JAVA 任意实体集合形成树形结构

通过泛型+反射+加自定义注解，任意实体集合递归形成树形结构
先上代码
第一个自定义注解TreeId (打在实体类的主键ID上)

import java.lang.annotation.*;

@Target({ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
@documented
public @interface TreeId {
    String value() default "";
}

第二个自定义注解TreeParentId(打在实体类的父类ID上)

import java.lang.annotation.*;

@Target({ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
@documented
public @interface TreeParentId{
    String value() default "";
}

第三个自定义注解TreeList(打在实体类的集合上)

import java.lang.annotation.*;

@Target({ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
@documented
public @interface TreeParentId{
    String value() default "";
}

然后是最重要的工具类TreeUtil

import cn.hutool.core.util.ObjectUtil;

import java.lang.annotation.Annotation;
import java.lang.reflect.Field;
import java.util.Collection;
import java.util.Iterator;
import java.util.linkedList;

public class TreeUtil {
    //递归形成树形结构
    public static  Collection buildTree(Collection  collection, Long id) {
        if (ObjectUtil.isNull(collection) || collection.size() == 0) {
            return null;
        }
        Collection cs = new linkedList<>();
        try {
            for (Iterator it = collection.iterator(); it.hasNext(); ) {
                T tree = it.next();
                Class obj = tree.getClass();
                Field[] fields = obj.getDeclaredFields();
                Field parentIdField = getTreeFile(fields, TreeParentId.class);
                if(ObjectUtil.isNotNull(parentIdField)){
                    if (parentIdField.get(tree).equals(id)) {
                        cs.add(tree);
                        it.remove();
                    }
                }else{
                    throw new Exception("未找到父类Id");
                }
            }
            if (ObjectUtil.isNull(cs) || cs.size() == 0) {
                return null;
            }
            for (T tree : cs) {
                Class obj = tree.getClass();
                Field[] fields = obj.getDeclaredFields();
                Field ListField = getTreeFile(fields, TreeList.class);
                Field IdField = getTreeFile(fields, TreeId.class);
                if(ObjectUtil.isNull(ListField)){
                    throw new Exception("未找到集合");
                }
                if(ObjectUtil.isNull(IdField)){
                    throw new Exception("未找到Id");
                }
                ListField.setAccessible(true);
                ListField.set(tree,buildTree(collection,(Long) IdField.get(tree)));
            }
        }catch (Exception ex){
            ex.printStackTrace();
        }
        return cs;
    }

    public static Field getTreeFile(Field[] fields, Class t) {
        for (Field field : fields) {
            if(field.isAnnotationPresent(t)) {
                field.setAccessible(true);
                return field;
            }
        }
        return null;
    }
}

然后随便创建一个实体类并且在相对应的屬性上面打上对应的注解

@Data
public class user{
	@TreeId()
	private Long id;

	private String name;
	
	@TreeParentId()
	private Long parentId;
	
	@TreeList()
	private List users;
	
}

最后是测试主方法

    public static void main(String[] args) {
        List users = new ArrayList<>();
        for (int i=1;i<4;i++){
            user user = new user();
            user.setId(10l+i);
            user.setParentId(0l);
            users.add(user);
        }
        for (int i=1;i<4;i++){
            user user = new user();
            user.setId(20l+i);
            user.setParentId(11l);
            users.add(user);
        }
        for (int i=1;i<4;i++){
            user user = new user();
            user.setId(30l+i);
            user.setParentId(21l);
            users.add(user);
        }
        System.out.println(TreeUtil.buildTree(users,0l));
    }

以下是结果：

[
user(id=11, name=null, parentId=0, users=[
	user(id=21, name=null, parentId=11, users=[
		user(id=31, name=null, parentId=21, users=null), 
		user(id=32, name=null, parentId=21, users=null), 
		user(id=33, name=null, parentId=21, users=null)]), 
	user(id=22, name=null, parentId=11, users=null), 
	user(id=23, name=null, parentId=11, users=null)]), 
user(id=12, name=null, parentId=0, users=null),
user(id=13, name=null, parentId=0, users=null)
]