Spring Utility Classes Overview: Assertions, ObjectUtils, StringUtils, CollectionUtils, File/IO, Reflection and AOP

Assertions

Assertions are logical checks used to verify conditions that should never occur.

The -enableassertions JVM flag enables the assert keyword introduced in JDK 1.4.

Spring Boot provides the Assert utility class for data validation.

// require parameter object to be non‑null, otherwise throw exception
void notNull(Object object, String message)
// require parameter to be null, otherwise throw exception
void isNull(Object object, String message)
// require parameter to be true, otherwise throw exception
void isTrue(boolean expression, String message)
// require collection to be non‑empty, otherwise throw exception
void notEmpty(Collection collection, String message)
// require string to have length (not empty), otherwise throw exception
void hasLength(String text, String message)
// require string to contain non‑blank text, otherwise throw exception
void hasText(String text, String message)
// require object to be an instance of the given type
void isInstanceOf(Class type, Object obj, String message)
// require subType to be a subclass or implementation of superType
void isAssignable(Class superType, Class subType, String message)

ObjectUtils

// get class name of object; returns "null" if argument is null
String nullSafeClassName(Object obj)
// returns 0 if argument is null
int nullSafeHashCode(Object object)
// returns "null" if argument is null
String nullSafeToString(boolean[] array)
// get object's identity hash code as hex string; returns 0 if null
String getIdentityHexString(Object obj)
// get class name and hash code; returns "" if null
String identityToString(Object obj)
// similar to toString(), returns "" if null
String getDisplayString(Object obj)

StringUtils

String utility methods for validation and manipulation.

// check if string is null or empty (whitespace counts as non‑empty)
boolean isEmpty(Object str)
// check if string ends with suffix, ignoring case
boolean endsWithIgnoreCase(String str, String suffix)
// check if string starts with prefix, ignoring case
boolean startsWithIgnoreCase(String str, String prefix)
// check if string contains any whitespace
boolean containsWhitespace(String str)
// check if string has length (not empty)
boolean hasLength(CharSequence str)
// check if string has non‑blank text
boolean hasText(CharSequence str)
// check if substring matches at given index
boolean substringMatch(CharSequence str, int index, CharSequence substring)
// count occurrences of a substring
int countOccurrencesOf(String str, String sub)

// replace a substring
String replace(String inString, String oldPattern, String newPattern)
// trim trailing character
String trimTrailingCharacter(String str, char trailingCharacter)
// trim leading character
String trimLeadingCharacter(String str, char leadingCharacter)
// trim leading whitespace
String trimLeadingWhitespace(String str)
// trim trailing whitespace
String trimTrailingWhitespace(String str)
// trim both leading and trailing whitespace
String trimWhitespace(String str)
// trim all whitespace
String trimAllWhitespace(String str)
// delete a specific pattern
String delete(String inString, String pattern)
// delete any of the given characters
String deleteAny(String inString, String charsToDelete)
// trim each element of a string array
String[] trimArrayElements(String[] array)
// decode a URL string
String uriDecode(String source, Charset charset)

CollectionUtils

// check if collection is empty
boolean isEmpty(Collection<?> collection)
// check if map is empty
boolean isEmpty(Map<?,?> map)
// check if collection contains an element
boolean containsInstance(Collection<?> collection, Object element)
// check if iterator contains an element
boolean contains(Iterator<?> iterator, Object element)
// check if collection contains any of the candidates
boolean containsAny(Collection<?> source, Collection<?> candidates)
// check if collection elements are unique
boolean hasUniqueObject(Collection<?> collection)

File and I/O Utilities

Helpers for copying data between files, streams, and byte arrays.

// read file into byte array
byte[] copyToByteArray(File in)
// read InputStream into byte array
byte[] copyToByteArray(InputStream in)
// read InputStream into String
String copyToString(Reader in)

// write byte array to file
void copy(byte[] in, File out)
// copy file to file
int copy(File in, File out)
// write byte array to OutputStream
void copy(byte[] in, OutputStream out)
// copy InputStream to OutputStream
int copy(InputStream in, OutputStream out)
// copy Reader to Writer
int copy(Reader in, Writer out)
// write String to Writer
void copy(String in, Writer out)

Reflection and AOP Utilities

Methods for locating, invoking, and manipulating members via reflection, and for working with Spring AOP proxies.

// find method by name
Method findMethod(Class<?> clazz, String name)
// find method by name and parameter types
Method findMethod(Class<?> clazz, String name, Class<?>... paramTypes)
// get all declared methods, including inherited
Method[] getAllDeclaredMethods(Class<?> leafClass)
// find accessible constructor
Constructor<T> accessibleConstructor(Class<T> clazz, Class<?>... parameterTypes)
// check if method is equals()
boolean isEqualsMethod(Method method)
// check if method is hashCode()
boolean isHashCodeMethod(Method method)
// check if method is toString()
boolean isToStringMethod(Method method)
// check if method originates from Object
boolean isObjectMethod(Method method)
// check if method declares a specific exception
boolean declaresException(Method method, Class<?> exceptionType)

// invoke method without arguments
Object invokeMethod(Method method, Object target)
// invoke method with arguments
Object invokeMethod(Method method, Object target, Object... args)
// make method accessible
void makeAccessible(Method method)
// make constructor accessible
void makeAccessible(Constructor<?> ctor)

// find field by name
Field findField(Class<?> clazz, String name)
// find field by name and type
Field findField(Class<?> clazz, String name, Class<?> type)
// check if field is public static final
boolean isPublicStaticFinal(Field field)

// get field value
Object getField(Field field, Object target)
// set field value
void setField(Field field, Object target, Object value)
// shallow copy field state between objects
void shallowCopyFieldState(Object src, Object dest)
// make field accessible
void makeAccessible(Field field)
// iterate over fields with callback
void doWithFields(Class<?> clazz, ReflectionUtils.FieldCallback fc)
// iterate over fields with filter
void doWithFields(Class<?> clazz, ReflectionUtils.FieldCallback fc, ReflectionUtils.FieldFilter ff)
// iterate over local fields only
void doWithLocalFields(Class<?> clazz, ReflectionUtils.FieldCallback fc)

// check if object is a Spring AOP proxy
boolean isAopProxy()
// check if object is a JDK dynamic proxy
boolean isJdkDynamicProxy()
// check if object is a CGLIB proxy
boolean isCglibProxy()
// get target class of a proxy
Class<?> getTargetClass()
// obtain current proxy from AopContext
Object currentProxy()