Java 8 Supplier 使用

在Java 8, Supplier是一个函数接口,它没有参数,返回了一个T.查了下字典,supplier被翻译成"供应商",那么它到底供应了啥呢,从代码上看,就是供应了一个任意对象T呗，下面我们去看看几个DEMO吧.

思考: 写JDK代码的大神们,为什么取名叫Supplier?为啥不叫Vendor或者Provider呢...我想了很久.

1package java.util.function;
2
3@FunctionalInterface
4public interface Supplier<T> {
5    T get();
6}

1、使用Supplier打印字符串

1package com.cattles.function;
2
3import java.time.LocalDateTime;
4import java.time.format.DateTimeFormatter;
5import java.util.function.Supplier;
6
7/**
8 * @author cattle -  稻草鸟人
9 * @date 2020/3/22 下午12:56
10 */
11public class Java8Supplier1 {
12
13    private static final DateTimeFormatter dtf = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
14
15    public static void main(String[] args) {
16        // print simple string
17        Supplier<String> supplier = () -> "cattle";
18        System.out.println(supplier.get());
19        // print date time
20        Supplier<LocalDateTime> time = () -> LocalDateTime.now();
21        System.out.println(time.get());
22
23        
24        Supplier<String> s = () -> dtf.format(time.get());
25        System.out.println(s.get());
26    }
27}
28

输出:

1cattle
22020-03-22T13:45:53.926364
32020-03-22 13:45:53

2、返回一个Supplier

下面我们创建一个简单的工厂方法返回一个Developer 对象

1package com.cattles.function;
2
3import java.math.BigDecimal;
4import java.util.ArrayList;
5import java.util.List;
6import java.util.Optional;
7import java.util.function.Supplier;
8
9/**
10 * @author cattle -  稻草鸟人
11 * @date 2020/3/22 下午12:56
12 */
13public class Java8Supplier3 {
14
15
16    public static void main(String[] args) {
17        Developer developer = factory(Developer::new);
18        System.out.println(developer);
19
20        Developer developer1 = factory(()-> new Developer("tony"));
21        System.out.println(developer1);
22
23    }
24
25    public static Developer factory(Supplier<? extends  Developer> supplier) {
26        Developer developer = supplier.get();
27        if(Optional.ofNullable(developer.getName()).isEmpty()) {
28            developer.setName("cattle");
29        }
30        //可怜的人啊,薪水是zero
31        developer.setSalary(BigDecimal.ZERO);
32        //没日没夜干活的码农啊
33        developer.setTitle("Coder");
34        return developer;
35    }
36
37
38    static class Developer {
39        /**
40         * 姓名
41         */
42        private String name;
43        /**
44         * 职位
45         */
46        private String title;
47        /**
48         * 薪水
49         */
50        private BigDecimal salary;
51
52        public Developer(String name) {
53            this.name = name;
54        }
55
56        // 省略 gettter setter toString 方法
57    }
58}
59

看看结果:

1Developer{name='cattle', title='Coder', salary=0}
2Developer{name='tony', title='Coder', salary=0}