本文例項為大家分享了java轉樹形結構工具類的具體程式碼，供大家參考，具體內容如下

import com.alibaba.fastjson.JSON;
import lombok.Data;
import lombok.ToString;
import org.springframework.util.ReflectionUtils;
import org.springframework.util.StringUtils;

import java.lang.reflect.Field;
import java.util.*;

/**
 * @author : liyk
 * @version 1.0
 * @date : 2020/6/9 
 */
public class TreeUtil {


  /**
   * 將 List 轉為樹形結構
   *
   * @param origList     : 要轉換的 List
   * @param idFieldName    : id欄位名
   * @param parentIdFieldName : parentId 欄位名
   * @param childrenFieldName : children 欄位名
   * @param <T>        : 擁有父子結構的 Entity
   * @return : 樹形結果
   * @throws Exception .
   */
  public static <T> List<T> convert(List<T> origList,String idFieldName,String parentIdFieldName,String childrenFieldName) throws Exception {
    // 用於儲存當前 id 索引的實體類
    Map<String,T> idMaps = new HashMap<>();
    // 暫存區,用於儲存沒有找到父 id 的控制元件
    List<T> tempList = new ArrayList<>();
    List<T> result = new ArrayList<>();
    for (T entity : origList) {
      // 獲取 id,parentId,children
      String id = Objects.toString(getFieldValue(entity,idFieldName),"");
      String parentId = Objects.toString(getFieldValue(entity,parentIdFieldName),"");
      if (StringUtils.isEmpty(id)) {
        throw new Exception("存在id為空的資料");
      }
      idMaps.put(id,entity);
      if (StringUtils.isEmpty(parentId)) {
        // 如果父 id 為空,則實體類為第一層
        result.add(entity);
      } else {
        // 根據父 id 獲取實體類
        T parentEntity = idMaps.get(parentId);
        if (parentEntity == null) {
          // 沒找到先放入暫存區
          tempList.add(entity);
        } else {
          // 父元件判斷是否存在 children,不存在新增,存在則直接假如
          setChildrenValue(childrenFieldName,entity,parentEntity);
        }
      }
    }
    // 處理暫存區,暫存區的一定不為根節點,所以它只要父節點存在,那麼此輪查詢一定能找到父節點(上一輪已經將全部節點放入 idMaps)
    for (T entity : tempList) {
      // 獲取 parentId
      String parentId = Objects.toString(getFieldValue(entity,"");
      // 根據父id獲取實體類
      T parentEntity = idMaps.get(parentId);
      if (parentEntity == null) {
        throw new Exception("存在孤立的子節點");
      } else {
        // 父元件判斷是否存在children,存在則直接假如
        setChildrenValue(childrenFieldName,parentEntity);
      }
    }
    return result;
  }

  private static <T> void setChildrenValue(String childrenFieldName,T entity,T parentEntity) throws Exception {
    Object children = getFieldValue(parentEntity,childrenFieldName);
    List<T> childrenList;
    if (children == null) {
      childrenList = new ArrayList<>();
      childrenList.add(entity);
      setFieldValue(parentEntity,childrenFieldName,childrenList);
    } else {
      List<T> childrenReal = (List<T>) children;
      childrenReal.add(entity);
    }
  }

  private static <T> Object getFieldValue(T entity,String fieldName) throws Exception {
    Field field = ReflectionUtils.findField(entity.getClass(),fieldName);
    if (field == null) {
      throw new Exception(String.format("欄位名稱[%s]不存在",fieldName));
    }
    boolean accessible = field.isAccessible();
    field.setAccessible(true);
    Object result = ReflectionUtils.getField(field,entity);
    field.setAccessible(accessible);
    return result;
  }

  private static <T> void setFieldValue(T entity,String fieldName,Object value) throws Exception {
    Field field = ReflectionUtils.findField(entity.getClass(),fieldName));
    }
    boolean accessible = field.isAccessible();
    field.setAccessible(true);
    ReflectionUtils.setField(field,value);
    field.setAccessible(accessible);
  }

  public static void main(String[] args) throws Exception {
    List<Demo> list = new ArrayList<>();
    for (int i = 0; i < 5; i++) {
      Demo demo = new Demo(i,"一級節點" + i);
      list.add(demo);
    }
    for (int i = 5; i < 15; i++) {
      Demo demo = new Demo(i,i % 5,"二級節點" + i);
      list.add(demo);
    }
    for (int i = 15; i < 100; i++) {
      Demo demo = new Demo(i,i % 10 + 5,"三級節點" + i);
      list.add(demo);
    }
    Demo demo = new Demo(100,102,"非法節點");
    list.add(demo);
    List<Demo> convert = TreeUtil.convert(list,"id","pid","children");
    String s = JSON.toJSONString(convert);
    System.out.println(s);
  }

}

@Data
@ToString
class Demo {
  private Integer id;
  private Integer pid;
  private String name;
  private List<Demo> children;

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

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

以上就是本文的全部內容，希望對大家的學習有所幫助，也希望大家多多支援我們。