guava常见用法整理（不定期更新）

guava

1. 集合
   1. 不变Collection的创建
      1. ImmutableList iList = ImmutableList.of("a", "b", "c");
         ImmutableSet iSet = ImmutableSet.of("e1", "e2");
         ImmutableMap iMap = ImmutableMap.of("k1", "v1", "k2", "v2");
   2. 创建map集合(key=String，value=list)
      1. Multimap 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 set = HashMultiset.create();
   4. Multimap: key-value  key可以重复 
      1. Multimap teachers = ArrayListMultimap.create();
   5. BiMap: 双向Map(Bidirectional Map) 键与值都不能重复
       
      1. BiMap biMap = HashBiMap.create();
   6. Table: 双键的Map Map--> Table-->rowKey+columnKey+value
      1. Table tables = HashBasedTable.create();
   7. 将集合转换为特定规则的字符串
      1. List list = new ArrayList();
         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 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 list = Splitter.on("-").splitToList(str);
      2. String str = "xiaoming=11,xiaohong=23";
         Map map = Splitter.on(",").withKeyValueSeparator("=").split(str);
      3. String str = "1-2-3-4-  5-  6   "; 
         List 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 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 names = ImmutableList.of("begin", "code", "Guava", "Java");
          Iterable 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 m = ImmutableMap.of("begin", 12, "code", 15);
                  // Function F表示apply()方法input的类型，T表示apply()方法返回类型
                  Map m2 = Maps.transformValues(m, new Function() {
                      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 mapA = Maps.newHashMap();
          mapA.put("a", 1);mapA.put("b", 2);mapA.put("c", 3);
          
          HashMap 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}
2. 检查参数
   1. if(!Strings.isNullOrEmpty(str))
   2. Preconditions.checkArgument(count > 0, "must be positive: %s", count); 
3. 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}
4. 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 byOrdering = Ordering.natural().nullsFirst().onResultOf(new Function() {
             public Integer apply(Person person) {
                 return person.age;
             }
         });
         byOrdering.compare(person, ps);
         System.out.println(byOrdering.compare(person, ps)); // -1
5. 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);
6. 文件操作
   1. File file = new File("test.txt");
      List 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
7. guava 缓存
   1. CacheLoader
      1. LoadingCache cahceBuilder=CacheBuilder
                          .newBuilder()
                          .build(new CacheLoader(){
                              @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 cache = CacheBuilder.newBuilder().maximumSize(1000).build(); 
                   String resultVal = cache.get("code", new Callable() { 
                       public String call() { 
                           String strProValue="begin "+"code"+"!";               
                           return strProValue;
                       } 
                   }); 
          System.out.println("value : " + resultVal); //value : begin code!
8. 参考
   1. https://juejin.cn/post/6844903667498221581#heading-10