Loading large text files in JTextArea

Question

JTextArea can't seem to load an 8MB text file, as doing so will throw an OutOfMemoryError. The problem is, 8MB really isn't that much data, and there are files in our system which are much bigger than that. And I'm at a loss to find why a mere 8MB is causing Java to run out of its 64MB of memory.
So I'm starting to try another approach.
Here's the idea:
    public void doStuff() {
        Reader reader = dataStore.retrieve(...);
        RandomAccessFile tempFile = new RandomAccessFile(...);
        FileChannel tempChannel = tempFile.getChannel();
        // CODE OMITTED: copying reader to tempChannel as Java chars.
        // Now, map the file into memory.
        CharBuffer charBuffer = tempChannel.map(FileChannel.MapMode.READ_WRITE, 0, fileLength).asCharBuffer();
        Document doc = new CharBufferDocument(charBuffer);
        textArea.setDocument(doc);
    }This should work in theory. The problem I'm having is figuring out how to make this custom document.
Here's what I have so far:
    public class CharBufferDocument extends PlainDocument {
        private CharBufferDocument(CharBuffer charBuffer) {
            super(new CharBufferContent(charBuffer));
    class CharBuffeclass CharBufferContent implements AbstractDocument.Content {
        private CharBuffer charBuffer;
        private CharBufferContent(CharBuffer charBuffer) {
            this.charBuffer = charBuffer;
        public Position createPosition(int offset) throws BadLocationException {
            return new FixedPosition(offset);
        public int length() {
            return charBuffer.length();
        public UndoableEdit insertString(int where, String str) throws BadLocationException {
            throw new UnsupportedOperationException("Editing not supported");
        public UndoableEdit remove(int where, int nitems) throws BadLocationException {
            throw new UnsupportedOperationException("Editing not supported");
        public String getString(int where, int len) throws BadLocationException {
            Segment segment = new Segment();
            getChars(where, len, segment);
            return segment.toString();
        public void getChars(int where, int len, Segment txt) throws BadLocationException {
            char[] buf = new char[len];
            // Sync this, as the get method moves the cursor.
            synchronized (this) {
                charBuffer.get(buf, where, len);
                charBuffer.rewind();
            txt.array = buf;
            txt.offset = where;
            txt.count = len;
    class FixedPosition implements Position {
        private int offset;
        private FixedPosition(int offset) {
            this.offset = offset;
        public int getOffset() {
            return offset;
    }When I run this, I get a text area which only shows one character. What's happening is that my getChars(int,int,Segment) method is being called from Swing's classes, and only being asked for one character!
Does anyone have any idea how this is supposed to work? It seems that if Swing only ever asks for the first character, I'm never going to be able to display 8,000,000 characters. :-)

Answer 1

Not too sure though how to go about reading the last 5 lines say.One solution would be to read in an increasingly large block (estimate the typical line size * 5 + some bonus) of the file starting at position file size[i] - block size. As long as the block doesn't contains 5 complete lines (count newline chars), increase it by a given size and try again. Should still be faster than scanning the whole file from start to end.