How do I read a large file efficiently in Java?

I am trying to read a large text file in Java, but find that it's quite slow. How do I improve the efficiency of my code?

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Reading a large file efficiently in Java is quite a common problem. Here are some steps you can take to improve the efficiency of your code: **Use a BufferedReader** `BufferedReader` is the most efficient way of reading text in Java. It buffers characters so as not to access the disk for each byte, significantly reducing the I/O time. Here's an example: ```java try (BufferedReader br = new BufferedReader(new FileReader("file.txt"))) { String line; while ((line = br.readLine()) != null) { // process line } } catch (IOException e) { // Handle exception } ``` **Process Data While Reading** If you're performing heavy computations on each line, it would be better to process them right away rather than storing them in memory and dealing with them later. This would reduce your program’s memory footprint. **Use a LineIterator** Apache Commons IO library's `LineIterator` can be a faster alternative. It doesn't load the entire file into memory, making it a good choice for large files. Here's an example: ```java try (LineIterator it = FileUtils.lineIterator(new File("file.txt"), "UTF-8")) { while (it.hasNext()) { String line = it.nextLine(); // process line } } catch (IOException e) { // Handle exception } ``` **Use java.nio.file API** From Java 7 onwards, java.nio.file API has been introduced which has methods such as `Files.lines()`. They make use of Streams thus providing a modern and efficient way in terms of memory and speed. ```java try (Stream lines = Files.lines(Paths.get("file.txt"))) { lines.forEach(System.out::println); } catch (IOException e) { // Handle exception } ``` Remember always to close your resources (`BufferedReader`, `FileReader`, etc.), preferably using a try with resources statement as shown above. This ensures that the JVM does not leak any resources. Finally, profile your application to figure out the real bottleneck, it might not be the file reading but something else in your application.
Answered on August 5, 2023.
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