使用流api循环字段而不是对象

Question

我想使用Java8的流api进行以下练习：

• 给定列表 person
• Person是一个简单的POJO，具有name（string）和age（int）属性
• 构造以下字符串names=[joe,diana,Thomas]&ages=[34,52,19]

String result = persons.stream()
    .map(p -> "(" + p.getName() + "," + p.getAge() + ")")
    .collectors(Collectors.joining("&","persons=[","]");

Answer 1

我想如果有一个类person（正如您所描述的那样），您将需要一个自定义收集器：

 String result = List.of(new Person(1, "david"), new Person(33, "eugene"))
            .stream()
            .parallel()
            .collect(Collector.of(
                    () -> new StringJoiner[]{new StringJoiner(",", "[", "]"), new StringJoiner(",", "[", "]")},
                    (sj, per) -> {
                        sj[0] = sj[0].add("" + per.getAge());
                        sj[1] = sj[1].add(per.getName());
                    },
                    (left, right) -> {
                        left[0] = left[0].merge(right[0]);
                        left[1] = left[1].merge(right[1]);
                        return left;
                    },

                    x -> "Names = " + x[1].toString() + "&Ages = " + x[0].toString()
            ));