CollUtils Tutorial

This tutorial provides an overview of the CollUtils class, which is part of the lightweight-component/aj-util library. The CollUtils class provides utility methods for working with collections and arrays in Java applications.

Introduction

The CollUtils class contains static methods for common collection and array operations, including empty checks, conversions, merging, and filtering.

Main Features

• Empty/null checks for arrays, collections and maps
• Safe collection access
• Array merging and concatenation
• Collection/array conversions
• Filtering and searching collections
• Specialized int array handling

Methods

1. Empty Checks

1. isEmpty(Object[] array) - Check if array is null or empty
2. isEmpty(Collection<?> collection) - Check if collection is null or empty
3. isEmpty(Map<?, ?> map) - Check if map is null or empty

2. Safe Access

1. getList(List<T> list) - Returns empty list if input is null

3. Array Operations

1. printArray(Object[] arr) - Print array contents for debugging
2. concat(T[] first, T[] second) - Concatenate two arrays
3. addAll(T[]... arrays) - Merge multiple arrays
4. newArray(Class<?> componentType, int newSize) - Create new empty array

4. Conversions

1. arrayList(E... elements) - Convert array to ArrayList
2. intList2Arr(List<Integer> list) - Convert Integer list to int[]
3. stringArr2intArr(String value) - Convert comma-separated string to int[]

5. Filtering/Searching

1. findOne(List<T> list, Predicate<T> filter) - Find first matching element
2. findSome(List<T> list, Predicate<T> filter) - Find all matching elements

Usage Examples

Empty Checks

String[] arr = null;
boolean empty = CollUtils.isEmpty(arr); // true

List<String> list = new ArrayList<>();
empty = CollUtils.isEmpty(list); // true

Safe Access

List<String> list = null;
List<String> safeList = CollUtils.getList(list); // returns empty list

Array Operations

String[] a = {"a", "b"};
String[] b = {"c", "d"};
String[] combined = CollUtils.concat(a, b); // ["a", "b", "c", "d"]

Conversions

List<String> list = CollUtils.arrayList("a", "b", "c");

List<Integer> intList = Arrays.asList(1, 2, 3);
int[] intArr = CollUtils.intList2Arr(intList); // [1, 2, 3]

int[] nums = CollUtils.stringArr2intArr("1,2,3"); // [1, 2, 3]

Filtering

List<String> names = Arrays.asList("John", "Jane", "Doe");
String result = CollUtils.findOne(names, n -> n.startsWith("J")); // "John"
List<String> allJ = CollUtils.findSome(names, n -> n.startsWith("J")); // ["John", "Jane"]

Conclusion

The CollUtils class provides comprehensive utility methods for working with collections and arrays, making common operations more convenient and safer in Java applications.