一、简述
之前遇到过一个表里含有父类和子类关系的,有时候取值需要用到递归,递归有多重实现方式:
1、Mysql和Oracle递归查询实现记录 2、java实现多级递归查询
下面就介绍下第三种递归实现方法,用java8里面的Stream来简单实现。
二、实现
1、实体类:
@Data
@EqualsAndHashCode(callSuper = true)
@Accessors(chain = true)
@TableName("SYS_USER")
public class User {
private static final long serialVersionUID = -3089138238598051744L;
/**
* 账号
*/
@TableField("NAME")
private String name;
/**
* 密码
*/
@TableField("PASSWORD")
private String password;
/**
* 昵称
*/
@TableField("NICK_NAME")
private String nickName;
/**
* 备注
*/
@TableField("REMARK")
private String remark;
/**
* 工号
*/
@TableField("WORK_NUM")
private Integer workNum;
@TableField("LEVEL_ID")
private String levelId;
@TableField(exist = false)
private List<User> childList;
}
2、递归代码:
@GetMapping("/getUser")
public HttpResponses<List<User>> getUser(){
long startTime=System.currentTimeMillis(); //获取开始时间
List<User> list = this.userService.query().eq(User::getStatus,StatusEnum.NORMAL)
.eq(User::getDirty,StatusEnum.NORMAL).list();
//用map写法
/*List<User> listUser = list.stream().filter(user -> user.getLevelId().equals("0")).map(user -> {
user.setChildList(getChildrens(user,list));
return user;
}).collect(Collectors.toList());*/
//用peek写法
List<User> listUser = list.stream().filter(user -> user.getLevelId().equals("0"))
.peek(user -> user.setChildList(getChildrens(user,list))).collect(Collectors.toList());
long endTime=System.currentTimeMillis(); //获取结束时间
System.out.println("程序运行时间: "+(endTime-startTime)+"ms");
return success(listUser);
}
3、获取子类数据:
public List<User> getChildrens(User user,List<User> userList){
List<User> childrens = userList.stream().filter(u -> Objects.equals(u.getLevelId(),user.getId())).map(
u -> {
u.setChildList(getChildrens(u,userList));
return u;
}
).collect(Collectors.toList());
return childrens;
}
代码里面用map和peek都实现了,这两种实现执行时间都差不多,自己可以选一种来用就可以;
4、执行结果
{
"status": 200,
"result": [
{
"id": "2",
"name": "admin",
"password": "admin",
"nickName": "管理员",
"levelId": "0",
"childList": [
{
"id": "d0cd4677f0034374a22d02bc86eaf49d",
"name": "fgs",
"password": "123456",
"nickName": "分公司",
"levelId": "2",
"childList": [
{
"id": "437dfd84996d464bbd3649b55792954f",
"name": "gj",
"password": "123456",
"nickName": "主管运营",
"levelId": "d0cd4677f0034374a22d02bc86eaf49d",
"childList": [
{
"id": "9dea449deab44e86aa7541655accc6cb",
"name": "gjywy",
"password": "123456",
"nickName": "业务员2",
"levelId": "437dfd84996d464bbd3649b55792954f",
"childList": []
}
]
}
]
},
{
"id": "00c62e69824e44a7a4bec82ce66aac8c",
"name": "feg2",
"password": "123456",
"nickName": "分公司2",
"levelId": "2",
"childList": [
{
"id": "0901a1d5264041eca9839dad4622a93f",
"name": "yyzg2",
"password": "123456",
"nickName": "运营主管2",
"levelId": "00c62e69824e44a7a4bec82ce66aac8c",
"childList": [
{
"id": "284f51f194f3426eb1a2e11baefb1790",
"name": "ywy",
"password": "123456",
"nickName": "业务员",
"levelId": "0901a1d5264041eca9839dad4622a93f",
"childList": []
}
]
}
]
}
]
}
]
}
三、比较
和普通的for循环相比,Stream第一次执行的时候会慢一点,但是不影响页面展示效果,普通for循环还是比较快的,这里没有用多数据来测试,大家可以用多数据测试下效果;