dubbo 3.2.0 的filterChain 的核心类是DefaultFilterChainBuilder 。

Builder

public class DefaultFilterChainBuilder implements FilterChainBuilder {

的buildInvokerChain函数

对于consumer refer

 @Override
    public <T> Invoker<T> buildInvokerChain(final Invoker<T> originalInvoker, String key, String group) 

的参数如上图，如果是provider，group值不同。

dubbo 通group识别出带有@Activate annotation的filter，并按照order进行排序。

/**
 * TraceFilter
 */
@Activate(group = CommonConstants.PROVIDER)
public class TraceFilter implements Filter {
   
@Activate(group = CONSUMER, order = Integer.MIN_VALUE)
public class ConsumerContextFilter implements ClusterFilter, ClusterFilter.Listener {
  
  @Activate(group = CONSUMER,onClass = "org.apache.dubbo.metrics.collector.DefaultMetricsCollector")
public class MetricsClusterFilter implements ClusterFilter, BaseFilter.Listener, ScopeModelAware {
  @Activate(group = CONSUMER, order = -1, onClass = "io.micrometer.observation.NoopObservationRegistry")
public class ObservationSenderFilter implements ClusterFilter, BaseFilter.Listener, ScopeModelAware {

consumer 默认的filter如下

FutureFilter是异步future调用的处理

@Override
public void onResponse(Result result, Invoker<?> invoker, Invocation invocation) {
if (result.hasException()) {
fireThrowCallback(invoker, invocation, result.getException());
} else {
fireReturnCallback(invoker, invocation, result.getValue());
}
}

@Override
public void onError(Throwable t, Invoker<?> invoker, Invocation invocation) {
    fireThrowCallback(invoker, invocation, t);
}

后面3个都是可观察性相关。

调用过程

stack信息

buildClusterInvokerChain:86, DefaultFilterChainBuilder (org.apache.dubbo.rpc.cluster.filter)
<init>:87, AbstractCluster$ClusterFilterInvoker (org.apache.dubbo.rpc.cluster.support.wrapper)
buildClusterInterceptors:47, AbstractCluster (org.apache.dubbo.rpc.cluster.support.wrapper)
join:61, AbstractCluster (org.apache.dubbo.rpc.cluster.support.wrapper)
join:39, MockClusterWrapper (org.apache.dubbo.rpc.cluster.support.wrapper)
join:40, ScopeClusterWrapper (org.apache.dubbo.rpc.cluster.support.wrapper)
doCreateInvoker:583, RegistryProtocol  

类MockClusterWrapper的

@Override
public <T> Invoker<T> join(Directory<T> directory, boolean buildFilterChain) throws RpcException {
    return new MockClusterInvoker<T>(directory,
            this.cluster.join(directory, buildFilterChain));
}

调用public abstract class AbstractCluster 的

  @Override
    public <T> Invoker<T> join(Directory<T> directory, boolean buildFilterChain) throws RpcException {
        if (buildFilterChain) {
 
            return buildClusterInterceptors(doJoin(directory));
        } else {
            return doJoin(directory);
        }
    }

然后调用到

public ClusterFilterInvoker(AbstractClusterInvoker<T> invoker) {
    List<FilterChainBuilder> builders = ScopeModelUtil.getApplicationModel(invoker.getUrl().getScopeModel()).getExtensionLoader(FilterChainBuilder.class).getActivateExtensions();
    if (CollectionUtils.isEmpty(builders)) {
        filterInvoker = invoker;
    } else {
        ClusterInvoker<T> tmpInvoker = invoker;
        for (FilterChainBuilder builder : builders) {
            tmpInvoker = builder.buildClusterInvokerChain(tmpInvoker, REFERENCE_FILTER_KEY, CommonConstants.CONSUMER);
        }
        filterInvoker = tmpInvoker;
    }
}

可以看到，可以扩展builder 进行filter组装，在循环过程中调用到DefaultFilterChainBuilder的buildClusterInvokerChain。

@Override
    public <T> ClusterInvoker<T> buildClusterInvokerChain(final ClusterInvoker<T> originalInvoker, String key, String group) {
        ClusterInvoker<T> last = originalInvoker;
        URL url = originalInvoker.getUrl();
        List<ModuleModel> moduleModels = getModuleModelsFromUrl(url);
        List<ClusterFilter> filters;
        if (moduleModels != null && moduleModels.size() == 1) {
            filters = ScopeModelUtil.getExtensionLoader(ClusterFilter.class, moduleModels.get(0)).getActivateExtension(url, key, group);
        } else if (moduleModels != null && moduleModels.size() > 1) {
            filters = new ArrayList<>();
            List<ExtensionDirector> directors = new ArrayList<>();
            for (ModuleModel moduleModel : moduleModels) {
                List<ClusterFilter> tempFilters = ScopeModelUtil.getExtensionLoader(ClusterFilter.class, moduleModel).getActivateExtension(url, key, group);
                filters.addAll(tempFilters);
                directors.add(moduleModel.getExtensionDirector());
            }
            filters = sortingAndDeduplication(filters, directors);

        } else {
            filters = ScopeModelUtil.getExtensionLoader(ClusterFilter.class, null).getActivateExtension(url, key, group);
        }

        if (!CollectionUtils.isEmpty(filters)) {
            for (int i = filters.size() - 1; i >= 0; i--) {
                final ClusterFilter filter = filters.get(i);
                final Invoker<T> next = last;
                last = new CopyOfClusterFilterChainNode<>(originalInvoker, next, filter);
            }
            return new ClusterCallbackRegistrationInvoker<>(originalInvoker, last, filters);
        }

        return last;
    }