工作中因業務需求，將資料庫中的樹狀結構的資料根據父節點獲取所有的子節點

實現思路

1.獲取整個資料的list集合資料

2.將資料分組，java8 list有groupby分組，java8之前的自己遍歷整理

3.分組後遞迴獲取子節點，有子節點的新增，沒有的設定子節點並刪除分組的資料，知道分組資料刪完

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,\"key\":\"node2\",\"value\": \"node2\"}," +
        "{\"id\":3000,\"key\":\"node3\",\"value\": \"node3\"}," +
        "{\"id\":1100,\"pId\":1000,\"key\":\"node11\",\"value\": \"node11\"}," +
        "{\"id\":1200,\"key\":\"node12\",\"value\": \"node12\"}," +
        "{\"id\":1110,\"pId\":1100,\"key\":\"node111\",\"value\": \"node111\"}," +
        "{\"id\":1120,\"key\":\"node112\",\"value\": \"node112\"}," +
        "{\"id\":2100,\"pId\":2000,\"key\":\"node21\",\"value\": \"node21\"}," +
        "{\"id\":2200,\"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,key=node112,value=node112,childList=null)]),*             Tree(id=1200,key=node12,value=node12,*           Tree(id=2000,key=node2,value=node2,childList=[
     *             Tree(id=2100,pId=2000,key=node21,value=node21,childList=[
     *               Tree(id=2110,pId=2100,key=node211,*               Tree(id=2200,key=node22,value=node22,*           Tree(id=3000,key=node3,value=node3,childList=null)]]
     */
    System.out.println("tree:" + ToStringBuilder.reflectionToString(tree));
  }

  private static Tree metaTree(List<Tree> treeList,Integer id) {
//此處getId getPId根據自己實際情況更改
    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;
  }
}

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