一文教你搞定Java Optional类判空操作

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();
            }
        }
    }
}

String result = Optional.ofNullable(user)
    .map(u -> u.getAddress())
    .map(a -> a.getCountry())
    .map(c -> c.getIsocode())
    .orElse("default");

@Test
public void testOf() {
    Integer value = 2;
    // 正常
    Optional<Integer> op = Optional.of(value);

    value = null;
    // 报空指针
    op = Optional.of(value);
}

@Test
    public void testOfNullable() {
        Integer value = 2;
        // 正常
        Optional<Integer> op = Optional.ofNullable(value);
        value = null;
        // 不报错
        op = Optional.ofNullable(value);
    }

@Test
public void testGet() {
    Integer value = 2;
    // 正常
    Optional<Integer> op = Optional.ofNullable(value);
    Integer opVal = op.get();
    Assert.assertEquals(opVal, value);
    
    op = Optional.ofNullable(null);
    // 会抛出异常
    op.get();
}

@Test
public void testOrElse() {
    // 正常
    Optional<Integer> op = Optional.ofNullable(2);
    Integer opVal = op.orElse(3);
    Assert.assertEquals(opVal, new Integer(2));

    op = Optional.ofNullable(null);
    // 为空，则返回3
    opVal = op.orElse(3);
    Assert.assertEquals(opVal, new Integer(3));
}

@Test
public void testOrElseGet() {
    // 正常
    Optional<Integer> op = Optional.ofNullable(2);
    Integer opVal = op.orElseGet(()-> {
        return new Integer(3);
    });
    Assert.assertEquals(opVal, new Integer(2));

    op = Optional.ofNullable(null);
    // 为空，则返回3
    opVal = op.orElseGet(()-> {
        return new Integer(3);
    });
    Assert.assertEquals(opVal, new Integer(3));
}

@Test
public void testOrElseThrow() {
    Optional<Integer> op = Optional.ofNullable(null);
    // 为空，则抛出指定的异常类型
    Integer opVal = op.orElseThrow(()-> {
        return new RuntimeException();
    });
    // 或抛出runtime异常
    Assert.assertEquals(opVal, new Integer(3));
}

@Test
public void testIsPresent() {
    Optional<Integer> op = Optional.ofNullable(null);
    // 为空
    Assert.assertFalse(op.isPresent());
}

@Test
public void testIfPresent() {
    Optional<Integer> op = Optional.ofNullable(5);
    op.ifPresent(value -> {
        // 如果存在，打印出来
        System.out.println(value);
    });
}

@Test
public void testFilter() {
    // 不满足过滤条件，返回空 Optional
    Optional<String> op = Optional.ofNullable("10").filter(item -> "15".equals(item));
    Assert.assertFalse(op.isPresent());
}