java - TomCat-构造函数在尝试从文件读取时抛出异常

我下面有一些方法，基本上我的问题是当我尝试从.txt文件读取时。该应用程序在内存中运行良好。将decode()添加到重载的构造函数时，我在Tomcat服务器日志中得到以下错误：

Constructor threw exception; nested exception is java.lang.NumberFormatException: For input string: ""

当我更多地查看它时，它指向了解码方法中的这一行
currentDVD.setDvdId(Integer.parseInt((currentTokens[0])));但我似乎无法弄清楚问题是什么。有一次，我能够从文件中读取内容，然后试图使编码方法起作用，并且在某个时刻发生了某些事情。任何帮助，将不胜感激。

public class DvdLibraryInFileImpl implements DvdLibraryDao {

    private Map<Integer, DVD> dvdMap = new HashMap<>();
    public static final String DVD_FILE = "dvd.txt";
    public static final String DELIMITER = "::";
    private static int dvdIdCounter = 0;

    public DvdLibraryInFileImpl() throws FileNotFoundException {
      decode();

    }


    @Override
    public DVD addDVD(DVD dvd) {

        dvd.setDvdId(dvdIdCounter);

        dvdIdCounter++;

        dvdMap.put(dvd.getDvdId(), dvd);

        return dvd;
    }

    @Override
    public DVD getDVDById(int dvdId) {
        return dvdMap.get(dvdId);
    }

    @Override
    public List<DVD> getAllDVDSByName(String searchByName) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    @Override
    public List<DVD> getAllDVDS() {
        List<DVD> allDVDS = new ArrayList<>(dvdMap.values());
        return allDVDS;
    }

    @Override
    public void updateDVD(DVD dvd) {
        dvdMap.put(dvd.getDvdId(), dvd);
    }

    @Override
    public void removeDVD(int dvdId) {
        dvdMap.remove(dvdId);
    }


    @Override
    public void decode() throws FileNotFoundException {
        Scanner sc = new Scanner(new BufferedReader(new FileReader(DVD_FILE)));
        String[] currentTokens;
        while (sc.hasNextLine()) {
            String currentLine = sc.nextLine();
            currentTokens = currentLine.split(DELIMITER);

            DVD currentDVD = new DVD();

            currentDVD.setDvdId(Integer.parseInt((currentTokens[0])));
            currentDVD.setTitle(currentTokens[1]);
            currentDVD.setReleaseDate(currentTokens[2]);
            currentDVD.setMpaaRating(currentTokens[3]);
            currentDVD.setDirectorsName(currentTokens[4]);
            currentDVD.setStudio(currentTokens[5]);
            currentDVD.setUserRating(currentTokens[6]);

            dvdMap.put(Integer.parseInt((currentTokens[0])), currentDVD);
        }

    }


    @Override
    public void encode() throws IOException {
        PrintWriter out = new PrintWriter(new FileWriter(DVD_FILE));
        Set<Integer> keySet = dvdMap.keySet();
        for (Integer i : keySet) {

            out.print((dvdMap.get(i)).getDvdId());
            out.print(DELIMITER);

            out.print((dvdMap.get(i)).getTitle());
            out.print(DELIMITER);

            out.print((dvdMap.get(i)).getReleaseDate());
            out.print(DELIMITER);

            out.print((dvdMap.get(i)).getMpaaRating());
            out.print(DELIMITER);

            out.print((dvdMap.get(i)).getDirectorsName());
            out.print(DELIMITER);

            out.print((dvdMap.get(i)).getStudio());
            out.print(DELIMITER);

            out.print((dvdMap.get(i)).getUserRating());
            out.println("");

        }
        out.flush();
        out.close();
    }
}

最佳答案

问题是因为currentLine没有接收到正确的输入数据（来自用户输入）。

您应该确保currentTokens设置了正确的DvdId（应为数字值），否则Integer.parseInt((currentTokens[0]))行将为非数字或空（“”）数据抛出NumberFormatException。

您需要确保使用数字dvdid输入的输入数据正确无误。

例如，输入以下数据：
1234 :: DVDTITLE :: 29-OCT-2016 :: RATING1 :: DIRECTOR :: STUDIO :: RATING2

我强烈建议您添加输入验证以处理各种情况，例如输入非数字值或对包含数字值的最大值或导演名称评分更高等。