java父子节点parentid树形结构数据规整

这几天写一个父子节点的数据规整，在网上找了一些方法，都太繁琐，自己写了一个，感觉比较简单，分享给大家

先说一下原理

第一，我们从数据库中将需要的数据查询出来，得到一个Object集合的list

第二，定义一个map，key为id，value为Object，这个的目的是为了方便后面的查找

第三，遍历第一步中查询到的数据集合list，取出Object中的parentid，根据parentid从第二步map中取出它的父节点，将其放入到父节点中去

第四，删除map中父节点parentid不为空的数据，这样我们的数据结构就组成了。

这里主要使用了java在参数传递时，如果参数是一个object时，那么它传递的是引用这么一个思想来进行实现，贴出代码供大家参考

public class Test {

	public List<Goal> test(List<Goal> listGoal) {
	
		Map<Integer, Goal> goalMap = new HashMap<Integer, Goal>();
		for (Goal g : listGoal) {
			int id = g.getId();
			goalMap.put(id, g);
		}
		for (Goal g : listGoal) {
			int pid = g.getParentId();
			if (pid != 0) {
				Goal tempGoal = goalMap.get(pid);
				List<Goal> tempListGoal = tempGoal.getListGoal();
				if (tempListGoal == null) {
					tempListGoal = new ArrayList<Goal>();
				} 
				tempListGoal.add(g);
				tempGoal.setListGoal(tempListGoal);
			}
		}
		List<Integer> list = new ArrayList<Integer>();
		for (Integer k : goalMap.keySet()) {
			Goal tempGoal = goalMap.get(k);
			if (tempGoal.getParentId() != 0) {
				list.add(k);
			}
		}
		for (int i : list) {
			goalMap.remove(i);
		}
		return new ArrayList<Goal>(goalMap.values());
	}
	
	public static void main(String[] args) {
		List<Goal> listGoal = new ArrayList<Goal>();
		Goal g1 = new Goal();
		g1.setId(1);
		g1.setParentId(0);
		g1.setGoalName("g1");
		Goal g2 = new Goal();
		g2.setId(2);
		g2.setParentId(1);
		g2.setGoalName("g2");
		Goal g3 = new Goal();
		g3.setId(3);
		g3.setParentId(2);
		g3.setGoalName("g3");
		Goal g4 = new Goal();
		g4.setId(4);
		g4.setParentId(2);
		g4.setGoalName("g4");
		Goal g5 = new Goal();
		g5.setId(5);
		g5.setParentId(3);
		g5.setGoalName("g5");
		Goal g6 = new Goal();
		g6.setId(6);
		g6.setParentId(0);
		g6.setGoalName("g6");
		Goal g7 = new Goal();
		g7.setId(7);
		g7.setParentId(3);
		g7.setGoalName("g7");
		Goal g8 = new Goal();
		g8.setId(8);
		g8.setParentId(7);
		g8.setGoalName("g8");
		Goal g9 = new Goal();
		g9.setId(9);
		g9.setParentId(7);
		g9.setGoalName("g9");
		Goal g10 = new Goal();
		g10.setId(10);
		g10.setParentId(4);
		g10.setGoalName("g10");
		Goal g11 = new Goal();
		g11.setId(11);
		g11.setParentId(10);
		g11.setGoalName("g1");
		Goal g12 = new Goal();
		g12.setId(12);
		g12.setParentId(7);
		g12.setGoalName("g12");
		Goal g13 = new Goal();
		g13.setId(13);
		g13.setParentId(0);
		g13.setGoalName("g13");
		listGoal.add(g1);
		listGoal.add(g2);
		listGoal.add(g3);
		listGoal.add(g4);
		listGoal.add(g5);
		listGoal.add(g6);
		listGoal.add(g7);
		listGoal.add(g8);
		listGoal.add(g9);
		listGoal.add(g10);
		listGoal.add(g11);
		listGoal.add(g12);
		listGoal.add(g13);
		Test t = new Test();
		List<Goal> listT = t.test(listGoal);
		System.out.println(listT);
		
		
	}