Foreword

Guava 28.0 released, Guava is a Google open source project, contains many of Google's core Java commonly used libraries, such as: collection [collections], the cache [caching], native type support [primitives support], concurrency library [concurrency libraries], Common Annotations [common annotations], string processing [string processing] and I / O and the like.
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New features

collect: Adding Queues based method for some Durationheavy-duty ( 21d06cf )
net: For application / geo + json added MediaType( 36cd5cf )
net: In order to HttpHeadersadd a number of constants
concurrent: Removed deprecated CheckedFutureand related utilities ( 3dd22fe )
concurrent: Adding a method based on many Durationoverloaded
concurrent: From setFuturedeleted in @Beta( 5ec1360 )
concurrent: New deprecated FluentFuture.from(FluentFuture)to indicate redundant code ( f9f2807 )
graph: New GraphBuilder.immutable(), ValueGraphBuilder.immutable()and NetworkBuilder.immutable(), in a smooth manner for constructing immutable pattern
J2ObjC: Fixed using ImmutableMap.entrySet()crash caused ( 74fc49f )

Maven relies

<dependency>
  <groupId>com.google.guava</groupId>
  <artifactId>guava</artifactId>
  <version>28.0-jre</version>
  <!-- or, for Android: -->
  <version>28.0-android</version>
</dependency>

Download and update instructions

https://github.com/google/guava/releases/tag/v28.0

Getting Started

Introduced maven dependence

<dependency>
  <groupId>com.google.guava</groupId>
  <artifactId>guava</artifactId>
  <version>28.0-jre</version>
  <!-- or, for Android: -->
  <version>28.0-android</version>
</dependency>

Note: The version we can choice

Guava Collection Example

Ordinary collection Collection

List<String> list = Lists.newArrayList();
Set<String> set = Sets.newHashSet();
Map<String, String> map = Maps.newHashMap();

Create an immutable set of Guava

ImmutableList<String> iList = ImmutableList.of("a", "b", "c");
ImmutableSet<String> iSet = ImmutableSet.of("e1", "e2");
ImmutableMap<String, String> iMap = ImmutableMap.of("k1", "v1", "k2", "v2");

immutable objects immutable characteristics

1.在多线程操作下，是线程安全的。

2.所有不可变集合会比可变集合更有效的利用资源。

3.中途不可改变

Map-List Comparison

Longhand

1. Map<String,List<Integer>> map = new HashMap<String,List<Integer>>();
2. List<Integer> list = new ArrayList<Integer>();
3. list.add(1);
4. list.add(2);
5. map.put("test", list);
    System.out.println(map.get("test"));

#需要5步，执行结果[1, 2]

Guava wording

1. Multimap<String,Integer> mapM = ArrayListMultimap.create();
2. mapM.put("test",1);
3. mapM.put("test",2);
    System.out.println(mapM.get("test"));
#需要3步，执行结果[1, 2]

Note: the results are the same, but the code is nearly half less Oh ~ ~ ~

Guava string connector Joiner

Connecting the plurality of strings and to append StringBuilder

StringBuilder stringBuilder = new StringBuilder("嗨，");
// 字符串连接器，以|为分隔符，同时去掉null元素
Joiner joiner1 = Joiner.on("|").skipNulls();
// 构成一个字符串jim|jack|kevin并添加到stringBuilder
stringBuilder = joiner1.appendTo(stringBuilder, "jim", "jack", null, "kevin");
System.out.println(stringBuilder);

The results: Hey, jim | jack | kevin

The Map into a string

Map<String, String> testMap = Maps.newLinkedHashMap();
        testMap.put("Cookies", "12332");
        testMap.put("Content-Length", "30000");
        testMap.put("Date", "2018.07.04");
        testMap.put("Mime", "text/html");
        // 用:分割键值对，并用#分割每个元素，返回字符串
        String returnedString = Joiner.on("#").withKeyValueSeparator(":").join(testMap);
        System.out.println(returnedString);

The results: Cookies: 12332 # Content-Length: 30000 # Date: 2018.07.04 # Mime: text / html

Convert a string Map

// 接上一个，内部类的引用，得到分割器，将字符串解析为map
        Splitter.MapSplitter ms = Splitter.on("#").withKeyValueSeparator(':');
        Map<String, String> ret = ms.split(returnedString);
        for (String it2 : ret.keySet()) {
            System.out.println(it2 + " -> " + ret.get(it2));
        }

The results:
Cookies -> 12332
Content-the Length -> 30000
a Date -> 2018.07.04
Mime -> text / HTML

String Tools Strings

System.out.println(Strings.isNullOrEmpty("")); // true
System.out.println(Strings.isNullOrEmpty(null)); // true
System.out.println(Strings.isNullOrEmpty("hello")); // false
// 将null转化为""
 System.out.println(Strings.nullToEmpty(null)); // ""
 
// 从尾部不断补充T只到总共8个字符，如果源字符串已经达到或操作，则原样返回。类似的有padStart
System.out.println(Strings.padEnd("hello", 8, 'T')); // helloTTT

Character matcher CharMatcher

Replace blank

// 空白回车换行对应换成一个#，一对一换
String stringWithLinebreaks = "hello world\r\r\ryou are here\n\ntake it\t\t\teasy";
String s6 = CharMatcher.BREAKING_WHITESPACE.replaceFrom(stringWithLinebreaks,'#');
System.out.println(s6);

The results: hello # world ### you # are # here ## take # it ### easy

Continuously shrunk to a blank character

// 将所有连在一起的空白回车换行字符换成一个#，倒塌
String tabString = "  hello   \n\t\tworld   you\r\nare             here  ";
String tabRet = CharMatcher.WHITESPACE.collapseFrom(tabString, '#');
System.out.println(tabRet);

The results: # hello # world # you # are # here #

Before and after removing the blank and curling up in a character

// 在前面的基础上去掉字符串的前后空白，并将空白换成一个#
String trimRet = CharMatcher.WHITESPACE.trimAndCollapseFrom(tabString, '#');
System.out.println(trimRet);

The results: hello # world # you # are # here

Digital reserved

String letterAndNumber = "1234abcdABCD56789";
// 保留数字
String number = CharMatcher.JAVA_DIGIT.retainFrom(letterAndNumber);
System.out.println(number);

The results: 123456789

Remark

Well, we introduced here, and we often use tools Guava can meet, make code more concise and efficient.

Practical case

Micro Services Architecture actual articles (five): Spring boot2.x + Guava and use RateLimiter realize spike limiting demo

Google released the tool core Java libraries --Guava 28.0