加载这些 .csv 文件的最佳/最快方法是什么？

Question

我一直在尝试加载 6 个 .csv 文件。 我使用过 CSVReader 库和 BufferedReader 库。 我注意到使用 BufferedReader 库时文件加载速度更快。 尽管如此，这导致我出现 OutOfMemory 异常，因此我不得不在 Eclipse 中将最大内存使用量设置为 1024mb。 另一方面，当我使用 CSVReader 库时，我没有遇到这个问题。 我想知道我的代码是否有问题，考虑到它在速度和内存方面是最佳的，加载文件的最佳方法是什么。 这是我的代码（我在这里使用 BufferedReader）：

public void loadMovingViolations(int semestre)
{
    try
    {
        String path = ".\\data\\Moving_Violations_Issued_in_";
        String mth1Path = "";
        String mth2Path = "";
        String mth3Path = "";
        String mth4Path = "";
        String mth5Path = "";
        String mth6Path = "";

        if (semestre == 1)
        {
            mth1Path = path + "January_2018.csv";
            mth2Path = path + "February_2018.csv";
            mth3Path = path + "March_2018.csv";
            mth4Path = path + "April_2018.csv";
            mth5Path = path + "May_2018.csv";
            mth6Path = path + "June_2018.csv";
        }

        else if (semestre == 2)
        {
            mth1Path = path + "July_2018.csv";
            mth2Path = path + "August_2018.csv";
            mth3Path = path + "September_2018.csv";
            mth4Path = path + "October_2018.csv";
            mth5Path = path + "November_2018.csv";
            mth6Path = path + "December_2018.csv";
        }

        String[] mths = {mth1Path, mth2Path, mth3Path, mth4Path, mth5Path, mth6Path};
        String cPath = "";

        int numInfracs = 0;
        int[] infracs = new int[6];
        double xMin = Double.MAX_VALUE, yMin = Double.MAX_VALUE, xMax = 0, yMax = 0;
        BufferedReader br = null;

        int i = 0;
        while (i < mths.length)
        {
            int tempInfrac = 0;
            cPath = mths[i];
            br = new BufferedReader(new FileReader(cPath));
            String row = br.readLine();

            while ( (row = br.readLine()) != null)
            {   
                String[] columns = row.split(",");

                String in1 = columns[0];
                Integer objId = Integer.parseInt(in1);

                String location = columns[2];

                String in2 = columns[3];
                int adressId = 0;
                if ( !(in2.compareTo("") == 0) )
                    adressId = Integer.parseInt(in2);

                String in3 = columns[4];
                double streetId = 0;
                if ( !(in3.compareTo("") == 0) )
                    streetId = Double.parseDouble(in3);

                String in4 = columns[5];
                Double xCord = Double.parseDouble(in4);

                String in5 = columns[6];
                Double yCord = Double.parseDouble(in5);

                String ticketType = columns[7];

                String in6 = columns[8];
                Integer fineAmt = Integer.parseInt(in6);

                String in7 = columns[9];
                double totalPaid = Double.parseDouble(in7);

                String in8 = columns[10];
                Integer penalty1 =  Integer.parseInt(in8);

                String accident = columns[12];

                String date = columns[13];

                String vioCode = columns[14];

                String vioDesc = columns[15];

                VOMovingViolations vomv = new VOMovingViolations(objId, location, adressId, streetId, xCord, yCord, ticketType, fineAmt, totalPaid, penalty1, accident, date, vioCode, vioDesc);
                movingViolationsQueue.enqueue(vomv);
                tempInfrac++;

                if (xCord > xMax)
                    xMax = xCord;

                if (yCord > yMax)
                    yMax = yCord;

                if (xCord < xMin)
                    xMin = xCord;

                if (yCord < yMin)
                    yMin = yCord;
            }

            numInfracs += tempInfrac;
            infracs[i] = tempInfrac;
            i++;
            br.close();
        }

        System.out.println();
        int j = 0;
        for (int current: infracs)
        {
            String[] sa = mths[j].substring(35).split("_");
            String mth = sa[0];
            System.out.println("En el mes " + mth + " se encontraron " + 
                                current + " infracciones");
            j++;
        }
        System.out.println();
        System.out.println("Se encontraron " + numInfracs + " infracciones en el semestre.");
        System.out.println();
        System.out.println("Minimax: " + "("+xMin+", "+yMin+"), " + "("+xMax+", "+yMax+")");
        System.out.println();
    }

    catch (Exception e)
    {
        e.printStackTrace();
        System.out.println();
        System.out.println("No se pudieron cargar los datos");
        System.out.println();
    }
}

Answer 1

关于“更好”的方式，像往常一样取决于。

你正在重新发明轮子。 编写一个功能齐全的 csv 解析器来处理任意输入数据是非常困难的。 您的解析器对“,”进行了简单的拆分，这意味着只要其中一列包含带有逗号的字符串，它就会失败！ 当分隔符更改时，您也可能会遇到麻烦。

您的代码速度更快，因为它省略了 csv 解析器可以执行的大量操作。 因此，您的代码适用于您的表，但如果其他人为您提供了有效的 csv 文件，您的解析器将向您抛出异常。 真正的 csv 解析器会接受任何格式正确的输入！

因此：如果您的代码的唯一目的是读取具有给定结构的文件，当然，您可以使用更快的解决方案。 但是，如果您希望输入数据格式会随着时间而改变，那么每次更新都会使您更改代码。 更糟糕的是，随着时间的推移，此类更新可能会使您的代码变得更加复杂。 因此，您必须仔细权衡开发效率与运行时性能。

Answer 2

谢谢您的回答。 我试过使用另一个库，现在加载文件只需要大约 1.2 秒（我加载了大约 600k 个对象）。 但是当我没有在 Eclipse 命令中放置 Xms512m 和 Xml1024m 时，我仍然得到 OutOfMemory: java heap 异常。 有什么办法可以让我的加载方法使用更少的内存？

public void loadMovingViolations(int semestre)
{
    CsvParserSettings settings = new CsvParserSettings();
    settings.getFormat().setLineSeparator("\n");
    CsvParser parser = new CsvParser(settings);

    String path = ".\\data\\Moving_Violations_Issued_in_";
    String mth1Path = "";
    String mth2Path = "";
    String mth3Path = "";
    String mth4Path = "";
    String mth5Path = "";
    String mth6Path = "";

    if (semestre == 1)
    {
        mth1Path = path + "January_2018.csv";
        mth2Path = path + "February_2018.csv";
        mth3Path = path + "March_2018.csv";
        mth4Path = path + "April_2018.csv";
        mth5Path = path + "May_2018.csv";
        mth6Path = path + "June_2018.csv";
    }

    else if (semestre == 2)
    {
        mth1Path = path + "July_2018.csv";
        mth2Path = path + "August_2018.csv";
        mth3Path = path + "September_2018.csv";
        mth4Path = path + "October_2018.csv";
        mth5Path = path + "November_2018.csv";
        mth6Path = path + "December_2018.csv";
    }

    String[] mths = {mth1Path, mth2Path, mth3Path, mth4Path, mth5Path, mth6Path};
    String cPath = "";

    int numInfracs = 0;
    int[] infracs = new int[6];
    double xMin = Double.MAX_VALUE, yMin = Double.MAX_VALUE, xMax = 0, yMax = 0;

    try
    {
        int i = 0;
        while (i < mths.length)
        {
            int tempInfrac = 0;
            cPath = mths[i];
            parser.beginParsing(new FileReader(cPath));
            parser.parseNext();
            String[] row = null;
            while((row = parser.parseNext()) != null)
            {
                String in1 = row[0].toString();
                Integer objId = Integer.parseInt(in1);

                String location = row[2].toString();

                int addressId = 0;
                if (row[3] != null)
                {
                    String in2 = row[3].toString();
                    addressId = Integer.parseInt(in2);
                }

                double streetId = 0;
                if (row[4] != null)
                {
                    String in3 = row[4].toString();
                    streetId = Double.parseDouble(in3);
                }

                String in4 = row[5].toString();
                Double xCord = Double.parseDouble(in4);

                String in5 = row[6].toString();
                Double yCord = Double.parseDouble(in5);

                String ticketType = row[7].toString();

                String in6 = row[8].toString();
                Integer fineAmt = Integer.parseInt(in6);

                String in7 = row[9].toString();
                double totalPaid = Double.parseDouble(in7);

                String in8 = row[10].toString();
                Integer penalty1 =  Integer.parseInt(in8);

                String accident = row[12].toString();

                String date = "";
                if (row[13] != null)
                    date = row[13].toString();

                String vioCode = row[14].toString();

                String vioDesc = "";
                if (row[15] != null)
                    vioDesc = row[15].toString();

                VOMovingViolations vomv = new VOMovingViolations(objId, location, addressId, streetId, xCord, yCord, ticketType, fineAmt, totalPaid, penalty1, accident, date, vioCode, vioDesc);
                queue.enqueue(vomv);
                tempInfrac++;

                if (xCord > xMax)
                    xMax = xCord;

                if (yCord > yMax)
                    yMax = yCord;

                if (xCord < xMin)
                    xMin = xCord;

                if (yCord < yMin)
                    yMin = yCord;
            }

            numInfracs += tempInfrac;
            infracs[i] = tempInfrac;
            parser.stopParsing();
            i++;
        }

        System.out.println();
        int j = 0;
        for (int current: infracs)
        {
            String[] sa = mths[j].substring(35).split("_");
            String mth = sa[0];
            System.out.println("En el mes " + mth + " se encontraron " + 
                                current + " infracciones");
            j++;
        }
        System.out.println();
        System.out.println("Se encontraron " + numInfracs + " infracciones en el semestre.");
        System.out.println();
        System.out.println("Minimax: " + "("+xMin+", "+yMin+"), " + "("+xMax+", "+yMax+")");
        System.out.println();
    }

    catch (FileNotFoundException e)
    {
        e.printStackTrace();
        System.out.println();
        System.out.println("No se encontró el archivo");
        System.out.println();
    }
}