Unlock Java Power: Master Guava’s Joiner, Splitter, CharMatcher & More

Preface

Alibaba's Java coding standards are revered, but the author's company forbids using them.

Google Guava is widely used; this blog shares the author's experience with Guava, promising more enjoyable and elegant Java coding.

Object‑Oriented String Handling

Joiner / Splitter / CharMatcher

JDK's String API can be cumbersome; Guava offers Joiner and Splitter to simplify concatenation and splitting.

Joiner / Splitter

Example of Joiner and Splitter usage:

Joiner connects strings, Splitter splits them; both can be defined as static final and are well‑tested, more efficient than Apache Commons.

Common Joiner methods: skipNulls() , useForNull(String) .

Common Splitter methods: trimResults() , omitEmptyStrings() ; supports regex and fixed‑length splitting.

CharMatcher

Guava also provides CharMatcher for flexible character matching and processing.

It extends JDK primitive operations, offering utilities for Bytes, Shorts, Ints, Longs, Floats, Doubles, Chars, Booleans.

Guava Collections Enhancements

Multiset

Multiset is an unordered collection that allows duplicate elements, filling the gap between List and Set.

Immutable vs Unmodifiable

Unmodifiable collections are views of the original mutable collection; changes to the source affect the view.

Guava’s Immutable collections provide true immutability and thread‑safety via copy‑on‑write (e.g., ImmutableList, ImmutableSet, ImmutableMap).

Multimap

Multimap supports one key mapping to multiple values, avoiding manual Map<k, List<v>> handling.

All Guava collections have a create method to simplify generic declarations.

BiMap

BiMap provides a bidirectional map where both keys and values are unique, allowing lookup in both directions.

inverse() returns the reverse view; inverse().inverse() returns the original map.

Table

Table models a two‑dimensional map with rowKey , columnKey , and value , simplifying composite‑key scenarios.

Functional Programming Utilities

Functions

Functions enable transformation of collections, such as truncating strings and converting to uppercase.

Predicate

Predicate is commonly used for filtering collections; Guava provides Collections2.filter as an alternative to a non‑existent List.filter method.

Null‑Handling and Preconditions

Guava uses Preconditions.checkNotNull to fail fast on null arguments.

Cache

Guava’s local Cache offers a simple, efficient, thread‑safe caching solution without external services.

Asynchronous Callbacks

Guava can decorate JDK executors to add listener callbacks, simplifying asynchronous programming.

Summary

The article only scratches the surface of Guava; many more features exist, such as reflection, annotations, networking, concurrency, and I/O.