我正处于开发阶段，我有两个模块，其中一个我输出为OutputStream，第二个只接受InputStream。你知道如何将OutputStream转换为InputStream（反之亦然，我的意思是这样），我将能够连接这两个部分吗？
由于
答案 0 :(得分：162)
似乎有许多链接和其他类似的东西，但没有使用管道的实际代码。使用java.io.PipedInputStream和java.io.PipedOutputStream的优点是没有额外的内存消耗。 ByteArrayOutputStream.toByteArray()返回原始缓冲区的副本，这意味着无论你在内存中拥有什么，你现在都有两个副本。然后写入InputStream表示您现在有三个数据副本。
代码：
// 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
// note that in order for the below method to work, you need
// to ensure that the data has finished writing to the
// ByteArrayOutputStream
originalByteArrayOutputStream.writeTo(out);
}
catch (IOException e) {
// logging and exception handling should go here
}
finally {
// close the PipedOutputStream here because we're done writing data
// once this thread has completed its run
if (out != null) {
// close the PipedOutputStream cleanly
out.close();
}
}
}
}).start();
此代码假定originalByteArrayOutputStream是ByteArrayOutputStream，因为它通常是唯一可用的输出流，除非您正在写入文件。我希望这有帮助！关于这一点的好处是，因为它在一个单独的线程中，它也是并行工作的，所以无论消耗什么输入流都将流出旧的输出流。这是有益的，因为缓冲区可以保持较小，并且您可以减少延迟并减少内存使用。
答案 1 :(得分：95)
OutputStream是您将数据写入的地方。如果某个模块暴露了OutputStream，则期望在另一端读取某些内容。
另一方面，暴露InputStream的东西表明您需要收听此流，并且会有您可以阅读的数据。
因此可以将InputStream与OutputStream
InputStream----read---> intermediateBytes[n] ----write----> OutputStream
正如有人提到的，这就是IOUtils copy()方法允许你做的事情。走另一条路是没有意义的......希望这有点道理
<强>更新
当然，我越是想到这一点，我就越能看出这实际上是如何要求的。我知道一些评论提到Piped输入/输出流，但还有另一种可能性。
如果公开的输出流是ByteArrayOutputStream，那么您始终可以通过调用toByteArray()方法获取完整内容。然后，您可以使用ByteArrayInputStream子类创建输入流包装器。这两个是伪流，它们基本上只包装一个字节数组。因此，以这种方式使用流在技术上是可行的，但对我来说它仍然很奇怪......
答案 2 :(得分：28)
由于输入和输出流只是起点和终点，因此解决方案是以字节数组临时存储数据。因此，您必须创建中间ByteArrayOutputStream，您可以从中创建byte[]作为新ByteArrayInputStream的输入。
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);
}
希望它有所帮助。
答案 3 :(得分：20)
你需要一个中间类，它们之间会缓冲。每次调用InputStream.read(byte[]...)时，缓冲类将使用从OutputStream.write(byte[]...)传入的下一个块填充传入的字节数组。由于块的大小可能不同，因此适配器类需要存储一定量，直到它足以填充读缓冲区和/或能够存储任何缓冲区溢出。
本文对这个问题的几种不同方法进行了很好的细分：
http://blog.ostermiller.org/convert-java-outputstream-inputstream
答案 4 :(得分：17)
ByteArrayOutputStream buffer = (ByteArrayOutputStream) aOutputStream;
byte[] bytes = buffer.toByteArray();
InputStream inputStream = new ByteArrayInputStream(bytes);
答案 5 :(得分：16)
easystream开源库直接支持将OutputStream转换为InputStream：http://io-tools.sourceforge.net/easystream/tutorial/tutorial.html
他们还列出了其他选项：http://io-tools.sourceforge.net/easystream/OutputStream_to_InputStream.html
答案 6 :(得分：9)
我在将ByteArrayOutputStream转换为ByteArrayInputStream时遇到了同样的问题，并使用ByteArrayOutputStream中的派生类解决了该问题，该类可以返回ByteArrayInputStream，即ByteArrayOutputStream使用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;
}
}
的内部缓冲区初始化。这样就不会使用额外的内存和转换＆＃39;非常快：
{{1}}
我把这些东西放在github上：https://github.com/nickrussler/ByteArrayInOutStream
答案 7 :(得分：2)
图书馆io-extras可能很有用。例如，如果您想使用InputStream gzip GZIPOutputStream并希望它同步发生（使用默认缓冲区大小8192）：
InputStream is = ...
InputStream gz = IOUtil.pipe(is, o -> new GZIPOutputStream(o));
请注意，该库具有100％的单元测试覆盖率（当然，这是值得的！）并且在Maven Central上。 Maven的依赖是：
<dependency>
<groupId>com.github.davidmoten</groupId>
<artifactId>io-extras</artifactId>
<version>0.1</version>
</dependency>
请务必检查以后的版本。
答案 8 :(得分：0)
从我的角度来看，java.io.PipedInputStream / java.io.PipedOutputStream是考虑的最佳选择。在某些情况下，您可能希望使用ByteArrayInputStream / ByteArrayOutputStream。问题是您需要复制缓冲区以将ByteArrayOutputStream转换为ByteArrayInputStream。 ByteArrayOutpuStream / ByteArrayInputStream也限制为2GB。这是我编写的OutpuStream / InputStream实现，它绕过了ByteArrayOutputStream / ByteArrayInputStream限制（Scala代码，但对java开发人员来说很容易理解）：
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
}
}
}
}
易于使用，没有缓冲区重复，没有2GB内存限制
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(...)
...
答案 9 :(得分：-1)
如果要从InputStream创建OutputStream，则存在一个基本问题。写入OutputStream的方法将一直阻塞，直到完成为止。因此，当写入方法完成时，结果可用。这有两个后果：
变体1可以使用字节数组或字段来实现。 变体1可以使用pipies实现（直接或使用额外的抽象 - 例如RingBuffer或来自其他评论的google lib）。
确实使用标准java，没有其他方法可以解决问题。每个解决方案都是其中一个解决方案的实现。
有一个概念称为“延续”（详见wikipedia）。在这种情况下，基本上这意味着：
虽然有些语言内置了这个概念，但对于java来说，你需要一些“魔力”。例如，来自apache的“commons-javaflow”为java实现了这样的功能。缺点是这需要在构建时进行一些特殊的字节码修改。因此，将所有内容放在一个额外的库中并使用自定义构建脚本是有意义的。
答案 10 :(得分：-1)
旧帖但可能会帮助其他人，使用这种方式：
OutputStream out = new ByteArrayOutputStream();
...
out.write();
...
ObjectInputStream ois = new ObjectInputStream(new ByteArrayInputStream(out.toString().getBytes()));
答案 11 :(得分：-1)
虽然您无法将OutputStream转换为InputStream，但java提供了一种使用PipedOutputStream和PipedInputStream的方法，您可以将写入PipedOutputStream的数据通过关联的PipedInputStream变为可用。回到某些时候我遇到了类似的情况，处理需要将InputStream实例传递给它们而不是OutputStream实例的第三方库。
我解决这个问题的方法是使用PipedInputStream和PipedOutputStream 。
顺便说一句，它们使用起来很棘手，你必须使用多线程来实现你想要的。我最近在github上发布了一个你可以使用的实现。
这是link。您可以浏览wiki以了解如何使用它。