Popular Java Utility Classes and Their Most Common Methods

In Java, utility classes provide a set of common functions that can be reused across projects.

This article presents the most popular Java utility classes and their most frequently used methods, ranked by popularity based on analysis of 50,000 open‑source Java projects on GitHub.

Readers can browse the list to discover ready‑made functionality and avoid reinventing the wheel; method names usually indicate their purpose, and developers can also examine how other open‑source projects use them.

org.apache.commons.io.IOUtils

closeQuietly()
toString()
copy()
toByteArray()
write()
toInputStream()
readLines()
copyLarge()
lineIterator()
readFully()

org.apache.commons.io.FileUtils

deleteDirectory()
readFileToString()
deleteQuietly()
copyFile()
writeStringToFile()
forceMkdir()
write()
listFiles()
copyDirectory()
forceDelete()

org.apache.commons.lang.StringUtils

isBlank()
isNotBlank()
isEmpty()
isNotEmpty()
equals()
join()
split()
EMPTY
trimToNull()
replace()

org.apache.http.util.EntityUtils

toString()
consume()
toByteArray()
consumeQuietly()
getContentCharSet()

org.apache.commons.lang3.StringUtils

isBlank()
isNotBlank()
isEmpty()
isNotEmpty()
join()
equals()
split()
EMPTY
replace()
capitalize()

org.apache.commons.io.FilenameUtils

getExtension()
getBaseName()
getName()
concat()
removeExtension()
normalize()
wildcardMatch()
separatorsToUnix()
getFullPath()
isExtension()

org.springframework.util.StringUtils

hasText()
hasLength()
isEmpty()
commaDelimitedListToStringArray()
collectionToDelimitedString()
replace()
delimitedListToStringArray()
uncapitalize()
collectionToCommaDelimitedString()
tokenizeToStringArray()

org.apache.commons.lang.ArrayUtils

contains()
addAll()
clone()
isEmpty()
add()
EMPTY_BYTE_ARRAY()
subarray()
indexOf()
isEquals()
toObject()

org.apache.commons.lang.StringEscapeUtils

escapeHtml()
unescapeHtml()
escapeXml()
escapeSql()
unescapeJava()
escapeJava()
escapeJavaScript()
unescapeXml()
unescapeJavaScript()

org.apache.http.client.utils.URLEncodedUtils

format()
parse()

org.apache.commons.codec.digest.DigestUtils

md5Hex()
shaHex()
sha256Hex()
sha1Hex()
sha()
md5()
sha512Hex()
sha1()

org.apache.commons.collections.CollectionUtils

isEmpty()
isNotEmpty()
select()
transform()
filter()
find()
collect()
forAllDo()
addAll()
isEqualCollection()

org.apache.commons.lang3.ArrayUtils

contains()
isEmpty()
isNotEmpty()
add()
clone()
addAll()
subarray()
indexOf()
EMPTY_OBJECT_ARRAY()
EMPTY_STRING_ARRAY()

org.apache.commons.beanutils.PropertyUtils

getProperty()
setProperty()
getPropertyDescriptors()
isReadable()
copyProperties()
getPropertyDescriptor()
getSimpleProperty()
isWriteable()
setSimpleProperty()
getPropertyType()

org.apache.commons.lang3.StringEscapeUtils

unescapeHtml4()
escapeHtml4()
escapeXml()
unescapeXml()
escapeJava()
escapeEcmaScript()
unescapeJava()
escapeJson()
escapeXml10()

org.apache.commons.beanutils.BeanUtils

copyProperties()
getProperty()
setProperty()
describe()
populate()
copyProperty()
cloneBean()

By reviewing these classes and methods, developers can quickly identify existing utilities that meet their needs, reduce duplicate code, and learn common usage patterns from real‑world open‑source projects.