我一直在尝试加载6个.csv文件。我使用了CSVReader库和BufferedReader库。我注意到使用BufferedReader库时，文件加载速度更快。但是，这导致我有一个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，没有出现此问题。我想知道我的代码中是否有问题，考虑到速度和内存方面的最佳选择，什么是加载文件的最佳方法？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();
}
}
答案 0 :(得分：1)
关于“更好”的方式，通常要视情况而定。
您正在重新发明轮子。而且，编写与任意输入数据配合使用的功能全面的csv解析器非常困难。您的解析器对“，”进行了简单的拆分，这意味着一旦您的一列中包含一个带有逗号的字符串，解析器就会失败！更改分隔符时，您可能还会遇到麻烦。
您的代码更快，因为它省略了csv解析器可以执行的大量操作。因此，您的代码可以与表一起使用，但是如果其他人为您提供了有效的csv文件，则解析器将向您抛出异常。真正的csv解析器将接受任何格式正确的输入！
因此：如果代码的唯一目的是读取具有给定结构的文件，那么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更加复杂。因此，您必须仔细平衡开发效率与运行时性能之间的平衡。
答案 1 :(得分：0)
谢谢您的回答。我尝试使用另一个库，现在只需大约1.2秒即可加载文件（我正在加载约600k个对象）。但是当我不将Xms512m和Xml1024m放在Eclipse命令中时，我仍然遇到OutOfMemory：java堆异常。有什么办法可以使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();
}
}