Boost Java Productivity: 17 Essential Utility Classes Every Backend Developer Should Know

Preface

Java offers many handy utilities, often referred to as "wheels". By combining these utilities with IDE shortcuts, developers can dramatically improve productivity. This article shares 17 useful tools that can be applied in daily work.

1. Collections

The java.util.Collections class provides methods for operating on and returning collections.

1.1 Sorting

Sorting a list in ascending and descending order:

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);

Result:

[1, 2, 3]
[3, 2, 1]

1.2 Max/Min

Finding the maximum or minimum value in a collection:

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);

Result:

3
1

1.3 Thread‑Safe Collections

Convert a non‑thread‑safe collection to a synchronized version:

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

The underlying implementation creates SynchronizedRandomAccessList or SynchronizedList, which use synchronized locks.

1.4 Empty Collections

Return an immutable empty list when a collection is null or empty:

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

1.5 Binary Search

Perform a binary search on a sorted list:

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

Result:

2

1.6 Unmodifiable Collections

Create an immutable list that throws an exception on modification attempts:

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

Result:

Exception in thread "main" java.lang.UnsupportedOperationException

2. CollectionUtils

Beyond Collections, the CollectionUtils class from Spring ( org.springframework.util.CollectionUtils) and Apache Commons ( org.apache.commons.collections.CollectionUtils) provides additional utilities.

I personally recommend the Apache version because it offers more comprehensive methods.

2.1 Empty Check

Check if a collection is empty or not:

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

Union, intersection, disjunction, and subtraction of two collections:

Collection<Integer> union = CollectionUtils.union(list1, list2);
Collection<Integer> intersection = CollectionUtils.intersection(list1, list2);
Collection<Integer> disjunction = CollectionUtils.disjunction(list1, list2);
Collection<Integer> subtract = CollectionUtils.subtract(list1, list2);
System.out.println(union);
System.out.println(intersection);
System.out.println(disjunction);
System.out.println(subtract);

Result:

[1, 2, 3, 4]
[2]
[1, 3, 4]
[1, 3]

3. Lists (Guava)

The Guava library ( com.google.common.collect.Lists) 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);
System.out.println(list);

Result:

[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);

Result:

[[1, 4], [1, 5], [2, 4], [2, 5], [3, 4], [3, 5]]

3.4 Partition (Paging)

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

Result:

[[1, 2], [3, 4], [5]]

3.5 Transform (Stream‑like)

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

Result:

[A, B, C]

3.6 Reverse Order

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

Result:

[2, 1, 3]

4. Objects (JDK 7+)

4.1 Null Check

if (Objects.isNull(integer)) {
    System.out.println("Object is null");
}
if (Objects.nonNull(integer)) {
    System.out.println("Object is not null");
}

4.2 Require Non‑Null

Objects.requireNonNull(integer);
Objects.requireNonNull(integer, "Parameter cannot be null");
Objects.requireNonNull(integer, () -> "Parameter cannot be null");

4.3 Equality Check

System.out.println(Objects.equals(integer1, integer2));

Result:

true

4.4 Hash Code

System.out.println(Objects.hashCode(str));

Result:

96354

5. BooleanUtils (Apache Commons)

5.1 isTrue / isFalse

System.out.println(BooleanUtils.isTrue(aBoolean));
System.out.println(BooleanUtils.isFalse(aBoolean));

5.2 isNotTrue / isNotFalse

System.out.println(BooleanUtils.isNotTrue(aBoolean));
System.out.println(BooleanUtils.isNotTrue(aBoolean1));
System.out.println(BooleanUtils.isNotFalse(aBoolean));
System.out.println(BooleanUtils.isNotFalse(aBoolean1));

Result:

false
true
true
true

5.3 toInteger

System.out.println(BooleanUtils.toInteger(true));
System.out.println(BooleanUtils.toInteger(false));

Result:

1
0

5.4 toBoolean / toBooleanDefaultIfNull

System.out.println(BooleanUtils.toBoolean(aBoolean));
System.out.println(BooleanUtils.toBoolean(aBoolean1));
System.out.println(BooleanUtils.toBooleanDefaultIfNull(aBoolean1, false));

Result:

true
false
false

6. StringUtils (Apache Commons Lang)

6.1 Empty / Blank Checks

System.out.println(StringUtils.isEmpty(str1));
System.out.println(StringUtils.isBlank(str1));
System.out.println(StringUtils.isNotEmpty(str2));
System.out.println(StringUtils.isNotBlank(str2));

6.2 Split

System.out.println(StringUtils.split(null, ",")); // returns null

6.3 isNumeric

System.out.println(StringUtils.isNumeric("123"));
System.out.println(StringUtils.isNumeric("123q"));
System.out.println(StringUtils.isNumeric("0.33"));

Result:

true
false
false

6.4 Join

System.out.println(StringUtils.join(list, ","));
System.out.println(StringUtils.join(list2, " "));

Result:

a,b,c
1 2 3

7. Assert (Spring)

7.1 Parameter Null Check

Assert.isNull(str, "str must be null");
Assert.notNull(str, "str cannot be null");

7.2 Collection Empty Check

Assert.notEmpty(list, "list cannot be empty");
Assert.notEmpty(map, "map cannot be empty");

7.3 Condition Check

Assert.isTrue(CollectionUtils.isNotEmpty(list), "list cannot be empty");

8. IOUtils (Apache Commons IO)

8.1 Read File to String

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

8.2 Write String to File

IOUtils.write("abcde", 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 Read File to Byte Array

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

9. MDC (SLF4J)

MDC provides a thread‑local map for diagnostic context, useful for passing trace IDs across service calls. Example code shows a servlet filter that adds a UUID to MDC and a ClientHttpRequestInterceptor that copies the trace ID into HTTP headers.

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

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

public class MdcUtil {
    private static final String TRACE_ID = "TRACE_ID";
    public static String get() { return MDC.get(TRACE_ID); }
    public static void add(String value) { MDC.put(TRACE_ID, value); }
}

10. ClassUtils (Spring)

10.1 Get All Interfaces

Class<?>[] interfaces = ClassUtils.getAllInterfaces(new User());

10.2 Get Package Name

String pkg = ClassUtils.getPackageName(User.class);

10.3 Is Inner Class

System.out.println(ClassUtils.isInnerClass(User.class));

10.4 Is CGLIB Proxy

System.out.println(ClassUtils.isCglibProxy(new User()));

11. BeanUtils (Spring)

11.1 Copy Properties

User src = new User();
src.setId(1L);
src.setName("Example");
User dest = new User();
BeanUtils.copyProperties(src, dest);

11.2 Instantiate Class

User user = BeanUtils.instantiateClass(User.class);

11.3 Find Declared Method

Method m = BeanUtils.findDeclaredMethod(User.class, "getId");

11.4 Find Property for Method

PropertyDescriptor pd = BeanUtils.findPropertyForMethod(m);

12. ReflectionUtils (Spring)

12.1 Find Method

Method m = ReflectionUtils.findMethod(User.class, "getId");

12.2 Find Field

Field f = ReflectionUtils.findField(User.class, "id");

12.3 Invoke Method

ReflectionUtils.invokeMethod(m, beanInstance, param);

12.4 Is Public Static Final

System.out.println(ReflectionUtils.isPublicStaticFinal(f));

12.5 Is Equals Method

System.out.println(ReflectionUtils.isEqualsMethod(m));

13. Base64Utils (Spring)

String encoded = new String(Base64Utils.encode("abc".getBytes()));
String decoded = new String(Base64Utils.decode(encoded.getBytes()), "UTF-8");
System.out.println("Encoded: " + encoded);
System.out.println("Decoded: " + decoded);

Result:

Encoded: YWJj
Decoded: abc

14. StandardCharsets (Java)

String decoded = new String(Base64Utils.decode(encoded.getBytes()), StandardCharsets.UTF_8);

15. DigestUtils (Apache Commons Codec)

15.1 MD5

String md5 = DigestUtils.md5Hex("苏三说技术");
System.out.println(md5);

15.2 SHA‑256

String sha256 = DigestUtils.sha256Hex("苏三说技术");
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)

Instead of defining custom HTTP status constants, use the predefined enums in org.springframework.http.HttpStatus or org.apache.http.HttpStatus for standard codes such as 200, 404, 500, etc.