MySQL樹形遍歷(四)--程式碼優化

壹頁書發表於2015-12-07
MySql優化
MySQL樹形遍歷(三) 
http://blog.itpub.net/29254281/viewspace-1867455/

這個程式實際上在模擬之前的那個SQL寫法.
http://blog.itpub.net/29254281/viewspace-1851457/

但是實際上,使用遞迴造成了很多無效的重複的計算.
其實一個迴圈遍歷,就搞定了.

  1. import java.sql.Connection;
  2. import java.sql.DriverManager;
  3. import java.sql.ResultSet;
  4. import java.sql.SQLException;
  5. import java.util.ArrayList;
  6. import java.util.Collections;
  7. import java.util.HashMap;
  8. import java.util.List;
  9. import java.util.Map;

  11. public class TreeScan {
  12.     private static String URL = "jdbc:mysql://127.0.0.1:3306/mvbox";
  13.     private static String USERNAME = "xx";
  14.     private static String PWD = "xx";

  16.     public static void main(String[] args) throws ClassNotFoundException, SQLException, CloneNotSupportedException {
  17.         Map<Integer, Employee> map = new HashMap<Integer, Employee>();
  18.         Class.forName("com.mysql.jdbc.Driver");
  19.         Connection con = DriverManager.getConnection(URL, USERNAME, PWD);
  20.         ResultSet rs = con.createStatement().executeQuery("select employee_id,manager_id from employees");
  21.         while (rs.next()) {
  22.             Employee e = new Employee();
  23.             e.setEmployeeId(rs.getInt("employee_id"));
  24.             e.setManagerId(rs.getInt("manager_id"));
  25.             map.put(e.getEmployeeId(), e);
  26.         }
  27.         rs.close();
  28.         con.close();

  30.         // 組合節點
  31.         treeScan(map);

  33.         System.out.println("自頂向下訪問:");
  34.         printEmployee(getRoot(map));

  36.         System.out.println("自底向上訪問:");
  37.         List<Employee> list = new ArrayList<Employee>(map.values());
  38.         Collections.sort(list);
  39.         for (Employee ee : list) {
  40.             System.out.println(ee.toString());
  41.         }

  43.     }

  45.     private static void printEmployee(Employee e) {
  46.         System.out.println(e.toString());
  47.         Collections.sort(e.getChildren());
  48.         for (Employee child : e.getChildren()) {
  49.             printEmployee(child);
  50.         }
  51.     }

  53.     private static Employee getRoot(Map<Integer, Employee> map) {
  54.         Employee e = map.values().iterator().next();
  55.         while (e.getManager() != null) {
  56.             e = e.getManager();
  57.         }
  58.         return e;
  59.     }

  61.     private static void treeScan(Map<Integer, Employee> map) {
  62.         for (Employee e : map.values()) {
  63.             findManager(map, e);
  64.         }
  65.     }

  67.     private static Employee findManager(Map<Integer, Employee> map, Employee e) {
  68.         Employee manager = map.get(e.getManagerId());
  69.         e.setManager(manager);
  70.         if (manager != null)
  71.             manager.getChildren().add(e);
  72.         return manager;
  73.     }

  75. }

  77. class Employee implements Comparable<Employee> {
  78.     private Integer employeeId = null;
  79.     private Integer managerId = null;
  80.     private Employee manager = null;
  81.     private List<Employee> children = new ArrayList<Employee>();

  83.     public List<Employee> getChildren() {
  84.         return children;
  85.     }

  87.     public void setChildren(List<Employee> children) {
  88.         this.children = children;
  89.     }

  91.     public Integer getEmployeeId() {
  92.         return employeeId;
  93.     }

  95.     public void setEmployeeId(Integer employeeId) {
  96.         this.employeeId = employeeId;
  97.     }

  99.     public Integer getManagerId() {
  100.         return managerId;
  101.     }

  103.     public void setManagerId(Integer managerId) {
  104.         this.managerId = managerId;
  105.     }

  107.     public Employee getManager() {
  108.         return manager;
  109.     }

  111.     public void setManager(Employee manager) {
  112.         this.manager = manager;
  113.     }

  115.     @Override
  116.     public int hashCode() {
  117.         final int prime = 31;
  118.         int result = 1;
  119.         result = prime * result + ((employeeId == null) ? 0 : employeeId.hashCode());
  120.         return result;
  121.     }

  123.     @Override
  124.     public boolean equals(Object obj) {
  125.         if (this == obj)
  126.             return true;
  127.         if (obj == null)
  128.             return false;
  129.         if (getClass() != obj.getClass())
  130.             return false;
  131.         Employee other = (Employee) obj;
  132.         if (employeeId == null) {
  133.             if (other.employeeId != null)
  134.                 return false;
  135.         } else if (!employeeId.equals(other.employeeId))
  136.             return false;
  137.         return true;
  138.     }

  140.     public String toString() {
  141.         if (this.manager != null) {

  143.             return this.manager.toString() + "/" + this.getEmployeeId();
  144.         }
  145.         return this.getEmployeeId().toString();
  146.     }

  148.     @Override
  149.     public int compareTo(Employee o) {
  150.         return this.toString().compareTo(o.toString());
  151.     }
  152. }

來自 “ ITPUB部落格 ” ，連結：http://blog.itpub.net/29254281/viewspace-1867759/，如需轉載，請註明出處，否則將追究法律責任。

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