Class VariableSizeDataStore


  • public class VariableSizeDataStore
    extends java.lang.Object
    Provides a mechanism for storing variable length data in a file which can quickly be indexed via a reference number. The store maintains a master index file that contains a reference to all individual data records stored in the system. The data file contains all the data that has been stored.

    This file format is not intended to be a fully fledged file system. For example, we can not easily change the size of a data entry. To change the record, we must delete it then add a new.

    This system uses two files. One file is the index, and the second file stores the data. The index file contains sectors as follows:

       4 (int) : index  - The sector index of the data in the data file.
       4 (int) : length - Length of the data that was stored.
       4 (int) : status - 32 status bits.
     

    This employs a simple compression scheme when writing out data that would span more than one sector. It tries compressing the field. If the field can be compressed into less sectors than if left uncompressed, then the compressed field is put into the data store.

    Author:
    Tobias Downer
    • Method Summary

      All Methods Static Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      void close()
      Closes the data store.
      int completeRecordStreamWrite()
      Updates the record allocation table with the data in the output stream returned by 'getRecordOutputStream'.
      void copyTo​(java.io.File path)
      Copies this data store to the given path.
      void delete()
      Deletes the store from the file system.
      int delete​(int record)
      Deletes the data at the given index position.
      static boolean delete​(java.io.File path, java.lang.String name)
      Convenience for deleting a VariableSizeDataStore store.
      boolean exists()
      Returns true if the data store exists.
      static boolean exists​(java.io.File path, java.lang.String name)
      Convenience for checking if a given data store exists or not.
      void fix​(UserTerminal terminal)
      Attempts to fix a corrupt VariableSizeDataStore object.
      java.io.InputStream getRecordInputStream​(int record)
      Returns an InputStream that is used to read a record in this store with the given index.
      java.io.OutputStream getRecordOutputStream()
      Returns an OutputStream object that can be used to write data into the store.
      void hardSynch()
      Hard synchronizes the data from memory into the hard copy on disk.
      boolean isCompressed​(int record)
      Returns true if the given record is compressed.
      boolean isReadOnly()
      Returns true if the store was openned in read only mode.
      void lock()
      Locks the store so that not deleted elements may be overwritten.
      boolean locked()
      Returns true if we are locked.
      boolean open​(boolean read_only)
      Opens the data store.
      int rawRecordCount()
      Returns the total number of records that are in the store (including deleted records.
      int read​(int record, byte[] buf, int offset, int length)
      Reads a variable length byte[] array from the given index position.
      byte[] readRecord​(int record)
      Reads in a complete record and puts it into the returned byte[] array.
      int readRecordType​(int record_index)
      Reads the 32-bit type_key int for the given record.
      void readReservedBuffer​(byte[] info, int offset, int length)
      Reads reserved information from the variable data store.
      java.lang.String readString​(int record)  
      boolean recordDeleted​(int record_index)
      Returns true if the given record is marked as deleted or not.
      int recordSectorCount​(int record)
      Returns the number of sectors the given record takes up in the data store.
      int recordSize​(int record)
      Returns the size of the given record number (compressed size if applicable).
      static boolean rename​(java.io.File path_source, java.lang.String name_source, java.io.File path_dest, java.lang.String name_dest)
      Convenience for renaming a VariableSizeDataStore store to another name.
      int sectorSize()
      Returns the size (in bytes) of the sectors used to store information in the data file.
      void synch()
      Synchronizes all the data in memory with the hard copy on disk.
      long totalStoreSize()
      Returns the size of the data file that keeps all the data in this store.
      void unlock()
      Unlocks the store so that deleted elements can be reclaimed again.
      int usedRecordCount()
      Returns the number of records that are being used.
      int write​(byte[] buf, int offset, int length)
      Writes a variable length byte[] array to the first available index.
      int writeRecordType​(int record_index, int type_key)
      Updates the 32-bit type_key int of a record.
      void writeReservedBuffer​(byte[] info, int offset, int length)  
      void writeReservedBuffer​(byte[] info, int offset, int length, int res_offset)
      Writes reserved information to the variable data store.
      int writeString​(java.lang.String str)  
      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
    • Constructor Detail

      • VariableSizeDataStore

        public VariableSizeDataStore​(java.io.File name,
                                     int sector_size,
                                     DebugLogger logger)
        Constructs the variable size store.
      • VariableSizeDataStore

        public VariableSizeDataStore​(java.io.File name,
                                     DebugLogger logger)
    • Method Detail

      • synch

        public void synch()
                   throws java.io.IOException
        Synchronizes all the data in memory with the hard copy on disk.
        Throws:
        java.io.IOException
      • hardSynch

        public void hardSynch()
                       throws java.io.IOException
        Hard synchronizes the data from memory into the hard copy on disk. This is guarenteed to ensure the image on the disk will match the image in memory.
        Throws:
        java.io.IOException
      • locked

        public boolean locked()
        Returns true if we are locked.
      • lock

        public void lock()
        Locks the store so that not deleted elements may be overwritten.
      • unlock

        public void unlock()
        Unlocks the store so that deleted elements can be reclaimed again.
      • recordDeleted

        public boolean recordDeleted​(int record_index)
                              throws java.io.IOException
        Returns true if the given record is marked as deleted or not.
        Throws:
        java.io.IOException
      • usedRecordCount

        public int usedRecordCount()
        Returns the number of records that are being used.
      • rawRecordCount

        public int rawRecordCount()
                           throws java.io.IOException
        Returns the total number of records that are in the store (including deleted records.
        Throws:
        java.io.IOException
      • exists

        public boolean exists()
                       throws java.io.IOException
        Returns true if the data store exists.
        Throws:
        java.io.IOException
      • isReadOnly

        public boolean isReadOnly()
        Returns true if the store was openned in read only mode.
      • open

        public boolean open​(boolean read_only)
                     throws java.io.IOException
        Opens the data store. The data store can be opened in 'read only' mode. Returns 'true' if the open procedure should repair itself (dirty open) or false if the file was cleanly closed down.

        It is not possible to open a damaged store in read only mode.

        Parameters:
        read_only - if true, then the database is opened in read only mode, otherwise it is opened in read/write mode.
        Throws:
        java.io.IOException
      • close

        public void close()
                   throws java.io.IOException
        Closes the data store.
        Throws:
        java.io.IOException
      • delete

        public void delete()
        Deletes the store from the file system. Must be called after a 'close'.
      • fix

        public void fix​(UserTerminal terminal)
                 throws java.io.IOException
        Attempts to fix a corrupt VariableSizeDataStore object.

        The store should be open before this method is called.

        Throws:
        java.io.IOException
      • copyTo

        public void copyTo​(java.io.File path)
                    throws java.io.IOException
        Copies this data store to the given path. The store must be open when this is called.
        Throws:
        java.io.IOException
      • writeRecordType

        public int writeRecordType​(int record_index,
                                   int type_key)
                            throws java.io.IOException
        Updates the 32-bit type_key int of a record. Bit 1-8 are reserved for this data store, and are used to indicate such things as whether the record chain is compressed or not. The rest of the bits can be used for any purpose. It is recommended bits 8 through 16 are used for user-definable information.
        Throws:
        java.io.IOException
      • readRecordType

        public int readRecordType​(int record_index)
                           throws java.io.IOException
        Reads the 32-bit type_key int for the given record. The 'type_key' contains various bit flags set for the record.
        Throws:
        java.io.IOException
      • write

        public int write​(byte[] buf,
                         int offset,
                         int length)
                  throws java.io.IOException
        Writes a variable length byte[] array to the first available index. Returns the index reference for this element.
        Throws:
        java.io.IOException
      • read

        public int read​(int record,
                        byte[] buf,
                        int offset,
                        int length)
                 throws java.io.IOException
        Reads a variable length byte[] array from the given index position. This will read the first n bytes from the element, upto the maximum that was stored. It returns the number of bytes that were read.
        Throws:
        java.io.IOException
      • readRecord

        public byte[] readRecord​(int record)
                          throws java.io.IOException
        Reads in a complete record and puts it into the returned byte[] array.
        Throws:
        java.io.IOException
      • delete

        public int delete​(int record)
                   throws java.io.IOException
        Deletes the data at the given index position.
        Throws:
        java.io.IOException
      • getRecordOutputStream

        public java.io.OutputStream getRecordOutputStream()
                                                   throws java.io.IOException
        Returns an OutputStream object that can be used to write data into the store. When the 'completeWriteStream' method is called, the records in this store are updated appropriately for the data written in, and a record index is returned.

        NOTE: Only one open stream may be active at a time. While this stream is open this VariableSizeDataStore object may not be used in any other way.

        Throws:
        java.io.IOException
      • completeRecordStreamWrite

        public int completeRecordStreamWrite()
                                      throws java.io.IOException
        Updates the record allocation table with the data in the output stream returned by 'getRecordOutputStream'. Returns an index for how to reference this data later.

        After this method is called it is safe again to use this VariableSizeDataStore object.

        Throws:
        java.io.IOException
      • getRecordInputStream

        public java.io.InputStream getRecordInputStream​(int record)
                                                 throws java.io.IOException
        Returns an InputStream that is used to read a record in this store with the given index.

        NOTE: This can not handle compressed records.

        NOTE: This does not detect the end of stream (reading past the end of the record will return undefined data).

        Throws:
        java.io.IOException
      • sectorSize

        public int sectorSize()
                       throws java.io.IOException
        Returns the size (in bytes) of the sectors used to store information in the data file.
        Throws:
        java.io.IOException
      • recordSize

        public int recordSize​(int record)
                       throws java.io.IOException
        Returns the size of the given record number (compressed size if applicable).
        Throws:
        java.io.IOException
      • isCompressed

        public boolean isCompressed​(int record)
                             throws java.io.IOException
        Returns true if the given record is compressed.
        Throws:
        java.io.IOException
      • recordSectorCount

        public int recordSectorCount​(int record)
                              throws java.io.IOException
        Returns the number of sectors the given record takes up in the data store.
        Throws:
        java.io.IOException
      • totalStoreSize

        public long totalStoreSize()
        Returns the size of the data file that keeps all the data in this store. This is the file size of the data store.
      • writeReservedBuffer

        public void writeReservedBuffer​(byte[] info,
                                        int offset,
                                        int length,
                                        int res_offset)
                                 throws java.io.IOException
        Writes reserved information to the variable data store. You may only write upto 128 bytes to the reserved data buffer.
        Throws:
        java.io.IOException
      • writeReservedBuffer

        public void writeReservedBuffer​(byte[] info,
                                        int offset,
                                        int length)
                                 throws java.io.IOException
        Throws:
        java.io.IOException
      • readReservedBuffer

        public void readReservedBuffer​(byte[] info,
                                       int offset,
                                       int length)
                                throws java.io.IOException
        Reads reserved information from the variable data store. You may only read upto 128 bytes from the reserved data buffer.
        Throws:
        java.io.IOException
      • exists

        public static boolean exists​(java.io.File path,
                                     java.lang.String name)
                              throws java.io.IOException
        Convenience for checking if a given data store exists or not. Returns true if it exists.
        Throws:
        java.io.IOException
      • delete

        public static boolean delete​(java.io.File path,
                                     java.lang.String name)
                              throws java.io.IOException
        Convenience for deleting a VariableSizeDataStore store.
        Throws:
        java.io.IOException
      • rename

        public static boolean rename​(java.io.File path_source,
                                     java.lang.String name_source,
                                     java.io.File path_dest,
                                     java.lang.String name_dest)
                              throws java.io.IOException
        Convenience for renaming a VariableSizeDataStore store to another name.
        Throws:
        java.io.IOException
      • writeString

        public int writeString​(java.lang.String str)
                        throws java.io.IOException
        Throws:
        java.io.IOException
      • readString

        public java.lang.String readString​(int record)
                                    throws java.io.IOException
        Throws:
        java.io.IOException