比较映射和列表时如何将Java 7重构为Java 8[关闭]

这个怎么样?

tasks.forEach((key, task) -> {
    if (key != null && task != null) {
        key = String.join(".", Arrays.asList(key.split("\\.")).subList(0, 3));
        data.stream()
            .filter(d -> d.getCompKey().equals(key))
            .findAny()
            .ifPresent(d -> {
                task.setVal1(d.getVal1());
                task.setVal2(d.getVal2());
                task.setVal3(d.getVal3());
            });
    }
});

我不会说这比您的代码更具可读性,但这表明良好的ol’for循环仍然足够:

List<Data> data = ...;
Map<String, Task> tasks = ...;

UnaryOperator<String> function = s -> {
    return Joiner.on(".")
                 .useForNull("null")
                 .join(Arrays.copyOfRange(s.split("\\."), 0, 3));
};

data.forEach(datum -> {
    final String compKey = datum.getCompKey();

    tasks.entrySet()
         .stream()
         .filter(e -> e.getKey() != null && e.getValue() != null)
         .filter(e -> compKey.equals(function.apply(e.getKey())))
         .findFirst()
         .map(Map.Entry::getValue)
         .ifPresent(task -> {
             task.setVal1(datum.getVal1());
             task.setVal2(datum.getVal2());
             task.setVal3(datum.getVal3());
         });
});