arrays - Java OutOfMemoryError in reading a large text file

Question

I'm new to Java and working on reading very large files, need some help to understand the problem and solve it. We have got some legacy code which have to be optimized to make it run properly.The file size can vary from 10mb to 10gb only. only trouble start when file starting beyond 800mb size.

InputStream inFileReader = channelSFtp.get(path); // file reading from ssh.
byte[] localbuffer = new byte[2048];
ByteArrayOutputStream bArrStream = new ByteArrayOutputStream();

int i = 0;
while (-1 != (i = inFileReader.read(buffer))) {
bArrStream.write(localbuffer, 0, i);
}

byte[] data = bArrStream.toByteArray();
inFileReader.close();
bos.close();

We are getting the error

java.lang.OutOfMemoryError: Java heap space
    at java.util.Arrays.copyOf(Arrays.java:2271)
    at java.io.ByteArrayOutputStream.grow(ByteArrayOutputStream.java:113)
    at java.io.ByteArrayOutputStream.ensureCapacity(ByteArrayOutputStream.java:93)
    at java.io.ByteArrayOutputStream.write(ByteArrayOutputStream.java:140)

Any help would be appreciated?

Answer 1

Try to use java.nio.MappedByteBuffer.

http://docs.oracle.com/javase/7/docs/api/java/nio/MappedByteBuffer.html

You can map a file's content onto memory without copying it manually. High-level Operating Systems offer memory-mapping and Java has API to utilize the feature.

If my understanding is correct, memory-mapping does not load a file's entire content onto memory (meaning "loaded and unloaded partially as necessary"), so I guess a 10GB file won't eat up your memory.