Accessing metadata of files

[LianaN]

Hi!

I'm developing a simple file manager. So, I have two components: JTree & JTable. When I open some folder in JTree, then JTable is updated according to the content of that folder. JTable contains 3 columns: file_type, file_name, file_bytes. The code works correctly.

Now I need to add some more columns to describe each file in JTable, e.g. file_author, file_description, file_link. How could I assign/read these data to/from files? Should I use metadata?

[JosAH]

Now I need to add some more columns to describe each file in JTable, e.g. file_author, file_description, file_link. How could I assign/read these data to/from files? Should I use metadata?

Java 1.6 and earlier can't do that; you have to wait until Java 7 sees the light.

kind regards,

Jos

[LianaN]

Thank you, it's a pity:(

Is it possible to solve this problem without metadata? Maybe, I could add some tags "@file_description:..." at the top of the file? In this case, I don't know how to deal with "pdf" files...

[LianaN]

For instance, here Managing Metadata (File and File Store Attributes) (The Java™ Tutorials > Essential Classes > Basic I/O) I see some information about metadata. Could I use it in my case?

[JosAH]

For instance, here Managing Metadata (File and File Store Attributes) (The Java™ Tutorials > Essential Classes > Basic I/O) I see some information about metadata. Could I use it in my case?

That is a preliminary tutorial of the NIO2 package, part of Java 7 only.

kind regards,

Jos

[LianaN]

But what is this: Java Platform, Standard Edition 7 Binary Snapshot Releases? Isn't it JDK 7 installation? I've just installed Java SE Development Kit 7, will try it.

[JosAH]

But what is this: Java Platform, Standard Edition 7 Binary Snapshot Releases? Isn't it JDK 7 installation? I've just installed Java SE Development Kit 7, will try it.

Yep, that's a preliminary Java 7 installation. No warranties, no nothing, it's just a snapshot and can change overnight.

kind regards,

Jos

[LianaN]

Ok, thank you. Eh...So, my problem is unsolveable now.

[DarrylBurke]

How could I assign/read these data to/from files?

If this is Windows and the file system is NTFS, you can use alternate streams. Example:

import java.io.*;

public class AlternateStreamTest {

  public static void main(String[] args) {
    File outFile = new File("e:/java/outTest.txt:alternate");
    FileOutputStream fos = null;
    try {
      fos = new FileOutputStream(outFile);
      fos.write("The quick brown fox jumps over the lazy dog".getBytes());
    } catch (IOException ioe) {
      ioe.printStackTrace();
    } finally {
      if (fos != null) {
        try {
          fos.close();
        } catch (IOException ex) {
          ex.printStackTrace();
        }
      }
    }

    File inFile = new File("e:/java/inTest.txt");
    outFile.renameTo(inFile);
    
    inFile = new File("e:/java/outTest.txt:alternate");
    FileInputStream fis = null;
    try {
      fis = new FileInputStream(inFile);
      byte[] b = new byte[1024];
      while (fis.available() > 0) {
        fis.read(b);
        System.out.println(new String(b));
      }
    } catch (IOException ioe) {
      ioe.printStackTrace();
    } finally {
      if (fis != null) {
        try {
          fis.close();
        } catch (IOException ex) {
          ex.printStackTrace();
        }
      }
    }
  }
}

Otherwise you can save a companion file e.g. for myPDF.pdf you can save a file myPDF.pdf.txt with the metadata. This is not foolproof as it's theoretically possible that a myPdf.pdf.txt text file already exists. Using a long and obscure extension e.g.myPDF.pdf.myMetadata makes the chances of this happening astronomically low.

Note: in the example above, the alternate stream cannot be viewed in the usual editor (NotePad). Google "NTFS Alternate Streams" for more information.

db

[JosAH]

I didn't know that and I find it a strange feature; I guess an 'alternate stream' can't have another alternate stream, can it?

kind regards,

Jos

[DarrylBurke]

No, only a physical file can have an alternate stream. But a little juggling showed that the alternate stream can be a file that itself has an alternate stream.

This is going to be hard to read :-\

import java.io.*;

public class AlternateStreamTest {

  public static void main(String[] args) throws IOException {
    File fileOstreamA = new File("e:/java/outA.txt:alt");
    FileOutputStream fos = null;
    try {
      fos = new FileOutputStream(fileOstreamA);
      fos.write("The quick brown fox jumps over the lazy dog".getBytes());
    } finally {
      if (fos != null) {
        try {
          fos.close();
        } catch (IOException ex) {
          ex.printStackTrace();
        }
      }
    }

    File fileO = new File("e:/java/outA.txt");
    File fileO2 = new File("e:/java/outS.txt");

    File fileO2streamS = new File("e:/java/outS.txt:sub");
    fileO.renameTo(fileO2streamS);

    File fileI2 = new File("e:/java/inS.txt");
    fileO2.renameTo(fileI2);

    File fileI2streamS = new File("e:/java/inS.txt:sub");
    File fileI = new File("e:/java/outA.txt");
    fileI2streamS.renameTo(fileI);

    File fileIstreamA = new File("e:/java/outA.txt:alt");

    FileInputStream fis = null;
    try {
      fis = new FileInputStream(fileIstreamA);
      byte[] b = new byte[1024];
      while (fis.available() > 0) {
        fis.read(b);
        System.out.println(new String(b));
      }
    } finally {
      if (fis != null) {
        try {
          fis.close();
        } catch (IOException ex) {
          ex.printStackTrace();
        }
      }
    }
  }
}

db

[LianaN]

Thanks a lot!

I plan to run my application at different operating systems. Therefore, I've implemented the second solution - I'm creating metadata.txt files for each file in JTree.