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

简化代码

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