Popular Java Utility Classes and Their Most Frequently Used Methods

In Java, utility classes are collections of static methods that perform common tasks.

This article showcases the most popular Java utility classes and their most frequently used methods, with popularity rankings based on data collected from 50,000 randomly selected open‑source Java projects on GitHub.

By browsing the list you can get ideas of existing functionality, understand what is already provided, and avoid implementing these features yourself; method names usually indicate their purpose, and you can also see how other developers use them in real projects.

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()
isEmpty()
isNotEmpty()
add()
clone()
addAll()
subarray()
indexOf()
EMPTY_BYTE_ARRAY()
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.beanutils.PropertyUtils

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

org.apache.commons.lang3.ArrayUtils

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

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()

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