Boost Your Java Backend: Essential Spring Utility Classes Explained

Assert

Spring provides the Assert class for making assertions that throw exceptions when conditions are not met.

1.1 Assert null or not null

String str = null;
Assert.isNull(str, "str must be null");
Assert.notNull(str, "str must not be null");

Violations raise IllegalArgumentException.

1.2 Assert collection emptiness

List<String> list = null;
Map<String, String> map = null;
Assert.notEmpty(list, "list cannot be empty");
Assert.notEmpty(map, "map cannot be empty");

Violations raise IllegalArgumentException.

1.3 Assert boolean condition

List<String> list = null;
Assert.isTrue(CollectionUtils.isNotEmpty(list), "list cannot be empty");

StringUtils

Spring’s StringUtils extends JDK string handling.

2.1 Check length

if (!StringUtils.hasLength("")) {
    System.out.println("String is empty");
}

2.2 Remove all whitespace

@Test
public void testEmpty() {
    System.out.println("1" + StringUtils.trimAllWhitespace(" 苏三说技术 测试 ") + "1");
}

Result:

1苏三说技术测试1

2.3 Starts/ends with ignore case

@Test
public void testEmpty() {
    System.out.println(StringUtils.startsWithIgnoreCase("苏三说技术", "苏三"));
    System.out.println(StringUtils.endsWithIgnoreCase("苏三说技术", "技术"));
}

Both statements print true.

2.4 Collection to comma‑delimited string

@Test
public void testEmpty() {
    List<String> list = new ArrayList<>();
    list.add("a");
    list.add("b");
    list.add("c");
    System.out.println(StringUtils.collectionToCommaDelimitedString(list));
}

Output:

a,b,c

CollectionUtils

Utility methods for collection handling.

3.1 Check if collection is empty

List<Integer> list = new ArrayList<>();
list.add(2);
list.add(1);
list.add(3);
if (CollectionUtils.isEmpty(list)) {
    System.out.println("Collection is empty");
}

3.2 Check element existence

List<Integer> list = new ArrayList<>();
list.add(2);
list.add(1);
list.add(3);
if (CollectionUtils.contains(list.iterator(), 3)) {
    System.out.println("Element exists");
}

Note: iterator() is required.

ObjectUtils

Provides powerful null‑safe operations.

4.1 Null‑safe emptiness check

@Test
public void testEmpty() {
    String a = "123";
    Integer b = new Integer(1);
    List<String> c = new ArrayList<>();
    c.add(a);
    Map<String, String> e = new HashMap<>();
    e.put(a, a);
    Optional<String> f = Optional.of(a);
    if (!ObjectUtils.isEmpty(a)) System.out.println("a is not empty");
    if (!ObjectUtils.isEmpty(b)) System.out.println("b is not empty");
    if (!ObjectUtils.isEmpty(c)) System.out.println("c is not empty");
    if (!ObjectUtils.isEmpty(e)) System.out.println("e is not empty");
    if (!ObjectUtils.isEmpty(f)) System.out.println("f is not empty");
}

4.2 Null‑safe equality

@Test
public void testEquals() {
    String a = "123";
    String b = null;
    System.out.println(ObjectUtils.nullSafeEquals(a, b));
}

Prints false without NPE.

4.3 Identity hash code

@Test
public void testIdentityHex() {
    String a = "123";
    System.out.println(ObjectUtils.getIdentityHexString(a));
}

Example output:

2925bf5b

ClassUtils

Utility methods for class metadata.

5.1 Get all interfaces of an object

Class<?>[] allInterfaces = ClassUtils.getAllInterfaces(new User());

5.2 Get package name

String packageName = ClassUtils.getPackageName(User.class);
System.out.println(packageName);

5.3 Check if class is inner

System.out.println(ClassUtils.isInnerClass(User.class));

5.4 Check if object is a CGLIB proxy

System.out.println(ClassUtils.isCglibProxy(new User()));

BeanUtils

JavaBean manipulation utilities.

6.1 Copy properties

User user1 = new User();
user1.setId(1L);
user1.setName("苏三说技术");
user1.setAddress("成都");
User user2 = new User();
BeanUtils.copyProperties(user1, user2);
System.out.println(user2);

6.2 Instantiate class via reflection

User user = BeanUtils.instantiateClass(User.class);
System.out.println(user);

6.3 Find declared method

Method declaredMethod = BeanUtils.findDeclaredMethod(User.class, "getId");
System.out.println(declaredMethod.getName());

6.4 Find method’s property descriptor

Method declaredMethod = BeanUtils.findDeclaredMethod(User.class, "getId");
PropertyDescriptor pd = BeanUtils.findPropertyForMethod(declaredMethod);
System.out.println(pd.getName());

ReflectionUtils

Reflection helper methods.

7.1 Find method

Method method = ReflectionUtils.findMethod(User.class, "getId");

7.2 Find field

Field field = ReflectionUtils.findField(User.class, "id");

7.3 Invoke method

ReflectionUtils.invokeMethod(method, springContextsUtil.getBean(beanName), param);

7.4 Check if field is public static final

Field field = ReflectionUtils.findField(User.class, "id");
System.out.println(ReflectionUtils.isPublicStaticFinal(field));

7.5 Check if method is equals

Method method = ReflectionUtils.findMethod(User.class, "getId");
System.out.println(ReflectionUtils.isEqualsMethod(method));

Base64Utils

Encode and decode data using Base64.

String str = "abc";
String encode = new String(Base64Utils.encode(str.getBytes()));
System.out.println("Encoded: " + encode);
try {
    String decode = new String(Base64Utils.decode(encode.getBytes()), "utf8");
    System.out.println("Decoded: " + decode);
} catch (UnsupportedEncodingException e) {
    e.printStackTrace();
}

Output: Encoded: YWJj and

Decoded: abc

SerializationUtils

Simplify object serialization.

Map<String, String> map = Maps.newHashMap();
map.put("a", "1");
map.put("b", "2");
map.put("c", "3");
byte[] serialize = SerializationUtils.serialize(map);
Object deserialize = SerializationUtils.deserialize(serialize);
System.out.println(deserialize);

HttpStatus

Standard HTTP status codes are available via org.springframework.http.HttpStatus or org.apache.http.HttpStatus, eliminating the need to define custom constants.

HtmlUtils

Escape HTML special characters to prevent XSS and injection attacks.

@Test
public void testHtml() {
    String specialStr = "<div id=\"testDiv\">test1;test2</div>";
    String escaped = HtmlUtils.htmlEscape(specialStr);
    System.out.println(escaped);
}

Result:

<div id="testDiv">test1;test2</div&gt