Boost Java Development with Hutool: 16 Essential Utility Classes Explained

Hutool is a small yet comprehensive Java utility library that helps simplify code and avoid reinventing the wheel. This guide summarizes 16 commonly used utility classes.

Installation

Adding Hutool to a Maven project only requires adding the following dependency to pom.xml:

<dependency>
    <groupId>cn.hutool</groupId>
    <artifactId>hutool-all</artifactId>
    <version>5.4.0</version>
</dependency>

Common Utility Classes

Convert

Provides convenient type conversion methods, eliminating the need for repetitive try‑catch blocks.

// Convert to String
int a = 1;
String aStr = Convert.toStr(a);
// Convert to specific type array
String[] b = {"1","2","3","4"};
Integer[] bArr = Convert.toIntArray(b);
// Convert to Date
String dateStr = "2017-05-06";
Date date = Convert.toDate(dateStr);
// Convert to List
String[] strArr = {"a","b","c","d"};
List<String> strList = Convert.toList(String.class, strArr);

DateUtil

Offers a rich set of date‑time operations, making handling dates far easier than using JDK's Date and Calendar.

// Current time
Date date = DateUtil.date();
// Calendar to Date
date = DateUtil.date(Calendar.getInstance());
// Timestamp to Date
date = DateUtil.date(System.currentTimeMillis());
// Auto‑detect format parsing
String dateStr = "2017-03-01";
date = DateUtil.parse(dateStr);
// Custom format parsing
date = DateUtil.parse(dateStr, "yyyy-MM-dd");
// Format output
String format = DateUtil.format(date, "yyyy-MM-dd");
// Year and month
int year = DateUtil.year(date);
int month = DateUtil.month(date);
// Begin/end of day
Date beginOfDay = DateUtil.beginOfDay(date);
Date endOfDay = DateUtil.endOfDay(date);
// Offset calculation
Date newDate = DateUtil.offset(date, DateField.DAY_OF_MONTH, 2);
// Between days
long betweenDay = DateUtil.between(date, newDate, DateUnit.DAY);

JSONUtil

Handles conversion between objects and JSON strings.

PmsBrand brand = new PmsBrand();
brand.setId(1L);
brand.setName("小米");
brand.setShowStatus(1);
// Object to JSON string
String jsonStr = JSONUtil.parse(brand).toString();
LOGGER.info("jsonUtil parse:{}", jsonStr);
// JSON string to object
PmsBrand brandBean = JSONUtil.toBean(jsonStr, PmsBrand.class);
LOGGER.info("jsonUtil toBean:{}", brandBean);
List<PmsBrand> brandList = new ArrayList<>();
brandList.add(brand);
String jsonListStr = JSONUtil.parse(brandList).toString();
// JSON string to list
brandList = JSONUtil.toList(new JSONArray(jsonListStr), PmsBrand.class);
LOGGER.info("jsonUtil toList:{}", brandList);

StrUtil

Provides concise string manipulation methods.

// Empty check
String str = "test";
StrUtil.isEmpty(str);
StrUtil.isNotEmpty(str);
// Remove suffix/prefix
StrUtil.removeSuffix("a.jpg", ".jpg");
StrUtil.removePrefix("a.jpg", "a.");
// Format string
String template = "这只是个占位符:{}";
String str2 = StrUtil.format(template, "我是占位符");
LOGGER.info("/strUtil format:{}", str2);

ClassPathResource

Accesses files located on the classpath, useful for loading configuration files.

// Load a properties file from src/main/resources
ClassPathResource resource = new ClassPathResource("generator.properties");
Properties properties = new Properties();
properties.load(resource.getStream());
LOGGER.info("/classPath:{}", properties);

ReflectUtil

Facilitates reflection operations such as retrieving methods and creating instances.

// All methods of a class
Method[] methods = ReflectUtil.getMethods(PmsBrand.class);
// Specific method
Method method = ReflectUtil.getMethod(PmsBrand.class, "getId");
// Create instance via reflection
PmsBrand pmsBrand = ReflectUtil.newInstance(PmsBrand.class);
// Invoke method
ReflectUtil.invoke(pmsBrand, "setId", 1);

NumberUtil

Performs arithmetic and numeric checks on various number types.

double n1 = 1.234;
double n2 = 1.234;
double result;
result = NumberUtil.add(n1, n2);
result = NumberUtil.sub(n1, n2);
result = NumberUtil.mul(n1, n2);
result = NumberUtil.div(n1, n2);
BigDecimal roundNum = NumberUtil.round(n1, 2);
String n3 = "1.234";
NumberUtil.isNumber(n3);
NumberUtil.isInteger(n3);
NumberUtil.isDouble(n3);

BeanUtil

Converts between JavaBeans and Maps and copies bean properties.

// Bean to Map
Map<String, Object> map = BeanUtil.beanToMap(brand);
LOGGER.info("beanUtil bean to map:{}", map);
// Map to Bean
PmsBrand mapBrand = BeanUtil.mapToBean(map, PmsBrand.class, false);
LOGGER.info("beanUtil map to bean:{}", mapBrand);
// Copy properties
PmsBrand copyBrand = new PmsBrand();
BeanUtil.copyProperties(brand, copyBrand);
LOGGER.info("beanUtil copy properties:{}", copyBrand);

CollUtil

Offers common collection operations such as conversion, joining, and creation of new collections.

// Array to List
String[] array = new String[]{"a","b","c","d","e"};
List<String> list = CollUtil.newArrayList(array);
// Join list to string
String joinStr = CollUtil.join(list, ",");
LOGGER.info("collUtil join:{}", joinStr);
// Split string back to list
List<String> splitList = StrUtil.split(joinStr, ',');
LOGGER.info("collUtil split:{}", splitList);
// Create new collections
HashMap<Object, Object> newMap = CollUtil.newHashMap();
HashSet<Object> newHashSet = CollUtil.newHashSet();
ArrayList<Object> newList = CollUtil.newArrayList();
// Check emptiness
CollUtil.isEmpty(list);

MapUtil

Simplifies creation and emptiness checks of maps.

// Create map with multiple entries
Map<Object, Object> map = MapUtil.of(new String[][]{
    {"key1", "value1"},
    {"key2", "value2"},
    {"key3", "value3"}
});
// Emptiness checks
MapUtil.isEmpty(map);
MapUtil.isNotEmpty(map);

AnnotationUtil

Retrieves annotations and their values from classes, methods, fields, etc.

// Get all annotations on a class
Annotation[] annotationList = AnnotationUtil.getAnnotations(HutoolController.class, false);
LOGGER.info("annotationUtil annotations:{}", annotationList);
// Get specific annotation
Api api = AnnotationUtil.getAnnotation(HutoolController.class, Api.class);
LOGGER.info("annotationUtil api value:{}", api.description());
// Get annotation value
Object annotationValue = AnnotationUtil.getAnnotationValue(HutoolController.class, RequestMapping.class);

SecureUtil

Provides simple MD5 hashing.

String str = "123456";
String md5Str = SecureUtil.md5(str);
LOGGER.info("secureUtil md5:{}", md5Str);

CaptchaUtil

Generates image captchas.

// Create line captcha
LineCaptcha lineCaptcha = CaptchaUtil.createLineCaptcha(200, 100);
try {
    request.getSession().setAttribute("CAPTCHA_KEY", lineCaptcha.getCode());
    response.setContentType("image/png");
    response.setHeader("Pragma", "No-cache");
    response.setHeader("Cache-Control", "no-cache");
    response.setDateHeader("Expire", 0);
    lineCaptcha.write(response.getOutputStream());
} catch (IOException e) {
    e.printStackTrace();
}

Validator

Validates common data formats such as email, phone, IP, etc.

// Email validation
boolean result = Validator.isEmail("[email protected]");
LOGGER.info("Validator isEmail:{}", result);
// Mobile validation
result = Validator.isMobile("18911111111");
LOGGER.info("Validator isMobile:{}", result);
// IPv4 validation
result = Validator.isIpv4("192.168.3.101");
LOGGER.info("Validator isIpv4:{}", result);
// Chinese characters validation
result = Validator.isChinese("你好");
LOGGER.info("Validator isChinese:{}", result);
// ID card validation
result = Validator.isCitizenId("123456");
LOGGER.info("Validator isCitizenId:{}", result);
// URL validation
result = Validator.isUrl("http://www.baidu.com");
LOGGER.info("Validator isUrl:{}", result);
// Birthday validation
result = Validator.isBirthday("2020-02-01");
LOGGER.info("Validator isBirthday:{}", result);

DigestUtil

Supports various digest algorithms including MD5, SHA‑256, and Bcrypt.

// MD5 hex
String result = DigestUtil.md5Hex(password);
LOGGER.info("DigestUtil md5Hex:{}", result);
// SHA‑256 hex
result = DigestUtil.sha256Hex(password);
LOGGER.info("DigestUtil sha256Hex:{}", result);
// Bcrypt hash and verification
String hashPwd = DigestUtil.bcrypt(password);
boolean check = DigestUtil.bcryptCheck(password, hashPwd);
LOGGER.info("DigestUtil bcryptCheck:{}", check);

HttpUtil

Facilitates HTTP requests such as GET and POST.

String response = HttpUtil.get("http://localhost:8080/hutool/covert");
LOGGER.info("HttpUtil get:{}", response);