import java.util.List;

/**
 * 节点类继承接口，节点类必须继承此类
 * 
 */
public interface Treeable<T> {

    /**
     * 获取存入map key
     * @return
     */
    Object getMapKey();

    /**
     * 获取孩子节点的key值
     * @return
     */
    Object getChildrenKey();

    /**
     * 根节点key值
     * @return
     */
    Object getRootKey();

    /**
     * 子节点赋值
     * @param children
     */
    void setChildren(List<T> children);

}


/**
* ListToTree 一个函数式接口
*/
import java.util.List;

public interface ListToTree<T extends Treeable> {
	
	/**
	 * list转化tree结构
	 */
    List<T> toTree(List<T> list);

}


import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * 
 */
public class ListToTreeImpl implements ListToTree {

    @Override
    public List toTree(List list) {
        // TODO list 空判断，做处理
        Map<Object, List> map = new HashMap<Object, List>();
        Object rootKye = null;
        for(Object o : list) {
            Treeable t = (Treeable) o;
            Object key = t.getMapKey();
            if(map.containsKey(key)) {
                map.get(key).add(o);
            } else {
                List mapValue = new ArrayList();
                mapValue.add(o);
                map.put(key, mapValue);
            }
            // 获取根节点key值
            if(rootKye == null) {
                rootKye = t.getRootKey();
            }
        }
        List tree = map.get(rootKye);
        recursionToTree(tree, map);
        return tree;
    }

    private void recursionToTree(List list, Map<Object, List> map){
        // TODO list 空判断，做处理
        for(Object o : list){
            Treeable t = (Treeable) o;
            Object key = t.getChildrenKey();
            if(map.containsKey(key)) {
                List children = map.get(key);
                t.setChildren(children);
                recursionToTree(children, map);
            }
        }
    }

}









import lombok.Data;

import java.util.List;

/**
 * 
 */
@Data
public class TreeNode implements Treeable {
    private Integer id;
    private Integer pid;
    private String name;
    private List<TreeNode> children;

    public TreeNode() {
    }

    public TreeNode(Integer id, Integer pid, String name) {
        this.id = id;
        this.pid = pid;
        this.name = name;
    }

    @Override
    public Integer getMapKey() {
        return pid;
    }

    @Override
    public Integer getChildrenKey() {
        return id;
    }

    @Override
    public Integer getRootKey() {
        return 0;
    }

    @Override
    public void setChildren(List children) {
        this.children = children;
    }
}






import java.util.ArrayList;
import java.util.List;

/**
 * 
 */
public class Demo {

    public static void main(String[] args) {
        /**
         * 初始化一个list数据，pid=0为根节点
         */
        List<TreeNode> list = new ArrayList<TreeNode>();
        list.add(new TreeNode(1, 0, "1"));
        list.add(new TreeNode(2, 0, "2"));
        list.add(new TreeNode(3, 2, "3"));
        list.add(new TreeNode(4, 3, "4"));
        list.add(new TreeNode(5, 4, "5"));
        list.add(new TreeNode(6, 5, "6"));

        ListToTree treeBuilder = new ListToTreeImpl();
        List<TreeNode> tree = treeBuilder.toTree(list);
        System.out.println(tree);
    }

}