Add support for JSON Output format

build.gradle

@@ -13,6 +13,7 @@ repositories {
 
 dependencies {
     implementation 'uk.ac.gate:gate-core:8.6.1'
+    implementation 'uk.ac.gate.plugins:format-json:8.7'
     implementation 'com.amazonaws:aws-lambda-java-core:1.2.1'
     implementation 'com.amazonaws:aws-lambda-java-events:2.2.9'
 

src/main/java/co/zeroae/gate/App.java

@@ -6,14 +6,17 @@
 import com.amazonaws.services.lambda.runtime.events.APIGatewayProxyResponseEvent;
 
 import gate.*;
+import gate.corpora.export.GATEJsonExporter;
 import gate.creole.ExecutionException;
 import gate.creole.ResourceInstantiationException;
 import gate.util.GateException;
 import gate.util.persistence.PersistenceManager;
 import org.apache.log4j.LogManager;
 import org.apache.log4j.Logger;
 
+import java.io.ByteArrayOutputStream;
 import java.io.File;
+import java.io.IOException;
 import java.net.URL;
 import java.util.HashMap;
 import java.util.Objects;
@@ -34,8 +37,10 @@ public class App implements RequestHandler<APIGatewayProxyRequestEvent, APIGatew
 
     private static final Logger logger = LogManager.getLogger(App.class);
     private static final CorpusController application = loadApplication();
+    private static final GATEJsonExporter gateJsonExporter = new GATEJsonExporter();
 
     public APIGatewayProxyResponseEvent handleRequest(APIGatewayProxyRequestEvent input, final Context context) {
+        final String responseType = input.getHeaders().getOrDefault("Accept", "application/xml");
         final APIGatewayProxyResponseEvent response = new APIGatewayProxyResponseEvent()
                 .withHeaders(new HashMap<>());
         response.getHeaders().put("Content-Type", "text/plain");
@@ -46,9 +51,9 @@ public APIGatewayProxyResponseEvent handleRequest(APIGatewayProxyRequestEvent in
             corpus.add(doc);
             try {
                 application.execute();
-                response.getHeaders().put("Content-Type", "application/xml");
-                return response.withBody(doc.toXml()).withStatusCode(200);
-            } catch (ExecutionException e) {
+                response.getHeaders().put("Content-Type", responseType);
+                return response.withBody(encode(doc, responseType)).withStatusCode(200);
+            } catch (ExecutionException | IOException e) {
                 logger.error(e);
                 return response.withBody(e.getMessage()).withStatusCode(500);
             } finally {
@@ -61,6 +66,21 @@ public APIGatewayProxyResponseEvent handleRequest(APIGatewayProxyRequestEvent in
         }
     }
 
+    /**
+     * @param doc an instance of gate.Document
+     * @param responseType One of the supported response types
+     */
+    private String encode(Document doc, String responseType) throws IOException {
+        final ByteArrayOutputStream baos = new ByteArrayOutputStream();
+        if (responseType.equals("application/json")) {
+            gateJsonExporter.export(doc, baos);
+            return baos.toString();
+        }
+        else {
+            return doc.toXml();
+        }
+    }
+
     private static CorpusController loadApplication() {
         try {
             final String gappResourcePah = System.getenv("GATE_APP_NAME") + "/application.xgapp";

src/test/java/co/zeroae/gate/AppTest.java

@@ -2,7 +2,8 @@
 
 import com.amazonaws.services.lambda.runtime.events.APIGatewayProxyRequestEvent;
 import com.amazonaws.services.lambda.runtime.events.APIGatewayProxyResponseEvent;
-import org.junit.Before;
+import com.fasterxml.jackson.core.JsonFactory;
+import com.fasterxml.jackson.core.JsonParser;
 import org.junit.BeforeClass;
 import org.junit.Test;
 
@@ -57,4 +58,25 @@ public void testMissingContentType() throws Exception {
         final APIGatewayProxyResponseEvent result = app.handleRequest(input, context);
         assertEquals(result.getStatusCode().intValue(), 200);
     }
+
+    @Test
+    public void testApplicationJsonResponse() throws Exception {
+        final HashMap<String, String> inputHeaders = new HashMap<>();
+        inputHeaders.put("Accept", "application/json");
+        APIGatewayProxyRequestEvent input = new APIGatewayProxyRequestEvent()
+                .withHttpMethod("POST")
+                .withHeaders(Collections.unmodifiableMap(inputHeaders))
+                .withBody("My name is Lambda Function and I approve this test.");
+        final TestContext context = new TestContext();
+        final APIGatewayProxyResponseEvent result = app.handleRequest(input, context);
+        assertEquals(result.getStatusCode().intValue(), 200);
+
+        // Ensure we get back application/json back
+        assertEquals(result.getHeaders().get("Content-Type"), "application/json");
+        final JsonFactory factory = new JsonFactory();
+        final JsonParser parser = factory.createParser(result.getBody());
+        while (!parser.isClosed()) {
+            parser.nextToken();
+        }
+    }
 }