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.

package java.util.function;

@FunctionalInterface
public interface Supplier<T> {
    T get();
}

1、使用Supplier打印字符串

package com.cattles.function;

import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
import java.util.function.Supplier;

/**
 * @author cattle -  稻草鸟人
 * @date 2020/3/22 下午12:56
 */
public class Java8Supplier1 {

    private static final DateTimeFormatter dtf = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");

    public static void main(String[] args) {
        // print simple string
        Supplier<String> supplier = () -> "cattle";
        System.out.println(supplier.get());
        // print date time
        Supplier<LocalDateTime> time = () -> LocalDateTime.now();
        System.out.println(time.get());

        
        Supplier<String> s = () -> dtf.format(time.get());
        System.out.println(s.get());
    }
}

输出:

cattle
2020-03-22T13:45:53.926364
2020-03-22 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

package com.cattles.function;

import java.math.BigDecimal;
import java.util.ArrayList;
import java.util.List;
import java.util.Optional;
import java.util.function.Supplier;

/**
 * @author cattle -  稻草鸟人
 * @date 2020/3/22 下午12:56
 */
public class Java8Supplier3 {


    public static void main(String[] args) {
        Developer developer = factory(Developer::new);
        System.out.println(developer);

        Developer developer1 = factory(()-> new Developer("tony"));
        System.out.println(developer1);

    }

    public static Developer factory(Supplier<? extends  Developer> supplier) {
        Developer developer = supplier.get();
        if(Optional.ofNullable(developer.getName()).isEmpty()) {
            developer.setName("cattle");
        }
        //可怜的人啊,薪水是zero
        developer.setSalary(BigDecimal.ZERO);
        //没日没夜干活的码农啊
        developer.setTitle("Coder");
        return developer;
    }


    static class Developer {
        /**
         * 姓名
         */
        private String name;
        /**
         * 职位
         */
        private String title;
        /**
         * 薪水
         */
        private BigDecimal salary;

        public Developer(String name) {
            this.name = name;
        }

        // 省略 gettter setter toString 方法
    }
}

看看结果:

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

快上车，教你开车