java优化CSV解析以提高速度
我正在开发这个“程序”,它从两个大型csv文件(逐行)读取数据,比较文件中的数组元素,当找到匹配项时,它会将我所需的数据写入第三个文件。我唯一的问题是速度很慢。它每秒读取1-2行,速度非常慢,因为我有数百万条记录。有什么办法可以加快速度吗?这是我的密码:
public class ReadWriteCsv {
public static void main(String[] args) throws IOException {
FileInputStream inputStream = null;
FileInputStream inputStream2 = null;
Scanner sc = null;
Scanner sc2 = null;
String csvSeparator = ",";
String line;
String line2;
String path = "D:/test1.csv";
String path2 = "D:/test2.csv";
String path3 = "D:/newResults.csv";
String[] columns;
String[] columns2;
Boolean matchFound = false;
int count = 0;
StringBuilder builder = new StringBuilder();
FileWriter writer = new FileWriter(path3);
try {
// specifies where to take the files from
inputStream = new FileInputStream(path);
inputStream2 = new FileInputStream(path2);
// creating scanners for files
sc = new Scanner(inputStream, "UTF-8");
// while there is another line available do:
while (sc.hasNextLine()) {
count++;
// storing the current line in the temporary variable "line"
line = sc.nextLine();
System.out.println("Number of lines read so far: " + count);
// defines the columns[] as the line being split by ","
columns = line.split(",");
inputStream2 = new FileInputStream(path2);
sc2 = new Scanner(inputStream2, "UTF-8");
// checks if there is a line available in File2 and goes in the
// while loop, reading file2
while (!matchFound && sc2.hasNextLine()) {
line2 = sc2.nextLine();
columns2 = line2.split(",");
if (columns[3].equals(columns2[1])) {
matchFound = true;
builder.append(columns[3]).append(csvSeparator);
builder.append(columns[1]).append(csvSeparator);
builder.append(columns2[2]).append(csvSeparator);
builder.append(columns2[3]).append("\n");
String result = builder.toString();
writer.write(result);
}
}
builder.setLength(0);
sc2.close();
matchFound = false;
}
if (sc.ioException() != null) {
throw sc.ioException();
}
} finally {
//then I close my inputStreams, scanners and writer
# 1 楼答案
使用univocity-parsersCSV解析器,因为处理两个文件(每个文件有一百万行)所需的时间不会超过几秒钟:
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# 2 楼答案
使用现有的CSV库,而不是滚动您自己的库。它将比你现在拥有的更加强大
但是,您的问题不是CSV解析速度,而是您的算法是O(n^2),对于第一个文件中的每一行,您需要扫描第二个文件。这种算法会随着数据的大小而迅速膨胀,当您有数百万行时,您会遇到问题。你需要一个更好的算法
另一个问题是每次扫描都要重新解析第二个文件。您至少应该在程序开始时将其作为ArrayList或其他内容读入内存,这样您只需要加载和解析它一次