CODEWITHSUNDEEP
javaiostream
Matt Sheppard
Matt Sheppard

Reputation: 118063

Easy way to write contents of a Java InputStream to an OutputStream

I was surprised to find today that I couldn't track down any simple way to write the contents of an InputStream to an OutputStream in Java. Obviously, the byte buffer code isn't difficult to write, but I suspect I'm just missing something which would make my life easier (and the code clearer).

So, given an InputStream in and an OutputStream out, is there a simpler way to write the following?

byte[] buffer = new byte[1024];
int len = in.read(buffer);
while (len != -1) {
    out.write(buffer, 0, len);
    len = in.read(buffer);
}

Upvotes: 523

Views: 513198

Answers (24)

Jin Kwon
Jin Kwon

Reputation: 22027

Here comes how I'm doing with a simplest for loop.

private void copy(final InputStream in, final OutputStream out)
    throws IOException {
    final byte[] b = new byte[8192];
    for (int r; (r = in.read(b)) != -1;) {
        out.write(b, 0, r);
    }
}

Upvotes: 6

IPP Nerd
IPP Nerd

Reputation: 1124

Not very readable, but effective, has no dependencies and runs with any java version

byte[] buffer=new byte[1024];
for(int n; (n=inputStream.read(buffer))!=-1; outputStream.write(buffer,0,n));

Upvotes: 2

Badr Bujbara
Badr Bujbara

Reputation: 8691

I used ByteStreamKt.copyTo(src, dst, buffer.length) method

Here is my code

public static void replaceCurrentDb(Context context, Uri newDbUri) {
    try {
        File currentDb = context.getDatabasePath(DATABASE_NAME);
        if (currentDb.exists()) {
            InputStream src = context.getContentResolver().openInputStream(newDbUri);
            FileOutputStream dst = new FileOutputStream(currentDb);
            final byte[] buffer = new byte[8 * 1024];
            ByteStreamsKt.copyTo(src, dst, buffer.length);
            src.close();
            dst.close();
            Toast.makeText(context, "SUCCESS! Your selected file is set as current menu.", Toast.LENGTH_LONG).show();
        }
        else
            Log.e("DOWNLOAD:::: Database", " fail, database not found");
    }
    catch (IOException e) {
        Toast.makeText(context, "Data Download FAIL.", Toast.LENGTH_LONG).show();
        Log.e("DOWNLOAD FAIL!!!", "fail, reason:", e);
    }
}

Upvotes: 0

BullyWiiPlaza
BullyWiiPlaza

Reputation: 19233

The JDK uses the same code so it seems like there is no "easier" way without clunky third party libraries (which probably don't do anything different anyway). The following is directly copied from java.nio.file.Files.java:

// buffer size used for reading and writing
private static final int BUFFER_SIZE = 8192;

/**
  * Reads all bytes from an input stream and writes them to an output stream.
  */
private static long copy(InputStream source, OutputStream sink) throws IOException {
    long nread = 0L;
    byte[] buf = new byte[BUFFER_SIZE];
    int n;
    while ((n = source.read(buf)) > 0) {
        sink.write(buf, 0, n);
        nread += n;
    }
    return nread;
}

Upvotes: 23

Sivakumar
Sivakumar

Reputation: 1751

Using Java7 and try-with-resources, comes with a simplified and readable version.

try(InputStream inputStream = new FileInputStream("C:\\mov.mp4");
    OutputStream outputStream = new FileOutputStream("D:\\mov.mp4")) {

    byte[] buffer = new byte[10*1024];

    for (int length; (length = inputStream.read(buffer)) != -1; ) {
        outputStream.write(buffer, 0, length);
    }
} catch (FileNotFoundException exception) {
    exception.printStackTrace();
} catch (IOException ioException) {
    ioException.printStackTrace();
}

Upvotes: 8

Daniel De León
Daniel De León

Reputation: 13679

This is my best shot!!

And do not use inputStream.transferTo(...) because is too generic. Your code performance will be better if you control your buffer memory.

public static void transfer(InputStream in, OutputStream out, int buffer) throws IOException {
    byte[] read = new byte[buffer]; // Your buffer size.
    while (0 < (buffer = in.read(read)))
        out.write(read, 0, buffer);
}

I use it with this (improvable) method when I know in advance the size of the stream.

public static void transfer(int size, InputStream in, OutputStream out) throws IOException {
    transfer(in, out,
            size > 0xFFFF ? 0xFFFF // 16bits 65,536
                    : size > 0xFFF ? 0xFFF// 12bits 4096
                            : size < 0xFF ? 0xFF // 8bits 256
                                    : size
    );
}

Upvotes: 3

Archimedes Trajano
Archimedes Trajano

Reputation: 41662

I use BufferedInputStream and BufferedOutputStream to remove the buffering semantics from the code

try (OutputStream out = new BufferedOutputStream(...);
     InputStream in   = new BufferedInputStream(...))) {
  int ch;
  while ((ch = in.read()) != -1) {
    out.write(ch);
  }
}

Upvotes: 4

Andrejs
Andrejs

Reputation: 27737

Using Guava's ByteStreams.copy():

ByteStreams.copy(inputStream, outputStream);

Upvotes: 62

Ali Dehghani
Ali Dehghani

Reputation: 48193

Java 9

Since Java 9, InputStream provides a method called transferTo with the following signature:

public long transferTo(OutputStream out) throws IOException

As the documentation states, transferTo will:

Reads all bytes from this input stream and writes the bytes to the given output stream in the order that they are read. On return, this input stream will be at end of stream. This method does not close either stream.

This method may block indefinitely reading from the input stream, or writing to the output stream. The behavior for the case where the input and/or output stream is asynchronously closed, or the thread interrupted during the transfer, is highly input and output stream specific, and therefore not specified

So in order to write contents of a Java InputStream to an OutputStream, you can write:

input.transferTo(output);

Upvotes: 268

yegor256
yegor256

Reputation: 105193

Try Cactoos:

new LengthOf(new TeeInput(input, output)).value();

More details here: http://www.yegor256.com/2017/06/22/object-oriented-input-output-in-cactoos.html

Upvotes: -1

holmis83
holmis83

Reputation: 16644

For those who use Spring framework there is a useful StreamUtils class:

StreamUtils.copy(in, out);

The above does not close the streams. If you want the streams closed after the copy, use FileCopyUtils class instead:

FileCopyUtils.copy(in, out);

Upvotes: 21

Bohemian
Bohemian

Reputation: 425328

A IMHO more minimal snippet (that also more narrowly scopes the length variable):

byte[] buffer = new byte[2048];
for (int n = in.read(buffer); n >= 0; n = in.read(buffer))
    out.write(buffer, 0, n);

As a side note, I don't understand why more people don't use a for loop, instead opting for a while with an assign-and-test expression that is regarded by some as "poor" style.

Upvotes: 3

user1079877
user1079877

Reputation: 9398

If you are using Java 7, Files (in the standard library) is the best approach:

/* You can get Path from file also: file.toPath() */
Files.copy(InputStream in, Path target)
Files.copy(Path source, OutputStream out)

Edit: Of course it's just useful when you create one of InputStream or OutputStream from file. Use file.toPath() to get path from file.

To write into an existing file (e.g. one created with File.createTempFile()), you'll need to pass the REPLACE_EXISTING copy option (otherwise FileAlreadyExistsException is thrown):

Files.copy(in, target, StandardCopyOption.REPLACE_EXISTING)

Upvotes: 350

Dilum Ranatunga
Dilum Ranatunga

Reputation: 13374

PipedInputStream and PipedOutputStream should only be used when you have multiple threads, as noted by the Javadoc.

Also, note that input streams and output streams do not wrap any thread interruptions with IOExceptions... So, you should consider incorporating an interruption policy to your code:

byte[] buffer = new byte[1024];
int len = in.read(buffer);
while (len != -1) {
    out.write(buffer, 0, len);
    len = in.read(buffer);
    if (Thread.interrupted()) {
        throw new InterruptedException();
    }
}

This would be an useful addition if you expect to use this API for copying large volumes of data, or data from streams that get stuck for an intolerably long time.

Upvotes: 19

Nour Rteil
Nour Rteil

Reputation: 45

public static boolean copyFile(InputStream inputStream, OutputStream out) {
    byte buf[] = new byte[1024];
    int len;
    long startTime=System.currentTimeMillis();

    try {
        while ((len = inputStream.read(buf)) != -1) {
            out.write(buf, 0, len);
        }

        long endTime=System.currentTimeMillis()-startTime;
        Log.v("","Time taken to transfer all bytes is : "+endTime);
        out.close();
        inputStream.close();

    } catch (IOException e) {

        return false;
    }
    return true;
}

Upvotes: -1

Jordan LaPrise
Jordan LaPrise

Reputation: 1118

Simple Function

If you only need this for writing an InputStream to a File then you can use this simple function:

private void copyInputStreamToFile( InputStream in, File file ) {
    try {
        OutputStream out = new FileOutputStream(file);
        byte[] buf = new byte[1024];
        int len;
        while((len=in.read(buf))>0){
            out.write(buf,0,len);
        }
        out.close();
        in.close();
    } catch (Exception e) {
        e.printStackTrace();
    }
}

Upvotes: 31

Mikezx6r
Mikezx6r

Reputation: 16905

As WMR mentioned, org.apache.commons.io.IOUtils from Apache has a method called copy(InputStream,OutputStream) which does exactly what you're looking for.

So, you have:

InputStream in;
OutputStream out;
IOUtils.copy(in,out);
in.close();
out.close();

...in your code.

Is there a reason you're avoiding IOUtils?

Upvotes: 414

Pranav
Pranav

Reputation: 4250

you can use this method

public static void copyStream(InputStream is, OutputStream os)
 {
     final int buffer_size=1024;
     try
     {
         byte[] bytes=new byte[buffer_size];
         for(;;)
         {
           int count=is.read(bytes, 0, buffer_size);
           if(count==-1)
               break;
           os.write(bytes, 0, count);
         }
     }
     catch(Exception ex){}
 }

Upvotes: -7

DejanLekic
DejanLekic

Reputation: 19822

Use Commons Net's Util class:

import org.apache.commons.net.io.Util;
...
Util.copyStream(in, out);

Upvotes: 4

Alexander Volkov
Alexander Volkov

Reputation: 8407

I think it's better to use a large buffer, because most of the files are greater than 1024 bytes. Also it's a good practice to check the number of read bytes to be positive.

byte[] buffer = new byte[4096];
int n;
while ((n = in.read(buffer)) > 0) {
    out.write(buffer, 0, n);
}
out.close();

Upvotes: 2

Andrew Mao
Andrew Mao

Reputation: 36940

Another possible candidate are the Guava I/O utilities:

http://code.google.com/p/guava-libraries/wiki/IOExplained

I thought I'd use these since Guava is already immensely useful in my project, rather than adding yet another library for one function.

Upvotes: 0

WMR
WMR

Reputation: 12971

There's no way to do this a lot easier with JDK methods, but as Apocalisp has already noted, you're not the only one with this idea: You could use IOUtils from Jakarta Commons IO, it also has a lot of other useful things, that IMO should actually be part of the JDK...

Upvotes: 8

Arktronic
Arktronic

Reputation: 525

PipedInputStream and PipedOutputStream may be of some use, as you can connect one to the other.

Upvotes: 0

Mike Stone
Mike Stone

Reputation: 44613

I think this will work, but make sure to test it... minor "improvement", but it might be a bit of a cost at readability.

byte[] buffer = new byte[1024];
int len;
while ((len = in.read(buffer)) != -1) {
    out.write(buffer, 0, len);
}

Upvotes: 110

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