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本文主要研究一下dubbo的Filter
Filter
dubbo-2.7.2/dubbo-rpc/dubbo-rpc-api/src/main/java/org/apache/dubbo/rpc/Filter.java
@SPI
public interface Filter {
/**
* Does not need to override/implement this method.
*/
Result invoke(Invoker<?> invoker, Invocation invocation) throws RpcException;
/**
* Filter itself should only be response for passing invocation, all callbacks has been placed into {@link Listener}
*
* @param appResponse
* @param invoker
* @param invocation
* @return
*/
@Deprecated
default Result onResponse(Result appResponse, Invoker<?> invoker, Invocation invocation) {
return appResponse;
}
interface Listener {
void onResponse(Result appResponse, Invoker<?> invoker, Invocation invocation);
void onError(Throwable t, Invoker<?> invoker, Invocation invocation);
}
}
- Filter定义了invoke、onResponse方法，另外还定义了Listener接口，该接口定义了onResponse、onError方法
ProtocolFilterWrapper
dubbo-2.7.2/dubbo-rpc/dubbo-rpc-api/src/main/java/org/apache/dubbo/rpc/protocol/ProtocolFilterWrapper.java
public class ProtocolFilterWrapper implements Protocol {
private final Protocol protocol;
public ProtocolFilterWrapper(Protocol protocol) {
if (protocol == null) {
throw new IllegalArgumentException("protocol == null");
}
this.protocol = protocol;
}
private static <T> Invoker<T> buildInvokerChain(final Invoker<T> invoker, String key, String group) {
Invoker<T> last = invoker;
List<Filter> filters = ExtensionLoader.getExtensionLoader(Filter.class).getActivateExtension(invoker.getUrl(), key, group);
if (!filters.isEmpty()) {
for (int i = filters.size() - 1; i >= 0; i--) {
final Filter filter = filters.get(i);
final Invoker<T> next = last;
last = new Invoker<T>() {
@Override
public Class<T> getInterface() {
return invoker.getInterface();
}
@Override
public URL getUrl() {
return invoker.getUrl();
}
@Override
public boolean isAvailable() {
return invoker.isAvailable();
}
@Override
public Result invoke(Invocation invocation) throws RpcException {
Result asyncResult;
try {
asyncResult = filter.invoke(next, invocation);
} catch (Exception e) {
// onError callback
if (filter instanceof ListenableFilter) {
Filter.Listener listener = ((ListenableFilter) filter).listener();
if (listener != null) {
listener.onError(e, invoker, invocation);
}
}
throw e;
}
return asyncResult;
}
@Override
public void destroy() {
invoker.destroy();
}
@Override
public String toString() {
return invoker.toString();
}
};
}
}
return new CallbackRegistrationInvoker<>(last, filters);
}
@Override
public int getDefaultPort() {
return protocol.getDefaultPort();
}
@Override
public <T> Exporter<T> export(Invoker<T> invoker) throws RpcException {
if (REGISTRY_PROTOCOL.equals(invoker.getUrl().getProtocol())) {
return protocol.export(invoker);
}
return protocol.export(buildInvokerChain(invoker, SERVICE_FILTER_KEY, CommonConstants.PROVIDER));
}
@Override
public <T> Invoker<T> refer(Class<T> type, URL url) throws RpcException {
if (REGISTRY_PROTOCOL.equals(url.getProtocol())) {
return protocol.refer(type, url);
}
return buildInvokerChain(protocol.refer(type, url), REFERENCE_FILTER_KEY, CommonConstants.CONSUMER);
}
@Override
public void destroy() {
protocol.destroy();
}
static class CallbackRegistrationInvoker<T> implements Invoker<T> {
private final Invoker<T> filterInvoker;
private final List<Filter> filters;
public CallbackRegistrationInvoker(Invoker<T> filterInvoker, List<Filter> filters) {
this.filterInvoker = filterInvoker;
this.filters = filters;
}
@Override
public Result invoke(Invocation invocation) throws RpcException {
Result asyncResult = filterInvoker.invoke(invocation);
asyncResult.thenApplyWithContext(r -> {
for (int i = filters.size() - 1; i >= 0; i--) {
Filter filter = filters.get(i);
// onResponse callback
if (filter instanceof ListenableFilter) {
Filter.Listener listener = ((ListenableFilter) filter).listener();
if (listener != null) {
listener.onResponse(r, filterInvoker, invocation);
}
} else {
filter.onResponse(r, filterInvoker, invocation);
}
}
return r;
});
return asyncResult;
}
@Override
public Class<T> getInterface() {
return filterInvoker.getInterface();
}
@Override
public URL getUrl() {
return filterInvoker.getUrl();
}
@Override
public boolean isAvailable() {
return filterInvoker.isAvailable();
}
@Override
public void destroy() {
filterInvoker.destroy();
}
}
}
- ProtocolFilterWrapper实现了Protocol接口，它定义了一个静态类CallbackRegistrationInvoker，该类实现了Invoker接口，其invoke方法首先会调用filterInvoker的invoke方法获取asyncResult，之后通过thenApplyWithContext注册rpc调用完成时的回调，这里会挨个遍历filters，回调每个filter的onResponse方法
小结
- Filter定义了invoke、onResponse方法，另外还定义了Listener接口，该接口定义了onResponse、onError方法
- Filter定义的invoke方法返回的Result有个抽象类为AbstractResult，而AbstractResult有几个子类，分别为AppResponse、AsyncRpcResult(
替代原来的RpcResult) - ProtocolFilterWrapper定义了一个静态类CallbackRegistrationInvoker，该类实现了Invoker接口，其invoke方法首先会调用filterInvoker的invoke方法获取asyncResult，之后通过thenApplyWithContext注册rpc调用完成时的回调，这里会挨个遍历filters，回调每个filter的onResponse方法
