在Java中,在行首或行尾命中CSV文件
我使用这段代码来分割和处理csv文件,问题是块被设置在任意位置,可能在行的开头、中间或结尾 如何将起始位置设置为行尾或行尾,使块成为完整的CSV文件而不丢失任何数据在Java中,在行首或行尾命中CSV文件,java,csv,opencsv,Java,Csv,Opencsv,我使用这段代码来分割和处理csv文件,问题是块被设置在任意位置,可能在行的开头、中间或结尾 如何将起始位置设置为行尾或行尾,使块成为完整的CSV文件而不丢失任何数据 public static void main(String[] args) throws IOException { long start = System.currentTimeMillis(); CSVReader reader = new CSVReader(new FileReader("
public static void main(String[] args) throws IOException {
long start = System.currentTimeMillis();
CSVReader reader = new CSVReader(new FileReader("x_tran.csv"));
String[] columnsNames = reader.readNext();
reader.close();
FileInputStream fileInputStream = new FileInputStream("x_tran.csv");
FileChannel channel = fileInputStream.getChannel();
long remaining_size = channel.size(); //get the total number of bytes in the file
long chunk_size = remaining_size / 4; //file_size/threads
//Max allocation size allowed is ~2GB
if (chunk_size > (Integer.MAX_VALUE - 5))
{
chunk_size = (Integer.MAX_VALUE - 5);
}
//thread pool
ExecutorService executor = Executors.newFixedThreadPool(4);
long start_loc = 0;//file pointer
int i = 0; //loop counter
boolean first = true;
while (remaining_size >= chunk_size)
{
//launches a new thread
executor.execute(new FileRead(start_loc, toIntExact(chunk_size), channel, i, String.join(",", columnsNames), first));
remaining_size = remaining_size - chunk_size;
start_loc = start_loc + chunk_size;
i++;
first = false;
}
//load the last remaining piece
executor.execute(new FileRead(start_loc, toIntExact(remaining_size), channel, i, String.join(",", columnsNames), first));
//Tear Down
executor.shutdown();
//Wait for all threads to finish
while (!executor.isTerminated())
{
//wait for infinity time
}
System.out.println("Finished all threads");
fileInputStream.close();
long finish = System.currentTimeMillis();
System.out.println( "Time elapsed: " + (finish - start) );
}
您可以读取该文件一次,然后使每个线程处理的行数与线程数成模(例如,第一个线程处理的行数为0、4、8等)
包。。。;
导入java.io.IOException;
导入java.nio.file.Files;
导入java.nio.file.Path;
导入java.util.List;
导入java.util.concurrent.ExecutorService;
导入java.util.concurrent.Executors;
公共类CsvParallelReader{
私有静态最终整数线程数=4;
公共静态void main(字符串[]args){
ExecutorService executor=Executors.newFixedThreadPool(线程编号);
试一试{
列表行=Files.readAllLines(Path.of(“yourfile.csv”);
对于(int i=0;i
您想并行读取文件还是并行处理数据?事实上,我想到了两种方法,但开始位置问题(指针)阻止了我。最终,我需要尽可能快地处理该文件(~450MB)
package ...;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.List;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class CsvParallelReader {
private static final int THREAD_NUMBER = 4;
public static void main(String[] args) {
ExecutorService executor = Executors.newFixedThreadPool(THREAD_NUMBER);
try {
List<String> lines = Files.readAllLines(Path.of("yourfile.csv"));
for (int i = 0; i < THREAD_NUMBER; i++) {
Runnable readTask = new ReadTask(i, lines);
executor.submit(readTask);
}
} catch (IOException e) {
e.printStackTrace();
}
}
private static class ReadTask implements Runnable {
private final List<String> lines;
private int start;
public ReadTask(int start, List<String> lines) {
this.start = start;
this.lines = lines;
}
@Override
public void run() {
for (int i = start; i < lines.size(); i += THREAD_NUMBER) {
// do something with this line of data
}
}
}
}