Guava Google 核心 Java 类库使用总结

jar 包依赖

<dependency>
    <groupId>com.google.guava</groupId>
    <artifactId>guava</artifactId>
    <version>28.0-jre</version>
</dependency>

 

Joiner && Splitter

public class AnswerApp {
	// 定义连接器, 可支持正则表达式
    public static final Joiner JOINER = Joiner.on(",").useForNull("default");
    public static final Joiner.MapJoiner MAP_JOINER = Joiner.on(",").withKeyValueSeparator("@");

    // 定义分割器, 可支持正则表达式
    // trimResults: 去掉元素中的空格   omitEmptyStrings: 忽略空字符  limit: 限制分割的个数
    public static final Splitter SPLIT = Splitter.on(",").trimResults().omitEmptyStrings().limit(10);
    // 定义固定长度分割器
    public static final Splitter FIXLENGTH_SPLIT = Splitter.fixedLength(5);
    public static final Splitter.MapSplitter MAP_SPLIT = Splitter.on(",").withKeyValueSeparator("@");
    // 注意这里的固定长度5代表 key@value 的长度为 5
    public static final Splitter.MapSplitter FIXLENGTH_MAP_SPLIT = Splitter.fixedLength(5).withKeyValueSeparator("@");

    public static void main(String[] args) {
        List<String> list = Lists.newArrayList("answer", "", "AnswerAIL", null);
        System.out.println(JOINER.join(list));
        System.out.println();

        Map<String, String> map = ImmutableMap.of("name", "AnswerAIL", "email", "[email protected]");
        System.out.println(MAP_JOINER.join(map));
        System.out.println();

        for (String str: SPLIT.split(" answer, ,,AnswerAIL ,code")) {
            System.out.print(str + ">");
        }
        System.out.println("\n");

        for (String str: FIXLENGTH_SPLIT.split("aaaaabbbbbccccc")) {
            System.out.print(str + ">");
        }
        System.out.println("\n");

        Map<String, String> params = MAP_SPLIT.split("name@AnswerAIL,address@pt");
        System.out.println(params);
        System.out.println();

        System.out.println(FIXLENGTH_MAP_SPLIT.split("aa@a1bb@b2"));
    }

}

程序运行结果

answer,,AnswerAIL,default

name@AnswerAIL,email@[e-mail]

answer>AnswerAIL>code>

aaaaa>bbbbb>ccccc>

{name=AnswerAIL, address=pt}

{aa=a1, bb=b2}

 

Ints

public class AnswerApp {
    public static void main(String[] args) {
        // 快速转集合
        List<Integer> nums = Ints.asList(1, 2, 3, 4, 5);
        System.out.println(nums.size());		// 5
        System.out.println();

        // 集合转数组
        int[] array = Ints.toArray(nums);

        // 数组合并
        int[] concat = Ints.concat(array, new int[]{3, 4, 5});
        System.out.println(concat.length);		// 8
        System.out.println();

        // 数组中是否包含某元素
        System.out.println(Ints.contains(concat, 3));	// true
        System.out.println();

        // 数组元素最大值/最小值
        System.out.println(Ints.max(new int[]{1, 5, 3}));	// 5
        System.out.println(Ints.min(new int[]{1, 5, 3}));	// 1
        System.out.println();

        // 元素 3 在集合中出现的下标索引
        System.out.println(Ints.indexOf(concat, 3));		// 2
        // 元素 3 在集合中最后出现的下标索引
        System.out.println(Ints.lastIndexOf(concat, 3));	// 5
    }
}

 

Multiset 无序可重复的集合

public static void main(String[] args) {
    Multiset multiset = HashMultiset.create();
    multiset.add("a");
    multiset.add("a");
    multiset.add("b");
    // 往集合中新增 n 个 元素
    multiset.add("c", 5);

    // 查看集合的大小
    System.out.println(multiset.size());				// 8
    // 查看集合内不同元素的个数(会对元素进行去重)
    System.out.println(multiset.elementSet().size());	// 3
    // 查看集合内某个元素的个数
    System.out.println(multiset.count("c"));			// 5
}

 

Multimap 实现 key-value 一对多

public static void main(String[] args) {
    // Multimap 的实现类有: ArrayListMultimap/HashMultimap/LinkedHashMultimap/TreeMultimap/ImmutableMultimap/...
    // Multimap 实现 key-value 一对多的情况
    ArrayListMultimap<String, String> arrayListMultimap = ArrayListMultimap.create();
    arrayListMultimap.put("name", "answer");
    arrayListMultimap.put("name", "AnswerAIL");
    arrayListMultimap.put("address", "pt");
    
    // 2
    System.out.println(arrayListMultimap.get("name").size());
    // {address=[pt], name=[answer, AnswerAIL]}
    System.out.println(arrayListMultimap.asMap());
}

 

BiMap

• find key by value： biMap.get()
• find value by key： biMap.inverse().get()

public static void main(String[] args) {
    BiMap<String, String> biMap = HashBiMap.create();
    biMap.put("userName", "Answer");
    biMap.put("userName", "AnswerAIL");
    // 会抛异常, 不允许 value 重复
    //        biMap.put("loginName", "AnswerAIL");
    // 强制覆盖
    biMap.forcePut("loginName", "AnswerAIL");

    // 由于 value=AnswerAIL 被强制 loginName 覆盖, 所以 userName 对应的 value=null
    System.out.println(biMap.get("userName"));				// null
    // 如果 key 不存在, 则使用默认 value
    System.out.println(biMap.getOrDefault("email", "[email protected]"));
    // 根据 value 查找 key
    System.out.println(biMap.inverse().get("AnswerAIL"));	// loginName
}

 

Table<Row, Column, Value>

public static void main(String[] args) {
    Table<String, String, Integer> table = HashBasedTable.create();
    table.put("iris", "语文", 88);
    table.put("steven", "语文", 90);
    table.put("james", "语文", 85);
    table.put("iris", "数学", 98);
    table.put("steven", "数学", 93);
    table.put("james", "数学", 95);
    table.put("iris", "英语", 90);
    table.put("steven", "英语", 87);
    table.put("james", "英语", 86);

    System.out.println(table.row("iris"));
    System.out.println(table.column("数学"));
    System.out.println(table.get("iris", "数学"));
    System.out.println();

    System.out.println(table.containsRow("iris"));
    System.out.println(table.containsColumn("数学"));
    System.out.println(table.containsValue(100));
    System.out.println();

    System.out.println(table.rowKeySet());
    System.out.println(table.rowMap());
    System.out.println(table.columnKeySet());
    System.out.println(table.columnMap());
}

程序运行时输出

{语文=88, 数学=98, 英语=90}
{iris=98, steven=93, james=95}
98

true
true
false

[iris, steven, james]
{iris={语文=88, 数学=98, 英语=90}, steven={语文=90, 数学=93, 英语=87}, james={语文=85, 数学=95, 英语=86}}
[语文, 数学, 英语]
{语文={iris=88, steven=90, james=85}, 数学={iris=98, steven=93, james=95}, 英语={iris=90, steven=87, james=86}}

 

本地缓存的实现

• MyCache.java