read complete file without using loop in java

Question

Possible Duplicate:
How to create a Java String from the contents of a file
Whole text file to a String in Java

I am trying to read the contents of a file using FileReader . But i want to read the file without reading a line by line . Is it possible to read the whole file without loop. I am using the following code

 try
 {
     File ff=new File("abc.txt");
     FileReader fr=new FileReader(ff);

     String s;
     while(br.read()!=-1)
     {
          s=br.readLine();
     }
 }

 catch(Exception ex)
 {
     ex.printStackTrace();
 }

There is a one-line Java 11 solution to this: https://stackoverflow.com/a/52301018/942774 — Hendrik, Feb 26 '19 at 07:27

score 209 · Answer 1 · edited Feb 11 '14 at 16:42

209

Java 7 one line solution

List<String> lines = Files.readAllLines(Paths.get("file"), StandardCharsets.UTF_8);

or

 String text = new String(Files.readAllBytes(Paths.get("file")), StandardCharsets.UTF_8);

edited Feb 11 '14 at 16:42

Paul Vargas

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answered Jan 05 '13 at 07:36

Evgeniy Dorofeev

133,369
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1

Can't find that Files in Android. – akauppi Jun 13 '14 at 10:51
25

Not all Java answers have to be suited to Android, @akauppi! Just look for a solution that Android supports from another answer! – Isaac Woods Apr 04 '15 at 13:54
1

`String text = Files.readString(Paths.get("file"));` is even shorter, assuming that you want a UTF-8 String output. – Eagterrian Knight Nov 15 '18 at 18:48
And if you already have the File object, you can do `file.toPath()` inside `readAllBytes` – Kartik Chugh Aug 19 '19 at 15:35
Important for Android: `Call requires API level 26: java.nio.file.Files#readAllBytes` - same thing for `readString`. – Neph Mar 26 '20 at 13:12
@EagterrianKnight What `Files` is that exactly? `readString` doesn't exist for the `java.nio.file.Files` one in Java 8. – Neph Mar 31 '22 at 11:32
Related answer (more details): https://stackoverflow.com/a/326440/9549068 – Nor.Z Aug 30 '22 at 22:43

score 143 · Accepted Answer · edited Nov 24 '14 at 17:12

143

If the file is small, you can read the whole data once:

File file = new File("a.txt");
FileInputStream fis = new FileInputStream(file);
byte[] data = new byte[(int) file.length()];
fis.read(data);
fis.close();

String str = new String(data, "UTF-8");

edited Nov 24 '14 at 17:12

Paul Vargas

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answered Jan 05 '13 at 07:40

imxylz

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Does not work for InputStream's s.a. Android assets (no length) – akauppi Jun 13 '14 at 11:04
14

How small is "small"? – k_rollo Sep 26 '15 at 03:36
10

@silver Entire content of the file will be stored in memory. So, avoid reading 5GB files like this :-) – Thibaut D. Sep 29 '15 at 09:30
When I do this, the string `str` ends up with a lot of 0 characters () at the end. Not sure why. – LarsH Oct 21 '15 at 23:41
2

Note: `file.length()` may return 0 for files under `/proc`. And in those cases this snippet will return an empty string. – Mygod Aug 16 '16 at 05:35
2

Also `read` might not fill the entire buffer. It might work in practice with most JREs, but there's no guarantee in the API. – Daniel Lubarov Jun 22 '17 at 23:44

score 36 · Answer 3 · answered Jan 05 '13 at 07:30

36

You can try using Scanner if you are using JDK5 or higher.

Scanner scan = new Scanner(file);  
scan.useDelimiter("\\Z");  
String content = scan.next();

Or you can also use Guava

String data = Files.toString(new File("path.txt"), Charsets.UTF8);

answered Jan 05 '13 at 07:30

Jayamohan

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Note that the scanner should be closed after use. – Barry NL Feb 13 '15 at 11:27
`String data = Files.toString(new File("path.txt"), Charsets.UTF_8);`. Just a small typo. :-) – Pikachu Jun 12 '15 at 18:33
1

This code with `Scanner` only read first 1024 bytes from file. Look at source code. It read buffer and check it with this regexp. This always valid - then it return all buffer content. By default buffer have size of 1024 bytes. – Enyby Mar 01 '17 at 05:09
2

This is BAD approach. The correct solution (for Java 1.7 and higher) is `Files.readAllLines()`. For legacy JREs, `FileInputStream.read()` is probably best. I'm not sure if it's portable to all platforms (i.e. Ctl-Z is recognized everywhere), and it 's easy to miss doing a `Scanner.close()`. – paulsm4 Oct 02 '17 at 01:21

Paul Vargas · Answer 4 · 2014-11-24T17:10:24.683

36

If you are using Java 5/6, you can use Apache Commons IO for read file to string. The class org.apache.commons.io.FileUtils contais several method for read files.

e.g. using the method FileUtils#readFileToString:

File file = new File("abc.txt");
String content = FileUtils.readFileToString(file);

edited Nov 24 '14 at 17:10

answered Jan 05 '13 at 07:38

Paul Vargas

41,222
15
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1

This is probably the easiest solution using a 3rd-party lib. – k_rollo Oct 03 '15 at 01:50
3

Minimal code to write; Many more libraries to add to project. – NaN May 11 '17 at 13:27
3

The method readFileToString(File) from the type FileUtils is deprecated – JavaSheriff Oct 25 '18 at 16:07

score 18 · Answer 5 · answered Jul 07 '19 at 08:02

Since Java 11 you can do it even simpler:

import java.nio.file.Files;

Files.readString(Path path);
Files.readString(Path path, Charset cs)

Source: https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/nio/file/Files.html#readString(java.nio.file.Path)

read complete file without using loop in java

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