CODEWITHSUNDEEP
javajarzipbufferedreaderbufferedwriter
Imred_Gemu
Imred_Gemu

Reputation: 58

Read zip or jar file without unzipping it first

I'm not looking for any answers that involve opening the zip file in a zip input or output stream. My question is is it possible in java to just simply open a jar file like any other file (using buffered reader/writer), read it's contents, and write them somewhere else? For example:

import java.io.*;

public class zipReader {

public static void main(String[] args){

    BufferedReader br = new BufferedReader(new FileReader((System.getProperty("user.home").replaceAll("\\\\", "/") + "/Desktop/foo.zip")));
    BufferedWriter bw = new BufferedWriter(new FileWriter((System.getProperty("user.home").replaceAll("\\\\", "/") + "/Desktop/baf.zip")));
    char[] ch = new char[180000];

    while(br.read(ch) > 0){

        bw.write(ch);
        bw.flush();

    }

    br.close();
    bw.close();

}

}

This works on some small zip/jar files, but most of the time will just corrupt them making it impossible to unzip or execute them. I have found that setting the size of the char[] to 1 will not corrupt the file, just everything in it, meaning I can open the file in an archive program but all it's entries will be corrupted and unusable. Does anyone know how to write the above code so it won't corrupt the file? Also here is a line from a jar file I tested this on that became corrupted:

nèñà?G¾Þ§V ¨ö—‚?‰9³’?ÀM·p›a0„èwåÕüaEܵp‡aæOùR‰(JºJ´êgžè*?”6ftöãÝÈ—ê@qïc3âi,áž…¹¿Êð)V¢cã>Ê”G˜(†®9öCçM?€ÔÙÆC†ÑÝ×ok?ý—¥úûFs.‡

vs the original:

nèñàG¾Þ§V ¨ö—‚‰9³’ÀM·p›a0„èwåÕüaEܵp‡aæOùR‰(JºJ´êgžè*?”6ftöãÝÈ—ê@qïc3âi,áž…¹¿Êð)V¢cã>Ê”G˜(†®9öCçM€ÔÙÆC†ÑÝ×oký—¥úûFs.‡

As you can see either the reader or writer adds ?'s into the files and I can't figure out why. Again I don't want any answers telling me to open it entry by entry, I already know how to do that, if anyone knows the answer to my question please share it.

Upvotes: 0

Views: 1185

Answers (3)

mazaneicha
mazaneicha

Reputation: 9427

Why would you want to convert binary data to chars? I think it will be much better to InputStream/OutputStream using byte arrays. See http://www.javapractices.com/topic/TopicAction.do?Id=245 for examples.

Upvotes: 2

bmargulies
bmargulies

Reputation: 100042

bw.write(ch) will write the entire array. Read will only fill in some of it, and return a number telling you how much. This is nothing to do with zip files, just with how IO works.

You need to change your code to look more like:

 int charsRead = br.read(buffer);
 if (charsRead >= 0) {
       bw.write(buffer, 0, charsRead);
 } else {
       // whatever I do at the end.
 }

However, this is only 1/2 of your problem. You are also converting bytes to characters and back again, which will corrupt the data in other ways. Stick to streams.

Upvotes: 1

vandale
vandale

Reputation: 3650

see the ZipInputStream and ZipOutputStream classes

Edit: use plain FileInputStream and FileOutputStream. I suspect there may be some issues when the reader is interpreting the bytes as characters.

see also: Standard concise way to copy a file in Java? Since you ant to copy the whole file, there is nothing special about it being a zip file

Upvotes: 0

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