Java must have a tool library to reduce your code by 90%

Posted by zeh on Tue, 04 Jan 2022 18:49:59 +0100

After working for many years, I found that there are many tool class libraries, which can greatly simplify the amount of code and improve development efficiency, but junior developers don't know. These class libraries have long become the industry standard class libraries, and they are also used in large companies. If someone told me to use these tool class libraries when I first started working, how good it would be!

Take a look at the tool class libraries you have also used.

1. Java's own tools and methods

1.1 the list set is spliced into comma separated strings

// How to put list The collection is spliced into comma separated strings a,b,c  
List<String> list = Arrays.asList("a", "b", "c");  
// The first method can be used stream flow  
String join = list.stream().collect(Collectors.joining(","));  
System.out.println(join); // output a,b,c  
// The second method, in fact String Also join Method can implement this function  
String join = String.join(",", list);  
System.out.println(join); // output a,b,c

1.2 compare whether two strings are equal, ignoring case

if (strA.equalsIgnoreCase(strB)) {  
  System.out.println("equal");  
}

1.3 compare whether two objects are equal

When we use equals to compare whether two Objects are equal, we also need to judge the null of the object on the left, otherwise we may report a null pointer exception. We can use Java The method encapsulated by Objects under util package to compare whether they are equal

Objects.equals(strA, strB);

The source code is like this

public static boolean equals(Object a, Object b) {  
    return (a == b) || (a != null && a.equals(b));  
}

1.4 intersection of two List sets

List<String> list1 = new ArrayList<>();  
list1.add("a");  
list1.add("b");  
list1.add("c");  
List<String> list2 = new ArrayList<>();  
list2.add("a");  
list2.add("b");  
list2.add("d");  
list1.retainAll(list2);  
System.out.println(list1); // output[a, b]

2. apache commons tool class library

apache commons is the most powerful and widely used tool class library. There are many sub libraries. Here are some of the most commonly used tools

2.1 commons-lang，java. Enhanced version of Lang

It is recommended to use commons Lang 3. Some APIs have been optimized. The original commons Lang has stopped updating

Maven's dependencies are:

<dependency>  
    <groupId>org.apache.commons</groupId>  
    <artifactId>commons-lang3</artifactId>  
    <version>3.12.0</version>  
</dependency>

2.1.1 empty string

The passed parameter CharSequence type is the parent class of String, StringBuilder and StringBuffer, which can be directly null judged by the following methods. The following is the source code:

public static boolean isEmpty(final CharSequence cs) {  
    return cs == null || cs.length() == 0;  
}  
  
public static boolean isNotEmpty(final CharSequence cs) {  
    return !isEmpty(cs);  
}  
  
// Blank characters in the string, such as spaces, line breaks, and tabs, will be removed during blank judgment  
public static boolean isBlank(final CharSequence cs) {  
    final int strLen = length(cs);  
    if (strLen == 0) {  
        return true;  
    }  
    for (int i = 0; i < strLen; i++) {  
        if (!Character.isWhitespace(cs.charAt(i))) {  
            return false;  
        }  
    }  
    return true;  
}  
  
public static boolean isNotBlank(final CharSequence cs) {  
    return !isBlank(cs);  
}

2.1.2 capitalization of initial letters

String str = "yideng";  
String capitalize = StringUtils.capitalize(str);  
System.out.println(capitalize); // output Yideng

2.1.3 repeated splicing string

String str = StringUtils.repeat("ab", 2);  
System.out.println(str); // output abab

2.1.4 format date

No more handwritten SimpleDateFormat formatting

// Date Type conversion String type  
String date = DateFormatUtils.format(new Date(), "yyyy-MM-dd HH:mm:ss");  
System.out.println(date); // Output 2021-05-01 01:01:01  
  
// String Type conversion Date type  
Date date = DateUtils.parseDate("2021-05-01 01:01:01", "yyyy-MM-dd HH:mm:ss");  
  
// Calculate the date after one hour  
Date date = DateUtils.addHours(new Date(), 1);

2.1.5 temporary packaging objects

When a method needs to return two or more fields, we usually encapsulate it as a temporary object. Now we don't need it with Pair and Triple

// Return two fields  
ImmutablePair<Integer, String> pair = ImmutablePair.of(1, "yideng");  
System.out.println(pair.getLeft() + "," + pair.getRight()); // Output 1,yideng  
// Return three fields  
ImmutableTriple<Integer, String, Date> triple = ImmutableTriple.of(1, "yideng", new Date());  
System.out.println(triple.getLeft() + "," + triple.getMiddle() + "," + triple.getRight()); // Output 1,yideng,Wed Apr 07 23:30:00 CST 2021

2.2 common collections collection tool class

Maven's dependencies are:

<dependency>  
    <groupId>org.apache.commons</groupId>  
    <artifactId>commons-collections4</artifactId>  
    <version>4.4</version>  
</dependency>

2.2.1 collective empty judgment

Encapsulates the method of set empty judgment. The following is the source code:

public static boolean isEmpty(final Collection<?> coll) {  
    return coll == null || coll.isEmpty();  
}  
  
public static boolean isNotEmpty(final Collection<?> coll) {  
    return !isEmpty(coll);  
}  
// Intersection of two sets  
Collection<String> collection = CollectionUtils.retainAll(listA, listB);  
// Union of two sets  
Collection<String> collection = CollectionUtils.union(listA, listB);  
// Difference set of two sets  
Collection<String> collection = CollectionUtils.subtract(listA, listB);

2.3 common bean utils operation object

Maven dependency:

<dependency>  
    <groupId>commons-beanutils</groupId>  
    <artifactId>commons-beanutils</artifactId>  
    <version>1.9.4</version>  
</dependency>  
public class User {  
    private Integer id;  
    private String name;  
}

Set object properties

User user = new User();  
BeanUtils.setProperty(user, "id", 1);  
BeanUtils.setProperty(user, "name", "yideng");  
System.out.println(BeanUtils.getProperty(user, "name")); // output yideng  
System.out.println(user); // output {"id":1,"name":"yideng"}

Object and map rotate with each other

// Object rotation map  
Map<String, String> map = BeanUtils.describe(user);  
System.out.println(map); // output {"id":"1","name":"yideng"}  
// map Transfer object  
User newUser = new User();  
BeanUtils.populate(newUser, map);  
System.out.println(newUser); // output {"id":1,"name":"yideng"}

2.4 commons IO file stream processing

Maven dependency:

<dependency>  
    <groupId>commons-io</groupId>  
    <artifactId>commons-io</artifactId>  
    <version>2.8.0</version>  
</dependency>

File processing

File file = new File("demo1.txt");  
// read file  
List<String> lines = FileUtils.readLines(file, Charset.defaultCharset());  
// write file  
FileUtils.writeLines(new File("demo2.txt"), lines);  
// Copy file  
FileUtils.copyFile(srcFile, destFile);

3. Google Guava tool class library

Maven dependency:

<dependency>  
    <groupId>com.google.guava</groupId>  
    <artifactId>guava</artifactId>  
    <version>30.1.1-jre</version>  
</dependency>

3.1 creating collections

List<String> list = Lists.newArrayList();  
List<Integer> list = Lists.newArrayList(1, 2, 3);  
// reversal list  
List<Integer> reverse = Lists.reverse(list);  
System.out.println(reverse); // output [3, 2, 1]  
// list There are too many set elements, which can be divided into several sets, with 10 elements in each set  
List<List<Integer>> partition = Lists.partition(list, 10);  
  
Map<String, String> map = Maps.newHashMap();  
Set<String> set = Sets.newHashSet();

3.2 black technology collection

3.2.1 Multimap a key can map a HashMap of multiple value s

Multimap<String, Integer> map = ArrayListMultimap.create();  
map.put("key", 1);  
map.put("key", 2);  
Collection<Integer> values = map.get("key");  
System.out.println(map); // output {"key":[1,2]}  
// It also returns the bloated you used before Map  
Map<String, Collection<Integer>> collectionMap = map.asMap();

It's easy and concise to save you from creating map < string, list >

3.2.2 BiMap is a HashMap that cannot duplicate value s

BiMap<String, String> biMap = HashBiMap.create();  
// If value Repeat, put Method throws exceptions unless forcePut method  
biMap.put("key","value");  
System.out.println(biMap); // output {"key":"value"}  
// since value Can't repeat, why don't you realize a flip key/value There is already a way  
BiMap<String, String> inverse = biMap.inverse();  
System.out.println(inverse); // output {"value":"key"}

This is actually a two-way mapping, which is very practical in some scenarios.

3.2.3 Table is a HashMap with two key s

// A group of users, grouped by age and gender  
Table<Integer, String, String> table = HashBasedTable.create();  
table.put(18, "male", "yideng");  
table.put(18, "female", "Lily");  
System.out.println(table.get(18, "male")); // output yideng  
// This is actually a two-dimensional Map，You can view row data  
Map<String, String> row = table.row(18);  
System.out.println(row); // output {"male":"yideng","female":"Lily"}  
// View column data  
Map<Integer, String> column = table.column("male");  
System.out.println(column); // output {18:"yideng"}

3.2.4 Multiset is a Set used for counting

Multiset<String> multiset = HashMultiset.create();  
multiset.add("apple");  
multiset.add("apple");  
multiset.add("orange");  
System.out.println(multiset.count("apple")); // Output 2  
// View de duplicated elements  
Set<String> set = multiset.elementSet();  
System.out.println(set); // output ["orange","apple"]  
// You can also view elements that have not been de duplicated  
Iterator<String> iterator = multiset.iterator();  
while (iterator.hasNext()) {  
    System.out.println(iterator.next());  
}  
// You can also manually set the number of occurrences of an element  
multiset.setCount("apple", 5);

 

 

Source: https://mp.weixin.qq.com/s/1Uc_aSoDwhmLmUlQp3fnNA

 

Topics: Java

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