9 Ways to Read Resource Files in Spring Boot Applications

1. Use ClassLoader.getResourceAsStream()

Use the class loader to obtain an InputStream for a resource file. The method takes a resource path and returns an InputStream object.

InputStream inputStream = getClass().getClassLoader().getResourceAsStream("file.txt");

Note that the path is relative to the class loader root, so files under the resources directory need the prefix classpath:, e.g., classpath:file.txt.

2. Use Class.getResourceAsStream()

Use getResourceAsStream() of the Class object to read a resource file. It also returns an InputStream.

InputStream inputStream = getClass().getResourceAsStream("/file.txt");

The path is relative to the current class, so a leading “/” is required for resources in the root of the classpath.

3. Use Spring's ResourceLoader

Inject a ResourceLoader and call its getResource() method, which returns a Resource that can provide an InputStream.

Resource resource = resourceLoader.getResource("classpath:file.txt");
InputStream inputStream = resource.getInputStream();

Remember to autowire the ResourceLoader in the class.

4. Use ResourceUtils

ResourceUtils.getFile()

can obtain a File object for a classpath resource.

File file = ResourceUtils.getFile("classpath:file.txt");

This works for files on the local file system or inside JARs, but not for WAR files.

5. Use ApplicationContext

Inject ApplicationContext and call getResource() to obtain a Resource and then an InputStream.

Resource resource = applicationContext.getResource("classpath:file.txt");
InputStream inputStream = resource.getInputStream();

6. Use ServletContext

Inject ServletContext and call getResourceAsStream() with the path inside /WEB-INF/classes/.

InputStream inputStream = servletContext.getResourceAsStream("/WEB-INF/classes/file.txt");

7. Use the File API

Read the file directly with File and FileInputStream by providing the absolute path.

File file = new File("src/main/resources/file.txt");
InputStream inputStream = new FileInputStream(file);

8. Use Java NIO Paths and Files

Read the resource with Paths.get() and Files.newInputStream(), requiring the full file path.

Path path = Paths.get("src/main/resources/file.txt");
InputStream inputStream = Files.newInputStream(path);

9. Use ClassPathResource

Spring's ClassPathResource loads a resource from the classpath without needing a full path.

ClassPathResource resource = new ClassPathResource("file.txt");
InputStream inputStream = resource.getInputStream();

All nine methods can read files located in the resources directory of a Spring Boot project; choose the one that best fits your scenario.

Recommended approaches

Use ClassLoader.getResourceAsStream() for a general solution.

Use ResourceLoader when working within Spring.

Use ClassPathResource for simple classpath file access.