In Java, a utility class is a class that defines a set of methods that perform a common function.

This article shows the most commonly used Java utility classes and their most commonly used methods. The list of classes and its list of methods are sorted by popularity. The data is based on 50,000 open source Java projects randomly selected from GitHub.

Hopefully, you can browse the list to get an idea of some of the features that are already available and popular, so that you know you don’t need to implement them yourself. The names of these methods usually indicate what they do. If method names aren’t intuitive, you can also see how other developers use them in their open source projects.

org.apache.commons.io.IOUtils

isEmpty()  
isNotEmpty()  
select()  
transform()  
filter()  
find()  
collect()  
forAllDo()  
addAll()  
isEqualCollection() 
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org.apache.commons.io.FileUtils

deleteDirectory()  
readFileToString()  
deleteQuietly()  
copyFile()  
writeStringToFile()  
forceMkdir()  
write()  
listFiles()  
copyDirectory()  
forceDelete()  
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org.apache.commons.lang.StringUtils

isBlank()  
isNotBlank()  
isEmpty()  
isNotEmpty()  
equals()  
join()  
split()  
EMPTY  
trimToNull()  
replace()  
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org.apache.http.util.EntityUtils

toString()  
consume()  
toByteArray()  
consumeQuietly()  
getContentCharSet()  
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org.apache.commons.lang3.StringUtils

isBlank()  
isNotBlank()  
isEmpty()  
isNotEmpty()  
join()  
equals()  
split()  
EMPTY  
replace()  
capitalize()  
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org.apache.commons.io.FilenameUtils

getExtension()  
getBaseName()  
getName()  
concat()  
removeExtension()  
normalize()  
wildcardMatch()  
separatorsToUnix()  
getFullPath()  
isExtension()  
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org.springframework.util.StringUtils

hasText()  
hasLength()  
isEmpty()  
commaDelimitedListToStringArray()  
collectionToDelimitedString()  
replace()  
delimitedListToStringArray()  
uncapitalize()  
collectionToCommaDelimitedString()  
tokenizeToStringArray()  
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org.apache.commons.lang.ArrayUtils

contains()  
addAll()  
clone()  
isEmpty()  
add()  
EMPTY_BYTE_ARRAY  
subarray()  
indexOf()  
isEquals()  
toObject()  
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org.apache.commons.lang.StringEscapeUtils

escapeHtml()  
unescapeHtml()  
escapeXml()  
escapeSql()  
unescapeJava()  
escapeJava()  
escapeJavaScript()  
unescapeXml()  
unescapeJavaScript()  
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org.apache.http.client.utils.URLEncodedUtils

format()  
parse()  
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org.apache.commons.codec.digest.DigestUtils

md5Hex()  
shaHex()  
sha256Hex()  
sha1Hex()  
sha()  
md5()  
sha512Hex()  
sha1()  
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org.apache.commons.collections.CollectionUtils

isEmpty()  
isNotEmpty()  
select()  
transform()  
filter()  
find()  
collect()  
forAllDo()  
addAll()  
isEqualCollection()  
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org.apache.commons.lang3.ArrayUtils

contains()  
isEmpty()  
isNotEmpty()  
add()  
clone()  
addAll()  
subarray()  
indexOf()  
EMPTY_OBJECT_ARRAY  
EMPTY_STRING_ARRAY  
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org.apache.commons.beanutils.PropertyUtils

getProperty()  
setProperty()  
getPropertyDescriptors()  
isReadable()  
copyProperties()  
getPropertyDescriptor()  
getSimpleProperty()  
isWriteable()  
setSimpleProperty()  
getPropertyType()  
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org.apache.commons.lang3.StringEscapeUtils

unescapeHtml4()  
escapeHtml4()  
escapeXml()  
unescapeXml()  
escapeJava()  
escapeEcmaScript()  
unescapeJava()  
escapeJson()  
escapeXml10()  
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org.apache.commons.beanutils.BeanUtils

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