dubbo源码解析（九） Filter & Listener

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Filter解析

通过Filter接口我们可以轻松地实现服务提供方和消费方的拦截

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@SPI
public interface Filter {

    /**
     * do invoke filter.
     * <p>
     * <code>
     * // before filter
     * Result result = invoker.invoke(invocation);
     * // after filter
     * return result;
     * </code>
     *
     * @param invoker    service
     * @param invocation invocation.
     * @return invoke result.
     * @throws RpcException
     * @see com.alibaba.dubbo.rpc.Invoker#invoke(Invocation)
     */
    Result invoke(Invoker<?> invoker, Invocation invocation) throws RpcException;

}

我们注意到ReferenceConfig和ServiceConfig的共同父类AbstractInterfaceConfig

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// filter
protected String filter;
//key为reference.filter
@Parameter(key = Constants.REFERENCE_FILTER_KEY, append = true)
public String getFilter() {
    return filter;
}

//Parameter作用是将filter解析并放入key为service.filter的url
@Parameter(key = Constants.SERVICE_FILTER_KEY, append = true)
public String getFilter() {
   return super.getFilter();
}

//xxx,yyy
public void setFilter(String filter) {
    checkMultiExtension(Filter.class, "filter", filter);
    this.filter = filter;
}

自定义调用拦截使用方法

服务提供方和服务消费方调用过程拦截，Dubbo 本身的大多功能均基于此扩展点实现，每次远程方法执行，该拦截都会被执行，请注意对性能的影响。

约定：

  • 用户自定义 filter 默认在内置 filter 之后。
  • 特殊值 default，表示缺省扩展点插入的位置。比如：filter="xxx,default,yyy"，表示 xxx 在缺省 filter 之前，yyy 在缺省 filter 之后。
  • 特殊符号 -，表示剔除。比如：filter="-foo1"，剔除添加缺省扩展点 foo1。比如：filter="-default"，剔除添加所有缺省扩展点。
  • provider 和 service 同时配置的 filter 时，累加所有 filter，而不是覆盖。比如：<dubbo:provider filter="xxx,yyy"/> 和 <dubbo:service filter="aaa,bbb" />，则 xxx,yyy,aaa,bbb 均会生效。如果要覆盖，需配置：<dubbo:service filter="-xxx,-yyy,aaa,bbb" />

扩展接口

com.alibaba.dubbo.rpc.Filter

扩展配置

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<!-- 消费方调用过程拦截 -->
<dubbo:reference filter="xxx,yyy" />
<!-- 消费方调用过程缺省拦截器，将拦截所有reference -->
<dubbo:consumer filter="xxx,yyy"/>
<!-- 提供方调用过程拦截 -->
<dubbo:service filter="xxx,yyy" />
<!-- 提供方调用过程缺省拦截器，将拦截所有service -->
<dubbo:provider filter="xxx,yyy"/>

已知扩展

  • com.alibaba.dubbo.rpc.filter.EchoFilter
  • com.alibaba.dubbo.rpc.filter.GenericFilter
  • com.alibaba.dubbo.rpc.filter.GenericImplFilter
  • com.alibaba.dubbo.rpc.filter.TokenFilter
  • com.alibaba.dubbo.rpc.filter.AccessLogFilter
  • com.alibaba.dubbo.rpc.filter.CountFilter
  • com.alibaba.dubbo.rpc.filter.ActiveLimitFilter
  • com.alibaba.dubbo.rpc.filter.ClassLoaderFilter
  • com.alibaba.dubbo.rpc.filter.ContextFilter
  • com.alibaba.dubbo.rpc.filter.ConsumerContextFilter
  • com.alibaba.dubbo.rpc.filter.ExceptionFilter
  • com.alibaba.dubbo.rpc.filter.ExecuteLimitFilter
  • com.alibaba.dubbo.rpc.filter.DeprecatedFilter
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echo=com.alibaba.dubbo.rpc.filter.EchoFilter
generic=com.alibaba.dubbo.rpc.filter.GenericFilter
genericimpl=com.alibaba.dubbo.rpc.filter.GenericImplFilter
token=com.alibaba.dubbo.rpc.filter.TokenFilter
accesslog=com.alibaba.dubbo.rpc.filter.AccessLogFilter
activelimit=com.alibaba.dubbo.rpc.filter.ActiveLimitFilter
classloader=com.alibaba.dubbo.rpc.filter.ClassLoaderFilter
context=com.alibaba.dubbo.rpc.filter.ContextFilter
consumercontext=com.alibaba.dubbo.rpc.filter.ConsumerContextFilter
exception=com.alibaba.dubbo.rpc.filter.ExceptionFilter
executelimit=com.alibaba.dubbo.rpc.filter.ExecuteLimitFilter
deprecated=com.alibaba.dubbo.rpc.filter.DeprecatedFilter
compatible=com.alibaba.dubbo.rpc.filter.CompatibleFilter
timeout=com.alibaba.dubbo.rpc.filter.TimeoutFilter

扩展示例

Maven 项目结构：

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src
 |-main
    |-java
        |-com
            |-xxx
                |-XxxFilter.java (实现Filter接口)
    |-resources
        |-META-INF
            |-dubbo
                |-com.alibaba.dubbo.rpc.Filter (纯文本文件，内容为：xxx=com.xxx.XxxFilter)

XxxFilter.java：

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package com.xxx;

import com.alibaba.dubbo.rpc.Filter;
import com.alibaba.dubbo.rpc.Invoker;
import com.alibaba.dubbo.rpc.Invocation;
import com.alibaba.dubbo.rpc.Result;
import com.alibaba.dubbo.rpc.RpcException;

public class XxxFilter implements Filter {
    public Result invoke(Invoker<?> invoker, Invocation invocation) throws RpcException {
        // before filter ...
        Result result = invoker.invoke(invocation);
        // after filter ...
        return result;
    }
}

META-INF/dubbo/com.alibaba.dubbo.rpc.Filter：

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xxx=com.xxx.XxxFilter

具体是如何调用的呢？

ProtocolFilterWrapper

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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;
        //通过配置拿到所有filter
        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>() {

                    public Class<T> getInterface() {
                        return invoker.getInterface();
                    }

                    public URL getUrl() {
                        return invoker.getUrl();
                    }

                    public boolean isAvailable() {
                        return invoker.isAvailable();
                    }

                    public Result invoke(Invocation invocation) throws RpcException {
                        return filter.invoke(next, invocation);
                    }

                    public void destroy() {
                        invoker.destroy();
                    }

                    @Override
                    public String toString() {
                        return invoker.toString();
                    }
                };
            }
        }
        return last;
    }

    public int getDefaultPort() {
        return protocol.getDefaultPort();
    }
//服务暴露
    public <T> Exporter<T> export(Invoker<T> invoker) throws RpcException {
        if (Constants.REGISTRY_PROTOCOL.equals(invoker.getUrl().getProtocol())) {
            return protocol.export(invoker);
        }
        //通过读取service.filter构建filter链
        return protocol.export(buildInvokerChain(invoker, Constants.SERVICE_FILTER_KEY, Constants.PROVIDER));
    }
//服务引用
    public <T> Invoker<T> refer(Class<T> type, URL url) throws RpcException {
        if (Constants.REGISTRY_PROTOCOL.equals(url.getProtocol())) {
            return protocol.refer(type, url);
        }
        return buildInvokerChain(protocol.refer(type, url), 
                                 //通过读取reference.filter配置构建filter链
                                 Constants.REFERENCE_FILTER_KEY, Constants.CONSUMER);
    }

    public void destroy() {
        protocol.destroy();
    }

}

Listener解析

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@SPI
public interface InvokerListener {

    /**
     * The invoker referred
     *
     * @param invoker
     * @throws RpcException
     * @see com.alibaba.dubbo.rpc.Protocol#refer(Class, URL)
     */
    void referred(Invoker<?> invoker) throws RpcException;

    /**
     * The invoker destroyed.
     *
     * @param invoker
     * @see com.alibaba.dubbo.rpc.Invoker#destroy()
     */
    void destroyed(Invoker<?> invoker);

}
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@SPI
public interface ExporterListener {

    /**
     * The exporter exported.
     *
     * @param exporter
     * @throws RpcException
     * @see com.alibaba.dubbo.rpc.Protocol#export(Invoker)
     */
    void exported(Exporter<?> exporter) throws RpcException;

    /**
     * The exporter unexported.
     *
     * @param exporter
     * @throws RpcException
     * @see com.alibaba.dubbo.rpc.Exporter#unexport()
     */
    void unexported(Exporter<?> exporter);

}
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protected String listener;
//invoker.listener
@Parameter(key = Constants.INVOKER_LISTENER_KEY, append = true)
public String getListener() {
    checkMultiExtension(InvokerListener.class, "listener", listener);
    return listener;
}

//exporter.listener
@Parameter(key = Constants.EXPORTER_LISTENER_KEY, append = true)
public String getListener() {
   return super.getListener();
}

public void setListener(String listener) {
    this.listener = listener;
}

引用监听扩展

扩展说明

当有服务引用时，触发该事件。

扩展接口

com.alibaba.dubbo.rpc.InvokerListener

扩展配置

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<!-- 引用服务监听 -->
<dubbo:reference listener="xxx,yyy" /> 
<!-- 引用服务缺省监听器 -->
<dubbo:consumer listener="xxx,yyy" />

已知扩展

com.alibaba.dubbo.rpc.listener.DeprecatedInvokerListener

扩展示例

Maven 项目结构：

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src
 |-main
    |-java
        |-com
            |-xxx
                |-XxxInvokerListener.java (实现InvokerListener接口)
    |-resources
        |-META-INF
            |-dubbo
                |-com.alibaba.dubbo.rpc.InvokerListener (纯文本文件，内容为：xxx=com.xxx.XxxInvokerListener)

XxxInvokerListener.java：

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package com.xxx;

import com.alibaba.dubbo.rpc.InvokerListener;
import com.alibaba.dubbo.rpc.Invoker;
import com.alibaba.dubbo.rpc.RpcException;

public class XxxInvokerListener implements InvokerListener {
    public void referred(Invoker<?> invoker) throws RpcException {
        // ...
    }
    public void destroyed(Invoker<?> invoker) throws RpcException {
        // ...
    }
}

META-INF/dubbo/com.alibaba.dubbo.rpc.InvokerListener：

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xxx=com.xxx.XxxInvokerListener

暴露监听扩展

扩展说明

当有服务暴露时，触发该事件。

扩展接口

com.alibaba.dubbo.rpc.ExporterListener

扩展配置

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<!-- 暴露服务监听 -->
<dubbo:service listener="xxx,yyy" />
<!-- 暴露服务缺省监听器 -->
<dubbo:provider listener="xxx,yyy" />

已知扩展

com.alibaba.dubbo.registry.directory.RegistryExporterListener

扩展示例

Maven 项目结构：

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src
 |-main
    |-java
        |-com
            |-xxx
                |-XxxExporterListener.java (实现ExporterListener接口)
    |-resources
        |-META-INF
            |-dubbo
                |-com.alibaba.dubbo.rpc.ExporterListener (纯文本文件，内容为：xxx=com.xxx.XxxExporterListener)

XxxExporterListener.java：

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package com.xxx;

import com.alibaba.dubbo.rpc.ExporterListener;
import com.alibaba.dubbo.rpc.Exporter;
import com.alibaba.dubbo.rpc.RpcException;


public class XxxExporterListener implements ExporterListener {
    public void exported(Exporter<?> exporter) throws RpcException {
        // ...
    }
    public void unexported(Exporter<?> exporter) throws RpcException {
        // ...
    }
}

META-INF/dubbo/com.alibaba.dubbo.rpc.ExporterListener：

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xxx=com.xxx.XxxExporterListener

ProtocolListenerWrapper解析

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public class ProtocolListenerWrapper implements Protocol {

    private final Protocol protocol;

    public ProtocolListenerWrapper(Protocol protocol) {
        if (protocol == null) {
            throw new IllegalArgumentException("protocol == null");
        }
        this.protocol = protocol;
    }

    public int getDefaultPort() {
        return protocol.getDefaultPort();
    }
//暴露
    public <T> Exporter<T> export(Invoker<T> invoker) throws RpcException {
        if (Constants.REGISTRY_PROTOCOL.equals(invoker.getUrl().getProtocol())) {
            return protocol.export(invoker);
        }
        return new ListenerExporterWrapper<T>(protocol.export(invoker),
//exporter.listener
                                              Collections.unmodifiableList(ExtensionLoader.getExtensionLoader(ExporterListener.class)
                        .getActivateExtension(invoker.getUrl(), Constants.EXPORTER_LISTENER_KEY)));
    }
//引用
    public <T> Invoker<T> refer(Class<T> type, URL url) throws RpcException {
        if (Constants.REGISTRY_PROTOCOL.equals(url.getProtocol())) {
            return protocol.refer(type, url);
        }
        return new ListenerInvokerWrapper<T>(protocol.refer(type, url),
                Collections.unmodifiableList(
                    //invoker.listener
                        ExtensionLoader.getExtensionLoader(InvokerListener.class)
                                .getActivateExtension(url, Constants.INVOKER_LISTENER_KEY)));
    }

    public void destroy() {
        protocol.destroy();
    }

}

ListenerExporterWrapper

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public class ListenerExporterWrapper<T> implements Exporter<T> {

    private static final Logger logger = LoggerFactory.getLogger(ListenerExporterWrapper.class);

    private final Exporter<T> exporter;

    private final List<ExporterListener> listeners;

    public ListenerExporterWrapper(Exporter<T> exporter, List<ExporterListener> listeners) {
        if (exporter == null) {
            throw new IllegalArgumentException("exporter == null");
        }
        this.exporter = exporter;
        this.listeners = listeners;
        if (listeners != null && !listeners.isEmpty()) {
            RuntimeException exception = null;
            for (ExporterListener listener : listeners) {
                if (listener != null) {
                    try {
                        listener.exported(this);
                    } catch (RuntimeException t) {
                        logger.error(t.getMessage(), t);
                        exception = t;
                    }
                }
            }
            if (exception != null) {
                throw exception;
            }
        }
    }

    public Invoker<T> getInvoker() {
        return exporter.getInvoker();
    }

    public void unexport() {
        try {
            exporter.unexport();
        } finally {
            if (listeners != null && !listeners.isEmpty()) {
                RuntimeException exception = null;
                for (ExporterListener listener : listeners) {
                    if (listener != null) {
                        try {
                            listener.unexported(this);
                        } catch (RuntimeException t) {
                            logger.error(t.getMessage(), t);
                            exception = t;
                        }
                    }
                }
                if (exception != null) {
                    throw exception;
                }
            }
        }
    }

}

ListenerInvokerWrapper

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public class ListenerInvokerWrapper<T> implements Invoker<T> {

    private static final Logger logger = LoggerFactory.getLogger(ListenerInvokerWrapper.class);

    private final Invoker<T> invoker;

    private final List<InvokerListener> listeners;

    public ListenerInvokerWrapper(Invoker<T> invoker, List<InvokerListener> listeners) {
        if (invoker == null) {
            throw new IllegalArgumentException("invoker == null");
        }
        this.invoker = invoker;
        this.listeners = listeners;
        if (listeners != null && !listeners.isEmpty()) {
            for (InvokerListener listener : listeners) {
                if (listener != null) {
                    try {
                        listener.referred(invoker);
                    } catch (Throwable t) {
                        logger.error(t.getMessage(), t);
                    }
                }
            }
        }
    }

    public Class<T> getInterface() {
        return invoker.getInterface();
    }

    public URL getUrl() {
        return invoker.getUrl();
    }

    public boolean isAvailable() {
        return invoker.isAvailable();
    }

    public Result invoke(Invocation invocation) throws RpcException {
        return invoker.invoke(invocation);
    }

    @Override
    public String toString() {
        return getInterface() + " -> " + (getUrl() == null ? " " : getUrl().toString());
    }

    public void destroy() {
        try {
            invoker.destroy();
        } finally {
            if (listeners != null && !listeners.isEmpty()) {
                for (InvokerListener listener : listeners) {
                    if (listener != null) {
                        try {
                            listener.destroyed(invoker);
                        } catch (Throwable t) {
                            logger.error(t.getMessage(), t);
                        }
                    }
                }
            }
        }
    }

}