I need to read a large text file of around 5-6 GB line by line using Java.
How can I do this quickly?
I need to read a large text file of around 5-6 GB line by line using Java.
How can I do this quickly?
A common pattern is to use
try (BufferedReader br = new BufferedReader(new FileReader(file))) {
String line;
while ((line = br.readLine()) != null) {
// process the line.
}
}
You can read the data faster if you assume there is no character encoding. e.g. ASCII-7 but it won't make much difference. It is highly likely that what you do with the data will take much longer.
EDIT: A less common pattern to use which avoids the scope of line
leaking.
try(BufferedReader br = new BufferedReader(new FileReader(file))) {
for(String line; (line = br.readLine()) != null; ) {
// process the line.
}
// line is not visible here.
}
UPDATE: In Java 8 you can do
try (Stream<String> stream = Files.lines(Paths.get(fileName))) {
stream.forEach(System.out::println);
}
NOTE: You have to place the Stream in a try-with-resource block to ensure the #close method is called on it, otherwise the underlying file handle is never closed until GC does it much later.
Look at this blog:
The buffer size may be specified, or the default size may be used. The default is large enough for most purposes.
// Open the file
FileInputStream fstream = new FileInputStream("textfile.txt");
BufferedReader br = new BufferedReader(new InputStreamReader(fstream));
String strLine;
//Read File Line By Line
while ((strLine = br.readLine()) != null) {
// Print the content on the console
System.out.println (strLine);
}
//Close the input stream
fstream.close();
Once Java 8 is out (March 2014) you'll be able to use streams:
try (Stream<String> lines = Files.lines(Paths.get(filename), Charset.defaultCharset())) {
lines.forEachOrdered(line -> process(line));
}
Printing all the lines in the file:
try (Stream<String> lines = Files.lines(file, Charset.defaultCharset())) {
lines.forEachOrdered(System.out::println);
}
Here is a sample with full error handling and supporting charset specification for pre-Java 7. With Java 7 you can use try-with-resources syntax, which makes the code cleaner.
If you just want the default charset you can skip the InputStream and use FileReader.
InputStream ins = null; // raw byte-stream
Reader r = null; // cooked reader
BufferedReader br = null; // buffered for readLine()
try {
String s;
ins = new FileInputStream("textfile.txt");
r = new InputStreamReader(ins, "UTF-8"); // leave charset out for default
br = new BufferedReader(r);
while ((s = br.readLine()) != null) {
System.out.println(s);
}
}
catch (Exception e)
{
System.err.println(e.getMessage()); // handle exception
}
finally {
if (br != null) { try { br.close(); } catch(Throwable t) { /* ensure close happens */ } }
if (r != null) { try { r.close(); } catch(Throwable t) { /* ensure close happens */ } }
if (ins != null) { try { ins.close(); } catch(Throwable t) { /* ensure close happens */ } }
}
Here is the Groovy version, with full error handling:
File f = new File("textfile.txt");
f.withReader("UTF-8") { br ->
br.eachLine { line ->
println line;
}
}
I documented and tested 10 different ways to read a file in Java and then ran them against each other by making them read in test files from 1KB to 1GB. Here are the fastest 3 file reading methods for reading a 1GB test file.
Note that when running the performance tests I didn't output anything to the console since that would really slow down the test. I just wanted to test the raw reading speed.
1) java.nio.file.Files.readAllBytes()
Tested in Java 7, 8, 9. This was overall the fastest method. Reading a 1GB file was consistently just under 1 second.
import java.io..File;
import java.io.IOException;
import java.nio.file.Files;
public class ReadFile_Files_ReadAllBytes {
public static void main(String [] pArgs) throws IOException {
String fileName = "c:\\temp\\sample-1GB.txt";
File file = new File(fileName);
byte [] fileBytes = Files.readAllBytes(file.toPath());
char singleChar;
for(byte b : fileBytes) {
singleChar = (char) b;
System.out.print(singleChar);
}
}
}
2) java.nio.file.Files.lines()
This was tested successfully in Java 8 and 9 but it won't work in Java 7 because of the lack of support for lambda expressions. It took about 3.5 seconds to read in a 1GB file which put it in second place as far as reading larger files.
import java.io.File;
import java.io.IOException;
import java.nio.file.Files;
import java.util.stream.Stream;
public class ReadFile_Files_Lines {
public static void main(String[] pArgs) throws IOException {
String fileName = "c:\\temp\\sample-1GB.txt";
File file = new File(fileName);
try (Stream linesStream = Files.lines(file.toPath())) {
linesStream.forEach(line -> {
System.out.println(line);
});
}
}
}
3) BufferedReader
Tested to work in Java 7, 8, 9. This took about 4.5 seconds to read in a 1GB test file.
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
public class ReadFile_BufferedReader_ReadLine {
public static void main(String [] args) throws IOException {
String fileName = "c:\\temp\\sample-1GB.txt";
FileReader fileReader = new FileReader(fileName);
try (BufferedReader bufferedReader = new BufferedReader(fileReader)) {
String line;
while((line = bufferedReader.readLine()) != null) {
System.out.println(line);
}
}
}
You can find the complete rankings for all 10 file reading methods here.
In Java 8, you could do:
try (Stream<String> lines = Files.lines (file, StandardCharsets.UTF_8))
{
for (String line : (Iterable<String>) lines::iterator)
{
;
}
}
Some notes: The stream returned by Files.lines
(unlike most streams) needs to be closed. For the reasons mentioned here I avoid using forEach()
. The strange code (Iterable<String>) lines::iterator
casts a Stream to an Iterable.
What you can do is scan the entire text using Scanner and go through the text line by line. Of course you should import the following:
import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
public static void readText throws FileNotFoundException {
Scanner scan = new Scanner(new File("samplefilename.txt"));
while(scan.hasNextLine()){
String line = scan.nextLine();
//Here you can manipulate the string the way you want
}
}
Scanner basically scans all the text. The while loop is used to traverse through the entire text.
The .hasNextLine()
function is a boolean that returns true if there are still more lines in the text. The .nextLine()
function gives you an entire line as a String which you can then use the way you want. Try System.out.println(line)
to print the text.
Side Note: .txt is the file type text.
FileReader won't let you specify the encoding, use InputStreamReader
instead if you need to specify it:
try {
BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream(filePath), "Cp1252"));
String line;
while ((line = br.readLine()) != null) {
// process the line.
}
br.close();
} catch (IOException e) {
e.printStackTrace();
}
If you imported this file from Windows, it might have ANSI encoding (Cp1252), so you have to specify the encoding.
In Java 7:
String folderPath = "C:/folderOfMyFile";
Path path = Paths.get(folderPath, "myFileName.csv"); //or any text file eg.: txt, bat, etc
Charset charset = Charset.forName("UTF-8");
try (BufferedReader reader = Files.newBufferedReader(path , charset)) {
while ((line = reader.readLine()) != null ) {
//separate all csv fields into string array
String[] lineVariables = line.split(",");
}
} catch (IOException e) {
System.err.println(e);
}
In Java 8, there is also an alternative to using Files.lines()
. If your input source isn't a file but something more abstract like a Reader
or an InputStream
, you can stream the lines via the BufferedReader
s lines()
method.
For example:
try (BufferedReader reader = new BufferedReader(...)) {
reader.lines().forEach(line -> processLine(line));
}
will call processLine()
for each input line read by the BufferedReader
.
For reading a file with Java 8
package com.java.java8;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.stream.Stream;
/**
* The Class ReadLargeFile.
*
* @author Ankit Sood Apr 20, 2017
*/
public class ReadLargeFile {
/**
* The main method.
*
* @param args
* the arguments
*/
public static void main(String[] args) {
try {
Stream<String> stream = Files.lines(Paths.get("C:\\Users\\System\\Desktop\\demoData.txt"));
stream.forEach(System.out::println);
}
catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
The clear way to achieve this,
For example:
If you have dataFile.txt
on your current directory
import java.io.*;
import java.util.Scanner;
import java.io.FileNotFoundException;
public class readByLine
{
public readByLine() throws FileNotFoundException
{
Scanner linReader = new Scanner(new File("dataFile.txt"));
while (linReader.hasNext())
{
String line = linReader.nextLine();
System.out.println(line);
}
linReader.close();
}
public static void main(String args[]) throws FileNotFoundException
{
new readByLine();
}
}
BufferedReader br;
FileInputStream fin;
try {
fin = new FileInputStream(fileName);
br = new BufferedReader(new InputStreamReader(fin));
/*Path pathToFile = Paths.get(fileName);
br = Files.newBufferedReader(pathToFile,StandardCharsets.US_ASCII);*/
String line = br.readLine();
while (line != null) {
String[] attributes = line.split(",");
Movie movie = createMovie(attributes);
movies.add(movie);
line = br.readLine();
}
fin.close();
br.close();
} catch (FileNotFoundException e) {
System.out.println("Your Message");
} catch (IOException e) {
System.out.println("Your Message");
}
It works for me. Hope It will help you too.
I usually do the reading routine straightforward:
void readResource(InputStream source) throws IOException {
BufferedReader stream = null;
try {
stream = new BufferedReader(new InputStreamReader(source));
while (true) {
String line = stream.readLine();
if(line == null) {
break;
}
//process line
System.out.println(line)
}
} finally {
closeQuiet(stream);
}
}
static void closeQuiet(Closeable closeable) {
if (closeable != null) {
try {
closeable.close();
} catch (IOException ignore) {
}
}
}
By using the org.apache.commons.io package, it gave more performance, especially in legacy code which uses Java 6 and below.
Java 7 has a better API with fewer exceptions handling and more useful methods:
LineIterator lineIterator = null;
try {
lineIterator = FileUtils.lineIterator(new File("/home/username/m.log"), "windows-1256"); // The second parameter is optionnal
while (lineIterator.hasNext()) {
String currentLine = lineIterator.next();
// Some operation
}
}
finally {
LineIterator.closeQuietly(lineIterator);
}
<!-- https://mvnrepository.com/artifact/commons-io/commons-io -->
<dependency>
<groupId>commons-io</groupId>
<artifactId>commons-io</artifactId>
<version>2.6</version>
</dependency>
You can use this code:
import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
public class ReadTextFile {
public static void main(String[] args) throws IOException {
try {
File f = new File("src/com/data.txt");
BufferedReader b = new BufferedReader(new FileReader(f));
String readLine = "";
System.out.println("Reading file using Buffered Reader");
while ((readLine = b.readLine()) != null) {
System.out.println(readLine);
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
You can also use Apache Commons IO:
File file = new File("/home/user/file.txt");
try {
List<String> lines = FileUtils.readLines(file);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}