StringUtils
String input1 = null;
String input2 = "";
String input3 = " ";
String input4 = "Data";
System.out.println(StringUtils.isEmpty(input1)); // true
System.out.println(StringUtils.isBlank(input3)); // true
System.out.println(StringUtils.isNotBlank(input4)); // true
String raw = "apple,banana,orange";
String[] tokens = StringUtils.split(raw, ',');
// または
String[] safeTokens = StringUtils.split(null, ','); // nullを返却
System.out.println(StringUtils.isNumeric("98765")); // true
System.out.println(StringUtils.isNumeric("98.76")); // false
List values = Arrays.asList(10, 20, 30);
String combined = StringUtils.join(values, "|"); // "10|20|30"
Collections
List items = new ArrayList<>(Arrays.asList("carrot", "broccoli", "spinach"));
Collections.sort(items);
System.out.println(items); // [broccoli, carrot, spinach]
Collections.sort(items, Comparator.reverseOrder());
System.out.println(items); // [spinach, carrot, broccoli]
List temperatures = Arrays.asList(36.5, 37.2, 35.8);
double maxTemp = Collections.max(temperatures);
double minTemp = Collections.min(temperatures);
public List filterItems(List data) {
return (data != null && !data.isEmpty()) ? data : Collections.emptyList();
}
List mutableData = new ArrayList<>(Arrays.asList(5, 10, 15));
List immutableData = Collections.unmodifiableList(mutableData);
List threadSafeData = Collections.synchronizedList(new ArrayList<>(Arrays.asList(1, 2, 3)));
CollectionUtils
List setA = Arrays.asList(1, 3, 5);
List setB = Arrays.asList(3, 5, 7);
Collection merged = CollectionUtils.union(setA, setB); // {1,3,5,7}
Collection common = CollectionUtils.intersection(setA, setB); // {3,5}
Collection exclusive = CollectionUtils.disjunction(setA, setB); // {1,7}
Lists (Guava)
List values = Lists.newArrayList(7, 8, 9, 10);
List> chunks = Lists.partition(values, 3); // [[7,8,9],[10]]
List nums1 = Lists.newArrayList(1, 2);
List nums2 = Lists.newArrayList(3, 4);
List> cartesian = Lists.cartesianProduct(nums1, nums2);
// [[1,3],[1,4],[2,3],[2,4]]
List words = Lists.newArrayList("hello", "world");
List upperWords = Lists.transform(words, String::toUpperCase);
List reversed = Lists.reverse(Lists.newArrayList(5, 3, 1));
Objects
Integer value = 42;
Objects.requireNonNull(value, "値がnullです");
String str1 = "Test";
String str2 = "test";
System.out.println(Objects.equals(str1, str2.toLowerCase())); // true
BeanUtils
Employee source = new Employee();
source.setEmployeeId(1001);
source.setName("Alex Johnson");
Employee target = new Employee();
BeanUtils.copyProperties(source, target);
// targetのプロパティがsourceからコピー
Method getter = BeanUtils.findDeclaredMethod(Employee.class, "getEmployeeId");
PropertyDescriptor prop = BeanUtils.findPropertyForMethod(getter);
System.out.println(prop.getName()); // employeeId
ReflectionUtils
Field idField = ReflectionUtils.findField(Employee.class, "employeeId");
Method nameMethod = ReflectionUtils.findMethod(Employee.class, "getName");
ReflectionUtils.invokeMethod(nameMethod, employeeInstance);
System.out.println(ReflectionUtils.isPublicStaticFinal(idField));
DigestUtils
String md5Hash = DigestUtils.md5Hex("secure_password");
// 2a4d0e1a0a3b0c1d4e5f678901234567
String sha256Hash = DigestUtils.sha256Hex("secure_password");
// 7e1d3a8b9c0f1e2d3a4b5c6d7e8f9a0b1c2d3e4f5a6b7c8d9e0f1a2b3c4d5e6f7
HttpStatus
HttpStatus success = HttpStatus.CREATED;
System.out.println(success.value()); // 201
HttpStatus error = HttpStatus.NOT_FOUND;
System.out.println(error.getReasonPhrase()); // Not Found