jdk8中list的stream流的常用方法

一.判断List对象中是否包含对象的值

1.第一种方法：

boolean present1 = appCountStudentActionResults.stream().filter(m -> m.getActiveTypes().equals("3")).findAny().isPresent();

2.第二种方法：

boolean b = appCountStudentActionResults.stream().anyMatch(m -> m.getActiveTypes().equals("1"))

二.List按某个字段排序

1.第一种方法：

​
List newList = list.stream().sorted(Comparator.comparing(User::getAge))
                .collect(Collectors.toList());




List<类> list; 代表某集合
 
//返回 对象集合以类属性一升序排序
 
list.stream().sorted(Comparator.comparing(类::属性一));
 
//返回 对象集合以类属性一降序排序 注意两种写法
 
list.stream().sorted(Comparator.comparing(类::属性一).reversed());//先以属性一升序,结果进行属性一降序
 
list.stream().sorted(Comparator.comparing(类::属性一,Comparator.reverseOrder()));//以属性一降序
(多个属性排序)
原文链接：https://blog.csdn.net/qq_41999771/article/details/123045488

​

2.第二种方法>：

常见排序

public static void main(String args[]) throws IOException, ClassNotFoundException {
    testSorted(); 
}
 
public static void testSorted() {
    List> cpuRateList = setCpuRateValue();
 
 
    List> valueList = cpuRateList.stream()
            .sorted(Comparator.comparing(e -> MapUtils.getDouble(e, "value"))).collect(Collectors.toList());
    System.out.println("============排序 ===========");
    valueList.forEach(System.out::println);
    // 倒序
    //        Collections.reverse(valueList);
    List> reverseValueList = cpuRateList.stream()
            .sorted((c1, c2) -> MapUtils.getDouble(c2, "value").compareTo(MapUtils.getDouble(c1, "value"))).collect(Collectors.toList());
    System.out.println("============倒序===========");
    reverseValueList.forEach(System.out::println);
 
}

处理null的情况（如果排序中，值为null了，要怎么处理呢？）

public static void main(String args[]) throws IOException, ClassNotFoundException {     testMapWithNullSorted();
}
 
public static void testMapWithNullSorted() {
    List> cpuRateList = setCpuRateNullValue();
 
    List> filterValueList = cpuRateList.stream().filter(e -> MapUtils.getDouble(e, "value") != null)
            .sorted(Comparator.comparing(e -> MapUtils.getDouble(e, "value"))).collect(Collectors.toList());
    System.out.println("==========过滤null===========");
    filterValueList.forEach(System.out::println);
 
    List> valueNullFirstList = cpuRateList.stream().sorted(Comparator.comparing(e -> MapUtils.getDouble(e, "value"), Comparator.nullsFirst(Double::compareTo))).collect(Collectors.toList());
    System.out.println("==========null排前面===========");
    valueNullFirstList.forEach(System.out::println);
 
    List> valueNullLastList = cpuRateList.stream().sorted(Comparator.comparing(e -> MapUtils.getDouble(e, "value"), Comparator.nullsLast(Double::compareTo))).collect(Collectors.toList());
    System.out.println("==========null排后面===========");
    valueNullLastList.forEach(System.out::println);
}

JSONArray的排序同理（JSONArray排序）

public static void main(String args[]){
    testSorted();
    testJsonWithNullSorted();
}
 
public static void testSorted() {
    JSONArray fieldList = initFiledValue();
 
    List sortIdList = ListUtils.emptyIfNull(fieldList).stream().map(e -> (JSONObject) e)
            .sorted(Comparator.comparing(e -> MapUtils.getInteger(e, "sortId"))).collect(Collectors.toList());
    System.out.println("============排序 ===========");
    sortIdList.forEach(System.out::println);
    // 倒序
    List reverseSortIdList = ListUtils.emptyIfNull(fieldList).stream().map(e -> (JSONObject) e)
            .sorted((c1, c2) -> MapUtils.getInteger(c2, "sortId").compareTo(MapUtils.getInteger(c1, "sortId"))).collect(Collectors.toList());
    System.out.println("============倒序===========");
    reverseSortIdList.forEach(System.out::println);
}
 
public static void testJsonWithNullSorted() {
    JSONArray fieldList = initFiledNullValue();
 
    List filterValueList = ListUtils.emptyIfNull(fieldList).stream().map(e -> (JSONObject) e).filter(e -> MapUtils.getInteger(e, "sortId") != null)
            .sorted(Comparator.comparing(e -> MapUtils.getInteger(e, "sortId"))).collect(Collectors.toList());
    System.out.println("==========过滤null===========");
    filterValueList.forEach(System.out::println);
 
    List valueNullFirstList = ListUtils.emptyIfNull(fieldList).stream().map(e -> (JSONObject) e).sorted(Comparator.comparing(e -> MapUtils.getInteger(e, "sortId"), Comparator.nullsFirst(Integer::compareTo))).collect(Collectors.toList());
    System.out.println("==========null排前面===========");
    valueNullFirstList.forEach(System.out::println);
 
    List valueNullLastList = ListUtils.emptyIfNull(fieldList).stream().map(e -> (JSONObject) e).sorted(Comparator.comparing(e -> MapUtils.getInteger(e, "sortId"), Comparator.nullsLast(Integer::compareTo))).collect(Collectors.toList());
    System.out.println("==========null排后面===========");
    valueNullLastList.forEach(System.out::println);
}
//
public static JSONArray initFiledValue() {
    String data = "[{\n" +
            "\t\"fieldName\": \"model_name\",\n" +
            "\t\"sortId\": 2,\n" +
            "\t\"elementLabel\": \"模型名\"\n" +
            "}, {\n" +
            "\t\"elementName\": \"model_mod\",\n" +
            "\t\"sortId\": 1,\n" +
            "\t\"elementLabel\": \"模型ID\"\n" +
            "}, {\n" +
            "\t\"fieldName\": \"remark\", \n" +
            "\t\"sortId\": 3,\n" +
            "\t\"elementLabel\": \"备注\"\n" +
            "}, {\n" +
            "\t\"fieldName\": \"model_type\", \n" +
            "\t\"sortId\": 4,\n" +
            "\t\"elementLabel\": \"类型\" \n" +
            "}]";
    return JSONArray.parseArray(data);
}
 
public static JSONArray initFiledNullValue() {
    String data = "[{\n" +
            "\t\"fieldName\": \"model_name\",\n" +
            "\t\"sortId\": 2,\n" +
            "\t\"elementLabel\": \"模型名\"\n" +
            "}, {\n" +
            "\t\"elementName\": \"model_mod\",\n" +
            "\t\"sortId\": null,\n" +
            "\t\"elementLabel\": \"模型ID\"\n" +
            "}, {\n" +
            "\t\"fieldName\": \"remark\", \n" +
            "\t\"sortId\": 3,\n" +
            "\t\"elementLabel\": \"备注\"\n" +
            "}, {\n" +
            "\t\"fieldName\": \"model_type\", \n" +
            "\t\"sortId\": 4,\n" +
            "\t\"elementLabel\": \"类型\" \n" +
            "}]";
    return JSONArray.parseArray(data);
}

三.Java对list多个字段进行去重以及过滤

1.对年龄和名字同时进行去重(多个字段)

		 public static void main(String[] args) {
				        us u=fa.fa(1);
				        us u2=fa.fa(1);
				        us u3=fa.fa(1);
				        List list=new ArrayList<>();
				        u.setAge(10);
				        u.setName("张三");
				        list.add(u);
				        u2.setAge(13);
				        u2.setName("李四");
				        list.add(u2);
				        u3.setAge(13);
				        u3.setName("李四");
				        list.add(u3);
				        List usList=list.stream().collect(Collectors.collectingAndThen(Collectors.toCollection(()->new TreeSet<>(Comparator.comparing(s->s.getName()+";"+s.getAge()))),ArrayList::new));
				        usList.forEach(userList->{
				        System.out.println(userList.getName()+userList.getAge());
				        });
				    }

2.对年龄进行过滤筛选(单个字段)

 List userDiscont=list.stream().filter(us -> us.getAge()==10).collect(Collectors.toList());



List> list2 = selectChoasInfo.stream().distinct().collect(Collectors.toList());