read whole file in a folder

Question

Is there a way in Java where I can specify a directory in java and it reads the whole file one by one?

Otherwise is there a way to do a regex file read in java? So if all the files in the folder all starts with gh001_12312 gh002_12312, gh003_12911, gh004_22222, gh005_xxxxx, etc

Sometimes there are some features that can be magical that you never knew before, but others do — aherlambang, Feb 25 '11 at 06:08
I agree. Personally, I was not aware of the API's mentioned by @Pangea and thought they looked pretty interesting. — Tim Bender, Feb 25 '11 at 06:35

score 5 · Accepted Answer · answered Feb 25 '11 at 06:02

The standard Java library provides a way of obtaining an array of File elements which are in a directory via File#listFiles. Basically:

File theDirectory = new File("/home/example");
File[] children = theDirectory.listFiles();

Furthermore, there is an overloaded method that allows a filter to be specified which can be used to prune the elements returned in the list.

File theDirectory = new File("/home/example");
File[] children = theDirectory.listFiles(new FileFilter(){
    public boolean accept(File file) {
        if (file.isFile()) {
           //Check other conditions
           return true;
        }
        return false;
    }
});

If you want to do some filtering based on file name as well then have a look at String, Pattern, and Matcher. If you know there will be only files or files will follow a certain naming convention there is also a File.listFiles(FilenameFilter) options which provides only a String representing the file name.

is there a way to read BufferedReader as a whole string instead of doing the input.readLine(), where you have to do line by line? — aherlambang, Feb 25 '11 at 06:42

score 3 · Answer 2 · answered Feb 25 '11 at 05:41

3

You can use the combination of below methods from commons-io. The first method gives you option of iterating through all the files in a directory, recursively, that match a particular extension (there is another overloaded method that allows you to provide your own filter). The second method reads the entire contents of the file as a String object.

Iterator<File> iterateFiles(File directory,
                                          String[] extensions,
                                          boolean recursive)
String readFileToString(File file)
                               throws IOException

answered Feb 25 '11 at 05:41

Aravind Yarram

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what if I don't want to use that commons-io – aherlambang Feb 25 '11 at 05:47
You can do that too with the help of File (isDirectory(), listFiles()), FileNameFilter and BufferedReader....few e.g's here http://www.exampledepot.com/egs/java.io/GetFiles.html – Aravind Yarram Feb 25 '11 at 05:59

score 1 · Answer 3 · answered Feb 25 '11 at 06:49

I am reusing the the code from @Tim Bender here:

First get a list of all the needed files as shown by @Tim Bender (shown here again for completeness). And no third party libraries are needed.

File theDirectory = new File("/home/example");
File[] children = theDirectory.listFiles(new FileFilter(){
    public boolean accept(File file) {
        if (file.isFile()) {
           //Check other conditions
           return true;
        }
        return false;
    }
});

Now iterate over this array and use java.nio API for file reading in a single go (without br.readLine())

public StringBuilder readReplaceFile(File f) throws Exception
{
    FileInputStream fis = new FileInputStream(f);
    FileChannel fc = fis.getChannel();

    int sz = (int)fc.size();
    MappedByteBuffer bb = fc.map(FileChannel.MapMode.READ_ONLY, 0, sz);

    CharBuffer cb = decoder.decode(bb);

    StringBuilder outBuffer = new StringBuilder(cb);
    fc.close();
    return outBuffer;
}

Hope this help

read whole file in a folder

3 Answers3