Class ScratchFile

  • All Implemented Interfaces:
    java.io.Closeable, java.lang.AutoCloseable

    public class ScratchFile
    extends java.lang.Object
    implements java.io.Closeable
    Implements a memory page handling mechanism as base for creating (multiple) RandomAccess buffers each having its set of pages (implemented by ScratchFileBuffer). A buffer is created calling createBuffer().

    Pages can be stored in main memory or in a temporary file. A mixed mode is supported storing a certain amount of pages in memory and only the additional ones in temporary file (defined by maximum main memory to be used).

    Pages can be marked as 'free' in order to re-use them. For in-memory pages this will release the used memory while for pages in temporary file this simply marks the area as free to re-use.

    If a temporary file was created (done with the first page to be stored in temporary file) it is deleted when close() is called.

    Using this class for RandomAccess buffers allows for a direct control on the maximum memory usage and allows processing large files for which we otherwise would get an OutOfMemoryError in case of using RandomAccessBuffer.

    This base class for providing pages is thread safe (the buffer implementations are not).

    • Constructor Summary

      Constructors 
      Constructor Description
      ScratchFile​(java.io.File scratchFileDirectory)
      Initializes page handler.
      ScratchFile​(MemoryUsageSetting memUsageSetting)
      Initializes page handler.
    • Method Summary

      All Methods Static Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      void close()
      Closes and deletes the temporary file.
      RandomAccess createBuffer()
      Creates a new buffer using this page handler.
      RandomAccess createBuffer​(java.io.InputStream input)
      Creates a new buffer using this page handler and initializes it with the data read from provided input stream (input stream is copied to buffer).
      static ScratchFile getMainMemoryOnlyInstance()
      Getter for an instance using only unrestricted main memory for buffering (same as new ScratchFile(MemoryUsageSetting.setupMainMemoryOnly())).
      • Methods inherited from class java.lang.Object

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

      • ScratchFile

        public ScratchFile​(java.io.File scratchFileDirectory)
                    throws java.io.IOException
        Initializes page handler. If a scratchFileDirectory is supplied, then the scratch file will be created in that directory.

        All pages will be stored in the scratch file.

        Parameters:
        scratchFileDirectory - The directory in which to create the scratch file or null to created it in the default temporary directory.
        Throws:
        java.io.IOException - If scratch file directory was given but don't exist.
      • ScratchFile

        public ScratchFile​(MemoryUsageSetting memUsageSetting)
                    throws java.io.IOException
        Initializes page handler. If a scratchFileDirectory is supplied, then the scratch file will be created in that directory.

        Depending on the size of allowed memory usage a number of pages (memorySize/PAGE_SIZE) will be stored in-memory and only additional pages will be written to/read from scratch file.

        Parameters:
        memUsageSetting - set how memory/temporary files are used for buffering streams etc.
        Throws:
        java.io.IOException - If scratch file directory was given but don't exist.
    • Method Detail

      • getMainMemoryOnlyInstance

        public static ScratchFile getMainMemoryOnlyInstance()
        Getter for an instance using only unrestricted main memory for buffering (same as new ScratchFile(MemoryUsageSetting.setupMainMemoryOnly())).
        Returns:
        instance configured to only use main memory with no size restriction
      • createBuffer

        public RandomAccess createBuffer()
                                  throws java.io.IOException
        Creates a new buffer using this page handler.
        Returns:
        A new buffer.
        Throws:
        java.io.IOException - If an error occurred.
      • createBuffer

        public RandomAccess createBuffer​(java.io.InputStream input)
                                  throws java.io.IOException
        Creates a new buffer using this page handler and initializes it with the data read from provided input stream (input stream is copied to buffer). The buffer data pointer is reset to point to first byte.
        Parameters:
        input - The input stream that is to be copied into the buffer.
        Returns:
        A new buffer containing data read from input stream.
        Throws:
        java.io.IOException - If an error occurred.
      • close

        public void close()
                   throws java.io.IOException
        Closes and deletes the temporary file. No further interaction with the scratch file or associated buffers can happen after this method is called. It also releases in-memory pages.
        Specified by:
        close in interface java.lang.AutoCloseable
        Specified by:
        close in interface java.io.Closeable
        Throws:
        java.io.IOException - If there was a problem closing or deleting the temporary file.