How do I create a Java string from the contents of a file?

To create a Java String from the contents of a file, you can use one of the following methods, depending on your Java version and requirements:

1. Using Files.readString (Java 11+)

The simplest and most concise method for reading a file into a String with UTF-8 encoding:

import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;

public class ReadFileToString {
    public static void main(String[] args) throws Exception {
        Path path = Paths.get("path/to/file.txt");
        String content = Files.readString(path); // Default: UTF-8
        System.out.println(content);
    }
}

Specify Charset (e.g., ISO-8859-1):

String content = Files.readString(path, StandardCharsets.ISO_8859_1);

2. Using Files.readAllBytes (Java 7+)

Read the file as bytes and convert to a String with the desired charset:

import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.charset.StandardCharsets;

public class ReadFileToString {
    public static void main(String[] args) throws Exception {
        Path path = Paths.get("path/to/file.txt");
        byte[] bytes = Files.readAllBytes(path);
        String content = new String(bytes, StandardCharsets.UTF_8);
        System.out.println(content);
    }
}

3. Using BufferedReader (Legacy Approach)

Read line-by-line and append to a StringBuilder (suitable for large files):

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class ReadFileToString {
    public static void main(String[] args) throws IOException {
        StringBuilder contentBuilder = new StringBuilder();
        try (BufferedReader br = new BufferedReader(new FileReader("path/to/file.txt"))) {
            String line;
            while ((line = br.readLine()) != null) {
                contentBuilder.append(line).append(System.lineSeparator());
            }
        }
        String content = contentBuilder.toString();
        System.out.println(content);
    }
}

Note: This method may not preserve original line endings exactly, as readLine() strips them.

4. Using Scanner (Not Recommended)

Read the entire file in one go using a delimiter (\Z matches the end of input):

import java.io.File;
import java.io.IOException;
import java.util.Scanner;

public class ReadFileToString {
    public static void main(String[] args) throws IOException {
        File file = new File("path/to/file.txt");
        String content = new Scanner(file).useDelimiter("\\Z").next();
        System.out.println(content);
    }
}

Key Considerations

Method	Java Version	Pros	Cons
Files.readString	11+	Simplest, preserves encoding	Not for large files (> RAM)
Files.readAllBytes	7+	Works with any charset	Loads entire file into memory
BufferedReader	1.5+	Memory-efficient for large files	Manual line handling
Scanner	1.5+	Quick for small files	Less intuitive, slower

Handling Exceptions

All methods require handling IOException (e.g., file not found, read errors). Use try-with-resources (as shown) to auto-close streams.

Example: Read File with Custom Charset

import java.nio.charset.Charset;

// Read with ISO-8859-1 encoding
String content = new String(Files.readAllBytes(path), Charset.forName("ISO-8859-1"));

Choose the method that best fits your Java version and file size requirements!