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声明

这一系列文章旨在帮助大家理解 Collector 的执行流程，至于实现的是否高效、是否优雅、是否合理等暂且不论。

上一篇文章分享了 Collector 的执行流程。现在就来自定义一个最简单的 JoinCollector 看看。

若对 Collector 的各个流程有疑问请移驾此处：http://blog.csdn.net/hylexus/...

简单实现

static class JoinClollector implements Collector<String, StringBuilder, String> {      PRivate String seperator = ",";      @Override     public Supplier<StringBuilder> supplier() {         return () -> new StringBuilder();     }      @Override     public BiConsumer<StringBuilder, String> accumulator() {         return (sb, str) -> {             if (StringUtils.isNotBlank(str)) {                 sb.append(str).append(seperator);             }         };     }      @Override     public BinaryOperator<StringBuilder> combiner() {         return (l, r) -> l.append(r);     }      @Override     public Function<StringBuilder, String> finisher() {         return c -> {             String ret = c.toString();             if (ret.endsWith(seperator)) {                 return ret.substring(0, ret.length() - 1);             }             return ret;         };     }      @Override     public Set<Characteristics> characteristics() {         return new HashSet<>();     } }

简化代码

static class JoinClollector2 implements Collector<String, StringBuilder, String> {      private String seperator = ",";      @Override     public Supplier<StringBuilder> supplier() {         return StringBuilder::new;     }      @Override     public BiConsumer<StringBuilder, String> accumulator() {         return (sb, str) -> {             if (StringUtils.isNotBlank(str)) {                 sb.append(str).append(seperator);             }         };     }      @Override     public BinaryOperator<StringBuilder> combiner() {         return StringBuilder::append;     }      @Override     public Function<StringBuilder, String> finisher() {         return c -> {             String ret = c.toString();             if (ret.endsWith(seperator)) {                 return ret.substring(0, ret.length() - 1);             }             return ret;         };     }      @Override     public Set<Characteristics> characteristics() {         return Collections.emptySet();     } }

使用自定义Collector

@test public void test() {     String str = Lists.newArrayList("a", "B", "c", "d")             .stream().collect(new JoinClollector());     System.out.println(str); }

博客源码

https://github.com/hylexus/bl...