CODEWITHSUNDEEP
javamemory-mapped-files
Timothy Baldridge
Timothy Baldridge

Reputation: 10653

Memory map directly to string

I have a file I'm mapping into memory via 'FileChannel.map()'. However it seems a bit odd when reading a string to do the following:

1) read a int for the string length
2) allocate a byte[length] object
3) use .get to read length bytes
4) convert the byte[] to a string

Now I know from my C++ background that memory mapped files are given to the user as pointers to memory. So is there a good way to skip using a byte array and just have the string conversion go right off the mapped memory?

Upvotes: 3

Views: 1889

Answers (3)

Pih
Pih

Reputation: 2278

I suggest:

MappedByteBuffer mapped = fileChannel.map(mode, position, size);
String s = new String(mapped.array());

It is also possible to use the mapped.asCharBuffer() and get the chars by this way.

Upvotes: 3

rlibby
rlibby

Reputation: 6021

There's no getting around String wanting a private copy of the data. Strings are immutable and if it used a shared array, you could break that. It's unfortunate that there's no String(CharSequence) or String(ByteBuffer) constructor.

Upvotes: 1

ccleve
ccleve

Reputation: 15789

Ultimately, no. But there is a way to get a view of the data as characters. Look at ByteBuffer.asCharBuffer().

Internally, the asCharBuffer() method does the same thing you're proposing, but on a char-by-char basis.

Upvotes: 3

Related Questions