连接的工具类：JDBCTools

1.     package com.javaweb.userajax.serlet.list.show.tools;  
2.     
3. import com.mchange.v2.c3p0.ComboPooledDataSource;  
4.     
5. import javax.sql.DataSource;  
6. import java.sql.Connection;  
7. import java.sql.SQLException;  
8.     
9. /** 
10.  * Created by shkstart on 2017/12/05. 
11.  */  
12. public class JDBCTools {  
13.     
14.     private static DataSource dataSource;  
15.     static {  
16.         dataSource = new ComboPooledDataSource("listShow");  
17.     }  
18.     
19.     public static Connection getConnection() {  
20.         Connection connection = null;  
21.         try {  
22.             connection = dataSource.getConnection();  
23.         } catch (SQLException e) {  
24.             e.printStackTrace();  
25.         }  
26.         return connection;  
27.     }  
28.     
29.     public void releaseConnection(Connection connection) {  
30.         try {  
31.             connection.close();  
32.         } catch (SQLException e) {  
33.             e.printStackTrace();  
34.         }  
35.     }  
36. }  

    b. 获取某张数据表的所有数据以及根据限定的查询条件获取部分值的 DAO 类：DAO

37. package com.javaweb.userajax.serlet.list.show.dao;  
38.     
39. import com.javaweb.userajax.serlet.list.show.tools.JDBCTools;  
40. import org.apache.commons.dbutils.QueryRunner;  
41. import org.apache.commons.dbutils.handlers.BeanHandler;  
42. import org.apache.commons.dbutils.handlers.BeanListHandler;  
43.     
44. import java.lang.reflect.ParameterizedType;  
45. import java.lang.reflect.Type;  
46. import java.sql.Connection;  
47. import java.sql.SQLException;  
48. import java.util.List;  
49.     
50. /** 
51.  * Created by shkstart on 2017/12/05. 
52.  */  
53. public class DAO<T> {  
54.     
55.     private QueryRunner queryRunner;  
56.     private Class<T> type;  
57.     
58.     public DAO() {  
59.         queryRunner = new QueryRunner();  
60.         Type superClass = getClass().getGenericSuperclass();  
61.         if (superClass instanceof ParameterizedType) {  
62.             ParameterizedType parameterizedType = (ParameterizedType) superClass;  
63.             Type[] args = parameterizedType.getActualTypeArguments();  
64.     
65.             if (args != null && args.length > 0) {  
66.                 if (args[0] instanceof Class) {  
67.                     type = (Class<T>) args[0];  
68.                 }  
69.             }  
70.         }  
71.     }  
72.     
73.     public List<T> getAll(String sql) {  
74.         Connection connection = JDBCTools.getConnection();  
75.         List<T> list = null;  
76.         try {  
77.             list = queryRunner.query(connection, sql, new BeanListHandler<T>(type));  
78.         } catch (SQLException e) {  
79.             e.printStackTrace();  
80.         }  
81.         return list;  
82.     }  
83.     
84.     public List<T> getList(String sql, Object ... args) {  
85.         Connection connection = JDBCTools.getConnection();  
86.         List<T> list = null;  
87.         try {  
88.             list = queryRunner.query(connection, sql, new BeanListHandler<T>(type), args);  
89.         } catch (SQLException e) {  
90.             e.printStackTrace();  
91.         }  
92.         return list;  
93.     }  
94.     
95.     public T getValue(String sql, Object ... args) {  
96.         Connection connection = JDBCTools.getConnection();  
97.         T entity = null;  
98.         try {  
99.             entity = queryRunner.query(connection, sql, new BeanHandler<T>(type), args);  
100.         } catch (SQLException e) {  
101.             e.printStackTrace();  
102.         }  
103.         return entity;  
104.     }  
105. }  

     c. 根据案例需求定义数据表对应的 dao 接口

     DepartmentsDao:

106. package com.javaweb.userajax.serlet.list.show.dao;  
107.     
108. import com.javaweb.userajax.serlet.list.show.domain.Departments;  
109.     
110. import java.util.List;  
111.     
112. /** 
113.  * Created by shkstart on 2017/12/06. 
114.  */  
115. public interface DepartmentsDao {  
116.     List<Departments> getAll(Integer locationId);  
117. }  

     EmployeesDao:

118. package com.javaweb.userajax.serlet.list.show.dao;  
119.     
120. import com.javaweb.userajax.serlet.list.show.domain.Employees;  
121.     
122. import java.util.List;  
123.     
124. /** 
125.  * Created by shkstart on 2017/12/06. 
126.  */  
127. public interface EmployeesDao {  
128.     List<Employees> getAll(Integer departmentId);  
129.     Employees getEmp(Integer employeeId);  
130. }  

     LocationsDao:

131. package com.javaweb.userajax.serlet.list.show.dao;  
132.     
133. import com.javaweb.userajax.serlet.list.show.domain.Locations;  
134.     
135. import java.util.List;  
136.     
137. /** 
138.  * Created by shkstart on 2017/12/06. 
139.  */  
140. public interface LocationsDao {  
141.     List<Locations> getAll();  
142. }  

     d. 根据数据表编写对应的 domain 类

     Departments：

143. package com.javaweb.userajax.serlet.list.show.domain;  
144.     
145. /** 
146.  * Created by shkstart on 2017/12/06. 
147.  */  
148. public class Departments {  
149.     private Integer departmentId;  
150.     private String departmentName;  
151.     private Integer locationId;  
152.     
153.     public Integer getDepartmentId() {  
154.         return departmentId;  
155.     }  
156.     
157.     public void setDepartmentId(Integer departmentId) {  
158.         this.departmentId = departmentId;  
159.     }  
160.     
161.     public String getDepartmentName() {  
162.         return departmentName;  
163.     }  
164.     
165.     public void setDepartmentName(String departmentName) {  
166.         this.departmentName = departmentName;  
167.     }  
168.     
169.     public Integer getLocationId() {  
170.         return locationId;  
171.     }  
172.     
173.     public void setLocationId(Integer locationId) {  
174.         this.locationId = locationId;  
175.     }  
176.     
177.     public Departments(){  
178.     
179.     }  
180.     
181.     @Override  
182.     public String toString() {  
183.         return "Departments{" +  
184.                 "departmentId=" + departmentId +  
185.                 ", departmentName='" + departmentName + ''' +  
186.                 ", locationId=" + locationId +  
187.                 '}';  
188.     }  
189. }  

     Employees：

190. package com.javaweb.userajax.serlet.list.show.domain;  
191.     
192. /** 
193.  * Created by shkstart on 2017/12/06. 
194.  */  
195. public class Employees {  
196.     private Integer employeeId;  
197.     private Integer departmentId;  
198.     private String lastName;  
199.     private String email;  
200.     
201.     @Override  
202.     public String toString() {  
203.         return "Employees{" +  
204.                 "employeeId=" + employeeId +  
205.                 ", departmentId=" + departmentId +  
206.                 ", lastName='" + lastName + ''' +  
207.                 ", email='" + email + ''' +  
208.                 '}';  
209.     }  
210.     
211.     public Integer getDepartmentId() {  
212.         return departmentId;  
213.     }  
214.     
215.     public void setDepartmentId(Integer departmentId) {  
216.         this.departmentId = departmentId;  
217.     }  
218.     
219.     public Integer getEmployeeId() {  
220.         return employeeId;  
221.     }  
222.     
223.     public void setEmployeeId(Integer employeeId) {  
224.         this.employeeId = employeeId;  
225.     }  
226.     
227.     public String getLastName() {  
228.         return lastName;  
229.     }  
230.     
231.     public void setLastName(String lastName) {  
232.         this.lastName = lastName;  
233.     }  
234.     
235.     public String getEmail() {  
236.         return email;  
237.     }  
238.     
239.     public void setEmail(String email) {  
240.         this.email = email;  
241.     }  
242.     
243.     public Employees(){  
244.     
245.     }  
246.     
247. }  

     Locations：

248. package com.javaweb.userajax.serlet.list.show.domain;  
249.     
250. /** 
251.  * Created by shkstart on 2017/12/06. 
252.  */  
253. public class Locations {  
254.     private Integer locationId;  
255.     private String city;  
256.     
257.     public Integer getLocationId() {  
258.         return locationId;  
259.     }  
260.     
261.     public void setLocationId(Integer locationId) {  
262.         this.locationId = locationId;  
263.     }  
264.     
265.     public String getCity() {  
266.         return city;  
267.     }  
268.     
269.     public void setCity(String city) {  
270.         this.city = city;  
271.     }  
272.     
273.     public Locations() {  
274.     
275.     }  
276.     
277.     @Override  
278.     public String toString() {  
279.         return "Locations{" +  
280.                 "locationId=" + locationId +  
281.                 ", city='" + city + ''' +  
282.                 '}';  
283.     }  
284. }  

     e. 根据 DAO 类以及 domain类实现数据表对应的 dao 接口

     DepartmentsImpl：

285. package com.javaweb.userajax.serlet.list.show.daoimpl;  
286.     
287. import com.javaweb.userajax.serlet.list.show.dao.DAO;  
288. import com.javaweb.userajax.serlet.list.show.dao.DepartmentsDao;  
289. import com.javaweb.userajax.serlet.list.show.domain.Departments;  
290.     
291. import java.util.List;  
292.     
293. /** 
294.  * Created by shkstart on 2017/12/06. 
295.  */  
296. public class DepartmentsImpl extends DAO<Departments> implements DepartmentsDao {  
297.     @Override  
298.     public List<Departments> getAll(Integer locationId) {  
299.         String sql = "SELECT department_id departmentId, department_name departmentName, location_id locationId FROM departments WHERE location_id=?";  
300.         System.out.println(sql);  
301.         List<Departments> departmentsList = getList(sql, locationId);  
302.         return departmentsList;  
303.     }  
304. }  

     EmployeesImpl:

305. package com.javaweb.userajax.serlet.list.show.daoimpl;  
306.     
307. import com.javaweb.userajax.serlet.list.show.dao.DAO;  
308. import com.javaweb.userajax.serlet.list.show.dao.EmployeesDao;  
309. import com.javaweb.userajax.serlet.list.show.domain.Employees;  
310.     
311. import java.util.List;  
312.     
313. /** 
314.  * Created by shkstart on 2017/12/06. 
315.  */  
316. public class EmployessDaoImpl extends DAO<Employees> implements EmployeesDao {  
317.     @Override  
318.     public List<Employees> getAll(Integer departmentId) {  
319.         String sql = "SELECT employee_id employeeId, last_name lastName FROM employees WHERE department_id=?";  
320.         System.out.println(sql);  
321.         List<Employees> employeesList = getList(sql, departmentId);  
322.         return employeesList;  
323.     }  
324.     
325.     @Override  
326.     public Employees getEmp(Integer employeeId) {  
327.         String sql = "SELECT employee_id employeeId, department_id departmentId, last_name lastName, email FROM employees WHERE employee_id=?";  
328.         Employees employees = getValue(sql, employeeId);  
329.         return employees;  
330.     }  
331. }  

     LocationsImpl:

332. package com.javaweb.userajax.serlet.list.show.daoimpl;  
333.     
334. import com.javaweb.userajax.serlet.list.show.dao.DAO;  
335. import com.javaweb.userajax.serlet.list.show.dao.LocationsDao;  
336. import com.javaweb.userajax.serlet.list.show.domain.Locations;  
337.     
338. import java.util.List;  
339.     
340. /** 
341.  * Created by shkstart on 2017/12/06. 
342.  */  
343. public class LocationsDaoImpl extends DAO<Locations> implements LocationsDao {  
344.     
345.     @Override  
346.     public List<Locations> getAll() {  
347.         String sql = "SELECT location_id locationId, city FROM locations";  
348.     
349.         List<Locations> locationsList = getAll(sql);  
350.         return locationsList;  
351.     }  
352. }  
     1. JSP 页面实现

        a. 我们先需要从 servlet 转发到 JSP 页面，将所有的 locations 信息封装在 request 中传回 jsp 页面在页面初始化的时候将所有 locations 信息显示

        index.jsp（案例所访问的页面，此页面直接跳转到 servlet，在 Servlet 中获取 location 信息后转发会显示页面）

353. <%@ page contentType="text/html;charset=UTF-8" language="java" %>  
354. <%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>  
355. <html>  
356. <head>  
357.     <title>ForwardPage</title>  
358. <body>  
359. <h3></h3>  
360. <jsp:forward page="getCity.do"/>  
361. </body>  
362. </html>  

     getCity 方法（servlet 中利用反射处理多个请求，前面的博文已经讲述过，此方法将 location 信息封装到 request 中然后转发到 selectList.jsp 页面）

363. protected void getCity(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {  
364.     LocationsDao locationsDao = new LocationsDaoImpl();  
365.     List<Locations> locationsList = locationsDao.getAll();  
366.     request.setAttribute("locations", locationsList);  
367.     request.getRequestDispatcher("/selectList/selectList.jsp").forward(request, response);  
368. }  

     selectList.jsp （将转发回页面的 locations 信息显示）

369. <%--  
370.   Created by IntelliJ IDEA.  
371.   User: yin'zhao  
372.   Date: 2017/12/04  
373.   Time: 21:37  
374.   To change this template use File | Settings | File Templates.  
375. --%>  
376. <%@ page contentType="text/html;charset=UTF-8" language="java" %>  
377. <%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>  
378. <html>  
379. <head>  
380.     <title>ShowInfoPage</title>  
381. </head>  
382. <body>  
383. <spac>City:  </spac>  
384. <select name="citySelect" id="city">  
385.     <option value="choose">请选择</option>  
386.     <c:forEach items="${requestScope.locations}" var="location">  
387.         <option value="${location.locationId}">${location.city}</option>  
388.     </c:forEach>  
389. </select>  
390. <span>        </span>  
391. <span>Department:  </span>  
392.     
393. <select name="departmentSelect" id="department">  
394.     <option value="choose">请选择</option>  
395. </select>  
396. <span>        </span>  
397. <span>Employee:  </span>  
398.     
399. <select name="employeeSelect" id="employee">  
400.     <option value="choose">请选择</option>  
401. </select>  
402. <table cellspacing="0" border="1" cellpadding="10" id="table">  
403.     <tr>  
404.         <th>employeeId</th>  
405.         <th>lastName</th>  
406.         <th>email</th>  
407.     </tr>  
408.     <tr>  
409.         <td id="employeeId"></td>  
410.         <td id="lastName"></td>  
411.         <td id="email"></td>  
412.     </tr>  
413. </table>  
414. </body>  
415. </html>  

     b. 为下拉框添加 change 事件，每当 locations 改变后根据 location_id 获取departments 信息，并将其显示在对应的下拉框中（信息的显示利用 Ajax，若所选择 location 没有departments 则提示对应的消息）

     selectList.jsp （处理 Ajax 请求部分）

416. <script type="text/javascript" src="${pageContext.request.contextPath}/jquery-1.7.2.js"></script>  
417.     <script type="text/javascript">  
418.         $(function () {  
419.             $("#city").change(function () {  
420. //                每次选择都将除了第一个的所有选项移除即更新操作  
421.                 $("#department option:not(:first)").remove();  
422.                 var url = "${pageContext.request.contextPath}/getDepartment.do";  
423. //                获取选中的 value 值，locationId  
424.                 var val = $(this).val();  
425. //                如果所选值不是第一个那么就开始执行 Ajax 操作，并将所选择的location 的 id 传到 servlet 中  
426.                 if (val != "choose") {  
427.                     var args = {"time": new Date, "value": val};  
428.                     $.getJSON(url, args, function (data) {  
429.                         if (data == 0) {  
430. //                若传回的数据为空则提示错误消息  
431.                             alert("当前城市没有部门");  
432.                         } else {  
433. //                否则将其加入对应的下拉框中  
434.                             for (var i = 0; i < data.length; i++) {  
435.                                 var departmentId = data[i].departmentId;  
436.                                 var departmentName = data[i].departmentName;  
437.                                 $("#department").append("<option value='" + departmentId + "'>" + departmentName + "</option>");  
438.                             }  
439.                         }  
440.                     })  
441.                 }  
442.             })  
443.     
444.             $("#department").change(function () {  
445.                 $("#employee option:not(:first)").remove();  
446.                 var url = "${pageContext.request.contextPath}/getEmployee.do";  
447. //                获取选中的 value 值，departmentId  
448.                 var val = $(this).val();  
449.                 alert(val)  
450.                 if (val != "choose") {  
451.                     var args = {"time": new Date, "value": val};  
452.                     $.getJSON(url, args, function (data) {  
453.                         if (data == 0) {  
454.                             alert("当前部门没有员工");  
455.                         } else {  
456.                             for (var i = 0; i < data.length; i++) {  
457.                                 var employeeId = data[i].employeeId;  
458.                                 var lastName = data[i].lastName;  
459.                                 $("#employee").append("<option value='" + employeeId + "'>" + lastName + "</option>");  
460.                             }  
461.                         }  
462.                     })  
463.                 }  
464.             })  
465. </script>

     getDepartments（Servlet 方法，根据所选择的 location 信息获取对应的 departments 信息）

466. protected void getDepartment(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {  
467.     Integer locationId = Integer.valueOf(request.getParameter("value"));  
468.     DepartmentsDao departmentsDao = new DepartmentsImpl();  
469.     
470.     List<Departments> departmentsList = departmentsDao.getAll(locationId);  
471.     ObjectMapper mapper = new ObjectMapper();  
472.        将返回值转换为 json 格式  
473.     String result = mapper.writeValueAsString(departmentsList);  
474.     
475.     response.setContentType("text/javascript");  
476.     response.getWriter().print(result);  
477. }  

     getEmployees （Servlet 方法，根据所选择的 departments 信息获取对应的 employees 列表）

478. protected void getEmployee(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {  
479.     Integer departmentId = Integer.valueOf(request.getParameter("value"));  
480.     EmployeesDao departmentsDao = new EmployessDaoImpl();  
481.     
482.     List<Employees> employeesList = departmentsDao.getAll(departmentId);  
483.     ObjectMapper mapper = new ObjectMapper();  
484.     String result = mapper.writeValueAsString(employeesList);  
485.     
486.     response.setContentType("text/javascript");  
487.     response.getWriter().print(result);  
488. }  

     c. 选择对应的 employee 将其信息打印在页面（在这里我将完成的 jsp 页面和 servlet 代码粘贴在这里）

     selectList.jsp

489. <%--  
490.   Created by IntelliJ IDEA.  
491.   User: yin'zhao  
492.   Date: 2017/12/04  
493.   Time: 21:37  
494.   To change this template use File | Settings | File Templates.  
495. --%>  
496. <%@ page contentType="text/html;charset=UTF-8" language="java" %>  
497. <%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>  
498. <html>  
499. <head>  
500.     <title>ShowInfoPage</title>  
501.     <script type="text/javascript" src="${pageContext.request.contextPath}/jquery-1.7.2.js"></script>  
502.     <script type="text/javascript">  
503.         $(function () {  
504.             /*  
505.             * 刚开始将用于 employees 显示的表格隐藏  
506.             * */  
507.             $("#table").hide();  
508.             $("#city").change(function () {  
509.                 $("#department option:not(:first)").remove();  
510.                 var url = "${pageContext.request.contextPath}/getDepartment.do";  
511. //                获取选中的 value 值，locationId  
512.                 var val = $(this).val();  
513.                 if (val != "choose") {  
514.                     var args = {"time": new Date, "value": val};  
515.                     $.getJSON(url, args, function (data) {  
516.                         if (data == 0) {  
517.                             alert("当前城市没有部门");  
518.                         } else {  
519.                             for (var i = 0; i < data.length; i++) {  
520.                                 var departmentId = data[i].departmentId;  
521.                                 var departmentName = data[i].departmentName;  
522.                                 $("#department").append("<option value='" + departmentId + "'>" + departmentName + "</option>");  
523.                             }  
524.                         }  
525.                     })  
526.                 }  
527.             })  
528.     
529.             $("#department").change(function () {  
530.                 $("#employee option:not(:first)").remove();  
531.                 var url = "${pageContext.request.contextPath}/getEmployee.do";  
532. //                获取选中的 value 值，departmentId  
533.                 var val = $(this).val();  
534.                 alert(val)  
535.                 if (val != "choose") {  
536.                     var args = {"time": new Date, "value": val};  
537.                     $.getJSON(url, args, function (data) {  
538.                         if (data == 0) {  
539.                             alert("当前部门没有员工");  
540.                         } else {  
541.                             for (var i = 0; i < data.length; i++) {  
542.                                 var employeeId = data[i].employeeId;  
543.                                 var lastName = data[i].lastName;  
544.                                 $("#employee").append("<option value='" + employeeId + "'>" + lastName + "</option>");  
545.                             }  
546.                         }  
547.                     })  
548.                 }  
549.             })  
550.     
551.             $("#employee").change(function () {  
552.                 var url = "${pageContext.request.contextPath}/showEmployee.do";  
553. //                获取选中的 value 值，departmentId  
554.                 var val = $(this).val();  
555.                 if (val != "choose") {  
556.                     var args = {"time": new Date, "value": val};  
557.                     $.getJSON(url, args, function (data) {  
558.                         var employeeId = data.employeeId;  
559.                         var lastName = data.lastName;  
560.                         var email = data.email;  
561. //                        如果所选择的为 employees 而不是第一行，那么就将表格显示，并加入数据  
562.                         $("#table").show();  
563.                         $("#employeeId").text(employeeId);  
564.                         $("#lastName").text(lastName);  
565.                         $("#email").text(email);  
566.                     })  
567.                 } else {  
568. //                    若选择的不是 employees 则将其隐藏  
569.                     $("#table").hide();  
570.                 }  
571.             })  
572.         })  
573.     </script>  
574. </head>  
575. <body>  
576. <spac>City:  </spac>  
577. <select name="citySelect" id="city">  
578.     <option value="choose">请选择</option>  
579.     <c:forEach items="${requestScope.locations}" var="location">  
580.         <option value="${location.locationId}">${location.city}</option>  
581.     </c:forEach>  
582. </select>  
583. <span>        </span>  
584. <span>Department:  </span>  
585.     
586. <select name="departmentSelect" id="department">  
587.     <option value="choose">请选择</option>  
588. </select>  
589. <span>        </span>  
590. <span>Employee:  </span>  
591.     
592. <select name="employeeSelect" id="employee">  
593.     <option value="choose">请选择</option>  
594. </select>  
595. /*  
596.   将 employees 的详细信息打印在此表格中  
597. */  
598. <table cellspacing="0" border="1" cellpadding="10" id="table">  
599.     <tr>  
600.         <th>employeeId</th>  
601.         <th>lastName</th>  
602.         <th>email</th>  
603.     </tr>  
604.     <tr>  
605.         <td id="employeeId"></td>  
606.         <td id="lastName"></td>  
607.         <td id="email"></td>  
608.     </tr>  
609. </table>  
610. </body>  
611. </html>  

      

     ShowInfoServlet.java

612. package com.javaweb.userajax.serlet.list.show.servlet;  
613.     
614. import com.fasterxml.jackson.databind.ObjectMapper;  
615. import com.javaweb.userajax.serlet.list.show.dao.DepartmentsDao;  
616. import com.javaweb.userajax.serlet.list.show.dao.EmployeesDao;  
617. import com.javaweb.userajax.serlet.list.show.dao.LocationsDao;  
618. import com.javaweb.userajax.serlet.list.show.daoimpl.DepartmentsImpl;  
619. import com.javaweb.userajax.serlet.list.show.daoimpl.EmployessDaoImpl;  
620. import com.javaweb.userajax.serlet.list.show.daoimpl.LocationsDaoImpl;  
621. import com.javaweb.userajax.serlet.list.show.domain.Departments;  
622. import com.javaweb.userajax.serlet.list.show.domain.Employees;  
623. import com.javaweb.userajax.serlet.list.show.domain.Locations;  
624.     
625. import javax.servlet.ServletException;  
626. import javax.servlet.http.HttpServlet;  
627. import javax.servlet.http.HttpServletRequest;  
628. import javax.servlet.http.HttpServletResponse;  
629. import java.io.IOException;  
630. import java.lang.reflect.InvocationTargetException;  
631. import java.lang.reflect.Method;  
632. import java.util.List;  
633.     
634. /** 
635.  * Created by shkstart on 2017/12/06. 
636.  */  
637. public class ShowInfoServlet extends HttpServlet {  
638. //    获取请求的参数，利用反射执行当前类中对应的方法  
639.     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {  
640.         String servletPath = request.getServletPath();  
641.         String methodName = servletPath.substring(1, servletPath.length() - 3);  
642.         try {  
643.             Method method = getClass().getDeclaredMethod(methodName, HttpServletRequest.class, HttpServletResponse.class);  
644.             method.invoke(this, request, response);  
645.         } catch (NoSuchMethodException e) {  
646.             e.printStackTrace();  
647.         } catch (IllegalAccessException e) {  
648.             e.printStackTrace();  
649.         } catch (InvocationTargetException e) {  
650.             e.printStackTrace();  
651.         }  
652.     }  
653.     
654.     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {  
655.         doPost(request, response);  
656.     }  
657.     protected void getCity(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {  
658.         LocationsDao locationsDao = new LocationsDaoImpl();  
659.         List<Locations> locationsList = locationsDao.getAll();  
660.         request.setAttribute("locations", locationsList);  
661.         request.getRequestDispatcher("/selectList/selectList.jsp").forward(request, response);  
662.     }  
663.     protected void getDepartment(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {  
664.         Integer locationId = Integer.valueOf(request.getParameter("value"));  
665.         DepartmentsDao departmentsDao = new DepartmentsImpl();  
666.     
667.         List<Departments> departmentsList = departmentsDao.getAll(locationId);  
668.         ObjectMapper mapper = new ObjectMapper();  
669.         String result = mapper.writeValueAsString(departmentsList);  
670.     
671.         response.setContentType("text/javascript");  
672.         response.getWriter().print(result);  
673.     }  
674.     protected void getEmployee(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {  
675.         Integer departmentId = Integer.valueOf(request.getParameter("value"));  
676.         EmployeesDao departmentsDao = new EmployessDaoImpl();  
677.     
678.         List<Employees> employeesList = departmentsDao.getAll(departmentId);  
679.         ObjectMapper mapper = new ObjectMapper();  
680.         String result = mapper.writeValueAsString(employeesList);  
681.     
682.         response.setContentType("text/javascript");  
683.         response.getWriter().print(result);  
684.     }  
685.     
686.     protected void showEmployee(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {  
687.         Integer employeeId = Integer.valueOf(request.getParameter("value"));  
688.         EmployeesDao employeesDao = new EmployessDaoImpl();  
689.         Employees employees = employeesDao.getEmp(employeeId);  
690.     
691.         ObjectMapper mapper = new ObjectMapper();  
692.         String result = mapper.writeValueAsString(employees);  
693.         System.out.println(result);  
694.     
695.         response.setContentType("text/javascript");  
696.         response.getWriter().print(result);  
697.     }  
698. }  

     以上就是我这次博文的内容，如果哪位读者发现错误以及表述不正确的地方还望指出，谢谢！