refactor(java): resilient to network/http errors (#320)

flipt-java/src/main/java/io/flipt/api/FliptClient.java

@@ -2,9 +2,11 @@
 
 import io.flipt.api.authentication.AuthenticationStrategy;
 import io.flipt.api.evaluation.Evaluation;
+import io.flipt.api.evaluation.EvaluationException;
 import java.time.Duration;
 import java.util.HashMap;
 import java.util.Map;
+import java.util.function.Consumer;
 import okhttp3.OkHttpClient;
 
 public class FliptClient {
@@ -18,6 +20,7 @@ private FliptClient(FliptClientBuilder builder) {
             .baseURL(builder.baseURL)
             .authenticationStrategy(builder.authenticationStrategy)
             .headers(builder.headers)
+            .setUnhandledExceptionProcessor(builder.unhandledExceptionProcessor)
             .build();
   }
 
@@ -31,10 +34,15 @@ public static FliptClientBuilder builder() {
 
   public static final class FliptClientBuilder {
 
+    private static final Consumer<EvaluationException> nullProcessor =
+        new Consumer<EvaluationException>() {
+          public void accept(EvaluationException e) {}
+        };
     private String baseURL = "http://localhost:8080";
     private AuthenticationStrategy authenticationStrategy;
     private Map<String, String> headers = new HashMap<>();
     private Duration timeout = Duration.ofSeconds(60);
+    private Consumer<EvaluationException> unhandledExceptionProcessor = nullProcessor;
 
     private FliptClientBuilder() {}
 
@@ -63,6 +71,12 @@ public FliptClientBuilder timeout(int timeout) {
       return this;
     }
 
+    public FliptClientBuilder setUnhandledExceptionProcessor(
+        Consumer<EvaluationException> processor) {
+      this.unhandledExceptionProcessor = processor;
+      return this;
+    }
+
     public FliptClient build() {
       return new FliptClient(this);
     }

flipt-java/src/main/java/io/flipt/api/evaluation/Evaluation.java

@@ -13,6 +13,7 @@
 import java.net.URISyntaxException;
 import java.net.URL;
 import java.util.Map;
+import java.util.function.Consumer;
 import okhttp3.*;
 
 public class Evaluation {
@@ -21,6 +22,7 @@ public class Evaluation {
   private final AuthenticationStrategy authenticationStrategy;
   private final Map<String, String> headers;
   private final ObjectMapper objectMapper;
+  private final Consumer<EvaluationException> unhandledExceptionProcessor;
 
   private Evaluation(EvaluationBuilder builder) {
     this.httpClient = builder.httpClient;
@@ -32,6 +34,7 @@ private Evaluation(EvaluationBuilder builder) {
             .addModule(new Jdk8Module())
             .disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES)
             .build();
+    this.unhandledExceptionProcessor = builder.unhandledExceptionProcessor;
   }
 
   public static EvaluationBuilder builder() {
@@ -43,6 +46,7 @@ public static class EvaluationBuilder {
     private String baseURL;
     private AuthenticationStrategy authenticationStrategy;
     private Map<String, String> headers;
+    private Consumer<EvaluationException> unhandledExceptionProcessor;
 
     private EvaluationBuilder() {}
 
@@ -66,21 +70,90 @@ public EvaluationBuilder headers(Map<String, String> headers) {
       return this;
     }
 
+    public EvaluationBuilder setUnhandledExceptionProcessor(
+        Consumer<EvaluationException> processor) {
+      this.unhandledExceptionProcessor = processor;
+      return this;
+    }
+
     public Evaluation build() {
       return new Evaluation(this);
     }
   }
 
+  /**
+   * Evaluates a variant flag based on the {@link EvaluationRequest}.
+   *
+   * @param request the {@link EvaluationRequest}
+   * @return a {@link VariantEvaluationResponse} containing the evaluation result
+   * @throws EvaluationException if an error occurs during the process, such as a network issue or
+   *     invalid request
+   */
   public VariantEvaluationResponse evaluateVariant(EvaluationRequest request)
       throws EvaluationException {
     return this.makeRequest(request, "/evaluate/v1/variant", VariantEvaluationResponse.class);
   }
 
+  /**
+   * Evaluates a variant flag based on the {@link EvaluationRequest}. If the evaluation fails due to
+   * an {@link EvaluationException}, the specified fallback string will be returned. In the event of
+   * an exception, the exception is passed to an unhandled exception processor for further handling
+   * or logging.
+   *
+   * @param request the {@link EvaluationRequest}
+   * @param fallback the string value to return in case of an evaluation error
+   * @return the variant key if the evaluation is successful; otherwise, returns the fallback value
+   */
+  public String variantValue(EvaluationRequest request, String fallback) {
+    try {
+      return this.evaluateVariant(request).getVariantKey();
+    } catch (EvaluationException e) {
+      this.unhandledExceptionProcessor.accept(e);
+    }
+
+    return fallback;
+  }
+
+  /**
+   * Evaluates a boolean flag based on the {@link EvaluationRequest}.
+   *
+   * @param request the {@link EvaluationRequest}
+   * @return a {@link BooleanEvaluationResponse} containing the evaluation result
+   * @throws EvaluationException if an error occurs during the process, such as a network issue or
+   *     invalid request
+   */
   public BooleanEvaluationResponse evaluateBoolean(EvaluationRequest request)
       throws EvaluationException {
     return this.makeRequest(request, "/evaluate/v1/boolean", BooleanEvaluationResponse.class);
   }
 
+  /**
+   * Evaluates a boolean value based on the {@link EvaluationRequest}. If the evaluation fails due
+   * to an {@link EvaluationException}, the specified fallback boolean value will be returned. In
+   * the event of an exception, the exception is passed to an unhandled exception processor for
+   * further handling or logging.
+   *
+   * @param request the {@link EvaluationRequest}
+   * @param fallback the boolean value to return in case of an evaluation error
+   * @return the value if the evaluation is successful; otherwise, returns the fallback value
+   */
+  public boolean booleanValue(EvaluationRequest request, boolean fallback) {
+    try {
+      return this.evaluateBoolean(request).isEnabled();
+    } catch (EvaluationException e) {
+      this.unhandledExceptionProcessor.accept(e);
+    }
+    return fallback;
+  }
+
+  /**
+   * Evaluates a batch of flags based on the {@link BatchEvaluationRequest}.
+   *
+   * @param request the {@link BatchEvaluationRequest}
+   * @return a {@link BatchEvaluationResponse} containing the evaluation results
+   * @throws EvaluationException if an error occurs during the evaluation process, such as a network
+   *     issue or invalid request
+   */
   public BatchEvaluationResponse evaluateBatch(BatchEvaluationRequest request)
       throws EvaluationException {
     return this.makeRequest(request, "/evaluate/v1/batch", BatchEvaluationResponse.class);

flipt-java/src/test/java/TestFliptClient.java

@@ -30,18 +30,25 @@ void testVariantEvaluation() {
     Map<String, String> context = new HashMap<>();
     context.put("fizz", "buzz");
 
+    EvaluationRequest req =
+        new EvaluationRequest("default", "flag1", "entity", context, Optional.empty());
+
     VariantEvaluationResponse variant =
-        Assertions.assertDoesNotThrow(
-            () ->
-                fc.evaluation()
-                    .evaluateVariant(
-                        new EvaluationRequest(
-                            "default", "flag1", "entity", context, Optional.empty())));
+        Assertions.assertDoesNotThrow(() -> fc.evaluation().evaluateVariant(req));
     Assertions.assertTrue(variant.isMatch());
     Assertions.assertEquals("flag1", variant.getFlagKey());
     Assertions.assertEquals("MATCH_EVALUATION_REASON", variant.getReason().toString());
     Assertions.assertEquals("variant1", variant.getVariantKey());
     Assertions.assertEquals("segment1", variant.getSegmentKeys().get(0));
+
+    Assertions.assertEquals("variant1", fc.evaluation().variantValue(req, "fallback"));
+
+    Assertions.assertEquals(
+        "fallback",
+        fc.evaluation()
+            .variantValue(
+                new EvaluationRequest("default", "flag-none", "entity", context, Optional.empty()),
+                "fallback"));
   }
 
   @Test
@@ -67,17 +74,21 @@ void testBooleanEvaluation() {
     Map<String, String> context = new HashMap<>();
     context.put("fizz", "buzz");
 
+    EvaluationRequest req =
+        new EvaluationRequest("default", "flag_boolean", "entity", context, Optional.empty());
     BooleanEvaluationResponse booleanEvaluation =
-        Assertions.assertDoesNotThrow(
-            () ->
-                fc.evaluation()
-                    .evaluateBoolean(
-                        new EvaluationRequest(
-                            "default", "flag_boolean", "entity", context, Optional.empty())));
+        Assertions.assertDoesNotThrow(() -> fc.evaluation().evaluateBoolean(req));
 
     Assertions.assertTrue(booleanEvaluation.isEnabled());
     Assertions.assertEquals("flag_boolean", booleanEvaluation.getFlagKey());
     Assertions.assertEquals("MATCH_EVALUATION_REASON", booleanEvaluation.getReason().toString());
+
+    Assertions.assertTrue(fc.evaluation().booleanValue(req, false));
+    Assertions.assertTrue(
+        fc.evaluation()
+            .booleanValue(
+                new EvaluationRequest("default", "flag-none", "entity", context, Optional.empty()),
+                true));
   }
 
   @Test