Loading resources

Streaming applications frequently need to load side-inputs, reference datasets, encryption keys, and schema definitions across classpath and filesystem locations. Flinkboot provides the Resource API to unify and standardize these access patterns.

---

1. Unified resource API (Resource)

The Resource contract allows reading content via an InputStream without managing manual URL or file descriptors:

import io.github.sekelenao.flinkboot.core.api.resource.Resource;
import java.io.InputStream;
import java.nio.charset.StandardCharsets;

Resource rules = Resource.of("classpath:rules/fraud-rules.json");

try (InputStream in = rules.inputStream()) {
    String json = new String(in.readAllBytes(), StandardCharsets.UTF_8);
}

---

2. Supported scheme prefixes

Flinkboot resolves paths based on scheme prefixes:

Scheme Prefix	Target Location	Example
classpath:<path>	JAR classpath resources	Resource.of("classpath:schemas/event.avsc")
resource:<path>	Alias for classpath resources	Resource.of("resource:lookup.csv")
file:<path>	Local or mounted filesystem	Resource.of("file:/etc/secrets/tls.keystore")

Prefix matching is case-insensitive (file:, FILE:, classpath:).

---

3. Distributed streaming lifecycle

Resource instances are not Serializable.

When accessing resources inside distributed Flink streaming operators (such as a RichMapFunction or ProcessFunction), do not serialize the Resource instance across TaskManagers. Instead, pass the path string to the operator constructor, declare the resource or resulting state as transient, and read the input stream inside the operator's open(OpenContext) lifecycle method.