httpClient 远程调用接口，java8新特性Optional

import java.util.Optional;

/**
 * java 8新特性
 * 
 * @author wang-xiaoming
 * @date 2019年7月2日
 */
public class OptionalTest {

    public static void ofNullable(String value) {
        Optional<String> opt = Optional.ofNullable(value);
        System.out.println("【ofNullable】，value：" + opt.get());
    }

    public static void of(String value) {
        Optional<String> opt = Optional.of(value);
        System.out.println("【of】，value：" + opt.get());
    }

    /**
     * 有值则返回值，没有则返回【指定属性】
     * 
     * @param value
     */
    public static void orElse(String value) {
        String orElse = Optional.ofNullable(value).orElse("default");
        System.out.println("【orElse】，value：" + orElse);
    }

    /**
     * 有值则返回值，没有则执行‘->’后的【执行方法】
     * 
     * @param value
     */
    public static void orElseGet(String value) {
        String orElseGet = Optional.ofNullable(value).orElseGet(() -> "default");
        System.out.println("【orElseGet】，value：" + orElseGet);
    }

    /**
     * 判断当前value是否为null，为null，返回false；不为null，返回true
     * 
     * @param value
     */
    public static void isPresent(String value) {
        boolean present = Optional.ofNullable(value).isPresent();
        System.out.println("【isPresent】，result：" + present);
    }

    /**
     * ep：当抛出NPE时，可以自己指定异常
     * 
     * @param value
     */
    public static void orElseThrow(String value) {
        String orElseThrow = Optional.ofNullable(value).orElseThrow(() -> new IllegalArgumentException());
        System.out.println("【orElseThrow】，exception：" + orElseThrow);
    }

    /**
     * 转换值-map map() 对值应用(调用)作为参数的函数，然后将返回的值包装在 Optional 中。这就使对返回值进行链试调用的操作成为可能
     * 
     * @param user
     */
    public static void map(User user) {
        String map = Optional.ofNullable(user).map(u -> u.getName()).orElse("转换值-map");
        System.out.println("【map】，result：" + map);
    }

    /**
     * 转换值-flatMap 既然 getter 方法返回 String 值的 Optional，你可以在对 User 的 Optional 对象调用 flatMap() 时，用它作为参数
     * 
     * @param user
     */
    public static void flatMap(User user) {
        String flatMap = Optional.ofNullable(user).flatMap(u -> u.getHobby()).orElse("转换值-flatMap");
        System.out.println("【flatMap】，result：" + flatMap);
    }

    /**
     * 添加过滤
     * 
     * @param user
     */
    public static void filter(User user) {
        boolean filter =
            Optional.ofNullable(user).filter(u -> u.getName() != null && u.getName().contains("m")).isPresent();
        System.out.println("【filter】，result：" + filter);
    }

    /**
     * 简化if...else...?
     * 
     * @param user
     * @param type
     */
    public static void doCheck(User user, int type) {
        String countryName = "";
        if (type == 0) {
            countryName = Optional.ofNullable(user).flatMap(u -> u.getAddress()).flatMap(u -> u.getCountry())
                .map(c -> c.getName()).orElse("濮阳");
        } else if (type == 1) {
            countryName = Optional.ofNullable(user).flatMap(User::getAddress).flatMap(Address::getCountry)
                .map(Country::getName).orElse("濮阳");
        }
        System.out.println("【doCheck】，result：" + countryName);
    }

    public static final String value = null;
    public static final User user0 = new User();

    public static void main(String[] args) {
        // of(null);// Exception in thread "main" java.lang.NullPointerException
        // ofNullable(null);// Exception in thread "main" java.util.NoSuchElementException: No value present

        // orElse(null);// 【orElse】，value：default
        // orElseGet(null);// 【orElseGet】，value：default

        // isPresent(null);// 【isPresent】，result：false
        // orElseThrow(null);// Exception in thread "main" java.lang.IllegalArgumentException

        // map(new User(6, null, "篮球-basketball"));// 【map】，result：转换值-map
        // flatMap(new User(6, "xm", null));// 【flatMap】，result：转换值-flatMap

        // filter(new User(6, "xx", "篮球-basketball"));// 【filter】，result：false

        // 正常情况下，拿出用户城市名称
        /*if (user != null) {
            Address address = user.getAddress();
            if (address != null) {
                Country country = address.getCountry();
                if (country != null) {
                    String isocode = country.getIsocode();
                    if (isocode != null) {
                        isocode = isocode.toUpperCase();
                    }
                }
            }
        }*/
        doCheck(new User(6, "xx", "篮球-basketball"), 0);// 【doCheck】，result：濮阳s
        doCheck(new User(6, "xx", "篮球-basketball"), 1);// 【doCheck】，result：濮阳s

    }
}

/**
 * 用户
 * 
 * @author wang-xiaoming
 * @date 2019年7月1日
 */
class User {
    private Integer sno;
    private String name;
    private String hobby;
    private Address address;

    public Integer getSno() {
        return sno;
    }

    public void setSno(Integer sno) {
        this.sno = sno;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Optional<String> getHobby() {
        return Optional.ofNullable(hobby);
    }

    public void setHobby(String hobby) {
        this.hobby = hobby;
    }

    public Optional<Address> getAddress() {
        return Optional.ofNullable(address);
    }

    public void setAddress(Address address) {
        this.address = address;
    }

    public User(Integer sno, String name, String hobby) {
        super();
        this.sno = sno;
        this.name = name;
        this.hobby = hobby;
    }

    public User() {
        super();
    }

}

/**
 * 地址
 * 
 * @author wang-xiaoming
 * @date 2019年7月1日
 */
class Address {
    private Country country;

    public Optional<Country> getCountry() {
        return Optional.ofNullable(country);
    }

    public void setCountry(Country country) {
        this.country = country;
    }

}

/**
 * 城市
 * 
 * @author wang-xiaoming
 * @date 2019年7月1日
 */
class Country {
    private String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

}

// 求出集合中小于4的个数
// int[] arr = {0, 2, 5, 8, -6};
Integer[] arr = {null, 2, 5, 8, -6};
List<Integer> list = Arrays.asList(arr);
System.out.println(list.stream().filter(rand -> rand != null && rand < 4).count());