Reading Files from the Resources Folder in Spring Boot

In a typical Spring Boot application, it’s common to store static files such as configuration files, JSON data, or other resources in the resources folder. However, accessing these files programmatically can be tricky, especially when running the application from a JAR file.

This tutorial will guide you through the process of reading files from the resources folder in Spring Boot using various approaches.

Understanding the Resources Folder

In a Spring Boot project, the resources folder is used to store static files that are not part of the Java code. When the application is built and packaged into a JAR file, these resources are included in the archive. To access these files, you need to use the correct approach.

Using ClassPathResource

One way to read files from the resources folder is by using the ClassPathResource class provided by Spring. Here’s an example:

import org.springframework.core.io.ClassPathResource;
import java.io.File;

// Read a file from the resources folder
File file = new ClassPathResource("jsonschema.json").getFile();

This approach works well when running the application from within an IDE or from the exploded JAR file. However, it may not work when running the application from a packaged JAR file.

Using ResourceUtils

Another way to read files from the resources folder is by using the ResourceUtils class provided by Spring. Here’s an example:

import org.springframework.util.ResourceUtils;
import java.io.File;

// Read a file from the resources folder
File file = ResourceUtils.getFile("classpath:jsonschema.json");

This approach works well in most cases, including when running the application from a packaged JAR file.

Using getResourceAsStream

You can also read files from the resources folder by using the getResourceAsStream method provided by the ClassLoader. Here’s an example:

import java.io.InputStream;

// Read a file from the resources folder as an InputStream
InputStream inputStream = getClass().getClassLoader().getResourceAsStream("jsonschema.json");

This approach is useful when you need to read the file contents as a stream, rather than loading it into memory all at once.

Reading File Contents

To read the contents of a file from the resources folder, you can use the following method:

import java.io.File;
import java.nio.file.Files;

// Read file contents
String content = new String(Files.readAllBytes(file.toPath()));

This approach works well when you need to read small files. For larger files, it’s recommended to use a streaming approach to avoid loading the entire file into memory.

Example Use Case

Here’s an example use case that demonstrates how to read a JSON schema from a file in the resources folder:

import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;

// Read JSON schema from file
File file = new ClassPathResource("jsonschema.json").getFile();
ObjectMapper mapper = new ObjectMapper();
JsonNode jsonSchema = mapper.readTree(file);

This example uses the ClassPathResource class to read the JSON schema from a file in the resources folder and then parses it using the Jackson library.

Conclusion

In this tutorial, we’ve covered various approaches to reading files from the resources folder in Spring Boot. By using the correct approach, you can access your static resources programmatically, even when running the application from a packaged JAR file. Remember to choose the approach that best fits your use case and performance requirements.