在文本文件Java中写入大量数据的最快方法 [英] Fastest way to write huge data in text file Java

问题描述

我必须在 text[csv] 文件中写入大量数据.我使用 BufferedWriter 写入数据，写入 174 mb 数据大约需要 40 秒.这是java可以提供的最快速度吗?

I have to write huge data in text[csv] file. I used BufferedWriter to write the data and it took around 40 secs to write 174 mb of data. Is this the fastest speed java can offer?

bufferedWriter = new BufferedWriter ( new FileWriter ( "fileName.csv" ) );

注意:这 40 秒还包括迭代和从结果集中获取记录的时间.:) .174 mb 用于结果集中的 400000 行.

Note: These 40 secs include the time of iterating and fetching the records from resultset as well. :) . 174 mb is for 400000 rows in resultset.

推荐答案

您可以尝试移除 BufferedWriter 并直接使用 FileWriter.在现代系统上，您很有可能只是在写入驱动器的缓存.

You might try removing the BufferedWriter and just using the FileWriter directly. On a modern system there's a good chance you're just writing to the drive's cache memory anyway.

写入 175MB(400 万个字符串)需要 4-5 秒的时间——这是在运行 Windows XP 的双核 2.4GHz 戴尔上，使用 80GB、7200-RPM 日立磁盘.

It takes me in the range of 4-5 seconds to write 175MB (4 million strings) -- this is on a dual-core 2.4GHz Dell running Windows XP with an 80GB, 7200-RPM Hitachi disk.

你能区分出记录检索和文件写入的时间有多少吗?

Can you isolate how much of the time is record retrieval and how much is file writing?

import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.io.Writer;
import java.util.ArrayList;
import java.util.List;

public class FileWritingPerfTest {
    

private static final int ITERATIONS = 5;
private static final double MEG = (Math.pow(1024, 2));
private static final int RECORD_COUNT = 4000000;
private static final String RECORD = "Help I am trapped in a fortune cookie factory
";
private static final int RECSIZE = RECORD.getBytes().length;

public static void main(String[] args) throws Exception {
    List<String> records = new ArrayList<String>(RECORD_COUNT);
    int size = 0;
    for (int i = 0; i < RECORD_COUNT; i++) {
        records.add(RECORD);
        size += RECSIZE;
    }
    System.out.println(records.size() + " 'records'");
    System.out.println(size / MEG + " MB");
    
    for (int i = 0; i < ITERATIONS; i++) {
        System.out.println("
Iteration " + i);
        
        writeRaw(records);
        writeBuffered(records, 8192);
        writeBuffered(records, (int) MEG);
        writeBuffered(records, 4 * (int) MEG);
    }
}

private static void writeRaw(List<String> records) throws IOException {
    File file = File.createTempFile("foo", ".txt");
    try {
        FileWriter writer = new FileWriter(file);
        System.out.print("Writing raw... ");
        write(records, writer);
    } finally {
        // comment this out if you want to inspect the files afterward
        file.delete();
    }
}

private static void writeBuffered(List<String> records, int bufSize) throws IOException {
    File file = File.createTempFile("foo", ".txt");
    try {
        FileWriter writer = new FileWriter(file);
        BufferedWriter bufferedWriter = new BufferedWriter(writer, bufSize);
    
        System.out.print("Writing buffered (buffer size: " + bufSize + ")... ");
        write(records, bufferedWriter);
    } finally {
        // comment this out if you want to inspect the files afterward
        file.delete();
    }
}

private static void write(List<String> records, Writer writer) throws IOException {
    long start = System.currentTimeMillis();
    for (String record: records) {
        writer.write(record);
    }
    // writer.flush(); // close() should take care of this
    writer.close(); 
    long end = System.currentTimeMillis();
    System.out.println((end - start) / 1000f + " seconds");
}
}

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