Boost Java Productivity: Essential Utility Libraries and Code Snippets

Java provides built‑in utility methods for common tasks. The following examples show how to join a list, compare strings case‑insensitively, perform null‑safe equality checks, and compute the intersection of two lists.

1. Built‑in Java utilities

1.1 Join a List into a comma‑separated string

List<String> list = Arrays.asList("a", "b", "c");
// Stream API
String joined = list.stream().collect(Collectors.joining(","));
System.out.println(joined); // a,b,c

// String.join
String joined2 = String.join(",", list);
System.out.println(joined2); // a,b,c

1.2 Case‑insensitive string comparison

if (strA.equalsIgnoreCase(strB)) {
    System.out.println("equal");
}

1.3 Null‑safe object equality

boolean eq = Objects.equals(strA, strB);

Source implementation:

public static boolean equals(Object a, Object b) {
    return (a == b) || (a != null && a.equals(b));
}

1.4 Intersection of two lists

List<String> list1 = new ArrayList<>();
list1.add("a");
list1.add("b");
list1.add("c");

List<String> list2 = new ArrayList<>();
list2.add("a");
list2.add("b");
list2.add("d");

// retain common elements
list1.retainAll(list2);
System.out.println(list1); // [a, b]

2. Apache Commons utilities

2.1 commons‑lang3 (enhanced java.lang)

Maven dependency:

<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-lang3</artifactId>
    <version>3.12.0</version>
</dependency>

2.1.1 String emptiness checks

StringUtils.isEmpty(cs);      // true if cs is null or length 0
StringUtils.isNotEmpty(cs);   // opposite
StringUtils.isBlank(cs);      // true if cs is null, empty or whitespace only
StringUtils.isNotBlank(cs);   // opposite

2.1.2 Capitalize first letter

String s = "yideng";
String capitalized = StringUtils.capitalize(s);
System.out.println(capitalized); // Yideng

2.1.3 Repeat a string

String repeated = StringUtils.repeat("ab", 2);
System.out.println(repeated); // abab

2.1.4 Date formatting and parsing

// Date → String
String now = DateFormatUtils.format(new Date(), "yyyy-MM-dd HH:mm:ss");
System.out.println(now);

// String → Date
Date parsed = DateUtils.parseDate("2021-05-01 01:01:01", "yyyy-MM-dd HH:mm:ss");

// Add one hour
Date later = DateUtils.addHours(new Date(), 1);

2.1.5 Temporary object wrappers

// Pair
ImmutablePair<Integer, String> pair = ImmutablePair.of(1, "yideng");
System.out.println(pair.getLeft() + "," + pair.getRight()); // 1,yideng

// Triple
ImmutableTriple<Integer, String, Date> triple = ImmutableTriple.of(1, "yideng", new Date());
System.out.println(triple.getLeft() + "," + triple.getMiddle() + "," + triple.getRight());

2.2 commons‑collections4 (collection utilities)

Maven dependency:

<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-collections4</artifactId>
    <version>4.4</version>
</dependency>

2.2.1 Collection emptiness and set operations

CollectionUtils.isEmpty(coll);      // true if null or empty
CollectionUtils.isNotEmpty(coll);   // opposite

Collection<String> intersect = CollectionUtils.retainAll(listA, listB);
Collection<String> union = CollectionUtils.union(listA, listB);
Collection<String> diff = CollectionUtils.subtract(listA, listB);

2.3 commons‑beanutils (bean manipulation)

Maven dependency:

<dependency>
    <groupId>commons-beanutils</groupId>
    <artifactId>commons-beanutils</artifactId>
    <version>1.9.4</version>
</dependency>

2.3.1 Set and get bean properties, map conversion

User user = new User();
BeanUtils.setProperty(user, "id", 1);
BeanUtils.setProperty(user, "name", "yideng");
System.out.println(BeanUtils.getProperty(user, "name")); // yideng

Map<String, String> map = BeanUtils.describe(user);
System.out.println(map); // {id=1, name=yideng}

User newUser = new User();
BeanUtils.populate(newUser, map);
System.out.println(newUser); // {id=1, name=yideng}

2.4 commons‑io (I/O utilities)

Maven dependency:

<dependency>
    <groupId>commons-io</groupId>
    <artifactId>commons-io</artifactId>
    <version>2.8.0</version>
</dependency>

2.4.1 File read/write/copy

File src = new File("demo1.txt");
List<String> lines = FileUtils.readLines(src, Charset.defaultCharset());

File dest = new File("demo2.txt");
FileUtils.writeLines(dest, lines);

FileUtils.copyFile(src, new File("demoCopy.txt"));

3. Google Guava utilities

Maven dependency:

<dependency>
    <groupId>com.google.guava</groupId>
    <artifactId>guava</artifactId>
    <version>30.1.1-jre</version>
</dependency>

3.1 Collection factories

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

List<List<Integer>> partitions = Lists.partition(numbers, 10);
Map<String, String> map = Maps.newHashMap();
Set<String> set = Sets.newHashSet();

3.2 Advanced collection types

3.2.1 Multimap (one key → multiple values)

Multimap<String, Integer> multimap = ArrayListMultimap.create();
multimap.put("key", 1);
multimap.put("key", 2);
System.out.println(multimap); // {key=[1, 2]}

Map<String, Collection<Integer>> asMap = multimap.asMap();

3.2.2 BiMap (bijective map)

BiMap<String, String> biMap = HashBiMap.create();
biMap.put("key", "value");
System.out.println(biMap); // {key=value}

BiMap<String, String> inverse = biMap.inverse();
System.out.println(inverse); // {value=key}

3.2.3 Table (two‑dimensional map)

Table<Integer, String, String> table = HashBasedTable.create();
table.put(18, "male", "yideng");
table.put(18, "female", "Lily");

System.out.println(table.get(18, "male")); // yideng
System.out.println(table.row(18)); // {male=yideng, female=Lily}
System.out.println(table.column("male")); // {18=yideng}

3.2.4 Multiset (bag for counting)

Multiset<String> multiset = HashMultiset.create();
multiset.add("apple");
multiset.add("apple");
multiset.add("orange");

System.out.println(multiset.count("apple")); // 2
System.out.println(multiset.elementSet()); // [orange, apple]

multiset.setCount("apple", 5);