chore(batch): replace System.out.println with SLF4J logging

Author: bevzzz

pom.xml

@@ -170,9 +170,8 @@
     </dependency>
     <dependency>
         <groupId>org.slf4j</groupId>
-        <artifactId>slf4j-nop</artifactId>
+        <artifactId>slf4j-api</artifactId>
         <version>${slf4j.version}</version>
-        <scope>test</scope>
     </dependency>
     <dependency>
       <groupId>org.mock-server</groupId>
@@ -537,5 +536,13 @@
         <artifactId>central-publishing-maven-plugin</artifactId>
       </plugin>
     </plugins>
-  </build>
+    </build>
+    <profiles>
+      <profile>
+        <id>debug</id>
+        <properties>
+          <argLine>-Djava.util.logging.config.file=src/test/resources/logging.properties</argLine>
+        </properties>
+      </profile>
+    </profiles>
 </project>

src/main/java/io/weaviate/client6/v1/api/collections/batch/Batch.java

@@ -332,6 +332,24 @@ public int compare(BacklogItem a, BacklogItem b) {
     }
   }
 
+  /** Get total number of items in the batch. */
+  synchronized int size() {
+    return buffer.size() + backlog.size();
+  }
+
+  /** Get current size of the batch in bytes. */
+  synchronized long sizeBytes() {
+    return sizeBytes;
+  }
+
+  synchronized int maxSizeBytes() {
+    return maxSizeBytes;
+  }
+
+  synchronized int maxSize() {
+    return maxSize;
+  }
+
   /** Asserts the invariants of this class. */
   private synchronized void checkInvariants() {
     assert maxSize > 0 : "non-positive maxSize";