How to Read from an Input Stream Multiple Times Without Modifying it?

Preserving Input Streams for Sequential Reading

Reading from an input stream multiple times without modifying it or creating a new stream can be necessary in certain scenarios, such as when downloading an image and saving it locally. Fortunately, it is possible to duplicate an input stream for repeated access.

One approach involves utilizing the org.apache.commons.io.IOUtils.copy method to transfer input stream content into a byte array. This byte array can then be repeatedly read using a ByteArrayInputStream.

ByteArrayOutputStream baos = new ByteArrayOutputStream();
org.apache.commons.io.IOUtils.copy(in, baos);
byte[] bytes = baos.toByteArray();

From there, you can follow either approach:

• Repeated Creation of ByteArrayInputStream:

  while (needToReadAgain) {
    ByteArrayInputStream bais = new ByteArrayInputStream(bytes);
    yourReadMethodHere(bais);
  }

• Reset of ByteArrayInputStream:

  ByteArrayInputStream bais = new ByteArrayInputStream(bytes);
  while (needToReadAgain) {
    bais.reset();
    yourReadMethodHere(bais);
  }

Caution: Copying the full stream into memory may not be appropriate for large or infinite streams due to potential memory exhaustion. Alternative approaches, such as using a buffer or a separate data structure, may be necessary in such cases.

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