字符串如何在java中从txt文件中读取冒号分隔的值

Question

我试图从如下格式的文本文件中读取数据：

Operation: ADDITION Attempts: 3

我试图读入的数据是操作和每行的尝试次数，例如加法和数字3

这是我所能做到的，我仍然不确定

File inputFile = new File("mathFile.txt");
 Scanner input = new Scanner(inputFile);

 while(input.hasNext())
    {
        String token = input.nextLine();
        String[] details = token.split("Operation:");
        String operation = details[0];
}

Answer 1

有很多方法可以读取文本文件并根据某个分隔符拆分行。除了这里的所有其他答案之外，下面是另一个简洁明了的答案

（1）读取文件的行

List<String> lines = Files.lines(Paths.get("mathFile.txt")).collect(Collectors.toList());

（2）从每一行解析你想要的内容

List<String> operations = lines.stream().map(line -> line.split("Operation:")[0]).collect(Collectors.toList());

Answer 2

最简单的选择是在空间上拆分：

String[] parts = token.split(" ");
String operation = parts[1];
String attempts = parts[3];

如果你想变得更时尚，可以使用正则表达式：

String token = "Operation: ADDITION Attempts: 3";
Matcher matcher = Pattern.compile("^Operation: (\\w+) Attempts: (\\d+)$").matcher(token);
if (matcher.find()) {
    String operation = matcher.group(1);
    String attempts = matcher.group(2);
}

Answer 3

// Model: line representation
public final class MathFileLine {

    private final String operation;
    private final int attempts;

    public MathFileLine(String operation, int attempts) {
        this.operation = operation;
        this.attempts = attempts;
    }

}

// client code
public static void main(String... args) throws IOException {
    List<MathFileLine> lines = readMathFile(Paths.get("mathFile.txt"));
}

#1：使用Stream读取带有RegEx

public static List<MathFileLine> readMathFile(Path path) throws IOException {
    final Pattern pattern = Pattern.compile("^Operation:\\s+(?<operation>\\w+)\\s+Attempts:\\s+(?<attempts>\\d+)$");
    return Files.lines(path)
                .map(pattern::matcher)
                .filter(Matcher::matches)
                .map(matcher -> new MathFileLine(matcher.group("operation"), Integer.parseInt(matcher.group("attempts"))))
                .collect(Collectors.toList());
}

#2：使用带有自定义分隔符的扫描仪读取对

public static List<MathFileLine> readMathFile(Path path) throws IOException {
    try (Scanner scan = new Scanner(path.toFile())) {
        scan.useDelimiter("\\s*(?:Operation:|Attempts:)?\\s+");
        List<MathFileLine> lines = new LinkedList<>();

        while (scan.hasNext()) {
            lines.add(new MathFileLine(scan.next(), scan.nextInt()));
        }

        return lines;
    }
}