Comment convertir OutputStream en InputStream?
Je suis au stade du développement, où j’ai deux modules et dont l’un m’a donné une sortie sous la forme OutputStream et le deuxième, qui accepte uniquement InputStream. Savez-vous comment convertir OutputStream en InputStream (et non l'inverse, je veux dire vraiment de cette façon) que je pourrai connecter ces deux parties?
Merci
Un OutputStream est celui où vous écrivez des données. Si un module expose une OutputStream, on s'attend à lire quelque chose à l'autre bout.
Quelque chose qui expose une InputStream, d'autre part, indique que vous devrez écouter ce flux et que vous pourrez lire des données.
Il est donc possible de connecter une InputStream à une OutputStream
InputStream----read---> intermediateBytes[n] ----write----> OutputStream
Comme l'a dit quelqu'un, voici ce que la méthode copy() de IOUtils vous permet de faire. Cela n'a pas de sens d'aller dans l'autre sens ... espérons que cela a du sens
METTRE À JOUR:
Bien sûr, plus je pense à cela, plus je peux voir à quel point cela serait une exigence. Je connais certains des commentaires mentionnés dans Piped flux d'entrée/sortie, mais il existe une autre possibilité.
Si le flux de sortie exposé est une ByteArrayOutputStream, vous pouvez toujours obtenir le contenu complet en appelant la méthode toByteArray(). Ensuite, vous pouvez créer un wrapper de flux d'entrée en utilisant la sous-classe ByteArrayInputStream. Ces deux sont des pseudo-flux, ils enveloppent simplement un tableau d'octets. Utiliser les flux de cette façon est donc techniquement possible, mais pour moi cela reste très étrange ...
Il semble y avoir de nombreux liens et autres éléments similaires, mais aucun code utilisant des tubes. L'avantage d'utiliser Java.io.PipedInputStream et Java.io.PipedOutputStream est qu'il n'y a pas de consommation supplémentaire de mémoire. ByteArrayOutputStream.toByteArray() renvoie une copie du tampon d'origine, ce qui signifie que tout ce que vous avez en mémoire, vous en avez maintenant deux copies. Ensuite, écrire dans un InputStream signifie que vous avez maintenant trois copies des données.
Le code:
// take the copy of the stream and re-write it to an InputStream
PipedInputStream in = new PipedInputStream();
final PipedOutputStream out = new PipedOutputStream(in);
new Thread(new Runnable() {
public void run () {
try {
// write the original OutputStream to the PipedOutputStream
originalByteArrayOutputStream.writeTo(out);
} catch (IOException e) {
// logging and exception handling should go here
}
}
}).start();
Ce code suppose que originalByteArrayOutputStream est un ByteArrayOutputStream car il s'agit généralement du seul flux de sortie utilisable, sauf si vous écrivez dans un fichier. J'espère que ça aide! L'avantage de cela est que, comme il s'agit d'un thread séparé, il fonctionne également en parallèle, de sorte que tout ce qui consomme votre flux d'entrée sera également diffusé en continu à partir de votre ancien flux. Cela est avantageux car le tampon peut rester plus petit et vous aurez moins de latence et moins d’utilisation de la mémoire.
Comme les flux d'entrée et de sortie ne sont que des points de départ et d'arrivée, la solution consiste à stocker temporairement les données dans un tableau d'octets. Vous devez donc créer la variable ByteArrayOutputStream intermédiaire, à partir de laquelle vous créez le byte[] utilisé comme entrée pour la nouvelle ByteArrayInputStream.
public void doTwoThingsWithStream(InputStream inStream, OutputStream outStream){
//create temporary bayte array output stream
ByteArrayOutputStream baos = new ByteArrayOutputStream();
doFirstThing(inStream, baos);
//create input stream from baos
InputStream isFromFirstData = new ByteArrayInputStream(baos.toByteArray());
doSecondThing(isFromFirstData, outStream);
}
J'espère que ça aide.
Vous aurez besoin d'une classe intermédiaire qui servira de tampon entre. À chaque appel de InputStream.read(byte[]...), la classe de mise en mémoire tampon remplira le tableau d'octets transmis avec le prochain bloc transmis à partir de OutputStream.write(byte[]...). Étant donné que les tailles des morceaux peuvent ne pas être les mêmes, la classe d'adaptateur devra stocker une certaine quantité jusqu'à ce qu'elle en ait assez pour remplir le tampon de lecture et/ou pouvoir stocker tout dépassement de tampon.
Cet article présente quelques approches différentes de ce problème:
http://blog.ostermiller.org/convert-Java-outputstream-inputstream
ByteArrayOutputStream buffer = (ByteArrayOutputStream) aOutputStream;
byte[] bytes = buffer.toByteArray();
InputStream inputStream = new ByteArrayInputStream(bytes);
La bibliothèque open source easystream supporte directement la conversion d’un OutputStream en un InputStream: http://io-tools.sourceforge.net/easystream/tutorial/tutorial.html
Ils listent également d'autres options: http://io-tools.sourceforge.net/easystream/OutputStream_to_InputStream.html
J'ai rencontré le même problème avec la conversion de ByteArrayOutputStream en ByteArrayInputStream et je l'ai résolu en utilisant une classe dérivée de ByteArrayOutputStream qui peut renvoyer une ByteArrayInputStream initialisée avec le tampon interne de la ByteArrayOutputStream. De cette façon, aucune mémoire supplémentaire n'est utilisée et la «conversion» est très rapide:
package info.whitebyte.utils;
import Java.io.ByteArrayInputStream;
import Java.io.ByteArrayOutputStream;
/**
* This class extends the ByteArrayOutputStream by
* providing a method that returns a new ByteArrayInputStream
* which uses the internal byte array buffer. This buffer
* is not copied, so no additional memory is used. After
* creating the ByteArrayInputStream the instance of the
* ByteArrayInOutStream can not be used anymore.
* <p>
* The ByteArrayInputStream can be retrieved using <code>getInputStream()</code>.
* @author Nick Russler
*/
public class ByteArrayInOutStream extends ByteArrayOutputStream {
/**
* Creates a new ByteArrayInOutStream. The buffer capacity is
* initially 32 bytes, though its size increases if necessary.
*/
public ByteArrayInOutStream() {
super();
}
/**
* Creates a new ByteArrayInOutStream, with a buffer capacity of
* the specified size, in bytes.
*
* @param size the initial size.
* @exception IllegalArgumentException if size is negative.
*/
public ByteArrayInOutStream(int size) {
super(size);
}
/**
* Creates a new ByteArrayInputStream that uses the internal byte array buffer
* of this ByteArrayInOutStream instance as its buffer array. The initial value
* of pos is set to zero and the initial value of count is the number of bytes
* that can be read from the byte array. The buffer array is not copied. This
* instance of ByteArrayInOutStream can not be used anymore after calling this
* method.
* @return the ByteArrayInputStream instance
*/
public ByteArrayInputStream getInputStream() {
// create new ByteArrayInputStream that respects the current count
ByteArrayInputStream in = new ByteArrayInputStream(this.buf, 0, this.count);
// set the buffer of the ByteArrayOutputStream
// to null so it can't be altered anymore
this.buf = null;
return in;
}
}
J'ai mis les choses sur github: https://github.com/nickrussler/ByteArrayInOutStream
La bibliothèque io-extras peut être utile. Par exemple, si vous voulez gzip une InputStream en utilisant GZIPOutputStream et que vous voulez que cela se produise synchrone (en utilisant la taille de mémoire tampon par défaut de 8192):
InputStream is = ...
InputStream gz = IOUtil.pipe(is, o -> new GZIPOutputStream(o));
Notez que la bibliothèque a une couverture de 100% des tests unitaires (pour ce que cela vaut, bien sûr!) Et se trouve sur Maven Central. La dépendance Maven est:
<dependency>
<groupId>com.github.davidmoten</groupId>
<artifactId>io-extras</artifactId>
<version>0.1</version>
</dependency>
Assurez-vous de rechercher une version ultérieure.
De mon point de vue, Java.io.PipedInputStream/Java.io.PipedOutputStream est la meilleure option à considérer. Dans certaines situations, vous pouvez utiliser ByteArrayInputStream/ByteArrayOutputStream. Le problème est que vous devez dupliquer le tampon pour convertir un ByteArrayOutputStream en un ByteArrayInputStream. De plus, ByteArrayOutpuStream/ByteArrayInputStream est limité à 2 Go. Voici une implémentation OutpuStream/InputStream que j'ai écrite pour contourner les limitations de ByteArrayOutputStream/ByteArrayInputStream (code Scala, mais facilement compréhensible pour les développeurs Java):
import Java.io.{IOException, InputStream, OutputStream}
import scala.annotation.tailrec
/** Acts as a replacement for ByteArrayOutputStream
*
*/
class HugeMemoryOutputStream(capacity: Long) extends OutputStream {
private val PAGE_SIZE: Int = 1024000
private val ALLOC_STEP: Int = 1024
/** Pages array
*
*/
private var streamBuffers: Array[Array[Byte]] = Array.empty[Array[Byte]]
/** Allocated pages count
*
*/
private var pageCount: Int = 0
/** Allocated bytes count
*
*/
private var allocatedBytes: Long = 0
/** Current position in stream
*
*/
private var position: Long = 0
/** Stream length
*
*/
private var length: Long = 0
allocSpaceIfNeeded(capacity)
/** Gets page count based on given length
*
* @param length Buffer length
* @return Page count to hold the specified amount of data
*/
private def getPageCount(length: Long) = {
var pageCount = (length / PAGE_SIZE).toInt + 1
if ((length % PAGE_SIZE) == 0) {
pageCount -= 1
}
pageCount
}
/** Extends pages array
*
*/
private def extendPages(): Unit = {
if (streamBuffers.isEmpty) {
streamBuffers = new Array[Array[Byte]](ALLOC_STEP)
}
else {
val newStreamBuffers = new Array[Array[Byte]](streamBuffers.length + ALLOC_STEP)
Array.copy(streamBuffers, 0, newStreamBuffers, 0, streamBuffers.length)
streamBuffers = newStreamBuffers
}
pageCount = streamBuffers.length
}
/** Ensures buffers are bug enough to hold specified amount of data
*
* @param value Amount of data
*/
private def allocSpaceIfNeeded(value: Long): Unit = {
@tailrec
def allocSpaceIfNeededIter(value: Long): Unit = {
val currentPageCount = getPageCount(allocatedBytes)
val neededPageCount = getPageCount(value)
if (currentPageCount < neededPageCount) {
if (currentPageCount == pageCount) extendPages()
streamBuffers(currentPageCount) = new Array[Byte](PAGE_SIZE)
allocatedBytes = (currentPageCount + 1).toLong * PAGE_SIZE
allocSpaceIfNeededIter(value)
}
}
if (value < 0) throw new Error("AllocSpaceIfNeeded < 0")
if (value > 0) {
allocSpaceIfNeededIter(value)
length = Math.max(value, length)
if (position > length) position = length
}
}
/**
* Writes the specified byte to this output stream. The general
* contract for <code>write</code> is that one byte is written
* to the output stream. The byte to be written is the eight
* low-order bits of the argument <code>b</code>. The 24
* high-order bits of <code>b</code> are ignored.
* <p>
* Subclasses of <code>OutputStream</code> must provide an
* implementation for this method.
*
* @param b the <code>byte</code>.
*/
@throws[IOException]
override def write(b: Int): Unit = {
val buffer: Array[Byte] = new Array[Byte](1)
buffer(0) = b.toByte
write(buffer)
}
/**
* Writes <code>len</code> bytes from the specified byte array
* starting at offset <code>off</code> to this output stream.
* The general contract for <code>write(b, off, len)</code> is that
* some of the bytes in the array <code>b</code> are written to the
* output stream in order; element <code>b[off]</code> is the first
* byte written and <code>b[off+len-1]</code> is the last byte written
* by this operation.
* <p>
* The <code>write</code> method of <code>OutputStream</code> calls
* the write method of one argument on each of the bytes to be
* written out. Subclasses are encouraged to override this method and
* provide a more efficient implementation.
* <p>
* If <code>b</code> is <code>null</code>, a
* <code>NullPointerException</code> is thrown.
* <p>
* If <code>off</code> is negative, or <code>len</code> is negative, or
* <code>off+len</code> is greater than the length of the array
* <code>b</code>, then an <tt>IndexOutOfBoundsException</tt> is thrown.
*
* @param b the data.
* @param off the start offset in the data.
* @param len the number of bytes to write.
*/
@throws[IOException]
override def write(b: Array[Byte], off: Int, len: Int): Unit = {
@tailrec
def writeIter(b: Array[Byte], off: Int, len: Int): Unit = {
val currentPage: Int = (position / PAGE_SIZE).toInt
val currentOffset: Int = (position % PAGE_SIZE).toInt
if (len != 0) {
val currentLength: Int = Math.min(PAGE_SIZE - currentOffset, len)
Array.copy(b, off, streamBuffers(currentPage), currentOffset, currentLength)
position += currentLength
writeIter(b, off + currentLength, len - currentLength)
}
}
allocSpaceIfNeeded(position + len)
writeIter(b, off, len)
}
/** Gets an InputStream that points to HugeMemoryOutputStream buffer
*
* @return InputStream
*/
def asInputStream(): InputStream = {
new HugeMemoryInputStream(streamBuffers, length)
}
private class HugeMemoryInputStream(streamBuffers: Array[Array[Byte]], val length: Long) extends InputStream {
/** Current position in stream
*
*/
private var position: Long = 0
/**
* Reads the next byte of data from the input stream. The value byte is
* returned as an <code>int</code> in the range <code>0</code> to
* <code>255</code>. If no byte is available because the end of the stream
* has been reached, the value <code>-1</code> is returned. This method
* blocks until input data is available, the end of the stream is detected,
* or an exception is thrown.
*
* <p> A subclass must provide an implementation of this method.
*
* @return the next byte of data, or <code>-1</code> if the end of the
* stream is reached.
*/
@throws[IOException]
def read: Int = {
val buffer: Array[Byte] = new Array[Byte](1)
if (read(buffer) == 0) throw new Error("End of stream")
else buffer(0)
}
/**
* Reads up to <code>len</code> bytes of data from the input stream into
* an array of bytes. An attempt is made to read as many as
* <code>len</code> bytes, but a smaller number may be read.
* The number of bytes actually read is returned as an integer.
*
* <p> This method blocks until input data is available, end of file is
* detected, or an exception is thrown.
*
* <p> If <code>len</code> is zero, then no bytes are read and
* <code>0</code> is returned; otherwise, there is an attempt to read at
* least one byte. If no byte is available because the stream is at end of
* file, the value <code>-1</code> is returned; otherwise, at least one
* byte is read and stored into <code>b</code>.
*
* <p> The first byte read is stored into element <code>b[off]</code>, the
* next one into <code>b[off+1]</code>, and so on. The number of bytes read
* is, at most, equal to <code>len</code>. Let <i>k</i> be the number of
* bytes actually read; these bytes will be stored in elements
* <code>b[off]</code> through <code>b[off+</code><i>k</i><code>-1]</code>,
* leaving elements <code>b[off+</code><i>k</i><code>]</code> through
* <code>b[off+len-1]</code> unaffected.
*
* <p> In every case, elements <code>b[0]</code> through
* <code>b[off]</code> and elements <code>b[off+len]</code> through
* <code>b[b.length-1]</code> are unaffected.
*
* <p> The <code>read(b,</code> <code>off,</code> <code>len)</code> method
* for class <code>InputStream</code> simply calls the method
* <code>read()</code> repeatedly. If the first such call results in an
* <code>IOException</code>, that exception is returned from the call to
* the <code>read(b,</code> <code>off,</code> <code>len)</code> method. If
* any subsequent call to <code>read()</code> results in a
* <code>IOException</code>, the exception is caught and treated as if it
* were end of file; the bytes read up to that point are stored into
* <code>b</code> and the number of bytes read before the exception
* occurred is returned. The default implementation of this method blocks
* until the requested amount of input data <code>len</code> has been read,
* end of file is detected, or an exception is thrown. Subclasses are encouraged
* to provide a more efficient implementation of this method.
*
* @param b the buffer into which the data is read.
* @param off the start offset in array <code>b</code>
* at which the data is written.
* @param len the maximum number of bytes to read.
* @return the total number of bytes read into the buffer, or
* <code>-1</code> if there is no more data because the end of
* the stream has been reached.
* @see Java.io.InputStream#read()
*/
@throws[IOException]
override def read(b: Array[Byte], off: Int, len: Int): Int = {
@tailrec
def readIter(acc: Int, b: Array[Byte], off: Int, len: Int): Int = {
val currentPage: Int = (position / PAGE_SIZE).toInt
val currentOffset: Int = (position % PAGE_SIZE).toInt
val count: Int = Math.min(len, length - position).toInt
if (count == 0 || position >= length) acc
else {
val currentLength = Math.min(PAGE_SIZE - currentOffset, count)
Array.copy(streamBuffers(currentPage), currentOffset, b, off, currentLength)
position += currentLength
readIter(acc + currentLength, b, off + currentLength, len - currentLength)
}
}
readIter(0, b, off, len)
}
/**
* Skips over and discards <code>n</code> bytes of data from this input
* stream. The <code>skip</code> method may, for a variety of reasons, end
* up skipping over some smaller number of bytes, possibly <code>0</code>.
* This may result from any of a number of conditions; reaching end of file
* before <code>n</code> bytes have been skipped is only one possibility.
* The actual number of bytes skipped is returned. If <code>n</code> is
* negative, the <code>skip</code> method for class <code>InputStream</code> always
* returns 0, and no bytes are skipped. Subclasses may handle the negative
* value differently.
*
* The <code>skip</code> method of this class creates a
* byte array and then repeatedly reads into it until <code>n</code> bytes
* have been read or the end of the stream has been reached. Subclasses are
* encouraged to provide a more efficient implementation of this method.
* For instance, the implementation may depend on the ability to seek.
*
* @param n the number of bytes to be skipped.
* @return the actual number of bytes skipped.
*/
@throws[IOException]
override def skip(n: Long): Long = {
if (n < 0) 0
else {
position = Math.min(position + n, length)
length - position
}
}
}
}
Facile à utiliser, pas de duplication de tampon, pas de limite de mémoire de 2 Go
val out: HugeMemoryOutputStream = new HugeMemoryOutputStream(initialCapacity /*may be 0*/)
out.write(...)
...
val in1: InputStream = out.asInputStream()
in1.read(...)
...
val in2: InputStream = out.asInputStream()
in2.read(...)
...