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Reading from a ZipInputStream into a ByteArrayOutputStream

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

Your loop looks valid – what does the following code (just on it’s own) return?

zipStream.read(tempBuffer)

if it’s returning -1, then the zipStream is closed before you get it, and all bets are off. It’s time to use your debugger and make sure what’s being passed to you is actually valid.

When you call getNextEntry(), does it return a value, and is the data in the entry meaningful (i.e. does getCompressedSize() return a valid value)? IF you are just reading a Zip file that doesn’t have read-ahead zip entries embedded, then ZipInputStream isn’t going to work for you.

Some useful tidbits about the Zip format:

Each file embedded in a zip file has a header. This header can contain useful information (such as the compressed length of the stream, it’s offset in the file, CRC) – or it can contain some magic values that basically say ‘The information isn’t in the stream header, you have to check the Zip post-amble’.

Each zip file then has a table that is attached to the end of the file that contains all of the zip entries, along with the real data. The table at the end is mandatory, and the values in it must be correct. In contrast, the values embedded in the stream do not have to be provided.

If you use ZipFile, it reads the table at the end of the zip. If you use ZipInputStream, I suspect that getNextEntry() attempts to use the entries embedded in the stream. If those values aren’t specified, then ZipInputStream has no idea how long the stream might be. The inflate algorithm is self terminating (you actually don’t need to know the uncompressed length of the output stream in order to fully recover the output), but it’s possible that the Java version of this reader doesn’t handle this situation very well.

I will say that it’s fairly unusual to have a servlet returning a ZipInputStream (it’s much more common to receive an inflatorInputStream if you are going to be receiving compressed content.

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When is a CDATA section necessary within a script tag?

Are CDATA tags ever necessary in script tags and if so when?

In other words, when and where is this:

<script type="text/javascript">
//<![CDATA[
...code...
//]]>
</script>

preferable to this:

<script type="text/javascript">
...code...
</script>

Answer

A CDATA section is required if you need your document to parse as XML (e.g. when an XHTML page is interpreted as XML) and you want to be able to write literal i<10 and a && b instead of i&lt;10 and a &amp;&amp; b, as XHTML will parse the JavaScript code as parsed character data as opposed to character data by default. This is not an issue with scripts that are stored in external source files, but for any inline JavaScript in XHTML you will probably want to use a CDATA section.

Note that many XHTML pages were never intended to be parsed as XML in which case this will not be an issue.

For a good writeup on the subject, see https://web.archive.org/web/20140304083226/http://javascript.about.com/library/blxhtml.htm

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Can a servlet determine if the posted data is multipart/form-data?

I have a servlet that is used for many different actions, used in the Front Controller pattern. Does anyone know if it is possible to tell if the data posted back to it is enctype=”multipart/form-data”? I can’t read the request parameters until I decide this, so I can’t dispatch the request to the proper controller.

Any ideas?

Answer

Yes, the Content-type header in the user agent’s request should include multipart/form-data as described in (at least) the HTML4 spec:

http://www.w3.org/TR/html401/interact/forms.html#h-17.13.4.2

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What’s the best HTML WYSISYG editor available to web developers and why? [closed]

There are many different flavored HTML WYSIWYG editors from javascript to ASP.Net web controls, but all too often the features are the same. Does anyone have a favorite HTML editor they like to use in projects? Why?

Answer

I’m partial to TinyMCE WYSIWYG editor due to the following reasons:

  1. Javascript – so it is broadly usable
    regardless of the platform I’m
    working in.

  2. Easy to use – just a couple lines of
    code and a textarea and the control is up and
    running.

  3. Easily themed – so I can quickly
    make it look like the site in which
    it is being used

  4. Most importantly – easily customized
    to show/hide particular buttons
    depending on my application needs

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How do you crash a JVM?

I was reading a book on programming skills wherein the author asks the interviewee, “How do you crash a JVM?” I thought that you could do so by writing an infinite for-loop that would eventually use up all the memory.

Anybody has any idea?

Answer

The closest thing to a single “answer” is System.exit() which terminates the JVM immediately without proper cleanup. But apart from that, native code and resource exhaustion are the most likely answers. Alternatively you can go looking on Sun’s bug tracker for bugs in your version of the JVM, some of which allow for repeatable crash scenarios. We used to get semi-regular crashes when approaching the 4 Gb memory limit under the 32-bit versions (we generally use 64-bit now).

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