JAVA MEMORY DISK MAP UPDATE
JAVA MEMORY DISK MAP CODE

A librarian will then bring your books to the front desk. Rather than you browsing the shelfs, trying to remember how the Dewey Decimal works, you'll enter your book selections from your phone.

NonReadableChannelException will be thrown if you request read on channel not open on read mode.Imagine this: your library is trying to step up its game and compete in the Internet age. Map()method will throw NonWritableChannelException if it try to write on MapMode.READ_WRITE mode. MappedByteBuffer will also not be visible to other programs that have mapped the same file instead, they will cause private copies of the modified portions of the buffer to be created.

PRIVATE: Change in MappedByteBuffer will not reflect to File.

There are three type of mapping mode in map() method If you increase the size larger than file size then file will also become large to match the size of MappedByteBuffer in write mode but throw IOException in read mode because file can not modified in read mode. We can also map entire file by using as belowįileChannel.map(_ONLY, 0, fileChannel.size())

JAVA MEMORY DISK MAP CODE

Long position, long size) throws IOException Īs per above code map () method on FileChannel pass the arguments as mode, position and size and return MappedByteBuffer for part of file. Public abstract MappedByteBuffer map(MapMode mode, Implements SeekableByteChannel, GatheringByteChannel, ScatteringByteChannel The other benefit of memory mapping is that operating system automatically manages VM space. Note: JVM invokes the shared VM, page fault generated that push the file data from OS to shared memory.

The file data always mapped with disk file data without using buffer transfer.

This also provides ability map a region or part of file.

It could be used more than one process based on locking provided by OS.

OS mostly take care of reading and writing from shared VM without using JVM.

JVM doesn’t load file in its memory besides it uses Virtual Memory that bring the ability to process large data in efficient manner.

The JVM directly process on Virtual Memory hence it will avoid system read () and write() call.The only drawback is the it throw page fault if requested page is not in Memory.īelow some of the key benefits of MappedByteBuffer: Apart from that File in Virtual Memory cache the memory pages that will directly access by MappedByteBuffer and doesn’t consumes JVM space. Processing file through MappedByteBuffer has big advantage because it doesn’t make any system call to read/write on file that improve the latency.

JAVA MEMORY DISK MAP UPDATE

In similar way put () method update the content directly on disk and modified content will be visible to other readers of the file. The get() method on MappedByteBuffer fetch the data from file which will represent current file data stored inside disk. The MappedByteBuffer object work like buffer but its data stored in a file on Virtual Memory. MappedByteBuffer directly map with open file in Virtual Memory by using map method in FileChannel.

Java maps the File pages to MappedByteBuffer directly and process these file without loading into JVM.īelo diagram show how JVM mapped the file with MappedByteBuffer and process the file without loading the file in JVM. OS uses Virtual Memory to cache the file in outside of Kernel space that could be sharable with other non-kernel process. This removes the overhead of transferring and coping the file’s content from OS kernel space to JVM space. In JDK version 1.4 and above Java provides MappedByteBuffer which help to establish a virtual memory mapping from JVM space to filesystem pages. File page convert to JVM system before processing the file data because OS handle file in page but JVM uses byte stream that is not compatible with page. JVM utilize it memory space to load and process file that causes trouble on large data file processes. Behind the scene JVM makes read () and write () system call to transfer data from OS kernel to JVM. In Java’s earlier version, It uses FileSystem conventional API to access system file.

Java memory disk map