Add exception handler api

src/main/java/com/brsanthu/googleanalytics/GoogleAnalyticsConfig.java

@@ -52,6 +52,7 @@ public class GoogleAnalyticsConfig {
     private boolean discoverRequestParameters = true;
     private boolean gatherStats = false;
     private RequestParameterDiscoverer requestParameterDiscoverer = new DefaultRequestParameterDiscoverer();
+    private GoogleAnalyticsExceptionHandler exceptionHandler;
 
     public RequestParameterDiscoverer getRequestParameterDiscoverer() {
         return requestParameterDiscoverer;
@@ -125,7 +126,7 @@ public GoogleAnalyticsConfig setDeriveSystemParameters(boolean deriveSystemPrope
      * </p>
      */
     public GoogleAnalyticsConfig setDiscoverRequestParameters(boolean discoverSystemParameters) {
-        this.discoverRequestParameters = discoverSystemParameters;
+        discoverRequestParameters = discoverSystemParameters;
         return this;
     }
 
@@ -404,4 +405,17 @@ public GoogleAnalyticsConfig setBatchSize(int batchSize) {
         return this;
     }
 
+    public GoogleAnalyticsExceptionHandler getExceptionHandler() {
+        return exceptionHandler;
+    }
+
+    /**
+     * Set an exception handler which will implement the behavior in case of any exceptions. If not set, default
+     * behavior is to log a warning message.
+     */
+    public GoogleAnalyticsConfig setExceptionHandler(GoogleAnalyticsExceptionHandler exceptionHandler) {
+        this.exceptionHandler = exceptionHandler;
+        return this;
+    }
+
 }

src/main/java/com/brsanthu/googleanalytics/GoogleAnalyticsExceptionHandler.java

@@ -0,0 +1,22 @@
+package com.brsanthu.googleanalytics;
+
+/**
+ * Models a handler which can be used to handle exceptions thrown while sending GA requests to google. This can be set
+ * as config parameter as below.
+ *
+ * <pre>
+ *  GoogleAnalytics propagatingGa = GoogleAnalytics.builder()withConfig(
+ *      new GoogleAnalyticsConfig().setExceptionHandler(new YourExceptionHandler())
+ *  ).build();
+ * </pre>
+ *
+ * <p>
+ * Library comes with following implementations.
+ * <ul>
+ * <li>{@link PropagatingExceptionHandler} which propagates the exceptions.
+ * </ul>
+ */
+@FunctionalInterface
+public interface GoogleAnalyticsExceptionHandler {
+    void handle(Throwable t);
+}

src/main/java/com/brsanthu/googleanalytics/PropagatingExceptionHandler.java

@@ -0,0 +1,16 @@
+package com.brsanthu.googleanalytics;
+
+/**
+ * Exception handler which propagates the exceptions instead of just logging.
+ */
+public class PropagatingExceptionHandler implements GoogleAnalyticsExceptionHandler {
+
+    @Override
+    public void handle(Throwable t) {
+        if (t instanceof RuntimeException) {
+            throw (RuntimeException) t;
+        }
+
+        throw new GoogleAnalyticsException(t);
+    }
+}

src/main/java/com/brsanthu/googleanalytics/internal/GoogleAnalyticsImpl.java

@@ -105,8 +105,12 @@ public GoogleAnalyticsResponse post(GoogleAnalyticsRequest<?> gaReq) {
                 response = postSingle(gaReq);
             }
 
-        } catch (Exception e) {
-            logger.warn("Exception while sending the Google Analytics tracker request " + gaReq, e);
+        } catch (Throwable e) {
+            if (config.getExceptionHandler() != null) {
+                config.getExceptionHandler().handle(e);
+            } else {
+                logger.warn("Exception while sending the Google Analytics tracker request " + gaReq, e);
+            }
         }
 
         return response;
@@ -217,7 +221,7 @@ protected void processParameters(GoogleAnalyticsRequest<?> request, HttpRequest
      * @param postParms
      */
     protected void processCustomDimensionParameters(GoogleAnalyticsRequest<?> request, HttpRequest req) {
-        Map<String, String> customDimParms = new HashMap<String, String>();
+        Map<String, String> customDimParms = new HashMap<>();
         for (String defaultCustomDimKey : defaultRequest.customDimensions().keySet()) {
             customDimParms.put(defaultCustomDimKey, defaultRequest.customDimensions().get(defaultCustomDimKey));
         }
@@ -239,7 +243,7 @@ protected void processCustomDimensionParameters(GoogleAnalyticsRequest<?> reques
      * @param postParms
      */
     protected void processCustomMetricParameters(GoogleAnalyticsRequest<?> request, HttpRequest req) {
-        Map<String, String> customMetricParms = new HashMap<String, String>();
+        Map<String, String> customMetricParms = new HashMap<>();
         for (String defaultCustomMetricKey : defaultRequest.custommMetrics().keySet()) {
             customMetricParms.put(defaultCustomMetricKey, defaultRequest.custommMetrics().get(defaultCustomMetricKey));
         }

src/test/java/com/brsanthu/googleanalytics/GoogleAnalyticsTest.java

@@ -132,4 +132,22 @@ public void testUserDetails() throws Exception {
         assertEquals("12345", response.getRequestParams().get("cid"));
         assertEquals("user2", response.getRequestParams().get("uid"));
     }
+
+    @Test
+    void testExceptionHandler() throws Exception {
+        HttpClient client = mock(HttpClient.class);
+        when(client.post(ArgumentMatchers.any())).thenThrow(new RuntimeException("Testing Exception"));
+
+        GoogleAnalytics ga = GoogleAnalytics.builder().withHttpClient(client).withConfig(new GoogleAnalyticsConfig()).build();
+
+        // Since default behavior is to log exception, this function call should work fine.
+        ga.screenView().send();
+
+        GoogleAnalytics propagatingGa = GoogleAnalytics.builder().withHttpClient(client).withConfig(
+                new GoogleAnalyticsConfig().setExceptionHandler(new PropagatingExceptionHandler())).build();
+
+        assertThatThrownBy(() -> propagatingGa.screenView().send()).hasMessage("Testing Exception");
+
+        assertThatThrownBy(() -> propagatingGa.screenView().sendAsync().get()).hasMessageContaining("Testing Exception");
+    }
 }