来自格式化文件的 Java 输入

Question

我正在尝试从具有各种不同行的文件中获取输入。

例如，格式为书名，作者：借阅人第二名名字：借阅人状态

这里有一些示例行。

The Lord of the Rings, JRR Tolkien:McInnes Elizabeth:13 11 10

Crime And Punishment, Fyodor Dostoyevsky

The Clan Of The Cave Bear, Jean M Auel

The God Of Small Things, Arundhati Roy:Robins Joshua:20 11 10

因此，我在设置扫描仪后尝试使用 useDelimiter，但由于有些行较短，我不知道该怎么做。

Answer 1

这是一个基于正则表达式的解决方案：

import java.io.*;
import java.util.regex.*;

public class Test {
    public static void main(String[] args) throws IOException {

        BufferedReader br = new BufferedReader(new FileReader("data.txt"));

        Pattern p = Pattern.compile("(.+?),(.+?)(?::(.+?):(\\d+ \\d+ \\d+))?");

        String line;
        while (null != (line = br.readLine())) {
            Matcher m = p.matcher(line);
            if (m.matches()) {
                String title = m.group(1);
                String author = m.group(2);
                String borrower = m.group(3);
                String data = m.group(4);

                System.out.println("Title:  " + title);
                System.out.println("Author: " + author);
                if (borrower != null) {
                    System.out.println("    Borrower: " + borrower);
                    System.out.println("    Data:     " + data);
                }
            }
            System.out.println();
        }

        br.close();
    }
}

给定您的示例输入，它会打印：

Title:  The Lord of the Rings
Author:  JRR Tolkien
    Borrower: McInnes Elizabeth
    Data:     13 11 10

Title:  Crime And Punishment
Author:  Fyodor Dostoyevsky

Title:  The Clan Of The Cave Bear
Author:  Jean M Auel

Title:  The God Of Small Things
Author:  Arundhati Roy
    Borrower: Robins Joshua
    Data:     20 11 10

Answer 2

逐行读取文件，使用[^,:]正则表达式匹配每行中的数据（顺序find将带来标题、作者、借阅者、状态、如果有的话）。

Answer 3

你可以使用 .split()

try {
    FileInputStream fstream = new FileInputStream("input.txt");
    DataInputStream in = new DataInputStream(fstream);
    BufferedReader br = new BufferedReader(new InputStreamReader(in));

    String line;
    String author;
    String title;
    String borrower;
    String date;

    while ((line = br.readLine()) != null)   {
      (author,title) = line.split(",");

      if (line.contains(":")
        (title,borrower,date) = title.split(":");

      /*** Do what you need to do with the values here ***/
    }

    in.close();

} catch (Exception e) {
    e.printStackTrace();
}

Answer 4

为什么总是建议对于如此琐碎的任务使用正则表达式之类的超大工具？为什么不简单地使用旧的 line.indexOf() 或 line.lastIndexOf() 方法呢？

Answer 5

我将分割每一行（使用 String.split），并传入冒号作为分隔符。然后对 split 返回的第一个元素使用 lastIndexOf(',') ，以便将作者与书籍分开：

public class ReadCrappyInput {

    public static List<String> testData() {
        List<String> lines = new ArrayList<String>();
        lines.add("The Lord of the Rings, JRR Tolkien:McInnes Elizabeth:13 11 10");
        lines.add("Crime And Punishment, Fyodor Dostoyevsky");
        lines.add("The Clan Of The Cave Bear, Jean M Auel");
        lines.add("The God Of Small Things, Arundhati Roy:Robins Joshua:20 11 10");
        return lines;
    }

    public Map<String, String> readLine(String line) {
        String[] parts = line.split(":");
        int endOfTitleIndex = parts[0].lastIndexOf(',');
        Map<String, String> map = new HashMap<String, String>();
        map.put("title", parts[0].substring(0, endOfTitleIndex));
        map.put("author", parts[0].substring(endOfTitleIndex + 1).trim());    
        if (parts.length > 1) {
            map.put("borrower", parts[1]);
        }
        if (parts.length > 2) {
            map.put("data", parts[2]);
        }
        return map;
    }

    public static void main(String[] args) {
        ReadCrappyInput r = new ReadCrappyInput();
        for (String s : testData()) {
            System.out.println(r.readLine(s));
        }
    }
}