Combining a Collection of Predicates 

public void whenFilterListWithCollectionOfPredicatesUsingAnd_thenSuccess(){
    List<Predicate<String>> allPredicates = new ArrayList<Predicate<String>>();
    allPredicates.add(str -> str.startsWith("A"));
    allPredicates.add(str -> str.contains("d"));        
    allPredicates.add(str -> str.length() > 4);
    
    List<String> result = names.stream()
      .filter(allPredicates.stream().reduce(x->true, Predicate::and))
      .collect(Collectors.toList());
    
    assertEquals(1, result.size());
    assertThat(result, contains("Alexander"));
}

 

 1 package fengliang.firstjava;
 2 
 3 import java.text.ParseException;
 4 import java.text.SimpleDateFormat;
 5 import java.util.*;
 6 import java.util.function.Predicate;
 7 
 8 class FilterContainer<T> {
 9     protected List<T> list = new ArrayList<>();
10 
11     public FilterContainer<T> addFilter(T predicate) {
12         list.add(predicate);
13         return this;
14     }
15 
16     public List<T> getList() {
17         return list;
18     }
19 }
20 public class LambdaExamination {
21 
22     protected static List<Employee> createDepartment() {
23 
24         return new ArrayList<>(Arrays.asList(
25                 new Employee("张三", 12, "2012-11-12"),
26                 new Employee("李四", 9, "2018-06-01"),
27                 new Employee("王五", 11.5, "2019-06-01"),
28                 new Employee("赵六", 11.2, "2018-11-02"),
29                 new Employee("孙七", 8, "2020-08-08")
30         ));
31     }
32 
33     protected static Comparator<Employee> sortBySalary() {
34 
35         return Comparator.comparingDouble(Employee::getSalary);
36     }
37 
38     protected static Date stringDateTimeFormat(String datetime) {
39         try {
40             return new SimpleDateFormat("y-MM-dd").parse(datetime);
41         } catch (ParseException e) {
42             e.printStackTrace();
43         }
44         throw new RuntimeException("datetime的格式必须符合2020-02-01");
45     }
46 
47     protected static Comparator<Employee> sortByHireDay() {
48         return Comparator.comparing((Employee e) -> stringDateTimeFormat(e.getHireDay()));
49     }
50 
51     protected static Predicate<Employee> filterBySalary(double salary) {
52         return (Employee e) -> Double.compare(e.getSalary(), salary) > 0;
53     }
54 
55     protected static Predicate<Employee> filterByHireDay(String hireDay) {
56         return (Employee e) -> stringDateTimeFormat(e.getHireDay()).compareTo(stringDateTimeFormat(hireDay)) > 0;
57     }
58 
59     public static void main(String[] args) {
60         List<Employee> department = createDepartment();
61         FilterContainer<Predicate<Employee>> filterContainer = new FilterContainer<>();
62         filterContainer.addFilter(filterBySalary(10.0))
63                 .addFilter(filterByHireDay("2018-10-10"));
64 
65         department.stream().filter(filterBySalary(10)).filter(
66                 filterContainer.getList().stream().reduce(f->true, Predicate::and)
67         ).sorted(sortBySalary())
68                 .forEach(
69                 employee -> System.out.println(employee.name+", "+ employee.salary+", "+employee.hireDay.toString())
70         );
71     }
72 }

 

 https://www.baeldung.com/java-predicate-chain

posted on 2020-12-15 01:08  冯亮  阅读(61)  评论(0)  编辑  收藏  举报

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