使用Google Guava工具类

小灰灰 2021-12-04 07:57 350阅读 0赞

package com.teriste.guava;
    
    import com.alibaba.fastjson.JSON;
    import com.google.common.base.CharMatcher;
    import com.google.common.base.Joiner;
    import com.google.common.base.Splitter;
    import com.google.common.collect.*;
    import com.google.common.primitives.Ints;
    
    import java.util.*;
    
    /**
     * 使用Google Guava工具类
     */
    public class GuavaAction {
    
        /**
         * guava连接器
         * 跳过null
         */
        private static final Joiner joinerSkipNull = Joiner.on(",").skipNulls();
    
        /**
         * guava连接器
         * 替换null
         */
        private static final Joiner joinerUseNull = Joiner.on(",").useForNull("empty");
    
        /**
         * guava分割器
         */
        private static final Splitter splitter = Splitter.on(",").omitEmptyStrings();
    
        /**
         * 字符匹配
         */
        private static final CharMatcher matchAny = CharMatcher.any();
    
        /**
         * 将list连接成字符串
         * @param sourceList
         * @return
         */
        public static String joinList2String(List<String> sourceList){
            String target = joinerSkipNull.join(sourceList.toArray());
            System.out.println("after join list skip null:"+target); //after join list skip null:a,b,c,null,d
            target = joinerUseNull.join(sourceList.toArray());
            System.out.println("after join list user null:"+target); //after join list user null:a,b,c,null,empty,d
            return target;
        }
    
        /**
         * 将字符串分割成list
         * @param sourceString
        * @return
         */
        public static List<String> splitString2List(String sourceString){
            List<String> target = splitter.splitToList(sourceString);
            System.out.println("after split string:"+ JSON.toJSONString(target)); //after split string:["a","b","c"," ","null","d"]
            return target;
        }
    
        /**
         * 使用Ints扩展原生类型的功能
         * 比如避免循环操作int数组
         */
        public static void extendType(){
            //将基本类型变量转换为数组
            List<Integer> ints= Ints.asList(1,3,4,3,5,7,7,6,8);
            int [] intArr=Ints.toArray(ints);
            System.out.println("int数组是否包含数字10:"+Ints.contains(intArr,6)); //int数组是否包含数字10:true
            System.out.println("join list:"+Ints.join(",",1,3,5,6,8)); //join list:1,3,5,6,8
            System.out.println("数字3在数组中的位置(第一次出现):"+Ints.indexOf(intArr,3)); //数字3在数组中的位置:1
            System.out.println("数字3在数组中最后一次出现的位置:"+Ints.lastIndexOf(intArr,3)); //数字3在数组中最后一次出现的位置:3
            System.out.println("数组中的最小值:"+Ints.min(intArr)+",数组中的最大值:"+Ints.max(intArr)); //数组中的最小值:1,数组中的最大值:8
        }
    
        /**
         * 使用MultiSet实现无序且可以重复的集合
         * List:有序且可以重复的集合
         * Set:无序且不可以重复的集合
         */
        public static void useMultiSet(){
            List<String> list=Arrays.asList("a","b","c","b","d","c","c");
            //创建HashMultiset对象
            Multiset<String> multiset = HashMultiset.create();
            multiset.add("a");
            multiset.add("a");
            multiset.add("c");
            multiset.add("b");
            multiset.add("c");
            System.out.println("multiset element:"+multiset.toString()); //multiset element:[a x 2, b, c x 2]
            multiset.forEach((x)-> System.out.print(x+"\t")); //a	a	b	c	c
            System.out.println();
        }
    
        /**
         * Collections Immutable与Guava
         */
        public static void immutaList(){
            List<String> list=new ArrayList<>();
            list.add("a");
            list.add("b");
            List<String> unmodifyList= Collections.unmodifiableList(list);
            //immutaList.add("xx");//java.lang.UnsupportedOperationException
            //修改源集合的值，不可变集合的值也被修改了，说明它们引用的是同一个集合
            //因此Collections.unmodifiableList()不能确保集合不可变
            list.add("zz");
            System.out.println("unmodifyList:"+JSON.toJSONString(unmodifyList)); //["a","b","zz"]
            //如果想要确保集合不可变，只能通过Arrays.asList()来实现
            List<String> list2= Arrays.asList("a","b","c","null",null,"d");
            //list2.add("yy"); //java.lang.UnsupportedOperationException
            System.out.println("list2:"+JSON.toJSONString(list2));
            System.out.println("#########################");
            //Guava ImmutableList
            List<String> immutableList = ImmutableList.of("a","b","c");
            //immutableList.add("s"); //java.lang.UnsupportedOperationException
            System.out.println("immutableList:"+JSON.toJSONString(immutableList));
        }
    
        /**
         * 使用Guava MultiMap代替Map<String,List<T>
         */
        public static void useMultiMap(){
            //创建Multimap
            Multimap<String,String> multimap = HashMultimap.create();
            multimap.put("11","aa");
            multimap.put("11","bb");
            //重复元素会覆盖，value是Set
            multimap.put("11","aa");
            multimap.put("11","cc");
            //获取multiMap中key对应的Collection
            System.out.println("map value:"+multimap.get("11")); //map value:[aa, bb, cc]
            //删除multiMap中key对应Collection中的指定值
            multimap.remove("11","bb");
            System.out.println("map value:"+multimap.get("11")); //map value:[aa, cc]
            //判断某个值在map的key对应的Collection中是否存在，底层实际上还是iterator遍历
            System.out.println("map value is contains aa:"+multimap.containsValue("aa"));
        }
    
        /**
         * key与value一对一的map
         */
        public static void useBiMap(){
            //BiMap内部维护了两个map，分别是键值相反的map
            BiMap<String,String> biMap = HashBiMap.create();
            biMap.put("zhangsan","11@email.com");
            //如果键已存在就无法put
            //biMap.put("zhangsan","22@email.com");//java.lang.IllegalArgumentException: value already present: 22@email.com
            //可以强制put，会更新键值
            biMap.forcePut("zhangsan","22@email.com");
            //如果值已存在就无法put
            //biMap.put("lisi","22@email.com"); //java.lang.IllegalArgumentException: value already present: 22@email.com
            biMap.put("lisi","33@email.com");
            System.out.println("biMap:"+JSON.toJSONString(biMap)); //biMap:{"zhangsan":"22@email.com","lisi":"33@email.com"}
            //通过值查询键
            System.out.println("22@email.com对应的key:"+biMap.inverse().get("22@email.com")); //22@email.com对应的key:zhangsan
        }
    
        /**
         * 使用Table来表示数据库表
         * 对应关系是某行、某列的值
         * row,column,value
         */
        public static void useTable(){
            //定义一个学生表，行是年级，列是班级，姓名，学科，成绩
            Table<String,String,String> students=HashBasedTable.create();
            students.put("王二","数学","90");
            students.put("王二","英语","95");
            students.put("王二","语文","80");
            students.put("张三","数学","88");
            students.put("张三","英语","85");
            students.put("张三","语文","90");
            Set<Table.Cell<String,String,String>> set = students.cellSet();
            for (Table.Cell cell:set){
                System.out.println(cell.getRowKey()+","+cell.getColumnKey()+","+cell.getValue());
            }
        }
    
        public static void main(String[] args) {
            List<String> sourceList= Arrays.asList("a","b","c","null",null,"d");
            //1.将list中的元素通过分隔符连接
            joinList2String(sourceList);
            String source="a,b,c, ,null,d";
            //2.将字符串根据分隔符拆分成list
            splitString2List(source);
            //3.匹配字符
            String matchString = " Hello,World! ";
            System.out.println(matchAny.trimFrom(matchString));
            //4.Ints扩展基本类型功能
            extendType();
            //5.使用MultiSet实现无序且可以重复的集合
            useMultiSet();
            //6.使用Guava ImmutableList实现不可变list，类似还有不可变map
            immutaList();
            //7.使用Guava MultiMap代替Map<String,List<T>
            //大大方便了对map value的增删改查
            useMultiMap();
            //8.key与value一对一的map
            useBiMap();
            //9.
            useTable();
        }
    
    }