Java: Read File into String

Reading a File into a Java String (Spring Boot Compatible)

This concise guide shows how to read a file's contents into a Java String, suitable for Java and Spring Boot applications. Several approaches exist, each with trade-offs.

Method 1: Using Files.readString() (Java 11+)

This is the simplest and most efficient for modern Java:

import java.nio.file.Files;
import java.nio.file.Paths;
import java.io.IOException;

String fileContent = Files.readString(Paths.get("my_file.txt")); 

Method 2: Using Scanner (All Java Versions)

More verbose but compatible with older Java versions:

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

String fileContent = "";
try (Scanner scanner = new Scanner(new File("my_file.txt"))) {
    while (scanner.hasNextLine()) {
        fileContent += scanner.nextLine() + "\n";
    }
} catch (FileNotFoundException e) {
    // Handle file not found exception
}

Method 3: Using BufferedReader (For large files)

For very large files, BufferedReader offers better performance by reading in chunks:

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

StringBuilder content = new StringBuilder();
try (BufferedReader br = new BufferedReader(new FileReader("my_file.txt"))) {
    String line;
    while ((line = br.readLine()) != null) {
        content.append(line).append("\n");
    }
} catch (IOException e) {
    // Handle IO exceptions
}
String fileContent = content.toString();

Error Handling: Always include robust error handling (e.g., try-catch blocks) to manage potential IOExceptions or FileNotFoundException. Remember to replace "my_file.txt" with your actual file path. Choose the method best suited to your Java version and file size. For Spring Boot, simply include these methods within your service or controller.