feat: add a main class for jar build sanity checking

Co-authored-by: aider (anthropic/claude-sonnet-4-20250514) <aider@aider.chat>

Author: realark

build.gradle

@@ -192,7 +192,8 @@ jar {
     attributes(
       'Implementation-Title': 'Braintrust Java SDK',
       'Implementation-Version': version,
-      'Implementation-Vendor': 'Braintrust'
+      'Implementation-Vendor': 'Braintrust',
+      'Main-Class': 'dev.braintrust.trace.SDKMain'
     )
   }
 }
@@ -273,14 +274,30 @@ task validateJavaVersion {
         "from ${System.getProperty('java.home')}"
       )
     }
+    // println "✓ Using Java ${currentVersion} from ${System.getProperty('java.home')}"
+  }
+}
+
+
+// Task to test the jar by running it
+task testJar(type: Exec) {
+  description = 'Test the jar by running it and fail build if non-zero exit code'
+  group = 'verification'
+  dependsOn jar
 
-    println "✓ Using Java ${currentVersion} from ${System.getProperty('java.home')}"
+  commandLine 'java', '-jar', jar.archiveFile.get().asFile.absolutePath
+
+  doFirst {
+    // println "Testing jar: ${jar.archiveFile.get().asFile.absolutePath}"
   }
 }
 
 // Run validation before compilation
 compileJava.dependsOn validateJavaVersion
 
+// Run jar test as part of check task
+check.dependsOn testJar
+
 // Task to install git hooks
 task installGitHooks(type: Exec) {
   description = 'Install git hooks for code formatting'

src/main/java/dev/braintrust/trace/BraintrustTracing.java

@@ -17,7 +17,6 @@
 import io.opentelemetry.sdk.trace.export.BatchSpanProcessor;
 import io.opentelemetry.semconv.resource.attributes.ResourceAttributes;
 import java.time.Duration;
-import java.util.Properties;
 import java.util.concurrent.TimeUnit;
 import java.util.stream.Stream;
 import javax.annotation.Nonnull;
@@ -32,7 +31,7 @@ public final class BraintrustTracing {
     public static final String PARENT_KEY = "braintrust.parent";
     static final String OTEL_SERVICE_NAME = "braintrust-app";
     static final String INSTRUMENTATION_NAME = "braintrust-java";
-    static final String INSTRUMENTATION_VERSION = loadVersionFromProperties();
+    static final String INSTRUMENTATION_VERSION = SDKMain.loadVersionFromProperties();
 
     /**
      * Quick start method that sets up global OpenTelemetry with Braintrust defaults. <br>
@@ -88,15 +87,7 @@ public static void enable(
         final Duration exportInterval = Duration.ofSeconds(5);
         final int maxQueueSize = 2048;
         final int maxExportBatchSize = 512;
-        log.info(
-                "Initializing Braintrust OpenTelemetry with service={}, instrumentation-name={},"
-                        + " instrumentation-version={}, jvm-version={}, jvm-vendor={}, jvm-name={}",
-                OTEL_SERVICE_NAME,
-                INSTRUMENTATION_NAME,
-                INSTRUMENTATION_VERSION,
-                System.getProperty("java.runtime.version"),
-                System.getProperty("java.vendor"),
-                System.getProperty("java.vm.name"));
+        log.info(sdkInfoLogMessage());
 
         // Create resource first so BraintrustSpanProcessor can access service.name
         var resourceBuilder =
@@ -164,14 +155,15 @@ public static Tracer getTracer(OpenTelemetry openTelemetry) {
         return openTelemetry.getTracer(INSTRUMENTATION_NAME, INSTRUMENTATION_VERSION);
     }
 
-    private static String loadVersionFromProperties() {
-        try (var is = BraintrustTracing.class.getResourceAsStream("/braintrust.properties")) {
-            var props = new Properties();
-            props.load(is);
-            return props.getProperty("sdk.version");
-        } catch (Exception e) {
-            throw new RuntimeException("unable to determine sdk version", e);
-        }
+    private static String sdkInfoLogMessage() {
+        return "Initializing Braintrust OpenTelemetry with service=%s, instrumentation-name=%s, instrumentation-version=%s, jvm-version=%s, jvm-vendor=%s, jvm-name=%s"
+                .formatted(
+                        OTEL_SERVICE_NAME,
+                        INSTRUMENTATION_NAME,
+                        INSTRUMENTATION_VERSION,
+                        System.getProperty("java.runtime.version"),
+                        System.getProperty("java.vendor"),
+                        System.getProperty("java.vm.name"));
     }
 
     private BraintrustTracing() {}

src/main/java/dev/braintrust/trace/SDKMain.java

@@ -0,0 +1,29 @@
+package dev.braintrust.trace;
+
+import java.util.Properties;
+
+class SDKMain {
+    /**
+     * Called by the build system to verify internals of the SDK. Prints sdk version to stdout.
+     *
+     * <p>Be mindful of classloading here. Otel is not shipped in the jar, so referencing otel
+     * classes directly or indirectly will fail the build with a NoClassDefFound error.
+     */
+    public static void main(String... args) {
+        var sdkVersion = loadVersionFromProperties();
+        if (null == sdkVersion || sdkVersion.isEmpty()) {
+            throw new RuntimeException("sdk version not found: %s".formatted(sdkVersion));
+        }
+        System.out.println(sdkVersion);
+    }
+
+    static String loadVersionFromProperties() {
+        try (var is = SDKMain.class.getResourceAsStream("/braintrust.properties")) {
+            var props = new Properties();
+            props.load(is);
+            return props.getProperty("sdk.version");
+        } catch (Exception e) {
+            throw new RuntimeException("unable to determine sdk version", e);
+        }
+    }
+}