MySQL树形遍历(三)
http://blog.itpub.net/29254281/viewspace-1867455/

这个程序实际上在模拟之前的那个SQL写法.
http://blog.itpub.net/29254281/viewspace-1851457/

但是实际上,使用递归造成了很多无效的重复的计算.
其实一个循环遍历,就搞定了.

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
public class TreeScan {
private static String URL = "jdbc:mysql://127.0.0.1:3306/mvbox";
private static String USERNAME = "xx";
private static String PWD = "xx";
public static void main(String[] args) throws ClassNotFoundException, SQLException, CloneNotSupportedException {
Map<Integer, Employee> map = new HashMap<Integer, Employee>();
Class.forName("com.mysql.jdbc.Driver");
Connection con = DriverManager.getConnection(URL, USERNAME, PWD);
ResultSet rs = con.createStatement().executeQuery("select employee_id,manager_id from employees");
while (rs.next()) {
Employee e = new Employee();
e.setEmployeeId(rs.getInt("employee_id"));
e.setManagerId(rs.getInt("manager_id"));
map.put(e.getEmployeeId(), e);
}
rs.close();
con.close();
// 组合节点
treeScan(map);
System.out.println("自顶向下访问:");
printEmployee(getRoot(map));
System.out.println("自底向上访问:");
List<Employee> list = new ArrayList<Employee>(map.values());
Collections.sort(list);
for (Employee ee : list) {
System.out.println(ee.toString());
}
}
private static void printEmployee(Employee e) {
System.out.println(e.toString());
Collections.sort(e.getChildren());
for (Employee child : e.getChildren()) {
printEmployee(child);
}
}
private static Employee getRoot(Map<Integer, Employee> map) {
Employee e = map.values().iterator().next();
while (e.getManager() != null) {
e = e.getManager();
}
return e;
}
private static void treeScan(Map<Integer, Employee> map) {
for (Employee e : map.values()) {
findManager(map, e);
}
}
private static Employee findManager(Map<Integer, Employee> map, Employee e) {
Employee manager = map.get(e.getManagerId());
e.setManager(manager);
if (manager != null)
manager.getChildren().add(e);
return manager;
}
}
class Employee implements Comparable<Employee> {
private Integer employeeId = null;
private Integer managerId = null;
private Employee manager = null;
private List<Employee> children = new ArrayList<Employee>();
public List<Employee> getChildren() {
return children;
}
public void setChildren(List<Employee> children) {
this.children = children;
}
public Integer getEmployeeId() {
return employeeId;
}
public void setEmployeeId(Integer employeeId) {
this.employeeId = employeeId;
}
public Integer getManagerId() {
return managerId;
}
public void setManagerId(Integer managerId) {
this.managerId = managerId;
}
public Employee getManager() {
return manager;
}
public void setManager(Employee manager) {
this.manager = manager;
}
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + ((employeeId == null) ? 0 : employeeId.hashCode());
return result;
}
@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
Employee other = (Employee) obj;
if (employeeId == null) {
if (other.employeeId != null)
return false;
} else if (!employeeId.equals(other.employeeId))
return false;
return true;
}
public String toString() {
if (this.manager != null) {
return this.manager.toString() + "/" + this.getEmployeeId();
}
return this.getEmployeeId().toString();
}
@Override
public int compareTo(Employee o) {
return this.toString().compareTo(o.toString());
}
}

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MySQL树形遍历(四)--代码优化

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