Java Stream如何寫出高雅又裝*的代碼

git倉庫直達

如何讓同事看不懂你寫的代碼 然后覺得你非常牛逼 這里用到了stream()與Lambda 需要有點基礎,沒基礎你炫個🔨

優雅永不過時~ 看下面文章時記得穿燕尾服 拿高腳杯

List<String> strings = Lists.newArrayList("name=kk", "sex=1", "tel=1111", "email=xx@qq.com","name=ww","name=yy");

一. 冷靜分析

如上代碼,你現在要做一個分組的Map將上面list的值讀取出來,然后分組統計類似于Map<String,List< String >> 將Key相同的Val全部存到一個list里面

二. 直接開裝

不會真有人還直接遍歷吧,那別人不就看的懂了~ 為了炫技直接裝一波

定義封裝物件

  	@Data
    @Builder
    static class ObiectMap{
        private String key;
        private String value;
    }

2.1 初級炫

 System.out.println("map1: ");
        Map<String, List<String>> collect1 = strings.stream().map(e -> { //封裝成物件
            String[] split = e.split("\\=", 2);
            return ObiectMap.builder().key(split[0]).value(split[1]).build();
        }).collect(Collectors.toMap(ObiectMap::getKey,v->Lists.newArrayList(v.getValue()), (List<String> newList, List<String> oldList) -> { // Collectors.toMap(a,b,(n1,n2)) -> a代表Map的key (這里直接用方法參考拿到key) b代表value (n1,n2)代表key相同時value的處理辦法,直接合并List
            oldList.addAll(newList);
            return oldList;
        }));
        collect1.forEach((k,v)->{
            System.out.printf(k+" { ");
            String vList = v.stream().collect(Collectors.joining(",")); //加上逗號,最后一個不加
            System.out.printf(vList);
            System.out.printf(" }");
            System.out.println();
        });
        System.out.println();

結果如下

2.2 普通炫

System.out.println("map2: ");
        Map<String, List<String>> collect2 = strings.stream().map(e -> {
            String[] split = e.split("\\=", 2);
            return ObiectMap.builder().key(split[0]).value(split[1]).build();
        }).collect(Collectors.groupingBy(ObiectMap::getKey, Collectors.mapping(ObiectMap::getValue, Collectors.toList()))); //Collectors.groupingBy(a,b) a還是通過key來分組 ,b將value收集起來做list value
        collect2.forEach((k,v)->{
            System.out.printf(k+" { ");
            String vList = v.stream().collect(Collectors.joining(",")); //加上逗號,最后一個不加
            System.out.printf(vList);
            System.out.printf(" }");
            System.out.println();
        });
        System.out.println();

結果如下

2.3 高級炫

用Guava來炫

import com.google.common.collect.*

System.out.println("map3: get name List with Multimap");
        List<ObiectMap> collect3 = strings.stream().map(e -> {
            String[] split = e.split("\\=", 2);
            return ObiectMap.builder().key(split[0]).value(split[1]).build();
        }).collect(Collectors.toList());
        Multimap<String, String> multiMap = ArrayListMultimap.create();  //使用Guava的Multimap來存 value直接是collection,可以隨意轉換
        collect3.forEach(c -> multiMap.put(c.getKey(), c.getValue()));
        System.out.println(multiMap.get("name").stream().collect(Collectors.joining(","))); 
        System.out.println();

結果如下

2.4 再炫一波 拿到當前key與對應的數量

System.out.println("map4: get name with count");
        Map<String, Long> collect4 = strings.stream().map(e -> {
            String[] split = e.split("\\=", 2);
            return ObiectMap.builder().key(split[0]).value(split[1]).build();
        }).collect(Collectors.groupingBy(ObiectMap::getKey, Collectors.counting())); // 拿到數量
        collect4.forEach((k,v)->{
            System.out.printf(k+" { ");
            System.out.printf("%d",v);
            System.out.printf(" }");
            System.out.println();
        });
        System.out.println();

結果如下

2.5 Map Reduce炫

這個不能處理重復value,只是將單一Map聚合到一個Map

List<String> strings = Lists.newArrayList("name=kk", "sex=1", "tel=1111", "email=xx@qq.com");
        Map<String, String> reduce = strings.stream().map(e -> {
            String[] split = e.split("\\=", 2); // 正則劃分為單map
            return Collections.singletonMap(split[0], split[1]);
        }).reduce(new HashMap<String, String>(), (accMap, singleMap) -> { // reduce(a,(b,c))-> a 為初始值 b為累加值 c為當前值 操作回傳當前值與累加值后的結果 將多個單KV的Map組合成一個Map
            accMap.putAll(singleMap);
            return accMap;
        });

        reduce.forEach((k,v)->{
            System.out.println(k+" = "+v);
        });

好家伙直接裝一波,直接起飛~ 制作不易,轉載請標注