Add the API-Version HTTP header to every response, with the version n…

…umber provided as a property or environment variable.

examples/nlgov-adr/README.md

@@ -31,9 +31,8 @@ API-20   Yes
 API-48   Yes     
 API-51   No      CORS policy is invalid
 API-56   Yes     
-API-57   No      API-Version header not found
+API-57   Yes     
 
 Validation failed
 ```
 There is currently nothing configured for CORS in the API so it is expected to fail that test.
-The API-Version header is currently only documented in the OpenAPI Specification but it is not yet returned by the API. This can be easily fixed with a JAX-RS filter that adds this header to every response.

examples/nlgov-adr/build.gradle

@@ -19,6 +19,7 @@ application{
 bootRun {
     environment "server.port", "8888"
     environment "SIMPLYRESTFUL_URI_HTTP_HEADER", "xoriginalurl"
+    environment "API_VERSION" "0.0.1"
 }
 
 dependencies {

examples/nlgov-adr/src/main/java/example/nlgov_adr/ApiVersionFilter.java

@@ -0,0 +1,37 @@
+package example.nlgov_adr;
+
+import java.io.IOException;
+
+import jakarta.inject.Named;
+import jakarta.ws.rs.container.ContainerRequestContext;
+import jakarta.ws.rs.container.ContainerResponseContext;
+import jakarta.ws.rs.container.ContainerResponseFilter;
+
+/**
+ * Add an HTTP header named "API-Version" to every response.
+ *
+ * It contains the version of the API which can be defined in a property or
+ * environment variable called "API_VERSION".
+ */
+@Named
+public class ApiVersionFilter implements ContainerResponseFilter {
+	public static final String API_VERSION_HTTP_HEADER_NAME = "API-Version";
+	public static final String API_VERSION_ENV_NAME = "API_VERSION";
+
+	@Override
+	public void filter(ContainerRequestContext requestContext, ContainerResponseContext responseContext)
+			throws IOException {
+		String apiVersion = getApiVersion();
+		if(apiVersion != null) {
+			responseContext.getHeaders().add(API_VERSION_HTTP_HEADER_NAME, apiVersion);
+		}
+	}
+
+	private String getApiVersion() {
+		String apiVersion = System.getProperty(API_VERSION_ENV_NAME);
+		if (apiVersion == null) {
+			apiVersion = System.getenv(API_VERSION_ENV_NAME);
+		}
+		return apiVersion;
+	}
+}

examples/nlgov-adr/src/main/java/example/nlgov_adr/ExampleResourceConfig.java

@@ -12,6 +12,7 @@
 public class ExampleResourceConfig extends ResourceConfig {
     public ExampleResourceConfig() {
         register(ExampleWebResource.class);
+        register(ApiVersionFilter.class);
         property(ServletProperties.FILTER_FORWARD_ON_404, true);
     }
 }