[TOC]
聲明
這一系列文章旨在幫助大家理解 Collector 的執(zhí)行流程，至于實現(xiàn)的是否高效皆刺、是否優(yōu)雅针饥、是否合理等暫且不論。
上一篇文章分享了 Collector 的執(zhí)行流程±嗣兀現(xiàn)在就來自定義一個最簡單的 JoinCollector 看看蒋情。
若對 Collector 的各個流程有疑問請移駕此處：http://blog.csdn.net/hylexus/article/details/78941843
簡單實現(xiàn)
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<>();
}
}
簡化代碼
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();
}
}
使用自定義Collector
@Test
public void test() {
String str = Lists.newArrayList("a", "B", "c", "d")
.stream().collect(new JoinClollector());
System.out.println(str);
}
