Popular Java Utility Classes and Their Most Frequently Used Methods

In Java, utility classes provide a set of common methods; this article presents the most frequently used and popular Java utility classes, ranked by popularity based on data from 50,000 randomly selected open‑source projects.

1. org.apache.commons.io.IOUtils

closeQuietly: Close an IO stream, socket, or selector without throwing exceptions, typically used in a finally block.

toString: Convert an IO stream, URI, or byte[] to a String.

copy: Copy data from an input stream to an output stream, supporting up to 2 GB.

toByteArray: Obtain a byte[] from an input stream or URI.

write: Write bytes or characters to an output stream.

toInputStream: Convert characters to an InputStream.

readLines: Read multiple lines from an input stream and return a List<String>.

copyLarge: Same as copy but supports data larger than 2 GB.

lineIterator: Return an iterator over lines from an input stream, reading all data or failing if insufficient.

2. org.apache.commons.io.FileUtils

deleteDirectory: Delete a directory.

readFileToString: Read file content as a String.

deleteQuietly: Delete a file or directory without throwing exceptions.

copyFile: Copy a file.

writeStringToFile: Write a String to a target file, creating the file if it does not exist.

forceMkdir: Force creation of a directory, creating parent directories if needed.

write: Write characters to a specified file.

listFiles: List files in a directory based on a filter.

copyDirectory: Copy a directory.

forceDelete: Force deletion of a file.

3. org.apache.commons.lang.StringUtils

isBlank: Check if a string is empty after trimming.

isEmpty: Check if a string is empty without trimming.

equals: Determine if two strings are equal.

join: Join an array into a single string with an optional separator.

split: Split a string.

EMPTY: Return an empty string.

trimToNull: Trim a string and return null if the result is empty.

replace: Replace substrings within a string.

4. org.apache.http.util.EntityUtils

toString: Convert an HttpEntity to a String.

consume: Ensure the entire content of an HttpEntity is consumed.

toByteArray: Convert an HttpEntity to a byte array.

consumeQuietly: Same as consume but suppresses exceptions.

getContentCharset: Retrieve the charset of the content.

5. org.apache.commons.lang3.StringUtils

isBlank: Check if a string is empty after trimming.

isEmpty: Check if a string is empty without trimming.

equals: Determine if two strings are equal.

join: Join an array into a single string with an optional separator.

split: Split a string.

EMPTY: Return an empty string.

replace: Replace substrings within a string.

capitalize: Capitalize the first character of a string.

6. org.apache.commons.io.FilenameUtils

getExtension: Return the file extension.

getBaseName: Return the file name without extension.

getName: Return the full file name.

concat: Concatenate file paths in a command‑line style.

removeExtension: Remove the file extension.

normalize: Normalize a file path.

wildcardMatch: Match a filename against a wildcard pattern.

separatorToUnix: Convert path separators to Unix style (/).

getFullPath: Get the directory path without the file name.

isExtension: Check if a file's extension is in a given list.

7. org.springframework.util.StringUtils

hasText: Check if a string contains non‑whitespace text.

hasLength: Check if a string's length is greater than zero.

isEmpty: Check if a string is empty (null or zero length).

commaDelimitedStringToArray: Convert a comma‑delimited string to an array.

collectionToDelimitedString: Convert a collection to a CSV‑style string.

replace: Replace substrings.

delimitedListToStringArray: Split a delimited string (similar to split).

uncapitalize: Convert the first character to lower case.

collectionToDelimitedCommaString: Convert a collection to a CSV string.

tokenizeToStringArray: Split a string and automatically trim empty tokens.

8. org.apache.commons.lang.ArrayUtils

contains: Check if an array contains a specific element.

addAll: Add all elements of one array to another.

clone: Clone an array.

isEmpty: Determine if an array is empty.

add: Add an element to an array.

subarray: Extract a sub‑array.

indexOf: Find the index of an element.

isEquals: Compare two arrays for equality.

toObject: Convert a primitive array to its corresponding Object array.

9. org.apache.commons.lang.StringEscapeUtils

Reference to org.apache.commons.lang3.StringEscapeUtils (deprecated).

10. org.apache.http.client.utils.URLEncodedUtils

format: Format parameters into an application/x-www-form-urlencoded string for HTTP POST or PUT.

parse: Convert a String or URI into a List<NameValuePair>.

11. org.apache.commons.codec.digest.DigestUtils

md5Hex: MD5 hash, returning a 32‑character hexadecimal string.

sha1Hex: SHA‑1 hash.

sha256Hex: SHA‑256 hash.

sha512Hex: SHA‑512 hash.

md5: MD5 hash, returning a 16‑character string.

12. org.apache.commons.collections.CollectionUtils

isEmpty: Check if a collection is empty.

select: Filter collection elements based on a condition.

transform: Apply a function to each element (similar to map).

filter: Filter elements (similar to List.filter).

find: Find an element matching a condition.

collect: Transform elements and return a new collection.

forAllDo: Apply a specified method to every element.

isEqualCollection: Determine whether two collections contain the same elements.

13. org.apache.commons.lang3.ArrayUtils

contains: Check if an array contains a specific string.

addAll: Add all elements of one array to another.

clone: Clone an array.

isEmpty: Determine if an array is empty.

add: Add an element to an array.

subarray: Extract a sub‑array.

indexOf: Find the index of an element.

isEquals: Compare two arrays for equality.

toObject: Convert a primitive array to its corresponding Object array.

14. org.apache.commons.beanutils.PropertyUtils

getProperty: Get the value of an object's property.

setProperty: Set the value of an object's property.

getPropertyDescriptor: Retrieve a property descriptor.

isReadable: Check if a property is readable.

copyProperties: Copy property values from one object to another.

getPropertyDescriptors: Retrieve all property descriptors.

isWriteable: Check if a property is writable.

getPropertyType: Get the type of a property.

15. org.apache.commons.lang3.StringEscapeUtils

unescapeHtml4: Unescape HTML entities.

escapeHtml4: Escape HTML entities.

escapeXml: Escape XML characters.

unescapeXml: Unescape XML characters.

escapeJava: Escape Unicode characters for Java source.

escapeEcmaScript: Escape characters for ECMAScript.

unescapeJava: Unescape Unicode characters.

escapeJson: Escape characters for JSON.

escapeXml10: Escape XML 1.0 characters.

This class is now deprecated; it is recommended to use the methods from the commons‑text package instead.

16. org.apache.commons.beanutils.BeanUtils

copyProperties: Copy property values from one bean to another.

getProperty: Get a bean property value.

setProperty: Set a bean property value.

populate: Populate bean properties from a Map.

copyProperty: Copy a single property value between beans.

cloneBean: Clone a bean instance.

Understanding these 16 most popular utility classes eliminates the need to write custom utilities, preventing duplicate effort. Most method names are self‑explanatory; if unclear, consult usage examples or online documentation. According to Alibaba's development guidelines, utility class packages should use the singular form "util" (e.g., XxxUtils).