How to Manage Metadata in Java?

[NIcaBoy]

Hi friends,
I am doing the Core Java from some time. I know very less about the Metadata. And now I want to manage the metadata. I have tried to do some things but I am not getting succeeded. I think since, I don't know much about the metadata that's why I am not able to do the things. Can anyone explain me what is metadata. And also please tell me how to Manage Metadata in Java? Hoping some help from you guys.!!

[Warner]

Before managing the metadata, I think that you should know about the metadata. Knowing the metadata is very important from coding point of view. Because nowadays, the latest trends in programming, especially in Java programming, is the use of metadata. You can use the metadata for creating documentation, tracking down dependencies in code, and with the help of metadata, you can also perform rudimentary compile-time checking. Metadata's benefits fall into three categories: documentation, compiler checking, and code analysis. In simple words, you can say that metadata is data about data.

[Allan.d]

With a file system, the data is contained in its files and directories, and the metadata tracks information. The package that provides an API to manage the file system's metadata is the java.nio.file.attribute package. You can store the metadata internally in the same file as the data or you can also store the metadata externally in a separate file. Metadata that is embedded with content is called embedded metadata. The core Java language came closest to a metadata facility with the Javadoc methodology. You use a special set of tags to mark up your code and then execute the javadoc command to turn the tags into a formatted HTML page.

[MELTRONICS]

I have given you an example in which readFileAttributes method returns an instance of FileAttributes, which provides a number of methods for retrieving the attribute information. The following code snippet reads and prints the basic file attributes for a given file :

Path file = ...;
FileAttributes fa = Attributes.readFileAttributes(file);

if (fa.creationTime() != null) {
    System.out.println("creationTime: " + fa.creationTime());
}
if (fa.lastAccessTime() != null) {
    System.out.println("lastAccessTime: " + fa.lastAccessTime());
}
if (fa.lastModifiedTime() != null) {
    System.out.println("lastModifiedTime: " + fa.lastModifiedTime());
}

System.out.println("isDirectory: " + fa.isDirectory());
System.out.println("isOther: " + fa.isOther());
System.out.println("isRegularFile: " + fa.isRegularFile());
System.out.println("isSymbolicLink: " + fa.isSymbolicLink());
System.out.println("size: " + fa.size());

[Solitario]

If you want to determine whether a file is a regular file that can be executed (and not a directory), the example provided by 'MELTRONICS' is extended to check the file type by using the basic file attributes. The following is the sample of coding :

import static java.nio.file.AccessMode.*;

Path file = .....give your path file here....;
boolean error=false;

try {
    file.checkAccess(READ, EXECUTE);
    if (!Attributes.readFileAttributes(file).isRegularFile()) {
        error = true;
    }
} catch (IOException x) {
    error = true;
}
if (error) {
    return;
}

[CodGuru]

In many scenarios you need to check the space available on file. For that you can use the readFileStoreSpaceAttributes(FileStore) method to learn how much space is available on a file store. The following coding may be useful to you :

Path file = ...;
FileStore fs = file.getFileStore();
FileStoreSpaceAttributes fa = Attributes.readFileStoreSpaceAttributes(store);

long total = fa.totalSpace() / 1024;
long used = (fa.totalSpace() - fa.unallocatedSpace()) / 1024;
long avail = fa.usableSpace() / 1024;

System.out.println("fs: " + store);
System.out.println("total: " + attr.totalSpace() / 1024);
System.out.println("used:  " + (attr.totalSpace() - attr.unallocatedSpace()) / 1024);
System.out.println("avail: " + fa.usableSpace() / 1024);