Module java.base
Package java.nio.file

Class FileStore

  • public abstract class FileStore
extends Object
    Storage for files. A FileStore represents a storage pool, device, partition, volume, concrete file system or other implementation specific means of file storage. The FileStore for where a file is stored is obtained by invoking the getFileStore method, or all file stores can be enumerated by invoking the getFileStores method.

    In addition to the methods defined by this class, a file store may support one or more FileStoreAttributeView classes that provide a read-only or updatable view of a set of file store attributes.

    Since:
    1.7

    • Constructor Detail

      • FileStore

        protected FileStore()
        Initializes a new instance of this class.

    • Method Detail

      • name

        public abstract String name()
        Returns the name of this file store. The format of the name is highly implementation specific. It will typically be the name of the storage pool or volume.

        The string returned by this method may differ from the string returned by the toString method.

        Returns:
        the name of this file store

      • type

        public abstract String type()
        Returns the type of this file store. The format of the string returned by this method is highly implementation specific. It may indicate, for example, the format used or if the file store is local or remote.
        Returns:
        a string representing the type of this file store

      • isReadOnly

        public abstract boolean isReadOnly()
        Tells whether this file store is read-only. A file store is read-only if it does not support write operations or other changes to files. Any attempt to create a file, open an existing file for writing etc. causes an IOException to be thrown.
        Returns:
        true if, and only if, this file store is read-only

      • getTotalSpace

        public abstract long getTotalSpace()
                            throws IOException
        Returns the size, in bytes, of the file store.
        Returns:
        the size of the file store, in bytes
        Throws:
        IOException - if an I/O error occurs

      • getUsableSpace

        public abstract long getUsableSpace()
                             throws IOException
        Returns the number of bytes available to this Java virtual machine on the file store.

        The returned number of available bytes is a hint, but not a guarantee, that it is possible to use most or any of these bytes. The number of usable bytes is most likely to be accurate immediately after the space attributes are obtained. It is likely to be made inaccurate by any external I/O operations including those made on the system outside of this Java virtual machine.

        Returns:
        the number of bytes available
        Throws:
        IOException - if an I/O error occurs

      • getBlockSize

        public long getBlockSize()
                  throws IOException
        Returns the number of bytes per block in this file store.

        File storage is typically organized into discrete sequences of bytes called blocks. A block is the smallest storage unit of a file store. Every read and write operation is performed on a multiple of blocks.

        Implementation Requirements:
        The implementation in this class throws an UnsupportedOperationException.
        Returns:
        a positive value representing the block size of this file store, in bytes
        Throws:
        IOException - if an I/O error occurs
        UnsupportedOperationException - if the operation is not supported
        Since:
        10

      • getUnallocatedSpace

        public abstract long getUnallocatedSpace()
                                  throws IOException
        Returns the number of unallocated bytes in the file store.

        The returned number of unallocated bytes is a hint, but not a guarantee, that it is possible to use most or any of these bytes. The number of unallocated bytes is most likely to be accurate immediately after the space attributes are obtained. It is likely to be made inaccurate by any external I/O operations including those made on the system outside of this virtual machine.

        Returns:
        the number of unallocated bytes
        Throws:
        IOException - if an I/O error occurs

      • supportsFileAttributeView

        public abstract boolean supportsFileAttributeView​(Class<? extends FileAttributeView> type)
        Tells whether or not this file store supports the file attributes identified by the given file attribute view.

        Invoking this method to test if the file store supports BasicFileAttributeView will always return true. In the case of the default provider, this method cannot guarantee to give the correct result when the file store is not a local storage device. The reasons for this are implementation specific and therefore unspecified.

        Parameters:
        type - the file attribute view type
        Returns:
        true if, and only if, the file attribute view is supported

      • supportsFileAttributeView

        public abstract boolean supportsFileAttributeView​(String name)
        Tells whether or not this file store supports the file attributes identified by the given file attribute view.

        Invoking this method to test if the file store supports BasicFileAttributeView, identified by the name "basic" will always return true. In the case of the default provider, this method cannot guarantee to give the correct result when the file store is not a local storage device. The reasons for this are implementation specific and therefore unspecified.

        Parameters:
        name - the name of file attribute view
        Returns:
        true if, and only if, the file attribute view is supported

      • getFileStoreAttributeView

        public abstract <V extends FileStoreAttributeView> V getFileStoreAttributeView​(Class<V> type)
        Returns a FileStoreAttributeView of the given type.

        This method is intended to be used where the file store attribute view defines type-safe methods to read or update the file store attributes. The type parameter is the type of the attribute view required and the method returns an instance of that type if supported.

        Type Parameters:
        V - The FileStoreAttributeView type
        Parameters:
        type - the Class object corresponding to the attribute view
        Returns:
        a file store attribute view of the specified type or null if the attribute view is not available

      • getAttribute

        public abstract Object getAttribute​(String attribute)
                             throws IOException
        Reads the value of a file store attribute.

        The attribute parameter identifies the attribute to be read and takes the form:

        view-name:attribute-name
        where the character ':' stands for itself.

        view-name is the name of a AttributeView that identifies a set of file attributes. attribute-name is the name of the attribute.

        Usage Example: Suppose we want to know if ZFS compression is enabled (assuming the "zfs" view is supported): 

            boolean compression = (Boolean)fs.getAttribute("zfs:compression");

        Parameters:
        attribute - the attribute to read
        Returns:
        the attribute value; null may be valid for some attributes
        Throws:
        UnsupportedOperationException - if the attribute view is not available or it does not support reading the attribute
        IOException - if an I/O error occurs