昨天QA同事给我提了一个Bug
,后台配置的顺序跟浏览器展示页面的顺序不一致,感觉莫名其妙,于是进行debug
追踪,模拟代码如下:
public class Example { private Long id; private String desc; public Long getId() { return id; } public void setId(Long id) { this.id = id; } public String getDesc() { return desc; } public void setDesc(String desc) { this.desc = desc; } @Override public String toString() { return "Example{" + "id=" + id + ", desc='" + desc + '\'' + '}'; } }
public class Test { public static void main(String[] args) { List<Example> list = new ArrayList<>(); for (long i = 1; i <=5; i++) { Example example = new Example(); example.setId(new Random().nextLong()); example.setDesc(String.valueOf(example.getId())); list.add(example); } list.forEach(System.out::println); System.out.println("===================="); Map<Long, List<Example>> id2ExaMap = list.stream().collect(Collectors.groupingBy(Example::getId)); id2ExaMap.forEach((id,example)->{ System.out.println("id:" + id + " ,example" + example); }); } }
运行main
方法后,控制台输出如下:
于是我的bug
就诞生了。上网查了一下,解释如下:
链接在这里
所以为了解决顺序问题,可以使用LinkedHashMap
来进行接收。
public class Test { public static void main(String[] args) { List<Example> list = new ArrayList<>(); for (long i = 1; i <=5; i++) { Example example = new Example(); example.setId(new Random().nextLong()); example.setDesc(String.valueOf(example.getId())); list.add(example); } list.forEach(System.out::println); System.out.println("===================="); //这里使用LinkedHashMap来进行接收 LinkedHashMap<Long, List<Example>> id2ExaMap = list.stream() .collect(Collectors .groupingBy(Example::getId, LinkedHashMap::new, Collectors.toList())); id2ExaMap.forEach((id,example)->{ System.out.println("id:" + id + " ,example" + example); }); } }
运行main
方法,控制台输出如下: