Department.java

package test.combobox;
 
import java.util.ArrayList;
 
public class Department {
  private int id;
  private String name;
  public ArrayList<Employee> list;
 
  public Department(){
    list=new ArrayList<Employee> ();
  }
  public ArrayList<Employee> getEmployees() {
    return list;
  }
  public void addEmployees(Employee emp) {
    this.list.add(emp);
  }
  public void removeEmployees(Employee emp) {
    this.list.remove(emp);
  }
  public int getId() {
    return id;
  }
  public void setId(int id) {
    this.id = id;
  }
  public String getName() {
    return name;
  }
  public void setName(String name) {
    this.name = name;
  }
}

DepartmentDao

package test.combobox;
 
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
 
public class DepartmentDao {
  public List<Department> getDepartments() {
    HashMap<Integer, Department> depMap = new HashMap<Integer, Department>(); // 待回傳部門LIST
    
    String url = "jdbc:mysql://localhost:3306/test"; // 依環境變動
    try {
      Class.forName("com.mysql.jdbc.Driver");
      Connection conn = DriverManager.getConnection(url,"userid","passwd");
      Statement stDep = conn.createStatement();
 
      // loop1 SEARCH 部門資料
      ResultSet rsDep = stDep.executeQuery("Select id , name From dep");
 
      // 先撈部門再撈員工，避免過多的sql query，反正橫豎都是要建map。
      while (rsDep.next()) {
        Department depbean = new Department();
        depbean.setId(rsDep.getInt("id"));
        depbean.setName(rsDep.getString("name"));
        // 加入 BEAN 物件至 DepList
        depMap.put(depbean.getId(), depbean);
      }
 
      // 用完養成好習慣順手close
      rsDep.close();
 
      
      // loop1 SEARCH 員工資料 如果說要查詢的部門只有一部分的話，
      // 也可以把前一個map的key兜過來寫sql，但在這裡我先不考慮這個。      
      Statement stEmp = conn.createStatement();
      ResultSet rsEmp = stEmp.executeQuery("Select id , name,depId From emp ");
 
      while (rsEmp.next()) {
        Employee empBean = new Employee();
        empBean.setId(rsEmp.getString("id"));
        empBean.setName(rsEmp.getString("name"));
        // 加入 BEAN 物件至 DepList
        if (depMap.containsKey(rsEmp.getInt("depId"))) {
          Department depart = (Department) depMap.get(rsEmp.getInt("depId"));
          depart.addEmployees(empBean);
        }
      }
 
      // 用完養成好習慣順手close
      rsEmp.close();
      conn.close();
 
      return new ArrayList<Department>(depMap.values());
    } catch (Exception ex) {
      ex.printStackTrace();
      return null;
    }
 
  }
 
}

Employee.java

package test.combobox;
 
public class Employee {
 
  private String id;
 
  private String name;
 
  public String getId() {
    return id;
  }
 
  public void setId(String id) {
    this.id = id;
  }
 
  public String getName() {
    return name;
  }
 
  public void setName(String name) {
    this.name = name;
  }
 
}