Created
June 20, 2020 06:55
-
-
Save bobby569/0d8f6c086d738675d11d6f207aef3aab to your computer and use it in GitHub Desktop.
High-level implementation of a large file reader in java.
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| public class LargeFileReader { | |
| private static final long PAGE_SIZE = Integer.MAX_VALUE; | |
| private List<MappedByteBuffer> buffers = new ArrayList<>(); | |
| private final byte raw[] = new byte[1]; | |
| LargeFileReader(FileChannel channel) throws IOException { | |
| long start = 0, length = 0; | |
| for (long index = 0; start + length < channel.size(); index++) { | |
| length = channel.size() / PAGE_SIZE == index ? channel.size() - index * PAGE_SIZE : PAGE_SIZE; | |
| start = index * PAGE_SIZE; | |
| buffers.add(index, channel.map(READ_ONLY, start, length)); | |
| } | |
| } | |
| public String getString(long bytePosition) { | |
| int page = (int) (bytePosition / PAGE_SIZE); | |
| int index = (int) (bytePosition & PAGE_SIZE); | |
| raw[0] = buffers.get(page).get(index); | |
| return new String(raw); | |
| } | |
| public static void main(String[] args) throws IOException { | |
| File file = new File(args[1]); | |
| FileChannel fc = (new FileInuptStream(file)).getChannel(); | |
| LargeFileReader buffer = new LargeFileReader(fc); | |
| long position = file.length() / 2; | |
| String candidate = buffer.getString(position--); | |
| while (position >= 0 && !candidate.equals('\n')) { | |
| candidate = buffer.getString(position--); | |
| } | |
| } | |
| } |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment