Master Hutool: Essential Java Utility Classes and How to Use Them

Hutool is a Java utility library that helps simplify code and avoid reinventing the wheel. It provides many ready‑to‑use methods; this article introduces its most common utility classes and usage examples.

Installation

For Maven projects, add the following dependency to

pom.xml

:

<code>&lt;dependency&gt;
    &lt;groupId&gt;cn.hutool&lt;/groupId&gt;
    &lt;artifactId&gt;hutool-all&lt;/artifactId&gt;
    &lt;version&gt;4.6.3&lt;/version&gt;
&lt;/dependency&gt;</code>

Common Utility Classes

Convert

Type conversion utilities for various data types.

<code>// Convert to string
int a = 1;
String aStr = Convert.toStr(a);

// Convert to int 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);
</code>

DateUtil

Date and time utilities offering common operations.

<code>// Current date
Date date = DateUtil.date();

// Calendar to Date
date = DateUtil.date(Calendar.getInstance());

// Timestamp to Date
date = DateUtil.date(System.currentTimeMillis());

// Parse string (auto format)
String dateStr = "2017-03-01";
date = DateUtil.parse(dateStr);

// Parse with custom format
date = DateUtil.parse(dateStr, "yyyy-MM-dd");

// Format date
String format = DateUtil.format(date, "yyyy-MM-dd");

// Year, month (0‑based)
int year = DateUtil.year(date);
int month = DateUtil.month(date);

// Start/end of day
Date beginOfDay = DateUtil.beginOfDay(date);
Date endOfDay = DateUtil.endOfDay(date);

// Offset date
Date newDate = DateUtil.offset(date, DateField.DAY_OF_MONTH, 2);

// Difference in days
long betweenDay = DateUtil.between(date, newDate, DateUnit.DAY);
</code>

StrUtil

String utilities for common manipulations.

<code>// 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);
</code>

ClassPathResource

Load files from the classpath (e.g.,

WEB-INF/classes

in Tomcat).

<code>// 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);
</code>

ReflectUtil

Reflection utilities for accessing methods and creating objects.

<code>// Get all methods of a class
Method[] methods = ReflectUtil.getMethods(PmsBrand.class);

// Get a specific method
Method method = ReflectUtil.getMethod(PmsBrand.class, "getId");

// Create an instance via reflection
PmsBrand pmsBrand = ReflectUtil.newInstance(PmsBrand.class);

// Invoke a method
ReflectUtil.invoke(pmsBrand, "setId", 1);
</code>

NumberUtil

Number utilities for arithmetic and type checks.

<code>double n1 = 1.234;
double n2 = 1.234;
double result;

// Arithmetic operations
result = NumberUtil.add(n1, n2);
result = NumberUtil.sub(n1, n2);
result = NumberUtil.mul(n1, n2);
result = NumberUtil.div(n1, n2);

// Round to 2 decimal places
BigDecimal roundNum = NumberUtil.round(n1, 2);

String n3 = "1.234";
// Type checks
NumberUtil.isNumber(n3);
NumberUtil.isInteger(n3);
NumberUtil.isDouble(n3);
</code>

BeanUtil

Utilities for converting between JavaBeans and Maps and copying properties.

<code>PmsBrand brand = new PmsBrand();
brand.setId(1L);
brand.setName("小米");
brand.setShowStatus(0);

// 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);
</code>

CollUtil

Collection utilities for common operations.

<code>// 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 if empty
CollUtil.isEmpty(list);
</code>

MapUtil

Map utilities for creation and emptiness checks.

<code>// Create a 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);
</code>

AnnotationUtil

Annotation utilities for retrieving annotations and their values.

<code>// Get all annotations on a class
Annotation[] annotationList = AnnotationUtil.getAnnotations(HutoolController.class, false);
LOGGER.info("annotationUtil annotations:{}", annotationList);

// Get a 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);
</code>

SecureUtil

Encryption utilities, e.g., MD5 hashing.

<code>// MD5 hash
String str = "123456";
String md5Str = SecureUtil.md5(str);
LOGGER.info("secureUtil md5:{}", md5Str);
</code>

CaptchaUtil

Utility for generating image captchas.

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

Other Utility Classes

Hutool contains many more utilities; see the official site for the full list.

Project Source Code

https://github.com/macrozheng/mall-learning/tree/master/mall-tiny-hutool

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