Common Spring Framework Utility Classes: Assertions, ObjectUtils, StringUtils, CollectionUtils, File/Resource IO, Reflection and AOP Helpers

In this article, a senior architect shares a curated list of useful Spring Framework utility classes that can replace many custom helper methods, covering assertions, object and collection utilities, file and resource handling, as well as reflection and AOP helpers.

Assertions

Logical checks to guard against impossible conditions.

JDK -enableassertions flag enables the built‑in assert keyword.

Spring’s Assert class provides methods such as notNull, isTrue, notEmpty, etc.

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)

Object, Array, Collection Utilities

ObjectUtils

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

StringUtils

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)
boolean substringMatch(CharSequence str, int index, CharSequence substring)
int countOccurrencesOf(String str, String sub)

CollectionUtils

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)

File, Resource, IO Stream Utilities

FileCopyUtils

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

static boolean isUrl(String resourceLocation)
static URL getURL(String resourceLocation)
static File getFile(String resourceLocation)

StreamUtils

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)

Reflection and AOP Utilities

ReflectionUtils

Method findMethod(Class<?> clazz, String name)
Method findMethod(Class<?> clazz, String name, Class<?>... paramTypes)
Method[] getAllDeclaredMethods(Class<?> leafClass)
Constructor<T> accessibleConstructor(Class<T> 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)
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 makeAccessible(Method method)
void makeAccessible(Field field)
void doWithFields(Class<?> clazz, ReflectionUtils.FieldCallback fc)
void doWithFields(Class<?> clazz, ReflectionUtils.FieldCallback fc, ReflectionUtils.FieldFilter ff)

AopUtils

boolean isAopProxy()
boolean isJdkDynamicProxy()
boolean isCglibProxy()
Class<?> getTargetClass()

AopContext

Object currentProxy()