Boost Java Development Efficiency with 17 Essential Utility Classes

Preface

Java offers many handy utilities, often referred to as "wheels," that can dramatically improve development efficiency when combined with IDE shortcuts.

1. Collections

The java.util.Collections class provides common collection operations.

1.1 Sorting

List<Integer> list = new ArrayList<>();
list.add(2);
list.add(1);
list.add(3);
Collections.sort(list); // ascending
System.out.println(list);
Collections.reverse(list); // descending
System.out.println(list);

1.2 Max/Min

List<Integer> list = new ArrayList<>();
list.add(2);
list.add(1);
list.add(3);
Integer max = Collections.max(list);
Integer min = Collections.min(list);
System.out.println(max);
System.out.println(min);

1.3 Thread‑Safe Collections

List<Integer> list = new ArrayList<>();
list.add(2);
list.add(1);
list.add(3);
List<Integer> syncList = Collections.synchronizedList(list);
System.out.println(syncList);

1.4 Empty Collections

private List<Integer> fun(List<Integer> list) {
    if (list == null || list.size() == 0) {
        return Collections.emptyList();
    }
    // business logic
    return list;
}

1.5 Binary Search

List<Integer> list = new ArrayList<>();
list.add(2);
list.add(1);
list.add(3);
int i = Collections.binarySearch(list, 3);
System.out.println(i);

1.6 Unmodifiable Collections

List<Integer> list = new ArrayList<>();
list.add(2);
list.add(1);
list.add(3);
List<Integer> unmod = Collections.unmodifiableList(list);
unmod.add(4); // throws UnsupportedOperationException

2. CollectionUtils

Beyond Collections, the CollectionUtils class from Apache Commons or Spring provides additional helpers.

2.1 Empty Check

List<Integer> list = new ArrayList<>();
list.add(2);
list.add(1);
list.add(3);
if (CollectionUtils.isEmpty(list)) {
    System.out.println("Collection is empty");
}
if (CollectionUtils.isNotEmpty(list)) {
    System.out.println("Collection is not empty");
}

2.2 Set Operations

List<Integer> list = new ArrayList<>();
list.add(2);
list.add(1);
list.add(3);
List<Integer> list2 = new ArrayList<>();
list2.add(2);
list2.add(4);
Collection<Integer> union = CollectionUtils.union(list, list2);
Collection<Integer> intersection = CollectionUtils.intersection(list, list2);
Collection<Integer> disjunction = CollectionUtils.disjunction(list, list2);
Collection<Integer> subtract = CollectionUtils.subtract(list, list2);
System.out.println(union);
System.out.println(intersection);
System.out.println(disjunction);
System.out.println(subtract);

3. Lists (Guava)

Guava’s Lists class offers convenient list utilities.

3.1 Create Empty List

List<Integer> list = Lists.newArrayList();

3.2 Initialize List

List<Integer> list = Lists.newArrayList(1, 2, 3);

3.3 Cartesian Product

List<Integer> list1 = Lists.newArrayList(1, 2, 3);
List<Integer> list2 = Lists.newArrayList(4, 5);
List<List<Integer>> product = Lists.cartesianProduct(list1, list2);
System.out.println(product);

3.4 Partition

List<Integer> list = Lists.newArrayList(1, 2, 3, 4, 5);
List<List<Integer>> partitions = Lists.partition(list, 2);
System.out.println(partitions);

3.5 Transform

List<String> list = Lists.newArrayList("a", "b", "c");
List<String> upper = Lists.transform(list, x -> x.toUpperCase());
System.out.println(upper);

3.6 Reverse

List<Integer> list = Lists.newArrayList(3, 1, 2);
List<Integer> rev = Lists.reverse(list);
System.out.println(rev);

4. Objects (JDK 7+)

4.1 Null Checks

Integer i = new Integer(1);
if (Objects.isNull(i)) {
    System.out.println("null");
}
if (Objects.nonNull(i)) {
    System.out.println("not null");
}

4.2 requireNonNull

Integer i = new Integer(128);
Objects.requireNonNull(i);
Objects.requireNonNull(i, "parameter cannot be null");

4.3 Equality

Integer a = new Integer(1);
Long b = new Long(1);
System.out.println(Objects.equals(a, b)); // false

4.4 hashCode

String s = new String("abc");
System.out.println(Objects.hashCode(s));

5. BooleanUtils (Apache Commons)

5.1 isTrue / isFalse

Boolean b = new Boolean(true);
System.out.println(BooleanUtils.isTrue(b));
System.out.println(BooleanUtils.isFalse(b));

5.2 isNotTrue / isNotFalse

Boolean b = new Boolean(true);
Boolean bNull = null;
System.out.println(BooleanUtils.isNotTrue(b));
System.out.println(BooleanUtils.isNotTrue(bNull));
System.out.println(BooleanUtils.isNotFalse(b));
System.out.println(BooleanUtils.isNotFalse(bNull));

5.3 toInteger

Boolean b = new Boolean(true);
Boolean bFalse = new Boolean(false);
System.out.println(BooleanUtils.toInteger(b)); // 1
System.out.println(BooleanUtils.toInteger(bFalse)); // 0

5.4 toBoolean

Boolean b = new Boolean(true);
Boolean bNull = null;
System.out.println(BooleanUtils.toBoolean(b));
System.out.println(BooleanUtils.toBoolean(bNull));
System.out.println(BooleanUtils.toBooleanDefaultIfNull(bNull, false));

6. StringUtils (Apache Commons Lang)

6.1 Empty / Blank Checks

String s1 = null;
String s2 = "";
String s3 = " ";
String s4 = "abc";
System.out.println(StringUtils.isEmpty(s1));
System.out.println(StringUtils.isBlank(s3));
System.out.println(StringUtils.isNotBlank(s4));

6.2 Split

String s = null;
System.out.println(StringUtils.split(s, ",")); // null, no NPE

6.3 isNumeric

System.out.println(StringUtils.isNumeric("123")); // true
System.out.println(StringUtils.isNumeric("123a")); // false

6.4 join

List<String> list = Lists.newArrayList("a", "b", "c");
System.out.println(StringUtils.join(list, ","));

7. Assert (Spring)

String str = null;
Assert.isNull(str, "must be null");
Assert.notNull(str, "must not be null"); // throws IllegalArgumentException

8. IOUtils (Apache Commons IO)

8.1 Read File

String content = IOUtils.toString(new FileInputStream("/temp/a.txt"), StandardCharsets.UTF_8);
System.out.println(content);

8.2 Write File

String data = "abcde";
IOUtils.write(data, new FileOutputStream("/temp/b.txt"), StandardCharsets.UTF_8);

8.3 Copy File

IOUtils.copy(new FileInputStream("/temp/a.txt"), new FileOutputStream("/temp/b.txt"));

8.4 toByteArray

byte[] bytes = IOUtils.toByteArray(new FileInputStream("/temp/a.txt"));

9. MDC (SLF4J)

Using MDC to store a traceId per request and propagate it via a ClientHttpRequestInterceptor for logging and tracing.

public class LogFilter implements Filter {
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) {
        MdcUtil.add(UUID.randomUUID().toString());
        chain.doFilter(request, response);
    }
}

public class RestTemplateInterceptor implements ClientHttpRequestInterceptor {
    public ClientHttpResponse intercept(HttpRequest request, byte[] body, ClientHttpRequestExecution execution) {
        request.getHeaders().set("traceId", MdcUtil.get());
        return execution.execute(request, body);
    }
}

10. ClassUtils (Spring)

Class<?>[] interfaces = ClassUtils.getAllInterfaces(new User());
String pkg = ClassUtils.getPackageName(User.class);
System.out.println(ClassUtils.isInnerClass(User.class));
System.out.println(ClassUtils.isCglibProxy(new User()));

11. BeanUtils (Spring)

User u1 = new User();
u1.setId(1L);
u1.setName("SuSan");
User u2 = new User();
BeanUtils.copyProperties(u1, u2);
System.out.println(u2);

User u = BeanUtils.instantiateClass(User.class);
Method m = BeanUtils.findDeclaredMethod(User.class, "getId");
System.out.println(m.getName());

12. ReflectionUtils (Spring)

Method m = ReflectionUtils.findMethod(User.class, "getId");
Field f = ReflectionUtils.findField(User.class, "id");
ReflectionUtils.invokeMethod(m, userInstance);
System.out.println(ReflectionUtils.isPublicStaticFinal(f));

13. Base64Utils (Spring)

String str = "abc";
String encoded = new String(Base64Utils.encode(str.getBytes()));
String decoded = new String(Base64Utils.decode(encoded.getBytes()), StandardCharsets.UTF_8);
System.out.println(encoded);
System.out.println(decoded);

14. StandardCharsets (Java)

Use StandardCharsets.UTF_8 instead of string literals for charset specifications.

15. DigestUtils (Apache Commons Codec)

String md5 = DigestUtils.md5Hex("SuSan says tech");
String sha256 = DigestUtils.sha256Hex("SuSan says tech");
System.out.println(md5);
System.out.println(sha256);

16. SerializationUtils (Spring)

Map<String, String> map = new HashMap<>();
map.put("a", "1");
byte[] data = SerializationUtils.serialize(map);
Object obj = SerializationUtils.deserialize(data);
System.out.println(obj);

17. HttpStatus (Spring / Apache)

Use the predefined HttpStatus enum constants (e.g., HttpStatus.OK, HttpStatus.NOT_FOUND) instead of hard‑coding numeric status codes.