dubbo源碼分析系列——dubbo的SPI機制自適應Adpative類分析

時間  2019-11-11
標籤 dubbo 源碼 分析 系列 spi 機制 自適應 adpative 欄目 Dubbo 简体版
原文   原文鏈接

使用介紹

擴展點的Adpative類能夠有兩種方式實現，一種方式是人工實現Adpative類，而後配置成爲該類型的自適應類；另一種方法是若是沒有人工指定的Adpative類，則dubbo的SPI機制會自動生成和編譯一個動態的Adpative類。java

人工設置

人工設置擴展點自適應實現類會很是靈活，能夠由開發者靈活控制，可是缺點是若是有不少擴展點，自適應邏輯相同或者類似則會出現類爆炸的問題。express

咱們以編譯器擴展點Compiler爲例。apache

擴展點的源碼以下：app

/*
 * Copyright 1999-2011 Alibaba Group.
 *  
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *  
 *      http://www.apache.org/licenses/LICENSE-2.0
 *  
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.alibaba.dubbo.common.compiler;


import com.alibaba.dubbo.common.extension.SPI;

/**
 * Compiler. (SPI, Singleton, ThreadSafe)
 * 
 * @author william.liangf
 */
@SPI("javassist")
public interface Compiler {

	/**
	 * Compile java source code.
	 * 
	 * @param code Java source code
	 * @param classLoader TODO
	 * @return Compiled class
	 */
	Class<?> compile(String code, ClassLoader classLoader);

}

它的自適應擴展點實現類AdaptiveCompiler源碼以下：框架

/*
 * Copyright 1999-2011 Alibaba Group.
 *  
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *  
 *      http://www.apache.org/licenses/LICENSE-2.0
 *  
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.alibaba.dubbo.common.compiler.support;


import com.alibaba.dubbo.common.compiler.Compiler;
import com.alibaba.dubbo.common.extension.Adaptive;
import com.alibaba.dubbo.common.extension.ExtensionLoader;

/**
 * AdaptiveCompiler. (SPI, Singleton, ThreadSafe)
 * 
 * @author william.liangf
 */
@Adaptive
public class AdaptiveCompiler implements Compiler {

    private static volatile String DEFAULT_COMPILER;

    public static void setDefaultCompiler(String compiler) {
        DEFAULT_COMPILER = compiler;
    }

    public Class<?> compile(String code, ClassLoader classLoader) {
        Compiler compiler;
        ExtensionLoader<Compiler> loader = ExtensionLoader.getExtensionLoader(Compiler.class);
        String name = DEFAULT_COMPILER; // copy reference
        if (name != null && name.length() > 0) {
            compiler = loader.getExtension(name);
        } else {
            compiler = loader.getDefaultExtension();
        }
        return compiler.compile(code, classLoader);
    }

}

能夠看出自適應實現類自己並無實現compie方法，它是由參數DEFAULT_COMPILER指定一個默認的擴展點名稱，所以是能夠動態調整的。less

自動生成

因爲大部分的擴展點自適應實現類的代碼邏輯都類似，所以自動生成動態的自適應擴展類則會給開發者帶來很大的便利，省去了不少冗餘代碼。可是因爲dubbo的實現方式是經過代碼來自動生成自適應實現的代碼，代碼可讀性很是差。這也是缺點。咱們經過調試將其生成的代碼打印出來將大大提升代碼可讀性。ui

Protocol擴展點

咱們將以擴展點Protocol爲例來展現生成的代碼。this

/*
 * Copyright 1999-2011 Alibaba Group.
 *  
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *  
 *      http://www.apache.org/licenses/LICENSE-2.0
 *  
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.alibaba.dubbo.rpc;

import com.alibaba.dubbo.common.URL;
import com.alibaba.dubbo.common.extension.Adaptive;
import com.alibaba.dubbo.common.extension.SPI;

/**
 * Protocol. (API/SPI, Singleton, ThreadSafe)
 * 
 * @author william.liangf
 */
@SPI("dubbo")
public interface Protocol {
    
    /**
     * 獲取缺省端口，當用戶沒有配置端口時使用。
     * 
     * @return 缺省端口
     */
    int getDefaultPort();

    /**
     * 暴露遠程服務：<br>
     * 1. 協議在接收請求時，應記錄請求來源方地址信息：RpcContext.getContext().setRemoteAddress();<br>
     * 2. export()必須是冪等的，也就是暴露同一個URL的Invoker兩次，和暴露一次沒有區別。<br>
     * 3. export()傳入的Invoker由框架實現並傳入，協議不須要關心。<br>
     * 
     * @param <T> 服務的類型
     * @param invoker 服務的執行體
     * @return exporter 暴露服務的引用，用於取消暴露
     * @throws RpcException 當暴露服務出錯時拋出，好比端口已佔用
     */
    @Adaptive
    <T> Exporter<T> export(Invoker<T> invoker) throws RpcException;

    /**
     * 引用遠程服務：<br>
     * 1. 當用戶調用refer()所返回的Invoker對象的invoke()方法時，協議需相應執行同URL遠端export()傳入的Invoker對象的invoke()方法。<br>
     * 2. refer()返回的Invoker由協議實現，協議一般須要在此Invoker中發送遠程請求。<br>
     * 3. 當url中有設置check=false時，鏈接失敗不能拋出異常，並內部自動恢復。<br>
     * 
     * @param <T> 服務的類型
     * @param type 服務的類型
     * @param url 遠程服務的URL地址
     * @return invoker 服務的本地代理
     * @throws RpcException 當鏈接服務提供方失敗時拋出
     */
    @Adaptive
    <T> Invoker<T> refer(Class<T> type, URL url) throws RpcException;

    /**
     * 釋放協議：<br>
     * 1. 取消該協議全部已經暴露和引用的服務。<br>
     * 2. 釋放協議所佔用的全部資源，好比鏈接和端口。<br>
     * 3. 協議在釋放後，依然能暴露和引用新的服務。<br>
     */
    void destroy();

}

它生成的擴展自適應實現類源碼以下：url

package com.alibaba.dubbo.rpc;

import com.alibaba.dubbo.common.extension.ExtensionLoader;

public class Protocol$Adpative implements com.alibaba.dubbo.rpc.Protocol {
	public void destroy() {
		throw new UnsupportedOperationException(
				"method public abstract void com.alibaba.dubbo.rpc.Protocol.destroy() of interface com.alibaba.dubbo.rpc.Protocol is not adaptive method!");
	}

	public int getDefaultPort() {
		throw new UnsupportedOperationException(
				"method public abstract int com.alibaba.dubbo.rpc.Protocol.getDefaultPort() of interface com.alibaba.dubbo.rpc.Protocol is not adaptive method!");
	}

	public com.alibaba.dubbo.rpc.Exporter export(
			com.alibaba.dubbo.rpc.Invoker arg0)
			throws com.alibaba.dubbo.rpc.RpcException {
		if (arg0 == null)
			throw new IllegalArgumentException(
					"com.alibaba.dubbo.rpc.Invoker argument == null");
		if (arg0.getUrl() == null)
			throw new IllegalArgumentException(
					"com.alibaba.dubbo.rpc.Invoker argument getUrl() == null");
		com.alibaba.dubbo.common.URL url = arg0.getUrl();
		String extName = (url.getProtocol() == null ? "dubbo" : url
				.getProtocol());
		if (extName == null)
			throw new IllegalStateException(
					"Fail to get extension(com.alibaba.dubbo.rpc.Protocol) name from url("
							+ url.toString() + ") use keys([protocol])");
		com.alibaba.dubbo.rpc.Protocol extension = (com.alibaba.dubbo.rpc.Protocol) ExtensionLoader
				.getExtensionLoader(com.alibaba.dubbo.rpc.Protocol.class)
				.getExtension(extName);
		return extension.export(arg0);
	}

	public com.alibaba.dubbo.rpc.Invoker refer(java.lang.Class arg0,
			com.alibaba.dubbo.common.URL arg1)
			throws com.alibaba.dubbo.rpc.RpcException {
		if (arg1 == null)
			throw new IllegalArgumentException("url == null");
		com.alibaba.dubbo.common.URL url = arg1;
		String extName = (url.getProtocol() == null ? "dubbo" : url
				.getProtocol());
		if (extName == null)
			throw new IllegalStateException(
					"Fail to get extension(com.alibaba.dubbo.rpc.Protocol) name from url("
							+ url.toString() + ") use keys([protocol])");
		com.alibaba.dubbo.rpc.Protocol extension = (com.alibaba.dubbo.rpc.Protocol) ExtensionLoader
				.getExtensionLoader(com.alibaba.dubbo.rpc.Protocol.class)
				.getExtension(extName);
		return extension.refer(arg0, arg1);
	}
}

從生成的源碼能夠看出來這些特色：spa

  1. 只會代理擴展點接口上有@Adaptive標註的方法。沒有標註的方法調用會拋出不支持該方法的異常。
  2. 從類型爲url的參數或者參數的url屬性中得到url對象，從url中得到value做爲擴展點的名稱。
  3. 從擴展點加載器中得到對應名稱的擴展點。
  4. 再調用擴展點的方法。

Transporter擴展點

擴展點源碼以下。

/*
 * Copyright 1999-2011 Alibaba Group.
 *  
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *  
 *      http://www.apache.org/licenses/LICENSE-2.0
 *  
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.alibaba.dubbo.remoting;

import javax.sound.midi.Receiver;

import com.alibaba.dubbo.common.Constants;
import com.alibaba.dubbo.common.URL;
import com.alibaba.dubbo.common.extension.Adaptive;
import com.alibaba.dubbo.common.extension.SPI;

/**
 * Transporter. (SPI, Singleton, ThreadSafe)
 * 
 * <a href="http://en.wikipedia.org/wiki/Transport_Layer">Transport Layer</a>
 * <a href="http://en.wikipedia.org/wiki/Client%E2%80%93server_model">Client/Server</a>
 * 
 * @see com.alibaba.dubbo.remoting.Transporters
 * @author ding.lid
 * @author william.liangf
 */
@SPI("netty")
public interface Transporter {

    /**
     * Bind a server.
     * 
     * @see com.alibaba.dubbo.remoting.Transporters#bind(URL, Receiver, ChannelHandler)
     * @param url server url
     * @param handler
     * @return server
     * @throws RemotingException 
     */
    @Adaptive({Constants.SERVER_KEY, Constants.TRANSPORTER_KEY})
    Server bind(URL url, ChannelHandler handler) throws RemotingException;

    /**
     * Connect to a server.
     * 
     * @see com.alibaba.dubbo.remoting.Transporters#connect(URL, Receiver, ChannelListener)
     * @param url server url
     * @param handler
     * @return client
     * @throws RemotingException 
     */
    @Adaptive({Constants.CLIENT_KEY, Constants.TRANSPORTER_KEY})
    Client connect(URL url, ChannelHandler handler) throws RemotingException;

}

生成的自適應擴展實現源碼以下。

package com.alibaba.dubbo.remoting;

import com.alibaba.dubbo.common.extension.ExtensionLoader;

public class Transporter$Adpative implements
		com.alibaba.dubbo.remoting.Transporter {
	public com.alibaba.dubbo.remoting.Client connect(
			com.alibaba.dubbo.common.URL arg0,
			com.alibaba.dubbo.remoting.ChannelHandler arg1)
			throws com.alibaba.dubbo.remoting.RemotingException {
		if (arg0 == null)
			throw new IllegalArgumentException("url == null");
		com.alibaba.dubbo.common.URL url = arg0;
		String extName = url.getParameter("client", url.getParameter(
				"transporter", "netty"));
		if (extName == null)
			throw new IllegalStateException(
					"Fail to get extension(com.alibaba.dubbo.remoting.Transporter) name from url("
							+ url.toString()
							+ ") use keys([client, transporter])");
		com.alibaba.dubbo.remoting.Transporter extension = (com.alibaba.dubbo.remoting.Transporter) ExtensionLoader
				.getExtensionLoader(
						com.alibaba.dubbo.remoting.Transporter.class)
				.getExtension(extName);
		return extension.connect(arg0, arg1);
	}

	public com.alibaba.dubbo.remoting.Server bind(
			com.alibaba.dubbo.common.URL arg0,
			com.alibaba.dubbo.remoting.ChannelHandler arg1)
			throws com.alibaba.dubbo.remoting.RemotingException {
		if (arg0 == null)
			throw new IllegalArgumentException("url == null");
		com.alibaba.dubbo.common.URL url = arg0;
		String extName = url.getParameter("server", url.getParameter(
				"transporter", "netty"));
		if (extName == null)
			throw new IllegalStateException(
					"Fail to get extension(com.alibaba.dubbo.remoting.Transporter) name from url("
							+ url.toString()
							+ ") use keys([server, transporter])");
		com.alibaba.dubbo.remoting.Transporter extension = (com.alibaba.dubbo.remoting.Transporter) ExtensionLoader
				.getExtensionLoader(
						com.alibaba.dubbo.remoting.Transporter.class)
				.getExtension(extName);
		return extension.bind(arg0, arg1);
	}
}

區別點是調用了String extName = url.getParameter("server", url.getParameter( "transporter", "netty"));來得到擴展名稱。

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