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

@@ -56,57 +56,7 @@ 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)
-                        .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)
-                        .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();
-            } 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();
-            }
-            channelPool.add(channel);
+            channelPool.add(createChannelBuilder(host, grpcPort, sslContext, cn).build());
         }
 
         // Get filer configuration using first channel
@@ -120,6 +70,34 @@ public class FilerGrpcClient {
 
     }
 
+    /**
+     * 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)
+                .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);
+
+        if (sslContext == null) {
+            builder.usePlaintext();
+        } else {
+            builder.negotiationType(NegotiationType.TLS).sslContext(sslContext);
+            if (!cn.isEmpty()) {
+                builder.overrideAuthority(cn);
+            }
+        }
+        return builder;
+    }
+
     // Get a channel from the pool using round-robin
     private ManagedChannel getChannel() {
         int raw = channelIndex.getAndIncrement();