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三个实体类

Location.java

public class Location {
	private Integer location_id;
	private String city;
	//...
}

Department.java

public class Department {
	private Integer department_id;
	private String departmentName;
	private Integer location_id;
	//...
}

Employee.java

public class Employee {
	private Integer employeeId;
	private String lastName;
	private String email;
	private double salary;
	private Integer department_id;
	//...
}

WebContent下的emplooyes.jsp中只有一行代码，跳转到servlet

<%
	response.sendRedirect("EmployeeServlet?method=listLocations");
%>

EmployeeServlet.java

public class EmployeeServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		String methodName = request.getParameter("method");
		try {
			Method method = getClass().getDeclaredMethod(methodName, HttpServletRequest.class, HttpServletResponse.class);
			method.invoke(this, request, response);
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
	
	
	protected void listLocations(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		Connection connection = DBManager.getConnection();
		String sql = "select * from location";
		Listlocations = new ArrayList();
		Statement statement = null;
		ResultSet resultSet = null;
		Location location = null;
		try {
			statement = connection.createStatement();
			resultSet = statement.executeQuery(sql);
			while(resultSet.next()){
				location = new Location();
				location.setCity(resultSet.getString("city"));
				location.setLocation_id(resultSet.getInt("location_id"));
				locations.add(location);
			}
		} catch (SQLException e) {
			e.printStackTrace();
		}finally{
			DBManager.close(resultSet, statement, connection);
		}
		request.setAttribute("locations", locations);
		request.getRequestDispatcher("/WEB-INF/pages/employees.jsp").forward(request, response);
	}
	
	protected void listDepartments(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {
		int locationId = Integer.parseInt(request.getParameter("locationId"));
		String sql = "select * from department where location_id = " + locationId;
		Connection connection = DBManager.getConnection();
		Listdepartments = new ArrayList();
		Department department = null;
		ResultSet resultSet = null;
		Statement statement = null;
		try {
			statement = connection.createStatement();
			resultSet = statement.executeQuery(sql);
			while(resultSet.next()){
				department = new Department();
				department.setDepartmentName(resultSet.getString("departmentName"));
				department.setDepartment_id(resultSet.getInt("department_id"));
				department.setLocation_id(resultSet.getInt("location_id"));
				departments.add(department);
			}
		} catch (SQLException e) {
			e.printStackTrace();
		}finally{
			DBManager.close(resultSet, statement, connection);
		}
		ObjectMapper mapper = new ObjectMapper();
		String result = mapper.writeValueAsString(departments);
		System.out.println(result);
		response.setContentType("text/javascript");
		response.setCharacterEncoding("UTF-8");
		response.getWriter().print(result);
	}
	
	protected void listEmployees(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {
		int department_id = Integer.parseInt(request.getParameter("department_id"));
		String sql = "select * from employee where department_id = " + department_id;
		Connection connection = DBManager.getConnection();
		Statement statement = null;
		ResultSet resultSet = null;
		Listemployees = new ArrayList();
		Employee employee = null;
		try {
			statement = connection.createStatement();
			resultSet = statement.executeQuery(sql);
			while(resultSet.next()){
				employee = new Employee();
				employee.setDepartment_id(resultSet.getInt("department_id"));
				employee.setEmail(resultSet.getString("email"));
				employee.setEmployeeId(resultSet.getInt("employee_id"));
				employee.setLastName(resultSet.getString("last_name"));
				employee.setSalary(resultSet.getDouble("salary"));
				employees.add(employee);
			}
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}finally{
			DBManager.close(resultSet, statement, connection);
		}
		ObjectMapper mapper = new ObjectMapper();
		String result = mapper.writeValueAsString(employees);
		System.out.println(result);
		response.setContentType("text/javascript");
		response.setCharacterEncoding("UTF-8");
		response.getWriter().print(result);
	}
	
	protected void listEmployeeInfo(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {
		int employeeId = Integer.parseInt(request.getParameter("employeeId"));
		String sql = "select * from employee where employee_id = " + employeeId;
		System.err.println(sql);
		Connection connection = DBManager.getConnection();
		Statement statement = null;
		ResultSet resultSet = null;
		Employee employee = null;
		try {
			statement = connection.createStatement();
			resultSet = statement.executeQuery(sql);
			if (resultSet.next()) {
				employee = new Employee();
				employee.setDepartment_id(resultSet.getInt("department_id"));
				employee.setEmail(resultSet.getString("email"));
				employee.setEmployeeId(resultSet.getInt("employee_id"));
				employee.setLastName(resultSet.getString("last_name"));
				employee.setSalary(resultSet.getDouble("salary"));
			}
		}catch(Exception e){
			e.printStackTrace();
		}finally{
			DBManager.close(resultSet, statement, connection);
		}
		ObjectMapper mapper = new ObjectMapper();
		String result = mapper.writeValueAsString(employee);
		System.out.println(result);
		response.setContentType("text/javascript");
		response.setCharacterEncoding("UTF-8");
		response.getWriter().print(result);
	}
	
	public static void main(String[] args) {
		System.out.println(DBManager.getConnection());
	}
}

/WEB-INF/pages/employees.jsp浏览器不可达，只能通过servlet跳转到该页面

<%@ page language="java" contentType="text/html; charset=UTF-8"
	pageEncoding="UTF-8"%>
<%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>








	$(function(){
		$(document).ajaxStart(function(){
			//使用blockUI。ajax请求发出时执行
			$.blockUI({
			message:$('#loading'),
			css:{
				top:($(window).height() - 400)/2 + 'px',
				left:($(window).width() - 400)/2 + 'px',
				width:'400px'
			},
			overlayCSS:{backgroundColor:'#00f'}
			})
		}).ajaxStop($.unblockUI);
		
		
		$("#city").change(function(){
			$("#department option:not(:first)").remove();
			var location_id = $(this).val();
			if(location_id != ""){
				var url = "EmployeeServlet?method=listDepartments";
				var args = {"locationId":location_id, "time":new Date()};
				
				$.getJSON(url, args, function(data){
					if(data.length == 0){
						alert("当前城市没有部门");
					}else{
						for(var i = 0; i < data.length; i++){
							var deptName = data[i].departmentName;
							var deptId = data[i].department_id;
							//alert(deptName);
							$("#department").append(""+deptName+"");
						}
					}
				});
			}
		});
		$("#department").change(function(){
			$("#employee option:not(:first)").remove();
			var department_id = $(this).val();
			if(department_id != ""){
				var url = "EmployeeServlet?method=listEmployees";
				var args = {"department_id":department_id, "time":new Date()};
				$.getJSON(url, args, function(data){
					if(data.length == 0){
						alert("当前部门没有员工");
					}else{
						for(var i = 0; i < data.length; i ++){
							var lastName = data[i].lastName;
							var email = data[i].email;
							var salary = data[i].salary;
							var employeeId = data[i].employeeId;
							$("#employee").append(""+lastName+"");
						}
					}
				});
			}
		});
		$("#employee").change(function(){
			var employeeId = $(this).val();
			if(employeeId != ""){
				var url = "EmployeeServlet?method=listEmployeeInfo";
				var args = {"employeeId":employeeId, "time":new Date()};
				$.getJSON(url, args, function(data){
					if(data.length == 0){
						alert("数据丢失");
					}else{
						$("#employee_id").text(data.employeeId);
						$("#last_name").text(data.lastName);
						$("#email").text(data.email);
						$("#salary").text(data.salary);
					}
				});
			}
			//}
		});
	})



	
	City:
	
		请选择...
		
			${location.city}
		
	 Department:
	
		请选择...
	 Employee:
	
		请选择...

	
	 员工编号:
	
	 姓名：
	
	 email：
	
	 薪水：
	
	

源码 http://yunpan.cn/cgephkTV2Tcmh （提取码：2492）

文章题目：Ajax学习笔记-三级联动
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