How to read zip file as byte array and then convert the byte array to back to zip file?

Question

I have tried using this code for converting a ZIP file to a byte array:

private static byte[] readZipFile(String zipFnm)
// read in fnm, returning it as a single string
{

  FileInputStream fileInputStream=null;

  File file = new File(zipFnm);

  byte[] bFile = new byte[(int) file.length()];

  try{
    //convert file into array of bytes
    fileInputStream = new FileInputStream(zipFnm);
    fileInputStream.read(bFile);
    fileInputStream.close();
  }catch(Exception e){
    e.printStackTrace();
  }
  return bFile;
}

and this code for converting the byte array to back to ZIP, by calling writeByteToZip(fnm + ".zip");

private static String writeByteToZip(String outFnm)
{
  try {
    FileOutputStream fileOuputStream = new FileOutputStream(outFnm); 
    fileOuputStream.write(bFile);
    fileOuputStream.close();            

  } catch ( IOException iox ){
    iox.printStackTrace();
  }
  return outFnm;
}  // end of writeByteToZip()

What am I doing wrong? I get correct byte length of zip using

byte[] bzip = readZipFile(zipFnm);

int totalLen1 = bzip.length;
System.out.println("Total byte length of zip: " + totalLen1);

All I get is a zero size zip file and run time error in Netbeans as:

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at java.io.FileOutputStream.write(FileOutputStream.java:305)
    at steg.Steg.writeByteToZip(Steg.java:402)
    at steg.Steg.save(Steg.java:292)
    at steg.frame1.jButton2ActionPerformed(frame1.java:349)
    at steg.frame1.access$300(frame1.java:24)
    at steg.frame1$4.actionPerformed(frame1.java:172)
    at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
    at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
    at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
    at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
    at java.awt.Component.processMouseEvent(Component.java:6505)
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
    at java.awt.Component.processEvent(Component.java:6270)
    at java.awt.Container.processEvent(Container.java:2229)
    at java.awt.Component.dispatchEventImpl(Component.java:4861)
    at java.awt.Container.dispatchEventImpl(Container.java:2287)
    at java.awt.Component.dispatchEvent(Component.java:4687)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492)
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
    at java.awt.Container.dispatchEventImpl(Container.java:2273)
    at java.awt.Window.dispatchEventImpl(Window.java:2713)
    at java.awt.Component.dispatchEvent(Component.java:4687)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:707)
    at java.awt.EventQueue.access$000(EventQueue.java:101)
    at java.awt.EventQueue$3.run(EventQueue.java:666)
    at java.awt.EventQueue$3.run(EventQueue.java:664)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
    at java.awt.EventQueue$4.run(EventQueue.java:680)
    at java.awt.EventQueue$4.run(EventQueue.java:678)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:677)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:211)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:128)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:117)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:113)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:105)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:90)

Aaron Digulla · Accepted Answer · 2013-04-23 10:26:44Z

1

The problem is probably the variable bFile in writeByteToZip(). Make sure it is not null.

In the future, when you post code which throws an exception, mark the line where the exception happens with a comment (// <-- NullPointerException here)

answered Apr 23, 2013 at 10:26

Aaron Digulla

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Duncan Jones · Accepted Answer · 2013-04-23 10:41:28Z

1

The stacktrace you've provided will be caused because bFile is null.

The cause is likely to be the following line in your readZipFile method:

byte[] bFile = new byte[(int) file.length()];

Here you are assigning to a local variable, rather than your class field. Try replacing that line with:

bFile = new byte[file.length()];

Your code also demonstrates poor resource handling. Either use existing library methods to do your reading (e.g. commons-io or Java 7 Files) or write code such as:

FileInputStream fileInputStream = null;
try {
  fileInputStream = new //...
} finally {
  if (fileInputStream != null) {
    fileInputStream.close();
  }
}

If you have Java 7, you can use try-with-resources:

try (FileInputStream fileInputStream = new FileInputStream(zipFnm)) {
  // Use your stream
}

edited Apr 23, 2013 at 10:41

answered Apr 23, 2013 at 10:24

Duncan Jones

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1 Comment

drew moore Over a year ago

It's not zipFnm that's null - the exception is being thrown on the line where bfile is referenced.

Vithushan · Accepted Answer · 2014-09-15 10:43:00Z

1

I didnt check your code. But i was working with such requirement. SO felt like sharing my code.

To read zip file and convert to byte array:

public byte[] readXMLFile(){
        File file = new File("a.xml");

        byte[] b = new byte[(int) file.length()];
        try {
            FileInputStream fileInputStream = new FileInputStream(file);
            fileInputStream.read(b);
            fileInputStream.close();
        }catch (FileNotFoundException e) {
            System.out.println("File Not Found.");
            e.printStackTrace();
        }catch (IOException e1) {
            System.out.println("Error Reading The File.");
            e1.printStackTrace();
        }
        return b;
    }

To write to zip file from byte array:

public void writeXMLFile(byte[] fileContent){
        try {
            FileOutputStream fos = new FileOutputStream("abc.xml");

            fos.write(fileContent);
            fos.close();
        }catch(FileNotFoundException ex){
            System.out.println("FileNotFoundException : " + ex);
        }catch(IOException ioe)  {
            System.out.println("IOException : " + ioe);
        }
    }

Hope this helps.

answered Sep 15, 2014 at 10:43

Vithushan

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1 Comment

Ring Over a year ago

Always close your streams in a finally block.

Duncan Jones · Accepted Answer · 2013-04-23 10:35:30Z

0

As already said the file probably does not exist.

However, I just wanted to mention out the utility in Java 7 you can use. Files class offers:

static byte[] readAllBytes(Path path)
static Path write(Path path, byte[] bytes, OpenOption... options)

Seams like exactly what you need. It does not matter if the file is Zip or not, simply you can get the bytes easily and then use them to write them to some other file. Note that Path in Java 7 is representing the path to the file in question.

edited Apr 23, 2013 at 10:35

Duncan Jones

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answered Apr 23, 2013 at 10:32

Ivan Senic

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