Java中List转List树的通用解决方法~

首先是父接口，想要用这个通用List树生成的话就必须实现这个接口

import java.util.List;

/**
 * @author Mu
 *
 */
public interface TreeRootAndAutoid {
	/**
	 * 获取父节点号和自己的节点号
	 */
	Integer getParentid();

	/**
	 * 
	 * @return
	 */
	Integer getAutoid();
	/**
	 * 获取孩子树
	 * @return
	 */
	List<TreeRootAndAutoid> getTreeChildren();

	/**
	 * 设置孩子树
	 * @param list
	 */
	void setTreeChildren(List<TreeRootAndAutoid> list);
}

接下来时Model,主要实现了接口的四个方法

package com.gszh.wmcp.project.distribution.model;

import java.util.Date;
import java.util.List;

import com.gszh.wmcp.project.distribution.util.TreeRootAndAutoid;

public class DevSysMenu  implements TreeRootAndAutoid{
    private Integer autoid;

    private Integer parentid;

    private List<TreeRootAndAutoid> children; 

	public Integer getAutoid() {
        return autoid;
    }

    public Integer getParentid() {
        return parentid;
    }

	@Override
	public  List<TreeRootAndAutoid> getTreeChildren() {
		// TODO Auto-generated method stub
		return this.children;
	}

	@Override
	public void setTreeChildren(List<TreeRootAndAutoid> list) {
		this.children=list;

	}




}

最后，就是通用的List生成树工具类了

/**
<span style="white-space:pre">	</span> * 对List中的元素根据父节点Id进行分类
<span style="white-space:pre">	</span> * @param u
<span style="white-space:pre">	</span> * @param rootId
<span style="white-space:pre">	</span> * @return
<span style="white-space:pre">	</span> */
<span style="white-space:pre">	</span>public static Map<Integer, List<TreeRootAndAutoid>> groupListByParentId(List<? extends TreeRootAndAutoid> u){
<span style="white-space:pre">		</span>//定义一个map集合用于分组
<span style="white-space:pre">		</span>  Map<Integer, List<TreeRootAndAutoid>> mapList = new HashMap<Integer, List<TreeRootAndAutoid>>();
<span style="white-space:pre">		</span>//主要是把父亲节点相同的每个数据进行分组。然后存放到以父亲节点为Key，List<T>为value的Map中<span style="white-space:pre">		</span>  
<span style="white-space:pre">		</span>  for (int i=0; i<u.size(); i++) 
<span style="white-space:pre">		</span>  {
<span style="white-space:pre">			</span>   //将循环读取的结果放入对象中
<span style="white-space:pre">			</span>  TreeRootAndAutoid TreeRootAndAutoid =u.get(i);
<span style="white-space:pre">			</span>  
<span style="white-space:pre">			</span>   //如果在这个map中包含有相同的键，这创建一个集合将其存起来
<span style="white-space:pre">			</span>   if (mapList.containsKey(TreeRootAndAutoid.getParentid())) 
<span style="white-space:pre">			</span>   {
<span style="white-space:pre">				</span>    List<TreeRootAndAutoid> syn = mapList.get(TreeRootAndAutoid.getParentid());
<span style="white-space:pre">				</span>    syn.add(TreeRootAndAutoid);
<span style="white-space:pre">				</span>    mapList.put(TreeRootAndAutoid.getParentid(), syn);
<span style="white-space:pre">			</span>   //如果没有包含相同的键，在创建一个集合保存数据
<span style="white-space:pre">			</span>   } else {
<span style="white-space:pre">				</span>   List<TreeRootAndAutoid> treeRootAndAutoids = new ArrayList<TreeRootAndAutoid>();
<span style="white-space:pre">				</span>   treeRootAndAutoids.add(TreeRootAndAutoid);
<span style="white-space:pre">				</span>   mapList.put(TreeRootAndAutoid.getParentid(), treeRootAndAutoids);
<span style="white-space:pre">			</span>   }
<span style="white-space:pre">		</span>   }
<span style="white-space:pre">		</span>  
<span style="white-space:pre">		</span>  return mapList;
<span style="white-space:pre">	</span>}
<span style="white-space:pre">	</span>
<span style="white-space:pre">	</span>/**
<span style="white-space:pre">	</span> * 根据List创建List树
<span style="white-space:pre">	</span> * @param u
<span style="white-space:pre">	</span> * @param rootId
<span style="white-space:pre">	</span> * @throws ClassNotFoundException 
<span style="white-space:pre">	</span> * @throws IllegalAccessException 
<span style="white-space:pre">	</span> * @throws InstantiationException 
<span style="white-space:pre">	</span> */
<span style="white-space:pre">	</span>public static List<TreeRootAndAutoid> buildListTree(List<? extends TreeRootAndAutoid> u,Integer rootId,String className) throws InstantiationException, IllegalAccessException, ClassNotFoundException {
<span style="white-space:pre">		</span>return buildTree(groupListByParentId(u), rootId,className);
<span style="white-space:pre">	</span>}


<span style="white-space:pre">	</span>/**
<span style="white-space:pre">	</span> * 根据已经分组好的List和rootId来创建List树
<span style="white-space:pre">	</span> * 
<span style="white-space:pre">	</span> * @param groupListByParentId
<span style="white-space:pre">	</span> * @param rootId
<span style="white-space:pre">	</span> */


<span style="white-space:pre">	</span>static boolean mark = false;


<span style="white-space:pre">	</span>private static List<TreeRootAndAutoid> buildTree(Map<Integer, List<TreeRootAndAutoid>> mapList, Integer rootId,String className) throws InstantiationException, IllegalAccessException, ClassNotFoundException {
<span style="white-space:pre">		</span>
<span style="white-space:pre">		</span>// 遍历map集合，取出根节点,这里的rootId,是指最顶层节点的父节点,不管最顶层的节点是一个还是多个
<span style="white-space:pre">		</span>List<TreeRootAndAutoid> rootList = new ArrayList<TreeRootAndAutoid>();
<span style="white-space:pre">		</span>for (Map.Entry<Integer, List<TreeRootAndAutoid>> TempMap : mapList.entrySet()) {
<span style="white-space:pre">			</span>rootList = TempMap.getValue();
<span style="white-space:pre">			</span>if (rootList.get(0).getParentid().equals(rootId) ) {
<span style="white-space:pre">				</span>mapList.remove(rootId);
<span style="white-space:pre">				</span>break;
<span style="white-space:pre">				</span>
<span style="white-space:pre">			</span>}
<span style="white-space:pre">		</span>}
<span style="white-space:pre">		</span>
<span style="white-space:pre">		</span>Integer initSize=mapList.size();
<span style="white-space:pre">		</span>// keyList，主要用来记录找到了父亲节点的子树父亲节点ID，然后在Map中删除这些List<T>，
<span style="white-space:pre">		</span>List<Integer> keyList = new ArrayList<Integer>();
<span style="white-space:pre">		</span>// 遍历Map，由于遍历一次不一定可以全部找到字树父亲节点，所有有了上面的While循环，和KeyList.
<span style="white-space:pre">		</span>// 每当遍历一次，KeyList就记录那些找到了父亲节点的子树List<T>
<span style="white-space:pre">		</span>// 在每次遍历完成之后，通过KeyList去删除Map中对应的value（这么做的原因是因为在Map迭代的时候不允许修改其自身）
<span style="white-space:pre">		</span>while (mapList.size() != 0) {
<span style="white-space:pre">			</span>Integer size=mapList.size();
<span style="white-space:pre">			</span>for (Map.Entry<Integer, List<TreeRootAndAutoid>> firtMap : mapList.entrySet()) {
<span style="white-space:pre">				</span>// secList，一个等待挂载到父亲节点下的子树
<span style="white-space:pre">				</span>List<TreeRootAndAutoid> secList = firtMap.getValue();
<span style="white-space:pre">				</span>// 深度优先遍历
<span style="white-space:pre">				</span>for (int i = 0; i < rootList.size(); i++) {
<span style="white-space:pre">					</span>recursiveTree(rootList, secList);
<span style="white-space:pre">					</span>if (mark == true) {
<span style="white-space:pre">						</span>mark = false;
<span style="white-space:pre">						</span>keyList.add(secList.get(0).getParentid());
<span style="white-space:pre">						</span>break;
<span style="white-space:pre">					</span>}
<span style="white-space:pre">				</span>}
<span style="white-space:pre">			</span>}
<span style="white-space:pre">			</span>// 这里是删除Map中已经挂载成功的子树
<span style="white-space:pre">			</span>for (int i = 0; i < keyList.size(); i++) {
<span style="white-space:pre">				</span>mapList.remove(keyList.get(i));
<span style="white-space:pre">			</span>}
<span style="white-space:pre">			</span>//这个判断，主要用于判断根节点的父节点Id是否输入正确。如果不正确，在遍历一遍后，mapList的长度还是会和最初的长度一样
<span style="white-space:pre">			</span>if(initSize.equals(mapList.size())){
<span style="white-space:pre">				</span>throw new RuntimeException("根节点的父节点输入错误");
<span style="white-space:pre">			</span>}
<span style="white-space:pre">			</span>//讲道理，在上面这些代码执行完之后，如果mapList.size()还是和之前一样，就证明已经迭代完毕，剩下的，都是一些找不到父节点的子树
<span style="white-space:pre">			</span>if(size.equals(mapList.size())){
<span style="white-space:pre">				</span>for (Map.Entry<Integer, List<TreeRootAndAutoid>> firtMap : mapList.entrySet()) {
<span style="white-space:pre">					</span>// secList，一个等待挂载到父亲节点下的子树
<span style="white-space:pre">					</span>List<TreeRootAndAutoid> secList = firtMap.getValue();
<span style="white-space:pre">					</span>//首先，创建一个节点
<span style="white-space:pre">					</span>TreeRootAndAutoid newNode=(TreeRootAndAutoid)Class.forName(className).newInstance();
<span style="white-space:pre">					</span>//设置这个节点的名称，并把这个子树挂载到这个节点下
<span style="white-space:pre">					</span>newNode.SetNodeName("无区域-节点"+secList.get(0).getParentid());
<span style="white-space:pre">					</span>newNode.setTreeChildren(secList);
<span style="white-space:pre">					</span>
<span style="white-space:pre">					</span>rootList.get(0).getTreeChildren().add(newNode);
<span style="white-space:pre">				</span>}
<span style="white-space:pre">				</span>break;
<span style="white-space:pre">			</span>}


<span style="white-space:pre">		</span>}


<span style="white-space:pre">		</span>return rootList;


<span style="white-space:pre">	</span>}
<span style="white-space:pre">	</span>
<span style="white-space:pre">	</span>
<span style="white-space:pre">	</span>/**
<span style="white-space:pre">	</span> * 传递进来一个子树，一个待挂载的子树
<span style="white-space:pre">	</span> * 递归子树，直到挂载成功，或者，递归完毕。
<span style="white-space:pre">	</span> * @param list
<span style="white-space:pre">	</span> * @param chirldrenTree
<span style="white-space:pre">	</span> * @return
<span style="white-space:pre">	</span> */
<span style="white-space:pre">	</span>public static List<TreeRootAndAutoid> recursiveTree(List<TreeRootAndAutoid> list, List<TreeRootAndAutoid> chirldrenTree) {


<span style="white-space:pre">		</span>for (int i = 0; i < list.size(); i++) {
<span style="white-space:pre">			</span>if (list.get(i).getNodeAutoid() != null) {
<span style="white-space:pre">				</span>if (list.get(i).getNodeAutoid().equals(chirldrenTree.get(0).getParentid())) {
<span style="white-space:pre">					</span>list.get(i).setTreeChildren(chirldrenTree);
<span style="white-space:pre">					</span>mark = true;
<span style="white-space:pre">					</span>return list;
<span style="white-space:pre">				</span>} else if (list.get(i).getTreeChildren() != null) {
<span style="white-space:pre">					</span>list.get(i).setTreeChildren(
<span style="white-space:pre">							</span>recursiveTree(list.get(i).getTreeChildren(),
<span style="white-space:pre">									</span>chirldrenTree));
<span style="white-space:pre">				</span>}
<span style="white-space:pre">			</span>}
<span style="white-space:pre">		</span>}
<span style="white-space:pre">		</span>return list;
<span style="white-space:pre">	</span>}