refactor: eliminate code duplication in channel creation

- Extract common gRPC channel configuration to createChannelBuilder() method
- Reduce code duplication from 3 branches to single configuration
- Improve maintainability by centralizing channel settings
- Add Javadoc for the new helper method

other/java/client/src/main/java/seaweedfs/client/FilerGrpcClient.java

@@ -56,25 +56,26 @@ public class FilerGrpcClient {
         channelPool = new ArrayList<>(CHANNEL_POOL_SIZE);
 
         for (int i = 0; i < CHANNEL_POOL_SIZE; i++) {
-            ManagedChannel channel;
-            if (sslContext == null) {
-                // Use NettyChannelBuilder with optimized HTTP/2 settings
-                channel = NettyChannelBuilder.forAddress(host, grpcPort)
-                        .usePlaintext()
-                        .maxInboundMessageSize(1024 * 1024 * 1024)
-                        .maxInboundMetadataSize(1024 * 1024)
-                        .flowControlWindow(16 * 1024 * 1024)
-                        .initialFlowControlWindow(16 * 1024 * 1024)
-                        .maxHeaderListSize(16 * 1024 * 1024)
-                        .keepAliveTime(30, TimeUnit.SECONDS)
-                        .keepAliveTimeout(10, TimeUnit.SECONDS)
-                        .keepAliveWithoutCalls(true)
-                        .withOption(io.grpc.netty.shaded.io.netty.channel.ChannelOption.SO_RCVBUF, 16 * 1024 * 1024)
-                        .withOption(io.grpc.netty.shaded.io.netty.channel.ChannelOption.SO_SNDBUF, 16 * 1024 * 1024)
-                        .build();
-            } else if (cn.isEmpty()) {
-                // For TLS, we still need NettyChannelBuilder
-                channel = NettyChannelBuilder.forAddress(host, grpcPort)
+            channelPool.add(createChannelBuilder(host, grpcPort, sslContext, cn).build());
+        }
+
+        // Get filer configuration using first channel
+        FilerProto.GetFilerConfigurationResponse filerConfigurationResponse = SeaweedFilerGrpc
+                .newBlockingStub(channelPool.get(0)).getFilerConfiguration(
+                        FilerProto.GetFilerConfigurationRequest.newBuilder().build());
+        cipher = filerConfigurationResponse.getCipher();
+        collection = filerConfigurationResponse.getCollection();
+        replication = filerConfigurationResponse.getReplication();
+        randomClientId = new Random().nextInt();
+
+    }
+
+    /**
+     * Creates a NettyChannelBuilder with common gRPC configuration.
+     * Supports plaintext and TLS modes with optional authority override.
+     */
+    private NettyChannelBuilder createChannelBuilder(String host, int grpcPort, SslContext sslContext, String cn) {
+        NettyChannelBuilder builder = NettyChannelBuilder.forAddress(host, grpcPort)
                 .maxInboundMessageSize(1024 * 1024 * 1024)
                 .maxInboundMetadataSize(1024 * 1024)
                 .flowControlWindow(16 * 1024 * 1024)
@@ -83,41 +84,18 @@ public class FilerGrpcClient {
                 .keepAliveTime(30, TimeUnit.SECONDS)
                 .keepAliveTimeout(10, TimeUnit.SECONDS)
                 .keepAliveWithoutCalls(true)
-                        .negotiationType(NegotiationType.TLS)
-                        .sslContext(sslContext)
                 .withOption(io.grpc.netty.shaded.io.netty.channel.ChannelOption.SO_RCVBUF, 16 * 1024 * 1024)
-                        .withOption(io.grpc.netty.shaded.io.netty.channel.ChannelOption.SO_SNDBUF, 16 * 1024 * 1024)
-                        .build();
+                .withOption(io.grpc.netty.shaded.io.netty.channel.ChannelOption.SO_SNDBUF, 16 * 1024 * 1024);
+
+        if (sslContext == null) {
+            builder.usePlaintext();
         } else {
-                // For TLS with custom authority
-                channel = NettyChannelBuilder.forAddress(host, grpcPort)
-                        .maxInboundMessageSize(1024 * 1024 * 1024)
-                        .maxInboundMetadataSize(1024 * 1024)
-                        .flowControlWindow(16 * 1024 * 1024)
-                        .initialFlowControlWindow(16 * 1024 * 1024)
-                        .maxHeaderListSize(16 * 1024 * 1024)
-                        .keepAliveTime(30, TimeUnit.SECONDS)
-                        .keepAliveTimeout(10, TimeUnit.SECONDS)
-                        .keepAliveWithoutCalls(true)
-                        .negotiationType(NegotiationType.TLS)
-                        .overrideAuthority(cn)
-                        .sslContext(sslContext)
-                        .withOption(io.grpc.netty.shaded.io.netty.channel.ChannelOption.SO_RCVBUF, 16 * 1024 * 1024)
-                        .withOption(io.grpc.netty.shaded.io.netty.channel.ChannelOption.SO_SNDBUF, 16 * 1024 * 1024)
-                        .build();
+            builder.negotiationType(NegotiationType.TLS).sslContext(sslContext);
+            if (!cn.isEmpty()) {
+                builder.overrideAuthority(cn);
             }
-            channelPool.add(channel);
         }
-
-        // Get filer configuration using first channel
-        FilerProto.GetFilerConfigurationResponse filerConfigurationResponse = SeaweedFilerGrpc
-                .newBlockingStub(channelPool.get(0)).getFilerConfiguration(
-                        FilerProto.GetFilerConfigurationRequest.newBuilder().build());
-        cipher = filerConfigurationResponse.getCipher();
-        collection = filerConfigurationResponse.getCollection();
-        replication = filerConfigurationResponse.getReplication();
-        randomClientId = new Random().nextInt();
-
+        return builder;
     }
 
     // Get a channel from the pool using round-robin