Java traverses the parent-child tree relationship according to the parent id (general)

Execution effect chart

1. Create an entity class. This class is to store the id and parent id of the entity class that needs to traverse the parent-child relationship into this class, and finally use the tool class for unified traversal, so that the tool class can be universal ( most common tool classes will lose execution For the purpose of efficiency ), you can also refer to my traversal conditions to write a dedicated and more efficient method.

import lombok.Data;
//此注解为自动添加get、set、toString方法的，需要jar包，可自己生成getset，
@Data
public class Parent {
	private Integer id;
	private String name;
	private Integer parentId;
	public Parent(Integer id, String name, Integer parentId) {
		super();
		this.id = id;
		this.name = name;
		this.parentId = parentId;
	}
	
}

2. Add tool operation class

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

import com.xx.fresh.bean.Parent;

public class MakeList {
	private List<Parent> list;
	private List<Parent> resultList=new ArrayList<Parent>();
	private String addName;
	public void  setAddName(String add) {
		addName=add;
	}
	public void  setList(List<Parent> list) {
		this.list=list;
	}
	public List<Parent> getList(){
		make();
		return resultList;
	}
	private void make() {
		for(Parent p:list) {
			if(p.getParentId()==null) {
				resultList.add(p);
				//子菜单上加的横杠
				String h="";
				traverseList(p.getId(),h);
			}
		}
	}
	private void traverseList(int id,String h) {
		h=h+addName;
		for(Parent p:list) {
			
			if(p.getParentId()!=null&&p.getParentId()==id) {
				p.setName(h+p.getName());
				resultList.add(p);
				traverseList(p.getId(),h);
			}
		}
	}
	
}

3. Invoke the method

//Classify（分类）是要遍历父子关系的实体类，
	private List<Parent> doParent(List<Classify> list){
		List<Parent> list2=new ArrayList<Parent>();
		for(Classify c:list) {
			list2.add(new Parent(c.getClassifyId(), c.getClassifyName(), c.getClassifyParentId()));
		}
		MakeList makeList=new MakeList();
		makeList.setList(list2);
		//在父子级前加上标识，可自定义或不写
		makeList.setAddName("- ");
		//通过调用工具类返回一个id、name、父id的排序后的列表
		return makeList.getList();
	}