您可以使用org.apache.commons.io.IOUtils.copy
将InputStream的内容复制到一个字节数组中,然后再使用ByteArrayInputStream从字节数组中反复读取。例如:
ByteArrayOutputStream baos = new ByteArrayOutputStream();
org.apache.commons.io.IOUtils.copy(in, baos);
byte[] bytes = baos.toByteArray();
// either
while (needToReadAgain) {
ByteArrayInputStream bais = new ByteArrayInputStream(bytes);
yourReadMethodHere(bais);
}
// or
ByteArrayInputStream bais = new ByteArrayInputStream(bytes);
while (needToReadAgain) {
bais.reset();
yourReadMethodHere(bais);
}
根据InputStream的来源,您可能无法重置它。您可以使用markSupported()
检查是否支持mark()
和reset()
。
如果支持,您可以调用reset()
在InputStream上返回到开头。如果不支持,则需要再次从源中读取InputStream。
InputStream
的子类,比如 BufferedInputStream
,支持 'mark'。 - Dzmitry Bahdanovich如果你的 InputStream
支持使用 mark,那么你可以为其调用 mark()
方法并随后调用 reset()
方法。如果你的 InputStrem
不支持 mark,则可以使用 java.io.BufferedInputStream
类,将流嵌套在 BufferedInputStream
中,如下所示:
InputStream bufferdInputStream = new BufferedInputStream(yourInputStream);
bufferdInputStream.mark(some_value);
//read your bufferdInputStream
bufferdInputStream.reset();
//read it again
BufferedInputStream.fill()
,其中有“增加缓冲区”部分,新缓冲区大小仅与 marklimit
和 MAX_BUFFER_SIZE
进行比较。 - eugene82public class StreamTest {
public static void main(String[] args) throws IOException {
byte[] bytes = new byte[] { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
InputStream originalStream = new ByteArrayInputStream(bytes);
byte[] readBytes = getBytes(originalStream, 3);
printBytes(readBytes); // prints: 1 2 3
readBytes = getBytes(originalStream, 3);
printBytes(readBytes); // prints: 4 5 6
// now let's wrap it with PushBackInputStream
originalStream = new ByteArrayInputStream(bytes);
InputStream wrappedStream = new PushbackInputStream(originalStream, 10); // 10 means that maximnum 10 characters can be "written back" to the stream
readBytes = getBytes(wrappedStream, 3);
printBytes(readBytes); // prints 1 2 3
((PushbackInputStream) wrappedStream).unread(readBytes, 0, readBytes.length);
readBytes = getBytes(wrappedStream, 3);
printBytes(readBytes); // prints 1 2 3
}
private static byte[] getBytes(InputStream is, int howManyBytes) throws IOException {
System.out.print("Reading stream: ");
byte[] buf = new byte[howManyBytes];
int next = 0;
for (int i = 0; i < howManyBytes; i++) {
next = is.read();
if (next > 0) {
buf[i] = (byte) next;
}
}
return buf;
}
private static void printBytes(byte[] buffer) throws IOException {
System.out.print("Reading stream: ");
for (int i = 0; i < buffer.length; i++) {
System.out.print(buffer[i] + " ");
}
System.out.println();
}
}
public class TryReadInputStream extends FilterInputStream {
private final int maxPushbackBufferSize;
/**
* Creates a <code>FilterInputStream</code>
* by assigning the argument <code>in</code>
* to the field <code>this.in</code> so as
* to remember it for later use.
*
* @param in the underlying input stream, or <code>null</code> if
* this instance is to be created without an underlying stream.
*/
public TryReadInputStream(InputStream in, int maxPushbackBufferSize) {
super(new PushbackInputStream(in, maxPushbackBufferSize));
this.maxPushbackBufferSize = maxPushbackBufferSize;
}
/**
* Reads from input stream the <code>length</code> of bytes to given buffer. The read bytes are still avilable
* in the stream
*
* @param buffer the destination buffer to which read the data
* @param offset the start offset in the destination <code>buffer</code>
* @aram length how many bytes to read from the stream to buff. Length needs to be less than
* <code>maxPushbackBufferSize</code> or IOException will be thrown
*
* @return number of bytes read
* @throws java.io.IOException in case length is
*/
public int tryRead(byte[] buffer, int offset, int length) throws IOException {
validateMaxLength(length);
// NOTE: below reading byte by byte instead of "int bytesRead = is.read(firstBytes, 0, maxBytesOfResponseToLog);"
// because read() guarantees to read a byte
int bytesRead = 0;
int nextByte = 0;
for (int i = 0; (i < length) && (nextByte >= 0); i++) {
nextByte = read();
if (nextByte >= 0) {
buffer[offset + bytesRead++] = (byte) nextByte;
}
}
if (bytesRead > 0) {
((PushbackInputStream) in).unread(buffer, offset, bytesRead);
}
return bytesRead;
}
public byte[] tryRead(int maxBytesToRead) throws IOException {
validateMaxLength(maxBytesToRead);
ByteArrayOutputStream baos = new ByteArrayOutputStream(); // as ByteArrayOutputStream to dynamically allocate internal bytes array instead of allocating possibly large buffer (if maxBytesToRead is large)
// NOTE: below reading byte by byte instead of "int bytesRead = is.read(firstBytes, 0, maxBytesOfResponseToLog);"
// because read() guarantees to read a byte
int nextByte = 0;
for (int i = 0; (i < maxBytesToRead) && (nextByte >= 0); i++) {
nextByte = read();
if (nextByte >= 0) {
baos.write((byte) nextByte);
}
}
byte[] buffer = baos.toByteArray();
if (buffer.length > 0) {
((PushbackInputStream) in).unread(buffer, 0, buffer.length);
}
return buffer;
}
private void validateMaxLength(int length) throws IOException {
if (length > maxPushbackBufferSize) {
throw new IOException(
"Trying to read more bytes than maxBytesToRead. Max bytes: " + maxPushbackBufferSize + ". Trying to read: " +
length);
}
}
}
这个类有两个方法。一个用于将内容读入现有的缓冲区(与InputStream类的public int read(byte b[], int off, int len)
方法类似)。第二个方法则返回新的缓冲区(如果要读取的缓冲区大小未知,则此方法可能更有效)。
现在让我们看看我们的类如何运作:
public class StreamTest2 {
public static void main(String[] args) throws IOException {
byte[] bytes = new byte[] { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
InputStream originalStream = new ByteArrayInputStream(bytes);
byte[] readBytes = getBytes(originalStream, 3);
printBytes(readBytes); // prints: 1 2 3
readBytes = getBytes(originalStream, 3);
printBytes(readBytes); // prints: 4 5 6
// now let's use our TryReadInputStream
originalStream = new ByteArrayInputStream(bytes);
InputStream wrappedStream = new TryReadInputStream(originalStream, 10);
readBytes = ((TryReadInputStream) wrappedStream).tryRead(3); // NOTE: no manual call to "unread"(!) because TryReadInputStream handles this internally
printBytes(readBytes); // prints 1 2 3
readBytes = ((TryReadInputStream) wrappedStream).tryRead(3);
printBytes(readBytes); // prints 1 2 3
readBytes = ((TryReadInputStream) wrappedStream).tryRead(3);
printBytes(readBytes); // prints 1 2 3
// we can also call normal read which will actually read the bytes without "writing them back"
readBytes = getBytes(wrappedStream, 3);
printBytes(readBytes); // prints 1 2 3
readBytes = getBytes(wrappedStream, 3);
printBytes(readBytes); // prints 4 5 6
readBytes = ((TryReadInputStream) wrappedStream).tryRead(3); // now we can try read next bytes
printBytes(readBytes); // prints 7 8 9
readBytes = ((TryReadInputStream) wrappedStream).tryRead(3);
printBytes(readBytes); // prints 7 8 9
}
}
如何将一个输入流InputStream
分成两个,同时避免加载所有数据到内存中,然后独立地处理它们:
OutputStream
, precisely: PipedOutputStream
PipedInputStream
are the returned InputStream
.OutputStream
. So, everything read it from the sourcing InputStream
, would be written in both OutputStream
. There is not need to implement that, because it is done already in TeeInputStream
(commons.io).Within a separated thread read the whole sourcing inputStream, and implicitly the input data is transferred to the target inputStreams.
public static final List<InputStream> splitInputStream(InputStream input)
throws IOException
{
Objects.requireNonNull(input);
PipedOutputStream pipedOut01 = new PipedOutputStream();
PipedOutputStream pipedOut02 = new PipedOutputStream();
List<InputStream> inputStreamList = new ArrayList<>();
inputStreamList.add(new PipedInputStream(pipedOut01));
inputStreamList.add(new PipedInputStream(pipedOut02));
TeeOutputStream tout = new TeeOutputStream(pipedOut01, pipedOut02);
TeeInputStream tin = new TeeInputStream(input, tout, true);
Executors.newSingleThreadExecutor().submit(tin::readAllBytes);
return Collections.unmodifiableList(inputStreamList);
}
使用完流后一定要关闭inputStreams,并关闭运行的线程:TeeInputStream.readAllBytes()
如果需要将其拆分成多个InputStream
,而不仅仅是两个,请替换上一个代码片段中的TeeOutputStream
类为您自己的实现,该实现将封装一个List<OutputStream>
并覆盖OutputStream
接口:
public final class TeeListOutputStream extends OutputStream {
private final List<? extends OutputStream> branchList;
public TeeListOutputStream(final List<? extends OutputStream> branchList) {
Objects.requireNonNull(branchList);
this.branchList = branchList;
}
@Override
public synchronized void write(final int b) throws IOException {
for (OutputStream branch : branchList) {
branch.write(b);
}
}
@Override
public void flush() throws IOException {
for (OutputStream branch : branchList) {
branch.flush();
}
}
@Override
public void close() throws IOException {
for (OutputStream branch : branchList) {
branch.close();
}
}
}
Executors.newSingleThreadExecutor().submit(() -> {
try {
tin.readAllBytes();
tin.close();
} catch (IOException ioException) {
ioException.printStackTrace();
}
});
- Tobias OttoInputStream
的方法,你可以检查InputStream#markSupported()
的结果,以确定是否可以使用mark()
/reset()
方法。
如果你可以在读取时标记流,那么可以调用reset()
返回开始位置。
如果不能,则必须重新打开流。
另一种解决方案是将InputStream转换为字节数组,然后根据需要多次迭代数组。您可以在这篇文章Convert InputStream to byte array in Java中找到几个使用第三方库或不使用第三方库的解决方案。请注意,如果读取的内容太大,可能会遇到一些内存问题。
最后,如果您需要读取图像,请使用:
BufferedImage image = ImageIO.read(new URL("http://www.example.com/images/toto.jpg"));
ImageIO#read(java.net.URL)
,还可以利用缓存。ImageIO#read(java.net.URL)
时需要注意:一些Web服务器和CDN可能会拒绝裸调用(即没有用户代理使服务器相信该调用来自Web浏览器)由ImageIO#read
发出。在这种情况下,使用URLConnection.openConnection()
设置用户代理到该连接+使用ImageIO.read(InputStream)
通常可以解决问题。 - Clint EastwoodInputStream
不是一个接口。 - bric3如果有人正在运行Spring Boot应用程序,并且您想要读取RestTemplate
的响应正文(这就是为什么我想要两次读取流),那么有一种更加清晰的方法可以解决这个问题。
首先,您需要使用Spring的StreamUtils
将流复制到一个字符串中:
String text = StreamUtils.copyToString(response.getBody(), Charset.defaultCharset()))
但这还不够。您还需要使用一个可以为您缓冲流的请求工厂,如下所示:
ClientHttpRequestFactory factory = new BufferingClientHttpRequestFactory(new SimpleClientHttpRequestFactory());
RestTemplate restTemplate = new RestTemplate(factory);
如果你正在使用工厂Bean,则可以按照以下方式操作(以下示例为Kotlin语言):
@Bean
@Scope(ConfigurableBeanFactory.SCOPE_PROTOTYPE)
fun createRestTemplate(): RestTemplate = RestTemplateBuilder()
.requestFactory { BufferingClientHttpRequestFactory(SimpleClientHttpRequestFactory()) }
.additionalInterceptors(loggingInterceptor)
.build()
本文介绍了如何记录RestTemplate请求和响应的内容,同时不破坏消息体。通过创建自定义拦截器,可以在请求发送前和响应返回后记录请求和响应的详细信息。此外,本文还提供了一个示例程序来演示如何实现该功能。if (stream.markSupported() == false) {
// lets replace the stream object
ByteArrayOutputStream baos = new ByteArrayOutputStream();
IOUtils.copy(stream, baos);
stream.close();
stream = new ByteArrayInputStream(baos.toByteArray());
// now the stream should support 'mark' and 'reset'
}
将输入流转换为字节,然后将其传递给savefile函数,在该函数中将其组装成输入流。 另外在原始函数中使用字节来执行其他任务。
ByteArrayInputStream ins = new ByteArrayInputStream("Hello".getBytes());
System.out.println("ins.available() at begining:: " + ins.available());
ins.mark(0);
// Read input stream for some operations
System.out.println("ins.available() after reading :: " + ins.available());
ins.reset();
System.out.println("ins.available() after resetting :: " + ins.available());
// ins is ready for reading once again.