Java按指定日期过滤读取文件需求实现求助（附现有代码）

Let's walk through fixing your code to meet the new requirement—only reading files with the date 04/17/2019, while giving clear feedback for non-matching files. First, let's spot the key issues in your original code that were blocking this functionality:

• The filesort() method returns immediately after the first file: This means it never checks all files in the list, so you'll only ever get the date of the first file.
• Incorrect date format pattern: You used yyyymmdd where mm represents minutes, not months. You need yyyyMMdd instead (uppercase MM is for months).
• Missing full file path: When creating a File object with just the filename, it looks in your current working directory, not the root path C: you specified.
• Redundant method calls: Calling filesort() multiple times per file in the loop wastes resources and leads to inconsistent results.

Here's the revised code that fixes all these issues and implements your desired logic:

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.InputStreamReader;
import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.zip.GZIPInputStream;

public class FileDateFilterReader {

    // Keeps your original logic to filter files starting with "B"
    public static String[] find(String rootPath) {
        File root = new File(rootPath);
        FilenameFilter beginsWithB = new FilenameFilter() {
            public boolean accept(File directory, String filename) {
                return filename.startsWith("B");
            }
        };
        String[] files = root.list(beginsWithB);
        return files != null ? files : new String[]{"nofile"};
    }

    // Helper method to extract and format the date from a file's name
    private static String getFormattedFileDate(File file) throws ParseException {
        String fileName = file.getName();
        // Pull out the numeric part of the filename (e.g., "20190417" from "BProce.Arr.20190417..ball10.gz")
        String numericPart = fileName.replaceAll("\\D+", "");
        if (numericPart.length() < 8) {
            return null; // Invalid date format in filename
        }
        String dateString = numericPart.substring(0, 8);
        // Correct date pattern (MM for months, not mm)
        DateFormat inputFormatter = new SimpleDateFormat("yyyyMMdd");
        Date date = inputFormatter.parse(dateString);
        // Format to your desired mm/dd/yyyy style
        DateFormat outputFormatter = new SimpleDateFormat("MM/dd/yyyy");
        return outputFormatter.format(date);
    }

    public static void main(String[] args) {
        String rootPath = "C:";
        String[] filesList = find(rootPath);
        String targetDate = "04/17/2019";

        for (String fileName : filesList) {
            // Build the full file path using File.separator for cross-platform compatibility
            File file = new File(rootPath + File.separator + fileName);
            if (!file.exists()) {
                System.out.println("File not found: " + fileName);
                continue;
            }

            try {
                String fileDate = getFormattedFileDate(file);
                if (targetDate.equals(fileDate)) {
                    // Read the GZIP file with try-with-resources to auto-close streams
                    try (BufferedReader reader = new BufferedReader(
                            new InputStreamReader(
                                    new GZIPInputStream(
                                            new FileInputStream(file))))) {
                        String content;
                        System.out.println("\nReading content from: " + fileName);
                        while ((content = reader.readLine()) != null) {
                            System.out.println(content);
                        }
                    } catch (Exception e) {
                        System.out.println("Error reading file " + fileName + ": " + e.getMessage());
                    }
                } else {
                    System.out.println("Skipping file (date mismatch): " + fileName + " | File date: " + fileDate);
                }
            } catch (ParseException e) {
                System.out.println("Error parsing date from file " + fileName + ": " + e.getMessage());
            }
        }
    }
}

Key Improvements: #

1. Reusable Date Logic: The getFormattedFileDate() method handles all date extraction and formatting, making the code cleaner and easier to adjust later.
2. Correct Date Handling: Fixed the format pattern to avoid mixing up months and minutes, which was a critical bug in the original code.
3. Full Path & Cross-Platform Support: Uses File.separator instead of hardcoding // to work on Windows, macOS, or Linux.
4. Proper Resource Management: Try-with-resources ensures streams are closed automatically, preventing resource leaks.
5. Clear Feedback: Tells you exactly which files are being read, skipped, or causing errors, so you can debug easily.

This code will correctly read only the 04/17/2019 files (BProce.Arr.20190417..ball10.gz and BProce.Arr.20190417.ball23.gz) and skip the 20190416 file, with clear status updates for each file.

内容的提问来源于stack exchange，提问作者SAM