[TOC]
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/article/details/78941843
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);
}
