java isnull方法_Java 检查判断变量null(空值)的方法示例代码
1、一般方法判断null值if(country != null && country.getCity() != null && country.getCity().getSchool() != null && country.getCity().getSchool().getStudent() != null .....) {
isValid = true;
}
2、通过Optional判断null值if (Optional.ofNullable(country)
.map(Country::getCity)
.map(City::getSchool)
.map(School::getStudent)
.isPresent()) {
isValid = true;
}
或boolean isValid = Optional.ofNullable(country)
.map(Country::getCity)
.map(City::getSchool)
.map(School::getStudent)
.isPresent();
或boolean isValid = Optional.ofNullable(country)
.map(country -> country.getCity()) //Or use method reference Country::getCity
.map(city -> city.getSchool())
.map(school -> school.getStudent())
.map(student -> true)
.orElse(false);
3、使用Supplier var-args参数判断null值
boolean isValid = isValid(() -> address, // first level
() -> address.getCity(), // second level
() -> address.getCountry(),// second level
() -> address.getStreet(), // second level
() -> address.getZip(), // second level
() -> address.getCountry() // third level
.getISO()
@SafeVarargs
public static boolean isValid(Supplier... suppliers) {
for (Supplier supplier : suppliers) {
if (Objects.isNull(supplier.get())) {
// log, handle specific thing if required
return false;
}
}
return true;
}
或
boolean isValid = isValid( Arrays.asList("address", "city", "country",
"street", "zip", "Country ISO"),
() -> address, // first level
() -> address.getCity(), // second level
() -> address.getCountry(),// second level
() -> address.getStreet(), // second level
() -> address.getZip(), // second level
() -> address.getCountry() // third level
.getISO()
);
@SafeVarargs
public static boolean isValid(List fieldNames, Supplier... suppliers) {
if (fieldNames.size() != suppliers.length){
throw new IllegalArgumentException("...");
}
for (int i = 0; i < suppliers.length; i++) {
if (Objects.isNull(suppliers.get(i).get())) {
LOGGER.info( fieldNames.get(i) + " is null");
return false;
}
}
return true;
}