Java, the fastest class to read from a txt file [closed]

问题

I have to read txt files in my program. Im currently using FileReader and BufferedReader. I tried to use Scanner but its slower than FileReader and BufferedReader. Is there any class, which can read files faster ? It must be written in Java Language.

I need to read all words(strings splited by white space) from text file

回答1:

If the files being read is huge then you would want to use BufferedReader on top of a FileReader to improve read performance.

or you may try something likethis:-

 BufferedReader br = new BufferedReader(new FileReader("file.txt"));
try {
    StringBuilder sb = new StringBuilder();
    String line = br.readLine();

    while (line != null) {
        sb.append(line);
        sb.append("\n");
        line = br.readLine();
    }
    String everything = sb.toString();
   } finally {
    br.close();
}

or you can try this program. It works faster for larger files:-

public String readDoc(File f) {
String text = "";
int read, N = 1024 * 1024;
char[] buffer = new char[N];

try {
    FileReader fr = new FileReader(f);
    BufferedReader br = new BufferedReader(fr);

    while(true) {
        read = br.read(buffer, 0, N);
        text += new String(buffer, 0, read);

        if(read < N) {
            break;
        }
    }
} catch(Exception ex) {
    ex.printStackTrace();
}

return text;
}

回答2:

Assuming you read all the file in memory, the fastest, from a code writing perspective, is:

List<String> lines = Files.readAllLines(yourFile, charset);

I would expect performance, from an execution perspective, to be as good if not better (this has supposedly been optimised by the team who wrote it).

You can then split or do whatever you need.

回答3:

If your file is big Files.readAllLines wont work. But if you still want to try out NIO it's easy:

FileInputStream fis = new FileInputStream("test.txt");
Reader rdr = Channels.newReader(fis.getChannel(), "UTF-8");
BufferedReader br = new BufferedReader(rdr);
...

回答4:

The speed of reading and splitting is 85 MB/sec. I used 560 MB file with 20 columns in each line. Here is the code:

package csvreader_speedtest;

import java.io.*;

public class Csvreader_SpeedTest {

    final char delimiter = ',';
    String[] splitted = new String[64];

    Csvreader_SpeedTest(String filename) throws Throwable {
        File file = new File(filename);
        BufferedReader reader = new BufferedReader(new FileReader(file));
        String line;
        long t0 = System.currentTimeMillis();
        while ((line = reader.readLine()) != null) {
            split(line);
        }
        long t1 = System.currentTimeMillis();
        reader.close();
        System.out.println("read " + file.length() + " bytes in " + (t1 - t0) + " ms");
    }

    private void split(String line) {
        int idxComma, idxToken = 0, fromIndex = 0;
        while ((idxComma = line.indexOf(delimiter, fromIndex)) != -1) {
            splitted[idxToken++] = line.substring(fromIndex, idxComma);
            fromIndex = idxComma + 1;
        }
        splitted[idxToken] = line.substring(fromIndex);
    }
}

output:

read 561362951 bytes in 6575 ms

update: if I use splitted = line.split(","); instead of split(line);, the speed drops to 32 MB/sec update 2: without splitting, the speed is 194 MB/sec. How fast do you need it to be?

来源：https://stackoverflow.com/questions/13480183/java-the-fastest-class-to-read-from-a-txt-file

标签

java

java-io