java list根据id获取子节点

工作中因业务需求，将数据库中的树状结构的数据根据父节点获取所有的子节点

实现思路

1.获取整个数据的list集合数据

2.将数据分组，java8 list有groupby分组，java8之前的自己遍历整理

3.分组后递归获取子节点，有子节点的添加，没有的设置子节点并删除分组的数据，知道分组数据删完

Tree.java

@Data
public class Tree {
    private Integer id;
    private Integer pId;
    private String key;
    private String value;
    private List<Tree> childList;
}

TreeUtils.java

public class TreeUtils {
    static List<Tree> trees ;
    static {
        String jsonStr = "[" +
                "{"id":100,"pId":1,"key":"root", "value": "root"}," +
                "{"id":1000,"pId":100,"key":"node1", "value": "node1"}," +
                "{"id":2000,"pId":100,"key":"node2","value": "node2"}," +
                "{"id":3000,"pId":100,"key":"node3","value": "node3"}," +
                "{"id":1100,"pId":1000,"key":"node11","value": "node11"}," +
                "{"id":1200,"pId":1000,"key":"node12","value": "node12"}," +
                "{"id":1110,"pId":1100,"key":"node111","value": "node111"}," +
                "{"id":1120,"pId":1100,"key":"node112","value": "node112"}," +
                "{"id":2100,"pId":2000,"key":"node21","value": "node21"}," +
                "{"id":2200,"pId":2000,"key":"node22","value": "node22"}," +
                "{"id":2110,"pId":2100,"key":"node211","value": "node21"}" +
                "]";
        trees = JSONObject.parseArray(jsonStr, Tree.class);
    }

    public static void main(String[] args) {
        Tree tree = metaTree(trees, 100);
        /**
         * Tree@6073f712[id=100,pId=1,key=root,value=root,childList=[
         *                     Tree(id=1000, pId=100, key=node1, value=node1, childList=[
         *                          Tree(id=1100, pId=1000, key=node11, value=node11, childList=[
         *                              Tree(id=1110, pId=1100, key=node111, value=node111, childList=null),
         *                              Tree(id=1120, pId=1100, key=node112, value=node112, childList=null)]),
         *                          Tree(id=1200, pId=1000, key=node12, value=node12, childList=null)]),
         *                     Tree(id=2000, pId=100, key=node2, value=node2, childList=[
         *                          Tree(id=2100, pId=2000, key=node21, value=node21, childList=[
         *                              Tree(id=2110, pId=2100, key=node211, value=node21, childList=null)]),
         *                              Tree(id=2200, pId=2000, key=node22, value=node22, childList=null)]),
         *                     Tree(id=3000, pId=100, key=node3, value=node3, childList=null)]]
         */
        System.out.println("tree:" + ToStringBuilder.reflectionToString(tree));
    }

    private static Tree metaTree(List<Tree> treeList, Integer id) {
//此处getId getPId根据自己实际情况更改
        Tree treeConfig = treeList.stream().filter(tree -> tree.getId().equals(id)).collect(Collectors.toList()).get(0);
        Map<Integer, List<Tree>> collect = treeList.stream().filter(type -> type.getPId() != null).collect(Collectors.groupingBy(Tree::getPId));
        if (collect != null && collect.size() > 0) {
            recursion(collect, treeConfig);
        }
        return treeConfig;
    }

    private static Tree recursion(Map<Integer, List<Tree>> maps, Tree tree) {
        if (tree.getChildList() == null) {
            if (maps.get(tree.getId()) != null) {
                tree.setChildList(maps.get(tree.getId()));
                maps.remove(tree.getId());
                if (maps.size() > 0) {
                    recursion(maps, tree);
                }
            }
        } else {
            List<Tree> metaTypeList = tree.getChildList();
            if (metaTypeList != null && metaTypeList.size() > 0) {
                for (Tree meta : metaTypeList) {
                    recursion(maps, meta);
                }
            }
        }
        return tree;
    }
}

@Data使用的lombok插件，自动生成get set方法

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