Ajax Study Notes-three levels of Association

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Three entity classes

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;//...}

There is only one line of code in emplooyes. jsp under webcontent, jump to 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";List<Location>locations = new ArrayList<Location>();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();List<Department>departments = new ArrayList<Department>();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;List<Employee>employees = new ArrayList<Employee>();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 blocke.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 browser not accessible, only through servlet jump to this page

<%@ page language="java" contentType="text/html; charset=UTF-8"pageEncoding="UTF-8"%><%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%><!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
 
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Ajax Study Notes-three levels of Association