Essential Java Utility Classes and Their Most Popular Methods

In Java, utility classes provide a set of common functions that can be reused across projects. This article showcases the most popular Java utility classes and their most frequently used methods, based on analysis of 50,000 open‑source Java projects from GitHub.

The goal is to give developers ideas about existing, widely adopted functionality so they know when they can reuse rather than implement from scratch.

org.apache.commons.io.IOUtils

closeQuietly()<br/>toString()<br/>copy()<br/>toByteArray()<br/>write()<br/>toInputStream()<br/>readLines()<br/>copyLarge()<br/>lineIterator()<br/>readFully()<br/>

org.apache.commons.io.FileUtils

deleteDirectory()<br/>readFileToString()<br/>deleteQuietly()<br/>copyFile()<br/>writeStringToFile()<br/>forceMkdir()<br/>write()<br/>listFiles()<br/>copyDirectory()<br/>forceDelete()<br/>

org.apache.commons.lang.StringUtils

isBlank()<br/>isNotBlank()<br/>isEmpty()<br/>isNotEmpty()<br/>equals()<br/>join()<br/>split()<br/>EMPTY<br/>trimToNull()<br/>replace()<br/>

org.apache.http.util.EntityUtils

toString()<br/>consume()<br/>toByteArray()<br/>consumeQuietly()<br/>getContentCharSet()<br/>

org.apache.commons.lang3.StringUtils

isBlank()<br/>isNotBlank()<br/>isEmpty()<br/>isNotEmpty()<br/>join()<br/>equals()<br/>split()<br/>EMPTY<br/>replace()<br/>capitalize()<br/>

org.apache.commons.io.FilenameUtils

getExtension()<br/>getBaseName()<br/>getName()<br/>concat()<br/>removeExtension()<br/>normalize()<br/>wildcardMatch()<br/>separatorsToUnix()<br/>getFullPath()<br/>isExtension()<br/>

org.springframework.util.StringUtils

hasText()<br/>hasLength()<br/>isEmpty()<br/>commaDelimitedListToStringArray()<br/>collectionToDelimitedString()<br/>replace()<br/>delimitedListToStringArray()<br/>uncapitalize()<br/>collectionToCommaDelimitedString()<br/>tokenizeToStringArray()<br/>

org.apache.commons.lang.ArrayUtils

contains()<br/>addAll()<br/>clone()<br/>isEmpty()<br/>add()<br/>EMPTY_BYTE_ARRAY<br/>subarray()<br/>indexOf()<br/>isEquals()<br/>toObject()<br/>

org.apache.commons.lang.StringEscapeUtils

escapeHtml()<br/>unescapeHtml()<br/>escapeXml()<br/>escapeSql()<br/>unescapeJava()<br/>escapeJava()<br/>escapeJavaScript()<br/>unescapeXml()<br/>unescapeJavaScript()<br/>

org.apache.http.client.utils.URLEncodedUtils

format()<br/>parse()<br/>

org.apache.commons.codec.digest.DigestUtils

md5Hex()<br/>shaHex()<br/>sha256Hex()<br/>sha1Hex()<br/>sha()<br/>md5()<br/>sha512Hex()<br/>sha1()<br/>

org.apache.commons.collections.CollectionUtils

isEmpty()<br/>isNotEmpty()<br/>select()<br/>transform()<br/>filter()<br/>find()<br/>collect()<br/>forAllDo()<br/>addAll()<br/>isEqualCollection()<br/>

org.apache.commons.lang3.ArrayUtils

contains()<br/>isEmpty()<br/>isNotEmpty()<br/>add()<br/>clone()<br/>addAll()<br/>subarray()<br/>indexOf()<br/>EMPTY_OBJECT_ARRAY<br/>EMPTY_STRING_ARRAY<br/>

org.apache.commons.beanutils.PropertyUtils

getProperty()<br/>setProperty()<br/>getPropertyDescriptors()<br/>isReadable()<br/>copyProperties()<br/>getPropertyDescriptor()<br/>getSimpleProperty()<br/>isWriteable()<br/>setSimpleProperty()<br/>getPropertyType()<br/>

org.apache.commons.lang3.StringEscapeUtils

unescapeHtml4()<br/>escapeHtml4()<br/>escapeXml()<br/>unescapeXml()<br/>escapeJava()<br/>escapeEcmaScript()<br/>unescapeJava()<br/>escapeJson()<br/>escapeXml10()<br/>

org.apache.commons.beanutils.BeanUtils

copyProperties()<br/>getProperty()<br/>setProperty()<br/>describe()<br/>populate()<br/>copyProperty()<br/>cloneBean()<br/>