How to transfer a list of strings from a file to property of application.properties (using Spring boot 2.3.x)

Question

I have a application.yaml

app:
  list: /list.txt

• list.txt

Also I have a file with list of strings. It locates into /resources(in the root /resource).

first
second
third

• class

public class Bean{

@Value("${app.list}")
private List<String> listProp = new ArrayList<>();

public void print(){
 System.out.println(listProp);
}

}

I have found that:

public class ResourceReader {

    public static String asString(Resource resource) {
        try (Reader reader = new InputStreamReader(resource.getInputStream(), UTF_8)) {
            return FileCopyUtils.copyToString(reader);
        } catch (IOException e) {
            throw new UncheckedIOException(e);
        }
    }

    public static String readFileToString(String path) {
        ResourceLoader resourceLoader = new DefaultResourceLoader();
        Resource resource = resourceLoader.getResource(path);
        return asString(resource);
    }
}

@Configuration
public class ConfigurationResource {
    
@Configuration
public class ConfigurationResource {

    @Value("${app.list}")
    private String pathToFile;

    @Bean
    public List<String> resourceString() {

        String blackList = ResourceReader.readFileToString(pathToFile);
        return List.of(blackList.split("\n"));

    }
}
}

@RequiredArgsConstructor
public class HelloController {

 
    private final List<String> resourceString;
...
}

This is necessary in order not to manually write a list of strings to the property app.name (there are several hundred lines).

However, I find it difficult to figure out how to do it at low cost. So that it can be easily maintained.

maybe there is an easier way? I would not like to add a hardcoding value in the configuration class

Maybe someone has some ideas?

Answer 1

Here is the solution from my understanding if you have to keep lines in the text file that you've shared:

public class Bean {

    @Value("${app.list}")
    private String listProp; // only get name of file

    public void print(){
        ClassLoader classLoader = getClass().getClassLoader();
        InputStream is = classLoader.getResourceAsStream(listProp);
        StringBuilder sb = new StringBuilder();
        try {
            for (int ch; (ch = is.read()) != -1; ) {
                sb.append((char) ch);
            }
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
        System.out.println(sb);
    }
}