Reading from a ZipInputStream into a ByteArrayOutp

Question

I am trying to read a single file from a java.util.zip.ZipInputStream, and copy it into a java.io.ByteArrayOutputStream (so that I can then create a java.io.ByteArrayInputStream and hand that to a 3rd party library that will end up closing the stream, and I don't want my ZipInputStream getting closed).

I'm probably missing something basic here, but I never enter the while loop here:

ByteArrayOutputStream streamBuilder = new ByteArrayOutputStream();
int bytesRead;
byte[] tempBuffer = new byte[8192*2];
try {
    while ((bytesRead = zipStream.read(tempBuffer)) != -1) {
        streamBuilder.write(tempBuffer, 0, bytesRead);
    }
} catch (IOException e) {
    // ...
}

What am I missing that will allow me to copy the stream?

Edit:

I should have mentioned earlier that this ZipInputStream is not coming from a file, so I don't think I can use a ZipFile. It is coming from a file uploaded through a servlet.

Also, I have already called getNextEntry() on the ZipInputStream before getting to this snippet of code. If I don't try copying the file into another InputStream (via the OutputStream mentioned above), and just pass the ZipInputStream to my 3rd party library, the library closes the stream, and I can't do anything more, like dealing with the remaining files in the stream.

Answer 1

You probably tried reading from a FileInputStream like this:

ZipInputStream in = new ZipInputStream(new FileInputStream(...));

This won’t work since a zip archive can contain multiple files and you need to specify which file to read.

You could use java.util.zip.ZipFile and a library such as IOUtils from Apache Commons IO or ByteStreams from Guava that assist you in copying the stream.

Example:

ByteArrayOutputStream out = new ByteArrayOutputStream();
try (ZipFile zipFile = new ZipFile("foo.zip")) {
    ZipEntry zipEntry = zipFile.getEntry("fileInTheZip.txt");

    try (InputStream in = zipFile.getInputStream(zipEntry)) {
        IOUtils.copy(in, out);
    }
}

Answer 2

You're missing call

ZipEntry entry = (ZipEntry) zipStream.getNextEntry();

to position the first byte decompressed of the first entry.

 ByteArrayOutputStream streamBuilder = new ByteArrayOutputStream();
 int bytesRead;
 byte[] tempBuffer = new byte[8192*2];
 ZipEntry entry = (ZipEntry) zipStream.getNextEntry();
 try {
     while ( (bytesRead = zipStream.read(tempBuffer)) != -1 ){
        streamBuilder.write(tempBuffer, 0, bytesRead);
     }
 } catch (IOException e) {
      ...
 }

Answer 3

I would call getNextEntry() on the ZipInputStream until it is at the entry you want (use ZipEntry.getName() etc.). Calling getNextEntry() will advance the "cursor" to the beginning of the entry that it returns. Then, use ZipEntry.getSize() to determine how many bytes you should read using zipInputStream.read().

Answer 4

Please try code bellow

private static byte[] getZipArchiveContent(File zipName) throws WorkflowServiceBusinessException {

  BufferedInputStream buffer = null;
  FileInputStream fileStream = null;
  ByteArrayOutputStream byteOut = null;
  byte data[] = new byte[BUFFER];

  try {
   try {
    fileStream = new FileInputStream(zipName);
    buffer = new BufferedInputStream(fileStream);
    byteOut = new ByteArrayOutputStream();

    int count;
    while((count = buffer.read(data, 0, BUFFER)) != -1) {
     byteOut.write(data, 0, count);
    }
   } catch(Exception e) {
    throw new WorkflowServiceBusinessException(e.getMessage(), e);
   } finally {
    if(null != fileStream) {
     fileStream.close();
    }
    if(null != buffer) {
     buffer.close();
    }
    if(null != byteOut) {
     byteOut.close();
    }
   }
  } catch(Exception e) {
   throw new WorkflowServiceBusinessException(e.getMessage(), e);
  }
  return byteOut.toByteArray();

 }