Package ucar.nc2.util

Class DiskCache2

  • public class DiskCache2
extends Object
    Manages a place on disk to persistently cache files, which are deleted when the last modified date exceeds a certain time. This starts up a thread to periodically scour itself; be sure to call exit() to terminate the thread.

    Each DiskCache has a "root directory", which may be set as an absolute path, or relative to the DiskCache "home directory". The root directory must be writeable. The DiskCache home directory is set in the following order:

    1. through the system property "nj22.cache" if it exists
    2. through the system property "user.home" if it exists
    3. through the system property "user.dir" if it exists
    4. to the current working directory
    TODO will move in ver 6

    • Constructor Detail

      • DiskCache2

        public DiskCache2​(String root,
                  boolean relativeToHome,
                  int persistMinutes,
                  int scourEveryMinutes)
        Create a cache on disk. Use default policy (CachePathPolicy.NestedDirectory)
        Parameters:
        root - the root directory of the cache. Must be writeable.
        relativeToHome - if the root directory is relative to the cache home directory.
        persistMinutes - a file is deleted if its last modified time is greater than persistMinutes
        scourEveryMinutes - how often to run the scour process. If <= 0, don't scour.

    • Method Detail

      • exit

        public static void exit()
        Be sure to call this when your application exits, otherwise your process may not exit without being killed.

      • getDefault

        public static DiskCache2 getDefault()
        Default DiskCache2 strategy: use $user_home/.unidata/cache/, no scouring, alwaysUseCache = false Mimics default DiskCache static class

      • setRootDirectory

        public void setRootDirectory​(String cacheDir)

      • getRootDirectory

        public String getRootDirectory()
        Get the cache root directory.
        Returns:
        the cache root directory.

      • getCacheFile

        public File getCacheFile​(String fileLocation)
        Get a File in the cache, corresponding to the fileLocation. File may or may not exist. If fileLocation has "/" in it, and cachePathPolicy == NestedDirectory, the nested directories will be created.
        Parameters:
        fileLocation - logical file location
        Returns:
        physical File in the cache.

      • getFile

        public File getFile​(String fileLocation)
        Get the named File. If exists or isWritable, return it. Otherwise get corresponding file in the cache directory. If fileLocation has "/" in it, and cachePathPolicy == NestedDirectory, the nested directories will be created.
        Parameters:
        fileLocation - logical file location
        Returns:
        physical File as named, or in the cache.

      • canWrite

        public static boolean canWrite​(File f)
        Returns true if we can write to the file.
        Parameters:
        f - a file. It may be a regular file or a directory. It may even be non-existent, in which case the writability of the file's parent dir is tested.
        Returns:
        true if we can write to the file.

      • getExistingFileOrCache

        public File getExistingFileOrCache​(String fileLocation)
        Looking for an existing file, in cache or no
        Parameters:
        fileLocation - the original name
        Returns:
        existing file if you can find it

      • createUniqueFile

        public File createUniqueFile​(String prefix,
                             String suffix)
        Reserve a new, uniquely named file in the root directory. Mimics File.createTempFile(), but does not actually create the file. Instead, a 0 byte file of the same name with the extension lock is created, thus "reserving" the name until it is used. The filename must be used before persistMinutes, or the lock will be scoured and the reservation will be lost.
        Parameters:
        prefix - The prefix string to be used in generating the file's name; must be at least three characters long
        suffix - The suffix string to be used in generating the file's name; may be null, in which case the suffix ".tmp" will be used
        Returns:
        unique, reserved file name

      • setPolicy

        public void setPolicy​(DiskCache2.CachePathPolicy cachePathPolicy)
        Set the cache path policy
        Parameters:
        cachePathPolicy - one of: OneDirectory (default) : replace "/" with "-", so all files are in one directory. NestedDirectory: cache files are in nested directories under the root. NestedTruncate: eliminate leading directories

      • setCachePathPolicy

        public void setCachePathPolicy​(DiskCache2.CachePathPolicy cachePathPolicy,
                               String cachePathPolicyParam)
        Set the cache path policy
        Parameters:
        cachePathPolicy - one of: OneDirectory (default) : replace "/" with "-", so all files are in one directory. NestedDirectory: cache files are in nested directories under the root. NestedTruncate: eliminate leading directories
        cachePathPolicyParam - for NestedTruncate, eliminate this string

      • setPolicy

        public void setPolicy​(String policy)

      • setAlwaysUseCache

        public void setAlwaysUseCache​(boolean alwaysUseCache)
        If true, always put the file in the cache. default false.
        Parameters:
        alwaysUseCache - If true, always put the file in the cache

      • setNeverUseCache

        public void setNeverUseCache​(boolean neverUseCache)
        If true, never put the file in the cache. default false.
        Parameters:
        neverUseCache - If true, never put the file in the cache

      • showCache

        public void showCache​(PrintStream pw)
        Show cache contents, for debugging.
        Parameters:
        pw - write to this PrintStream.

      • cleanCache

        public void cleanCache​(File dir,
                       Formatter sbuff,
                       boolean isRoot)
        Remove any files or directories whose last modified time greater than persistMinutes
        Parameters:
        dir - clean starting here
        sbuff - status messages here, may be null
        isRoot - delete empty directories, bit not root directory