There are three common ways to read files in Java. First, use BufferedReader to read line by line, which is suitable for large files. The steps include creating a FileReader, wrapping it into a BufferedReader, and reading and closing the stream with readLine(); Second, use Files.readAllLines() to read the content of the small file into the list at one time; Third, use Scanner to read and parse the data as needed, which is suitable for structured text. In addition, pay attention to issues such as path setting, resource closing and encoding specification. The selection method should be determined based on specific needs such as file size and processing methods.
Reading files is a common operation in Java, suitable for handling configuration, logs, data import and other scenarios. Java provides a variety of ways to implement this function, and different methods are suitable for different usage situations.
Read text files line by line using BufferedReader
This is one of the most common ways to read larger text files, especially when they need to be processed line by line.
- step:
- Create
FileReader
instance - Package it into
BufferedReader
- Use
readLine()
method to read content line by line - Finally close the stream to free the resource
- Create
try (BufferedReader reader = new BufferedReader(new FileReader("example.txt"))) { String line; while ((line = reader.readLine()) != null) { System.out.println(line); } } catch (IOException e) { e.printStackTrace(); }
The advantage of this method is that it is low memory footprint and is suitable for large files. But if you just want to read the entire file content at once, you can consider the following method.
Quickly read small files using Files.readAllLines()
For smaller text files, you can directly read everything into a list with one line of code:
List<String> lines = Files.readAllLines(Paths.get("example.txt")); lines.forEach(System.out::println);
This method is concise and clear, but not suitable for very large files, because it will load all the content into memory at once.
Use Scanner
to read content on demand (suitable for parsing)
If you want to parse while reading, such as reading numbers or data in a specific format, you can use Scanner
:
try (Scanner scanner = new Scanner(new File("data.txt"))) { while (scanner.hasNextLine()) { String line = scanner.nextLine(); // Process each line} }
The advantage of Scanner
is that it can flexibly read different types of data, such as nextInt()
, nextDouble()
, etc., which is suitable for processing structured text data.
Notes and details
The file path can be a relative or an absolute path, pay attention to whether the path is correct.
Always use try-with-resources to automatically close resources to avoid resource leakage.
If the file encoding is not the default platform encoding, it is recommended to specify a character set, for example:
new BufferedReader(new InputStreamReader(new FileInputStream("file.txt"), StandardCharsets.UTF_8));
If you are reading a binary file, you should use
FileInputStream
instead ofFileReader
.
Basically these methods are all about it. Which method to choose depends on your specific needs: file size, whether it needs to be processed line by line, whether the content needs to be parsed, etc.
The above is the detailed content of How to read a file in Java?. For more information, please follow other related articles on the PHP Chinese website!

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