当精细头记录时将文件分割成块（java 8）

我有一段代码，可以在找到起始记录时将文件“拆分”为一些块。

List<StringBuilder> list = new ArrayList<>();
StringBuilder jc = null;
try (BufferedReader br = Files.newBufferedReader(Paths.get("")) {
    for (String line = br.readLine(); line != null; line = br.readLine()) {
        if (line.startsWith("REQ00")) {
            jc = new StringBuilder();
            list.add(jc);
        }
        jc.append(line);
    }
} catch (IOException e) {
    e.printStackTrace();
}

有什么方法可以将此代码“转换”为 Java 8 Stream 方式吗？

使用适合工作的正确工具。和Scanner，就这么简单

List<String> list = new ArrayList<>();
try(Scanner s = new Scanner(Paths.get(path))) {
    s.useDelimiter(Pattern.compile("^(?=REQ00)", Pattern.MULTILINE));
    while(s.hasNext()) list.add(s.next());
} catch (IOException e) {
    e.printStackTrace();
}

现在您的代码有创建的特殊要求StringBuilders 并且不保留换行符。所以扩展版本是：

List<StringBuilder> list = new ArrayList<>();
try(Scanner s = new Scanner(Paths.get(path))) {
    s.useDelimiter(Pattern.compile("^(?=REQ00)", Pattern.MULTILINE));
    while(s.hasNext()) list.add(new StringBuilder(s.next().replaceAll("\\R", "")));
} catch (IOException e) {
    e.printStackTrace();
}

更有效的变体是

List<StringBuilder> list = new ArrayList<>();
try(Scanner s = new Scanner(Paths.get(path))) {
    s.useDelimiter(Pattern.compile("^(?=REQ00)", Pattern.MULTILINE));
    while(s.hasNext()) list.add(toStringBuilderWithoutLinebreaks(s.next()));
} catch (IOException e) {
    e.printStackTrace();
}

…

static final Pattern LINE_BREAK = Pattern.compile("\\R");
static StringBuilder toStringBuilderWithoutLinebreaks(String s) {
    Matcher m = LINE_BREAK.matcher(s);
    if(!m.find()) return new StringBuilder(s);
    StringBuilder sb = new StringBuilder(s.length());
    int last = 0;
    do { sb.append(s, last, m.start()); last = m.end(); } while(m.find());
    return sb.append(s, last, s.length());
}

从 Java 9 开始，您还可以使用Stream对其进行操作：

List<StringBuilder> list;
try(Scanner s = new Scanner(Paths.get(path))) {
    list = s.useDelimiter(Pattern.compile("^(?=REQ00)", Pattern.MULTILINE))
            .tokens()
            .map(string -> toStringBuilderWithoutLinebreaks(string))
            .collect(Collectors.toList());
} catch (IOException e) {
    e.printStackTrace();
    list = List.of();
}