Read Files Bundled in a WAR

In a Spring Boot project, you keep your static assets in the src/main/resources folder. They'll be bundled, untouched, into your final WAR file when you build your project for deployment. But you can't reference them like you would regular files, with a path name. You need to use a ResourceLoader to retrieve a reference to the file.

Inject a ResourceLoader into your class file using @AutoWired:

@Controller
public class WarResourceController {

    @Autowired
    private ResourceLoader resourceLoader;

    // ...
}

ResourceLoader reads from the root of the resources folder. When using the ResourceLoader, you must prefix the name and sub-path of the file to be read with classpath:. Thusly, to read src/main/resources/static/test.txt, we use resourceLoader.getResource() to return a Resource from classpath:static/test.txt:

String filename = "static/test.txt";
String warResourceName = "classpath:" + filename;
Resource resource = resourceLoader.getResource(warResourceName);

From there, we can obtain a File reference to the object with resource.getFile():

File file = resource.getFile();

And we can use the File object in whatever read operation we want:

byte[] bytes = new FileInputStream(file).readAllBytes();
String content = new String(bytes, StandardCharsets.UTF_8);

Our entire controller class looks something like this:

@Controller
public class WarResourceController {

    @Autowired
    private ResourceLoader resourceLoader;


    @GetMapping("/war-resource")
    ResponseEntity<String> getResponse() {
        try {
            String filename = "static/test.txt";
            String warResourceName = "classpath:" + filename;
            Resource resource = resourceLoader.getResource(warResourceName);
            File file = resource.getFile();
            byte[] bytes = new FileInputStream(file).readAllBytes();
            String content = new String(bytes, StandardCharsets.UTF_8);
            return ResponseEntity.ok(content);

        } catch (Exception e) {
            e.printStackTrace();
            return ResponseEntity.badRequest().build();
        }
    }

}