How to read a text file from the "assets" directory as a string?

Question

I have a file in my resources folder ... how to read it?

Now I am trying:

public static String readFileAsString(String filePath) throws java.io.IOException{ StringBuffer fileData = new StringBuffer(1000); BufferedReader reader = new BufferedReader( new FileReader(filePath)); char[] buf = new char[1024]; int numRead=0; while((numRead=reader.read(buf)) != -1){ String readData = String.valueOf(buf, 0, numRead); fileData.append(readData); buf = new char[1024]; } reader.close(); return fileData.toString(); } 

But he applied a null pointer exception ...

the file is called "origin" and it is in the folder

I tried using it:

 readFileAsString("file:///android_asset/origin"); 

and

 readFileAsString("asset/origin");`` 

but both refused ... any advice?

Answer 1

You can open the input stream using the AssetsManager .

 InputStream input = getAssets().open("origin"); Reader reader = new InputStreamReader(input, "UTF-8"); 

getAssets() - a method of the Context class.

Also note that you should not recreate the character buffer ( buf = new char[1024] , the last line of your loop).

Answer 2

The BufferedReader readLine () method returns null when the end of the file is reached, so you will need to monitor it and not try to add it to your line.

The following code should be fairly simple:

 public static String readFileAsString(String filePath) throws java.io.IOException { BufferedReader reader = new BufferedReader(new FileReader(filePath)); String line, results = ""; while( ( line = reader.readLine() ) != null) { results += line; } reader.close(); return results; } 

Simple and point to point.

Answer 3

Short answer, do the following:

 public static String readFile( String filePath ) throws IOException { Reader reader = new FileReader( filePath ); StringBuilder sb = new StringBuilder(); char buffer[] = new char[16384]; // read 16k blocks int len; // how much content was read? while( ( len = reader.read( buffer ) ) > 0 ){ sb.append( buffer, 0, len ); } reader.close(); return sb.toString(); } 

It is very simple, very fast and works well for unreasonable large text files (100+ MB).

---

Long answer:

(Code at the end)

Many times this does not matter, but this method is quite fast and quite readable. In fact, its complexity order is faster than the @Raceimation answer - O (n) instead of O (n ^ 2).

I tested six methods (from slow to fast):

• concat: reading line by line, concat with str + = ... * This is alarmingly slow even for small files (takes ~ 70 seconds for a 3 MB file) *
• guessing length strbuilder: StringBuilder initialized by file size. I guess it is slow because it is really trying to find such a huge chunk of linear memory.
• strbuilder with line buffer: StringBuilder, file read line by line
• strbuffer with char [] buffer: Concat with StringBuffer, read the file in 16k blocks
• strbuilder with char [] buffer: Concat with StringBuilder, read the file in 16k blocks
• preallocate byte [filesize] buffer: Allocate a byte [] buffer with the file size and let the java api decide how to buffer individual blocks.

Output:

The entire buffer preallocation is the fastest in very large files, but the method is not very universal, because the total file size must be known in advance. That's why I suggest using strBuilder with char [] buffers, it is still simple and, if necessary, easy to replace to accept any input streams, not just files. However, it is definitely fast enough for all reasonable cases.

Test Results + Code

 import java.io.*; public class Test { static final int N = 5; public final static void main( String args[] ) throws IOException{ test( "1k.txt", true ); test( "10k.txt", true ); // concat with += would take ages here, so we skip it test( "100k.txt", false ); test( "2142k.txt", false ); test( "pruned-names.csv", false ); // ah, what the heck, why not try a binary file test( "/Users/hansi/Downloads/xcode46graphicstools6938140a.dmg", false ); } public static void test( String file, boolean includeConcat ) throws IOException{ System.out.println( "Reading " + file + " (~" + (new File(file).length()/1024) + "Kbytes)" ); strbuilderwithchars( file ); strbuilderwithchars( file ); strbuilderwithchars( file ); tick( "Warm up... " ); if( includeConcat ){ for( int i = 0; i < N; i++ ) concat( file ); tick( "> Concat with += " ); } else{ tick( "> Concat with += **skipped** " ); } for( int i = 0; i < N; i++ ) strbuilderguess( file ); tick( "> StringBuilder init with length " ); for( int i = 0; i < N; i++ ) strbuilder( file ); tick( "> StringBuilder with line buffer " ); for( int i = 0; i < N; i++ ) strbuilderwithchars( file ); tick( "> StringBuilder with char[] buffer" ); for( int i = 0; i < N; i++ ) strbufferwithchars( file ); tick( "> StringBuffer with char[] buffer " ); for( int i = 0; i < N; i++ ) singleBuffer( file ); tick( "> Allocate byte[filesize] " ); System.out.println(); } public static long now = System.currentTimeMillis(); public static void tick( String message ){ long t = System.currentTimeMillis(); System.out.println( message + ": " + ( t - now )/N + " ms" ); now = t; } // StringBuilder with char[] buffer // + works if filesize is unknown // + pretty fast public static String strbuilderwithchars( String filePath ) throws IOException { Reader reader = new FileReader( filePath ); StringBuilder sb = new StringBuilder(); char buffer[] = new char[16384]; // read 16k blocks int len; // how much content was read? while( ( len = reader.read( buffer ) ) > 0 ){ sb.append( buffer, 0, len ); } reader.close(); return sb.toString(); } // StringBuffer with char[] buffer // + works if filesize is unknown // + faster than stringbuilder on my computer // - should be slower than stringbuilder, which confuses me public static String strbufferwithchars( String filePath ) throws IOException { Reader reader = new FileReader( filePath ); StringBuffer sb = new StringBuffer(); char buffer[] = new char[16384]; // read 16k blocks int len; // how much content was read? while( ( len = reader.read( buffer ) ) > 0 ){ sb.append( buffer, 0, len ); } reader.close(); return sb.toString(); } // StringBuilder init with length // + works if filesize is unknown // - not faster than any of the other methods, but more complicated public static String strbuilderguess(String filePath) throws IOException { File file = new File( filePath ); BufferedReader reader = new BufferedReader(new FileReader(file)); String line; StringBuilder sb = new StringBuilder( (int)file.length() ); while( ( line = reader.readLine() ) != null) { sb.append( line ); } reader.close(); return sb.toString(); } // StringBuilder with line buffer // + works if filesize is unknown // + pretty fast // - speed may (!) vary with line length public static String strbuilder(String filePath) throws IOException { BufferedReader reader = new BufferedReader(new FileReader(filePath)); String line; StringBuilder sb = new StringBuilder(); while( ( line = reader.readLine() ) != null) { sb.append( line ); } reader.close(); return sb.toString(); } // Concat with += // - slow // - slow // - really slow public static String concat(String filePath) throws IOException { BufferedReader reader = new BufferedReader(new FileReader(filePath)); String line, results = ""; int i = 0; while( ( line = reader.readLine() ) != null) { results += line; i++; } reader.close(); return results; } // Allocate byte[filesize] // + seems to be the fastest for large files // - only works if filesize is known in advance, so less versatile for a not significant performance gain // + shortest code public static String singleBuffer(String filePath ) throws IOException{ FileInputStream in = new FileInputStream( filePath ); byte buffer[] = new byte[(int) new File( filePath).length()]; // buffer for the entire file int len = in.read( buffer ); return new String( buffer, 0, len ); } } /** *** RESULTS *** Reading 1k.txt (~31Kbytes) Warm up... : 0 ms > Concat with += : 37 ms > StringBuilder init with length : 0 ms > StringBuilder with line buffer : 0 ms > StringBuilder with char[] buffer: 0 ms > StringBuffer with char[] buffer : 0 ms > Allocate byte[filesize] : 1 ms Reading 10k.txt (~313Kbytes) Warm up... : 0 ms > Concat with += : 708 ms > StringBuilder init with length : 2 ms > StringBuilder with line buffer : 2 ms > StringBuilder with char[] buffer: 1 ms > StringBuffer with char[] buffer : 1 ms > Allocate byte[filesize] : 1 ms Reading 100k.txt (~3136Kbytes) Warm up... : 7 ms > Concat with += **skipped** : 0 ms > StringBuilder init with length : 19 ms > StringBuilder with line buffer : 21 ms > StringBuilder with char[] buffer: 9 ms > StringBuffer with char[] buffer : 9 ms > Allocate byte[filesize] : 8 ms Reading 2142k.txt (~67204Kbytes) Warm up... : 181 ms > Concat with += **skipped** : 0 ms > StringBuilder init with length : 367 ms > StringBuilder with line buffer : 372 ms > StringBuilder with char[] buffer: 208 ms > StringBuffer with char[] buffer : 202 ms > Allocate byte[filesize] : 199 ms Reading pruned-names.csv (~11200Kbytes) Warm up... : 23 ms > Concat with += **skipped** : 0 ms > StringBuilder init with length : 54 ms > StringBuilder with line buffer : 57 ms > StringBuilder with char[] buffer: 32 ms > StringBuffer with char[] buffer : 31 ms > Allocate byte[filesize] : 32 ms Reading /Users/hansi/Downloads/xcode46graphicstools6938140a.dmg (~123429Kbytes) Warm up... : 1665 ms > Concat with += **skipped** : 0 ms > StringBuilder init with length : 2899 ms > StringBuilder with line buffer : 2978 ms > StringBuilder with char[] buffer: 2702 ms > StringBuffer with char[] buffer : 2684 ms > Allocate byte[filesize] : 1567 ms **/ 

Ps. You may have noticed that StringBuffer is a little faster than StringBuilder. This is a little stupid because the classes are the same, except that StringBuilder is not synchronized. If someone can (or) cannot reproduce this ... I am very curious :)

Answer 4

I wrote a function that does the same as yours. I wrote this a while ago, but I believe that it still works correctly.

 public static final String grabAsSingleString(File fileToUse) throws FileNotFoundException { BufferedReader theReader = null; String returnString = null; try { theReader = new BufferedReader(new FileReader(fileToUse)); char[] charArray = null; if(fileToUse.length() > Integer.MAX_VALUE) { // TODO implement handling of large files. System.out.println("The file is larger than int max = " + Integer.MAX_VALUE); } else { charArray = new char[(int)fileToUse.length()]; // Read the information into the buffer. theReader.read(charArray, 0, (int)fileToUse.length()); returnString = new String(charArray); } } catch (FileNotFoundException ex) { throw ex; } catch(IOException ex) { ex.printStackTrace(); } finally { try { theReader.close(); } catch (IOException ex) { ex.printStackTrace(); } } return returnString; } 

Now you can use this function if you want, but when you transfer a file either through a file object or a string, make sure you either specify the full path to the file, for example, "C: \ Program Files" \ test.dat "OR you pass the relative link from your working directory. Your working directory is usually the directory from which you start the application (if you did not change it). Therefore, if the file is in a folder called data, you must go to ". /data/test.dat "

Yes, I know that this works with Android, so the Windows URI is not applicable, but you should get my thought.

Answer 5

You should try org.appache.commons.io.IOUtils.toString(InputStream is) to get the contents of the file as a string. There you can pass an InputStream object that you get from

 getAssets().open("xml2json.txt") 

in Activity .

To get a String , use this:

 String xml = IOUtils.toString((getAssets().open("xml2json.txt")));