java_gen: add optional instrumentation
diff --git a/java_gen/pre-written/pom.xml b/java_gen/pre-written/pom.xml
index 5715704..e93b6f5 100644
--- a/java_gen/pre-written/pom.xml
+++ b/java_gen/pre-written/pom.xml
@@ -55,6 +55,11 @@
             <artifactId>guava</artifactId>
             <version>15.0</version>
         </dependency>
+        <dependency>
+            <groupId>org.slf4j</groupId>
+            <artifactId>slf4j-api</artifactId>
+            <version>1.7.5</version>
+        </dependency>
     </dependencies>
     <build>
         <plugins>