guava常见用法整理（不定期更新）

HolyCode_

已于 2022-11-15 08:52:33 修改

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分类专栏： java 文章标签： java guava

于 2022-11-15 08:02:17 首次发布

本文链接：https://blog.youkuaiyun.com/Primary_wind/article/details/127858767

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guava

集合
1. 不变Collection的创建
  1. 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");
2. 创建map集合(key=String，value=list)
  1. Multimap<String,Integer> map = ArrayListMultimap.create();
    map.put("aa", 1);
    map.put("aa", 2);
    System.out.println(map.get("aa")); //[1, 2]
3. MultiSet: 无序+可重复
  1. Multiset<String> set = HashMultiset.create();
4. Multimap: key-value key可以重复
  1. Multimap<String, String> teachers = ArrayListMultimap.create();
5. BiMap: 双向Map(Bidirectional Map) 键与值都不能重复
  1. BiMap<String, String> biMap = HashBiMap.create();
6. Table: 双键的Map Map--> Table-->rowKey+columnKey+value
  1. Table<String, String, Integer> tables = HashBasedTable.create();
7. 将集合转换为特定规则的字符串
  1. List<String> list = new ArrayList<String>();
    list.add("aa");
    list.add("bb");
    list.add("cc");
    String result = Joiner.on("-").join(list);
8. 把 map 集合转换为特定规则的字符串
  1. Map<String, Integer> map = Maps.newHashMap();
    map.put("xiaoming", 12);
    map.put("xiaohong",13);
    String result = Joiner.on(",").withKeyValueSeparator("=").join(map);
9. 将 String 转换为特定的集合
  1. String str = "1-2-3-4-5-6";
    List<String> list = Splitter.on("-").splitToList(str);
  2. String str = "xiaoming=11,xiaohong=23";
    Map<String,String> map = Splitter.on(",").withKeyValueSeparator("=").split(str);
  3. String str = "1-2-3-4- 5- 6 ";
    List<String> list = Splitter.on("-").omitEmptyStrings().trimResults().splitToList(str);
    System.out.println(list);
10. 多个字符切割，或者特定的正则分隔
  1. String input = "aa.dd,,ff,,.";
    List<String> result = Splitter.onPattern("[.|,]").omitEmptyStrings().splitToList(input);
  2. // 判断匹配结果
    boolean result = CharMatcher.inRange('a', 'z').or(CharMatcher.inRange('A', 'Z')).matches('K'); //true
    
    // 保留数字文本 CharMatcher.digit() 已过时 retain 保留
    //String s1 = CharMatcher.digit().retainFrom("abc 123 efg"); //123
    String s1 = CharMatcher.inRange('0', '9').retainFrom("abc 123 efg"); // 123
    
    // 删除数字文本 remove 删除
    // String s2 = CharMatcher.digit().removeFrom("abc 123 efg"); //abc efg
    String s2 = CharMatcher.inRange('0', '9').removeFrom("abc 123 efg"); // abc efg
11. 集合的过滤
  1. ImmutableList<String> names = ImmutableList.of("begin", "code", "Guava", "Java");
    Iterable<String> fitered = Iterables.filter(names, Predicates.or(Predicates.equalTo("Guava"), Predicates.equalTo("Java")));
    System.out.println(fitered);
  2. //自定义过滤条件   使用自定义回调方法对Map的每个Value进行操作
    ImmutableMap<String, Integer> m = ImmutableMap.of("begin", 12, "code", 15);
            // Function<F, T> F表示apply()方法input的类型，T表示apply()方法返回类型
            Map<String, Integer> m2 = Maps.transformValues(m, new Function<Integer, Integer>() {
                public Integer apply(Integer input) {
                      if(input>12){
                             return input;
                      }else{
                             return input+1;
                      }
                }
            });
    System.out.println(m2);   //{begin=13, code=15}
12. set 的交集，并集，差集
  1. HashSet setA = newHashSet(1, 2, 3, 4, 5);
    HashSet setB = newHashSet(4, 5, 6, 7, 8);
    
    SetView union = Sets.union(setA, setB);
    System.out.println("union:");
    for (Integer integer : union)
        System.out.println(integer);           //union 并集:12345867
    
    SetView difference = Sets.difference(setA, setB);
    System.out.println("difference:");
    for (Integer integer : difference)
        System.out.println(integer);        //difference 差集:123
    
    SetView intersection = Sets.intersection(setA, setB);
    System.out.println("intersection:");
    for (Integer integer : intersection)
        System.out.println(integer); //intersection 交集:45
13. map 的交集，并集，差集
  1. HashMap<String, Integer> mapA = Maps.newHashMap();
    mapA.put("a", 1);mapA.put("b", 2);mapA.put("c", 3);
    
    HashMap<String, Integer> mapB = Maps.newHashMap();
    mapB.put("b", 20);mapB.put("c", 3);mapB.put("d", 4);
    
    MapDifference differenceMap = Maps.difference(mapA, mapB);
    differenceMap.areEqual();
    Map entriesDiffering = differenceMap.entriesDiffering();
    Map entriesOnlyLeft = differenceMap.entriesOnlyOnLeft();
    Map entriesOnlyRight = differenceMap.entriesOnlyOnRight();
    Map entriesInCommon = differenceMap.entriesInCommon();
    
    System.out.println(entriesDiffering);   // {b=(2, 20)}
    System.out.println(entriesOnlyLeft);    // {a=1}
    System.out.println(entriesOnlyRight);   // {d=4}
    System.out.println(entriesInCommon);    // {c=3}
检查参数
1. if(!Strings.isNullOrEmpty(str))
2. Preconditions.checkArgument(count > 0, "must be positive: %s", count);
MoreObjects
1. Person person = new Person("aa",11);
  String str = MoreObjects.toStringHelper("Person").add("age", person.getAge()).toString();
  System.out.println(str);
  //输出Person{age=11}
强大的 Ordering 排序器
1. natural()     对可排序类型做自然排序，如数字按大小，日期按先后排序
  usingToString()     按对象的字符串形式做字典排序[lexicographical ordering]
  from(Comparator) 把给定的Comparator转化为排序器
  reverse()    获取语义相反的排序器
  nullsFirst() 使用当前排序器，但额外把null值排到最前面。
  nullsLast()   使用当前排序器，但额外把null值排到最后面。
  compound(Comparator) 合成另一个比较器，以处理当前排序器中的相等情况。
  lexicographical()    基于处理类型T的排序器，返回该类型的可迭代对象Iterable<T>的排序器。
  onResultOf(Function) 对集合中元素调用Function，再按返回值用当前排序器排序。
  1. Person person = new Person("aa", 144444); //String name ,Integer age
    Person ps = new Person("bb", 13);
    Ordering<Person> byOrdering = Ordering.natural().nullsFirst().onResultOf(new Function<Person, Integer>() {
        public Integer apply(Person person) {
            return person.age;
        }
    });
    byOrdering.compare(person, ps);
    System.out.println(byOrdering.compare(person, ps)); // -1
计算中间代码的运行时间
1. Stopwatch stopwatch = Stopwatch.createStarted();
  for(int i=0; i<100000; i++){
  // do some thing
  }
  long nanos = stopwatch.elapsed(TimeUnit.MILLISECONDS);
  System.out.println(nanos);
文件操作
1. File file = new File("test.txt");
  List<String> list = null;
  try {
  list = Files.readLines(file, Charsets.UTF_8);
  } catch (Exception e) {
  }
  
  Files.copy(from,to); //复制文件
  Files.deleteDirectoryContents(File directory); //删除文件夹下的内容(包括文件与子文件夹)
  Files.deleteRecursively(File file); //删除文件或者文件夹
  Files.move(File from, File to); //移动文件
  URL url = Resources.getResource("abc.xml"); //获取classpath根下的abc.xml文件url
guava 缓存
1. CacheLoader
  1. LoadingCache<String,String> cahceBuilder=CacheBuilder
                     .newBuilder()
                     .build(new CacheLoader<String, String>(){
                         @Override
                         public String load(String key) throws Exception {
                             String strProValue="hello "+key+"!";
                             return strProValue;
                         }
                     });
    System.out.println(cahceBuilder.apply("begincode")); //hello begincode!
    System.out.println(cahceBuilder.get("begincode")); //hello begincode!
    System.out.println(cahceBuilder.get("wen")); //hello wen!
    System.out.println(cahceBuilder.apply("wen")); //hello wen!
    System.out.println(cahceBuilder.apply("da"));//hello da!
    cahceBuilder.put("begin", "code");
    System.out.println(cahceBuilder.get("begin")); //code
2. callback
  1. Cache<String, String> cache = CacheBuilder.newBuilder().maximumSize(1000).build();
            String resultVal = cache.get("code", new Callable<String>() {
                public String call() {
                    String strProValue="begin "+"code"+"!";
                    return strProValue;
                }
            });
    System.out.println("value : " + resultVal); //value : begin code!
参考
1. https://juejin.cn/post/6844903667498221581#heading-10