Predicate基本用法

@Data
    class Person {
          
   
        private String name;
        private Integer age;

        @Override
        public boolean equals(Object o) {
          
   
            if (this == o) return true;
            if (o == null || getClass() != o.getClass()) return false;
            Person person = (Person) o;
            return name.equals(person.name) && age.equals(person.age);
        }

        @Override
        public int hashCode() {
          
   
            return Objects.hash(name, age);
        }

        public Person(String name, Integer age) {
          
   
            this.name = name;
            this.age = age;
        }
    }

@RequestMapping(value = "test6")
    public void test6(HttpServletResponse rsp) {
          
   

        //普通业务集合
        List<Person> personList = new ArrayList<>();
        personList.add(new Person("小D", 26));
        personList.add(new Person("佳欣", 24));
        personList.add(new Person("铭康", 28));
        personList.add(new Person("小鹏", 25));
        personList.add(new Person("宇轩", 22));
        personList.add(new Person("小明", 27));

        //条件
        Predicate<Person> predicate = person -> person.getAge() > 22 && StrUtil.contains(person.getName(), "小");

        //以下条件等价于上面条件
        Predicate<Person> predicate1 = person -> person.getAge() > 22;
        Predicate<Person> predicate2 = person -> StrUtil.contains(person.getName(), "小");


        Map<Integer, Person> result = new HashMap<>();
        for (int i = 0; i < personList.size(); i++) {
          
   
            Person person = personList.get(i);
            if (predicate.test(person)) {
          
   
                result.put(i, person);
            }
            //以下不同写法,对于条件特别多用下面这种
//            if (predicate1.and(predicate2).test(person)) {
          
   
//                result.put(i, person);
//            }

        }
        System.out.println(result);
        return;
    }

结果

{
          
   0=TestController.Person(name=小D, age=26), 3=TestController.Person(name=小鹏, age=25), 5=TestController.Person(name=小明, age=27)}

一般以下这样用的比较多

List<Person> presult = personList.stream().filter(predicate).collect(Collectors.toList());
        List<Person> presult2 = personList.stream().filter(predicate1.and(predicate2)).collect(Collectors.toList());
        System.out.println(presult);
        System.out.println(presult2);
        List<Person> presult3 = personList.stream().filter(predicate1.or(predicate2)).collect(Collectors.toList());
        System.out.println(presult3);

结果

[Person(name=小D, age=26), Person(name=小鹏, age=25), Person(name=小明, age=27)]
[Person(name=小D, age=26), Person(name=小鹏, age=25), Person(name=小明, age=27)]
[Person(name=小D, age=26), Person(name=佳欣, age=24), Person(name=铭康, age=28), Person(name=小鹏, age=25), Person(name=小明, age=27)]

其他

Predicate<String> pred = "hello" :: equalsIgnoreCase;
        List<String> strlist = new ArrayList<>();
        strlist.add("rocky");
        strlist.add("heLLO");
        strlist.add("rocky");
        boolean b = strlist.stream().anyMatch(pred::test);
        System.out.println(b);

结果

true