CODEWITHSUNDEEP
java
N Meibergen
N Meibergen

Reputation: 382

How to determine the compression method of a zip file

From a third party I am retrieving .zip files. I want to unzip these to another folder. To this end I found a method that does exactly that, see code below. It iterates through all files and unzips them to another folder. However, when observing the corresponding compression method I found out that this changes for some files. And for some files it states: "invalid compression method", after which it aborts further unzipping of the zip file.

As the compression method seems to change, I suspect I need to set the compression method to the correct one (however that might be a wrong assumption). So rises my question: how to determine the compression method needed?

The code I am using:

public void unZipIt(String zipFile, String outputFolder){

    //create output directory is not exists
    File folder = new File(OUTPUT_FOLDER);
    if(!folder.exists()){
        folder.mkdir();
    }

    FileInputStream fis = null;
    ZipInputStream zipIs = null;
    ZipEntry zEntry = null;
    try 
    {
        fis = new FileInputStream(zipFile);
        zipIs = new ZipInputStream(new BufferedInputStream(fis));

        while((zEntry = zipIs.getNextEntry()) != null){
            System.out.println(zEntry.getMethod());
            try{
                byte[] tmp = new byte[4*1024];
                FileOutputStream fos = null;
                String opFilePath = OUTPUT_FOLDER + "\\" + zEntry.getName();
                System.out.println("Extracting file to "+opFilePath);
                fos = new FileOutputStream(opFilePath);
                int size = 0;
                while((size = zipIs.read(tmp)) != -1){
                    fos.write(tmp, 0 , size);
                }
                fos.flush();
                fos.close();
            } catch(IOException e){
                System.out.println(e.getMessage());
            }
        }
        zipIs.close();
    } catch (FileNotFoundException e) {
        System.out.println(e.getMessage());
    } 
    catch(IOException ex){
        System.out.println(ex.getMessage());
    }

}

Currently I am retrieving the following output:

8
Extracting file to     C:\Users\nlmeibe2\Documents\Projects\Output_test\SOPHIS_cptyrisk_tradedata_1192_20140616.csv
8
Extracting file to C:\Users\nlmeibe2\Documents\Projects\Output_test\SOPHIS_cptyrisk_underlying_1192_20140616.csv
0
Extracting file to C:\Users\nlmeibe2\Documents\Projects\Output_test\10052013/
12
Extracting file to     C:\Users\nlmeibe2\Documents\Projects\Output_test\MRM_Daily_Position_Report_Package_Level_Underlying_View_EQB_v2_COBDATE_2014-06-16_RUNDATETIME_2014-06-17-04h15.csv
invalid compression method
invalid compression method

Upvotes: 2

Views: 5344

Answers (2)

jarnbjo
jarnbjo

Reputation: 34323

Since you only print the exception message and not the stack trace (with line numbers), it is impossible to know exactly where the exception is thrown, but I suppose it is not thrown until you actually try to read from the ZipEntry.

If the numbers in your output is the ZIP method, the last entry you encounter is compressed with method 12 (bzip2), which is not supported by the Java ZIP implementation. PKWare (the maintainers of the ZIP format) regularly add new compression methods to the ZIP specification and there are currently some 12-15 (not sure about the exact number) compression methods specified. Java only supports the methods 0 (stored) and 8 (deflated) and will throw an exception with the message "invalid compression method" if you try to decompress a ZIP file using an unsupported compression method.

Both WinZip and the ZIP functions in Windows may use compression methods not supported by the Java API.

Upvotes: 2

Marco Acierno
Marco Acierno

Reputation: 14847

Use zEntry.getMethod() to get the compression method

Returns the compression method of the entry, or -1 if not specified.

It will return an int which will be

public static final int STORED

public static final int DEFLATED

or -1 if it don't know the method.

Docs.

Upvotes: 2

Related Questions