ProxyFactory is implemented by default with javassist and Protocol by default with dubbo, so let's focus on two subclasses: JavassistProxyFactory and DubboProtocol.

 

1. The refer method of DubboProtocol returns a DubboInvoker.

2. JavassistProxyFactory generates a proxy class dynamically using DubboInvoker as a proxy object

 

The Invoker is generated in turn by ProtocolListener Wrapper, ProtocolFilter Wrapper, Registry Protocol, Dubbo Protocol.

In this process, you need to assemble instances that store the necessary information for service invocation, like the information in the registry. Many of these details, follow-up study.

 

So ProxyFactory is Javassist ProxyFactory, which was first implemented by StubProxyFactory Wrapper, as mentioned in the previous article. The constructor parameter of StubProxyFactoryWrapper is ProxyFactory, which was described in the previous article. Implementation of Listener in dubbo It's also involved. He did the logic in getProxy.

First understand Stub (stub). Calling a service remotely in dubbo is encapsulated as a local service. Usually we refer to the interface and can call its method. The implementation is in remote application. But we want to do something before making a remote request, such as doing ThreadLocal cache, validating parameters in advance, forging fault-tolerant data after the call fails. That's what stub does. This logic is in StubProxyFactoryWrapper's getProxy method. Let's look at its code:

public <T> T getProxy(Invoker<T> invoker) throws RpcException {
    T proxy = proxyFactory.getProxy(invoker);
    if (GenericService.class != invoker.getInterface()) {
       // Check to see if there is any stub attribute
        String stub = invoker.getUrl().getParameter(Constants.STUB_KEY, invoker.getUrl().getParameter(Constants.LOCAL_KEY));
        if (ConfigUtils.isNotEmpty(stub)) {
            Class<?> serviceType = invoker.getInterface();
            if (ConfigUtils.isDefault(stub)) {
                if (invoker.getUrl().hasParameter(Constants.STUB_KEY)) {
                    stub = serviceType.getName() + "Stub";
                } else {
                    stub = serviceType.getName() + "Local";
                }
            }
            try {
                Class<?> stubClass = ReflectUtils.forName(stub);
                if (! serviceType.isAssignableFrom(stubClass)) {
                    throw new IllegalStateException("The stub implemention class " + stubClass.getName() + " not implement interface " + serviceType.getName());
                }
                try {
                    // Judging whether there is a parameter is Ben service Constructor, which is required to be available
                    Constructor<?> constructor = ReflectUtils.findConstructor(stubClass, serviceType);
                    // Seen here is direct use constructor，No judgment, not very good, if there is no constructor to throw exceptions to print out friendly prompts may be better. Here it is. JavassistProxyFactory Well formed proxy A decoration example is generated as a parameter. So here it is stub The methods implemented in the class can perform operations such as capturing exceptional parameter checking.
                    proxy = (T) constructor.newInstance(new Object[] {proxy});
                    //export stub service
                    URL url = invoker.getUrl();
                    if (url.getParameter(Constants.STUB_EVENT_KEY, Constants.DEFAULT_STUB_EVENT)){
                        url = url.addParameter(Constants.STUB_EVENT_METHODS_KEY, StringUtils.join(Wrapper.getWrapper(proxy.getClass()).getDeclaredMethodNames(), ","));
                        url = url.addParameter(Constants.IS_SERVER_KEY, Boolean.FALSE.toString());
                        try{
                            export(proxy, (Class)invoker.getInterface(), url);
                        }catch (Exception e) {
                            LOGGER.error("export a stub service error.", e);
                        }
                    }
                } catch (NoSuchMethodException e) {
                    throw new IllegalStateException("No such constructor \"public " + stubClass.getSimpleName() + "(" + serviceType.getName() + ")\" in stub implemention class " + stubClass.getName(), e);
                }
            } catch (Throwable t) {
                LOGGER.error("Failed to create stub implemention class " + stub + " in consumer " + NetUtils.getLocalHost() + " use dubbo version " + Version.getVersion() + ", cause: " + t.getMessage(), t);
                // ignore
            }
        }
    }
    return proxy;
}

 

Returns the proxy instance, so the BuyFoodService declared at the beginning actually points to a wrapped proxy in the spring container.