supply-debug-log (apache#9239)

### Motivation
When in debug log, this doesn't provide useful informations
![image](https://user-images.githubusercontent.com/12933197/105045964-74c26c80-5aa3-11eb-9fa5-dcef81213ea1.png)


### Modifications
- add the toString method of OpAddEntry
- fix some java doc problems

managed-ledger/src/main/java/org/apache/bookkeeper/mledger/impl/EntryCacheImpl.java

@@ -97,7 +97,7 @@ public boolean insert(EntryImpl entry) {
                     entry.getLength());
         }
 
-        ByteBuf cachedData = null;
+        ByteBuf cachedData;
         if (copyEntries) {
             cachedData = copyEntry(entry);
             if (cachedData == null) {

managed-ledger/src/main/java/org/apache/bookkeeper/mledger/impl/EntryCacheManager.java

@@ -60,9 +60,7 @@ public class EntryCacheManager {
 
     private static final double evictionTriggerThresholdPercent = 0.98;
 
-    /**
-     *
-     */
+
     public EntryCacheManager(ManagedLedgerFactoryImpl factory) {
         this.maxSize = factory.getConfig().getMaxCacheSize();
         this.evictionTriggerThreshold = (long) (maxSize * evictionTriggerThresholdPercent);

managed-ledger/src/main/java/org/apache/bookkeeper/mledger/impl/EntryImpl.java

@@ -18,6 +18,7 @@
  */
 package org.apache.bookkeeper.mledger.impl;
 
+import com.google.common.annotations.VisibleForTesting;
 import com.google.common.collect.ComparisonChain;
 
 import io.netty.buffer.ByteBuf;
@@ -56,7 +57,7 @@ public static EntryImpl create(LedgerEntry ledgerEntry) {
         return entry;
     }
 
-    // Used just for tests
+    @VisibleForTesting
     public static EntryImpl create(long ledgerId, long entryId, byte[] data) {
         EntryImpl entry = RECYCLER.get();
         entry.timestamp = System.nanoTime();

managed-ledger/src/main/java/org/apache/bookkeeper/mledger/impl/ManagedLedgerFactoryMBeanImpl.java

@@ -64,8 +64,6 @@ public void recordCacheEviction() {
         cacheEvictions.recordEvent();
     }
 
-    // //
-
     @Override
     public int getNumberOfManagedLedgers() {
         return factory.ledgers.size();

managed-ledger/src/main/java/org/apache/bookkeeper/mledger/impl/ManagedLedgerImpl.java

@@ -197,7 +197,7 @@ public class ManagedLedgerImpl implements ManagedLedger, CreateCallback {
     private long lastLedgerCreationInitiationTimestamp = 0;
 
     private static final Random random = new Random(System.currentTimeMillis());
-    private long maximumRolloverTimeMs;
+    private final long maximumRolloverTimeMs;
     protected final Supplier<Boolean> mlOwnershipChecker;
 
     volatile PositionImpl lastConfirmedEntry;
@@ -265,8 +265,6 @@ public enum PositionBound {
     @VisibleForTesting
     Map<String, byte[]> createdLedgerCustomMetadata;
 
-    // //////////////////////////////////////////////////////////////////////
-
     public ManagedLedgerImpl(ManagedLedgerFactoryImpl factory, BookKeeper bookKeeper, MetaStore store,
             ManagedLedgerConfig config, OrderedScheduler scheduledExecutor, OrderedExecutor orderedExecutor,
             final String name) {

managed-ledger/src/main/java/org/apache/bookkeeper/mledger/impl/ManagedLedgerOfflineBacklog.java

@@ -51,8 +51,8 @@ public class ManagedLedgerOfflineBacklog {
     private final byte[] password;
     private final BookKeeper.DigestType digestType;
     private static final int META_READ_TIMEOUT_SECONDS = 60;
-    private boolean accurate = false;
-    private String brokerName;
+    private final boolean accurate;
+    private final String brokerName;
 
     public ManagedLedgerOfflineBacklog(DigestType digestType, byte[] password, String brokerName,
             boolean accurate) {

managed-ledger/src/main/java/org/apache/bookkeeper/mledger/impl/OpAddEntry.java

@@ -18,17 +18,11 @@
  */
 package org.apache.bookkeeper.mledger.impl;
 
-import static com.google.common.base.Preconditions.checkArgument;
-
 import io.netty.buffer.ByteBuf;
 import io.netty.util.Recycler;
 import io.netty.util.Recycler.Handle;
-
-import java.util.concurrent.TimeUnit;
-import java.util.concurrent.atomic.AtomicLongFieldUpdater;
-import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
-
 import io.netty.util.ReferenceCountUtil;
+import lombok.extern.slf4j.Slf4j;
 import org.apache.bookkeeper.client.AsyncCallback.AddCallback;
 import org.apache.bookkeeper.client.AsyncCallback.CloseCallback;
 import org.apache.bookkeeper.client.BKException;
@@ -37,13 +31,18 @@
 import org.apache.bookkeeper.mledger.ManagedLedgerException;
 import org.apache.bookkeeper.mledger.util.SafeRun;
 import org.apache.bookkeeper.util.SafeRunnable;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
+
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicLongFieldUpdater;
+import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
+
+import static com.google.common.base.Preconditions.checkArgument;
 
 /**
  * Handles the life-cycle of an addEntry() operation.
  *
  */
+@Slf4j
 public class OpAddEntry extends SafeRunnable implements AddCallback, CloseCallback {
     protected ManagedLedgerImpl ml;
     LedgerHandle ledger;
@@ -220,7 +219,7 @@ public void closeComplete(int rc, LedgerHandle lh, Object ctx) {
                 lh.getId());
 
         if (rc == BKException.Code.OK) {
-            log.debug("Successfuly closed ledger {}", lh.getId());
+            log.debug("Successfully closed ledger {}", lh.getId());
         } else {
             log.warn("Error when closing ledger {}. Status={}", lh.getId(), BKException.getMessage(rc));
         }
@@ -333,5 +332,15 @@ public void recycle() {
         recyclerHandle.recycle(this);
     }
 
-    private static final Logger log = LoggerFactory.getLogger(OpAddEntry.class);
+    @Override
+    public String toString() {
+        return "OpAddEntry{" +
+                "mlName" + ml.getName() +
+                "ledgerId=" + ledger.getId() +
+                ", entryId=" + entryId +
+                ", startTime=" + startTime +
+                ", dataLength=" + dataLength +
+                '}';
+    }
+
 }