Spring Framework Utility Classes Overview: Assertions, ObjectUtils, StringUtils, CollectionUtils, FileCopyUtils, ResourceUtils, StreamUtils, ReflectionUtils, AopUtils

Assertions – Assertions are logical checks used to verify conditions that should never occur. The -enableassertions JVM flag enables the assert keyword (added in JDK 1.4). Spring Boot offers the Assert utility class for data validation, with methods such as notNull , isNull , isTrue , notEmpty , hasLength , hasText , isInstanceOf , and isAssignable .

void notNull(Object object, String message)
void isNull(Object object, String message)
void isTrue(boolean expression, String message)
void notEmpty(Collection collection, String message)
void hasLength(String text, String message)
void hasText(String text, String message)
void isInstanceOf(Class type, Object obj, String message)
void isAssignable(Class superType, Class subType, String message)

ObjectUtils – Provides methods for obtaining basic object information and performing checks. Key methods include nullSafeClassName , nullSafeHashCode , nullSafeToString , getIdentityHexString , and identityToString .

String nullSafeClassName(Object obj)
int nullSafeHashCode(Object object)
String nullSafeToString(boolean[] array)
String getIdentityHexString(Object obj)
String identityToString(Object obj)

StringUtils – A collection of string‑handling utilities. It offers checks such as isEmpty , endsWithIgnoreCase , startsWithIgnoreCase , containsWhitespace , hasLength , and hasText , as well as manipulation methods like replace , trimTrailingCharacter , trimLeadingWhitespace , trimAllWhitespace , delete , uriDecode , etc.

boolean isEmpty(Object str)
boolean endsWithIgnoreCase(String str, String suffix)
boolean startsWithIgnoreCase(String str, String prefix)
boolean containsWhitespace(String str)
boolean hasLength(CharSequence str)
boolean hasText(CharSequence str)
String replace(String inString, String oldPattern, String newPattern)
String trimTrailingCharacter(String str, char trailingCharacter)
String trimLeadingWhitespace(String str)
String trimAllWhitespace(String str)
String delete(String inString, String pattern)
String deleteAny(String inString, String charsToDelete)
String[] trimArrayElements(String[] array)
String uriDecode(String source, Charset charset)

CollectionUtils – Offers collection‑related checks and operations. Important methods include isEmpty for collections and maps, containsInstance , contains , containsAny , hasUniqueObject , as well as manipulation utilities like mergeArrayIntoCollection , mergePropertiesIntoMap , lastElement , findFirstMatch , findValueOfType , and findCommonElementType .

boolean isEmpty(Collection
collection)
boolean isEmpty(Map
map)
boolean containsInstance(Collection
collection, Object element)
boolean contains(Iterator
iterator, Object element)
boolean containsAny(Collection
source, Collection
candidates)
boolean hasUniqueObject(Collection
collection)
void mergeArrayIntoCollection(Object array, Collection
collection)
void mergePropertiesIntoMap(Properties props, Map
map)
T lastElement(List
list)
T lastElement(Set
set)
E findFirstMatch(Collection
source, Collection
candidates)
T findValueOfType(Collection
collection, Class
type)
Object findValueOfType(Collection
collection, Class
[] types)
Class
findCommonElementType(Collection
collection)

FileCopyUtils – Simplifies file and stream copying. It provides methods to read from files or streams into byte arrays or strings and to write byte arrays, strings, or streams to files or other streams.

byte[] copyToByteArray(File in)
byte[] copyToByteArray(InputStream in)
String copyToString(Reader in)
void copy(byte[] in, File out)
int copy(File in, File out)
void copy(byte[] in, OutputStream out)
int copy(InputStream in, OutputStream out)
int copy(Reader in, Writer out)
void copy(String in, Writer out)

ResourceUtils – Helps resolve resources from location strings. It can determine if a location is a URL, obtain a URL or File , and work with various Resource implementations such as FileSystemResource , UrlResource , ClassPathResource , and ServletContextResource . Resource methods include exists , getFile , getURI , getURL , getInputStream , and getDescription .

static boolean isUrl(String resourceLocation)
static URL getURL(String resourceLocation)
static File getFile(String resourceLocation)
FileSystemResource
UrlResource
ClassPathResource
ServletContextResource
boolean exists()
File getFile()
URI getURI()
URL getURL()
InputStream getInputStream()
String getDescription()

StreamUtils – Provides low‑level stream copying utilities, supporting byte arrays, input/output streams, and character set handling. Methods include copy (various overloads), copyRange , copyToByteArray , copyToString , and drain .

void copy(byte[] in, OutputStream out)
int copy(InputStream in, OutputStream out)
void copy(String in, Charset charset, OutputStream out)
long copyRange(InputStream in, OutputStream out, long start, long end)
byte[] copyToByteArray(InputStream in)
String copyToString(InputStream in, Charset charset)
int drain(InputStream in)

ReflectionUtils – Facilitates reflection operations. It can locate methods, constructors, and fields, check method characteristics (e.g., isEqualsMethod , isHashCodeMethod ), invoke methods, and manipulate field values. It also provides utilities to make members accessible and to iterate over fields with callbacks and filters.

Method findMethod(Class
clazz, String name)
Method findMethod(Class
clazz, String name, Class
... paramTypes)
Method[] getAllDeclaredMethods(Class
leafClass)
Constructor
accessibleConstructor(Class
clazz, Class
... parameterTypes)
boolean isEqualsMethod(Method method)
boolean isHashCodeMethod(Method method)
boolean isToStringMethod(Method method)
boolean isObjectMethod(Method method)
boolean declaresException(Method method, Class
exceptionType)
Object invokeMethod(Method method, Object target)
Object invokeMethod(Method method, Object target, Object... args)
void makeAccessible(Method method)
void makeAccessible(Constructor
ctor)
Field findField(Class
clazz, String name)
Field findField(Class
clazz, String name, Class
type)
boolean isPublicStaticFinal(Field field)
Object getField(Field field, Object target)
void setField(Field field, Object target, Object value)
void shallowCopyFieldState(Object src, Object dest)
void makeAccessible(Field field)
void doWithFields(Class
clazz, ReflectionUtils.FieldCallback fc)
void doWithFields(Class
clazz, ReflectionUtils.FieldCallback fc, ReflectionUtils.FieldFilter ff)
void doWithLocalFields(Class
clazz, ReflectionUtils.FieldCallback fc)

AopUtils – Determines proxy types in Spring AOP. It can check whether an object is a Spring proxy, a JDK dynamic proxy, or a CGLIB proxy, and retrieve the target class of a proxy.

boolean isAopProxy()
boolean isJdkDynamicProxy()
boolean isCglibProxy()
Class
getTargetClass()

AopContext – Provides access to the current proxy object within an AOP invocation.

Object currentProxy()