Master Spring Assert & Utility Classes: Essential Java Backend Tools

Assert

Assert is a logical check used to verify conditions that should never occur. The assert keyword was introduced in JDK 1.4 and can be enabled with the JVM parameter -enableassertions. Spring Boot provides an Assert utility class for data validation.

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

ObjectUtils

Utility methods for handling objects safely.

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

StringUtils

String‑handling helpers.

boolean isEmpty(Object str)</code>
<code>boolean endsWithIgnoreCase(String str, String suffix)</code>
<code>boolean startsWithIgnoreCase(String str, String prefix)</code>
<code>boolean containsWhitespace(String str)</code>
<code>boolean hasLength(CharSequence str)</code>
<code>boolean hasText(CharSequence str)</code>
<code>boolean substringMatch(CharSequence str, int index, CharSequence substring)</code>
<code>int countOccurrencesOf(String str, String sub)</code>
<code>String replace(String inString, String oldPattern, String newPattern)</code>
<code>String trimTrailingCharacter(String str, char trailingCharacter)</code>
<code>String trimLeadingCharacter(String str, char leadingCharacter)</code>
<code>String trimLeadingWhitespace(String str)</code>
<code>String trimTrailingWhitespace(String str)</code>
<code>String trimWhitespace(String str)</code>
<code>String trimAllWhitespace(String str)</code>
<code>String delete(String inString, String pattern)</code>
<code>String deleteAny(String inString, String charsToDelete)</code>
<code>String[] trimArrayElements(String[] array)</code>
<code>String uriDecode(String source, Charset charset)

CollectionUtils

Helpers for collections.

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

FileCopyUtils

File and stream copy utilities.

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

ResourceUtils

Utilities for handling resources.

static boolean isUrl(String resourceLocation)</code>
<code>static URL getURL(String resourceLocation)</code>
<code>static File getFile(String resourceLocation)

StreamUtils

Stream copy helpers.

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

ReflectionUtils

Reflection helper methods.

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

AopUtils

Utilities for working with Spring AOP proxies.

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

AopContext

Access the current AOP proxy.

Object currentProxy()