@Data
@AllArgsConstructor
@NoArgsConstructor
class Student {
    private String name;
    private Integer age;
}

public void test1() {
    // 聲明一個(gè)空Optional
    Optional<Object> empty = Optional.empty();
    
    // 依據(jù)一個(gè)非空值創(chuàng)建Optional
    Student student = new Student();
    Optional<Student> os1 = Optional.of(student);
    
    // 可接受null的Optional
    Student student1 = null;
    Optional<Student> os2 = Optional.ofNullable(student1);
}    

public void test1() {
    Student student = new Student();
    Optional<Student> os1 = Optional.ofNullable(student);
    boolean present = os1.isPresent();
    System.out.println(present);

    // 利用Optional的ifPresent方法做出如下：當(dāng)student不為空的時(shí)候?qū)ame賦值為張三
    Optional.ofNullable(student).ifPresent(p -> p.setName("張三"));
}

public void test1() throws Exception {
    Student student = null;
    Optional<Student> os1 = Optional.ofNullable(student);
    // 使用get一定要注意，假如student對(duì)象為空，get是會(huì)報(bào)錯(cuò)的
    // java.util.NoSuchElementException: No value present
    Student student1 = os1.get();

    // 當(dāng)student為空的時(shí)候,返回我們新建的這個(gè)對(duì)象,有點(diǎn)像三目運(yùn)算的感覺(jué)
    Student student2 = os1.orElse(new Student("張三", 18));

    // orElseGet就是當(dāng)student為空的時(shí)候，返回通過(guò)Supplier供應(yīng)商函數(shù)創(chuàng)建的對(duì)象
    Student student3 = os1.orElseGet(() -> new Student("張三", 18));

    // orElseThrow就是當(dāng)student為空的時(shí)候，可以拋出我們指定的異常
    os1.orElseThrow(() -> new Exception());
}

public void test1() {
    Student student = new Student("李四", 3);
    Optional<Student> os1 = Optional.ofNullable(student);
    os1.filter(p -> p.getName().equals("張三")).ifPresent(x -> System.out.println("OK"));
}

public void test1() {
     Student student = new Student("李四", 3);
     Optional<Student> os1 = Optional.ofNullable(student);
     // 如果student對(duì)象不為空，就加一歲
     Optional<Student> emp = os1.map(e ->
     {
         e.setAge(e.getAge() + 1);
         return e;
     });
 }

public static Optional<Integer> stringToInt(String s) {
     try {
         return Optional.of(Integer.parseInt(s));
     } catch (NumberFormatException e) {
         e.printStackTrace();
         return Optional.empty();
     }
 }

Optional.ofNullable(props.getProperty(name))
        .flatMap(OptionalUtils::stringToInt)
        .filter(i -> i>0)
        .orElse(0);

PatientInfo patientInfo = patientInfoDao.getPatientInfoById(consultOrder.getPatientId());
if (patientInfo != null) {
    consultInfoResp.setPatientHead(patientInfo.getHead());
}

// 使用Optional 和函數(shù)式編程，一行搞定，而且像說(shuō)話一樣
Optional.ofNullable(patientInfo).ifPresent(p -> consultInfoResp.setPatientHead(p.getHead()));

public void test1() throws Exception {
    Student student = new Student(null, 3);
    if (student == null || isEmpty(student.getName())) {
        throw new Exception();
    }
    String name = student.getName();
    // 業(yè)務(wù)省略...

    // 使用Optional改造
    Optional.ofNullable(student).filter(s -> !isEmpty(s.getName())).orElseThrow(() -> new Exception());
}

public static boolean isEmpty(CharSequence str) {
    return str == null || str.length() == 0;
}

public static String getChampionName(Competition comp) throws IllegalArgumentException {
    if (comp != null) {
        CompResult result = comp.getResult();
        if (result != null) {
            User champion = result.getChampion();
            if (champion != null) {
                return champion.getName();
            }
        }
    }
    throw new IllegalArgumentException("The value of param comp isn't available.");
}

comp.getResult().getChampion().getName()

public static String getChampionName(Competition comp) throws IllegalArgumentException {
    return Optional.ofNullable(comp)
            .map(Competition::getResult)  // 相當(dāng)于c -> c.getResult()，下同
            .map(CompResult::getChampion)
            .map(User::getName)
            .orElseThrow(()->new IllegalArgumentException("The value of param comp isn't available."));
}

int timeout = Optional.ofNullable(redisProperties.getTimeout())
                      .map(x -> Long.valueOf(x.toMillis()).intValue())
                      .orElse(10000);