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@@ -5,7 +5,7 @@ description: 主要讲述如何配置dubbo，按照配置方式上可以分为 | |
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| # Dubbo基本用法之Provider配置 | ||
| --- | ||
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| ## Dubbo基本用法 | ||
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| --- | ||
| title: Dubbo 2.7.x repackage后的兼容实现方案 | ||
| keywords: Dubbo, repackage, 兼容 | ||
| description: 本文简单描述了2.7.x repackage后对老版本的兼容性实现方案。 | ||
| --- | ||
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| # Dubbo 2.7.x repackage后的兼容实现方案 | ||
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| Dubbo至加入Apache孵化器以来，一个很强的诉求就是需要rename groupId和package name，这两项工作在项目毕业前需要完成。其中rename package相对来说复杂一些，除了要修改所有类的包名为`org.apache.dubbo`外，更多的是需要考虑如何老版本的兼容性。 | ||
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| 常见的兼容性包括但不限于以下几种情况： | ||
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| * 用户API | ||
| * 编程API | ||
| * Spring注解 | ||
| * 扩展SPI | ||
| * 扩展Filter | ||
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| 2.7.x里就是通过增加了一个新的模块`dubbo-compatible`来解决以上兼容性问题。 | ||
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| ## 编程使用API | ||
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| 编程使用API是最直接最原始的使用方式，其他方式诸如Spring schema、注解等方式都是基于原始API的；因此非常有必要对API编程形式进行兼容。 | ||
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| 所有编程相关API的兼容代码均在`com.alibaba.dubbo.config`包下，下面我们看看几个常见API的兼容实现。 | ||
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| ### ApplicationConfig | ||
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| ```java | ||
| package com.alibaba.dubbo.config; | ||
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| @Deprecated | ||
| public class ApplicationConfig extends org.apache.dubbo.config.ApplicationConfig { | ||
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| public ApplicationConfig() { | ||
| super(); | ||
| } | ||
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| public ApplicationConfig(String name) { | ||
| super(name); | ||
| } | ||
| } | ||
| ``` | ||
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| ### ProtocolConfig | ||
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| ```java | ||
| package com.alibaba.dubbo.config; | ||
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| @Deprecated | ||
| public class ProtocolConfig extends org.apache.dubbo.config.ProtocolConfig { | ||
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| public ProtocolConfig() { | ||
| } | ||
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| public ProtocolConfig(String name) { | ||
| super(name); | ||
| } | ||
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| public ProtocolConfig(String name, int port) { | ||
| super(name, port); | ||
| } | ||
| } | ||
| ``` | ||
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| 可以看到： | ||
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| 1. 兼容类是直接通过继续repacakge后的类，达到最大程度的代码复用； | ||
| 2. 构造函数也需要保持兼容； | ||
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| 整个兼容包中，除了上述API以外，包括一些常用的类比如`Constants`、`URL`以及绝大部分的兼容类都是通过简单的继承，让用户基于老的API实现的类能正确运行。 | ||
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| ## Spring注解 | ||
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| Spring注解诸如`@EnableDubbo`、`@Service`以及`@Reference`，由于不能使用继承，故这些注解类是通过代码拷贝来实现的；用于处理这些注解的Spring BeanPostProcessor以及Parser等相关的类，也是通过拷贝来实现； | ||
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| 这类兼容代码分别位于兼容包的以下几个package中： | ||
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| * com.alibaba.dubbo.config.annotation | ||
| * com.alibaba.dubbo.config.spring.context.annotation | ||
| * org.apache.dubbo.config.spring | ||
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| 所以这里要特别强调的是，这类代码在2.7.x里存在2份，因此有修改的同时需要同步修改。 | ||
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| ## 扩展SPI | ||
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| Dubbo的SPI扩展机制，可以通过[Dubbo可扩展机制实战](http://dubbo.apache.org/zh-cn/blog/introduction-to-dubbo-spi.html)这篇博客详细了解。 | ||
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| 以Filter扩展为例，简单来说就是： | ||
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| 1. MyFilter需要实现Filter接口 | ||
| 2. 在META-INF/dubbo下，增加META-INF/dubbo/com.alibaba.dubbo.rpc.Filter，内容为： | ||
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| ``` | ||
| myFilter=com.test.MyFilter | ||
| ``` | ||
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| 看似简单的两点，对Dubbo框架来说，需要： | ||
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| 1. 正确加载配置文件META-INF/dubbo/com.alibaba.dubbo.rpc.Filter | ||
| 2. 正确加载MyFilter类并执行invoke方法 | ||
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| 下面分别介绍Dubbo框架怎么实现以上几点。 | ||
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| ### 正确加载META-INF/dubbo/com.alibaba.dubbo.rpc.Filter | ||
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| Dubbo SPI机制在查找配置文件时，是根据扩展点的类名来查找的，以Filter为例，在包名变为org.apache.dubbo后，查询的目录变成： | ||
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| * META-INF/dubbo/internal/org.apache.dubbo.rpc.Filter | ||
| * META-INF/dubbo/org.apache.dubbo.rpc.Filter | ||
| * META-INF/services/org.apache.dubbo.rpc.Filter | ||
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| 但是用户之前按老的包实现的Filter，其配置是放在类似`META-INF/dubbo/com.alibaba.dubbo.rpc.Filter`的，如果框架不做特殊处理，是不会加载老配置的。 | ||
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| 因此在`ExtensionLoader`这个类里，做了特殊的处理： | ||
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| ```java | ||
| // synchronized in getExtensionClasses | ||
| private Map<String, Class<?>> loadExtensionClasses() { | ||
| final SPI defaultAnnotation = type.getAnnotation(SPI.class); | ||
| if (defaultAnnotation != null) { | ||
| String value = defaultAnnotation.value(); | ||
| if ((value = value.trim()).length() > 0) { | ||
| String[] names = NAME_SEPARATOR.split(value); | ||
| if (names.length > 1) { | ||
| throw new IllegalStateException("more than 1 default extension name on extension " + type.getName() | ||
| + ": " + Arrays.toString(names)); | ||
| } | ||
| if (names.length == 1) cachedDefaultName = names[0]; | ||
| } | ||
| } | ||
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| Map<String, Class<?>> extensionClasses = new HashMap<String, Class<?>>(); | ||
| loadDirectory(extensionClasses, DUBBO_INTERNAL_DIRECTORY, type.getName()); | ||
| loadDirectory(extensionClasses, DUBBO_INTERNAL_DIRECTORY, type.getName().replace("org.apache", "com.alibaba")); | ||
| loadDirectory(extensionClasses, DUBBO_DIRECTORY, type.getName()); | ||
| loadDirectory(extensionClasses, DUBBO_DIRECTORY, type.getName().replace("org.apache", "com.alibaba")); | ||
| loadDirectory(extensionClasses, SERVICES_DIRECTORY, type.getName()); | ||
| loadDirectory(extensionClasses, SERVICES_DIRECTORY, type.getName().replace("org.apache", "com.alibaba")); | ||
| return extensionClasses; | ||
| } | ||
| ``` | ||
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| 可以看到，除了加载新配置外，老配置文件也会进行扫描。 | ||
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| ### 正确加载MyFilter类 | ||
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| `com.alibaba.dubbo.rpc.Filter`接口除了要继承自`org.apache.dubbo.rpc.Filter`以外，其唯一的方法invoke也需要做特殊处理。我们看看它的方法签名： | ||
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| `Result invoke(Invoker<?> invoker, Invocation invocation) throws RpcException;` | ||
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| 这里参数、返回值、异常都会被实现类`MyFilter`用到，因此这些类也需要有兼容类；而参数、返回值不同，对于接口来说是不同的方法，因此： | ||
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| * 需要在com.alibaba.dubbo.rpc.Filter里，定义老的invoke方法，MyFilter会覆盖这个方法； | ||
| * org.apache.dubbo.rpc.Filter里的invoke方法，需要找一个地方来实现桥接，框架调用Filter链执行到新的invoke方法时，新的参数如何转换成老参数，老返回值如何转换成新的返回值； | ||
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| 这里就用到了JDK8的新特性：接口default方法。 | ||
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| ```java | ||
| @Deprecated | ||
| public interface Filter extends org.apache.dubbo.rpc.Filter { | ||
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| Result invoke(Invoker<?> invoker, Invocation invocation) throws RpcException; | ||
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| default org.apache.dubbo.rpc.Result invoke(org.apache.dubbo.rpc.Invoker<?> invoker, | ||
| org.apache.dubbo.rpc.Invocation invocation) | ||
| throws org.apache.dubbo.rpc.RpcException { | ||
| Result.CompatibleResult result = (Result.CompatibleResult) invoke(new Invoker.CompatibleInvoker<>(invoker), | ||
| new Invocation.CompatibleInvocation(invocation)); | ||
| return result.getDelegate(); | ||
| } | ||
| } | ||
| ``` | ||
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| 可以看到，default方法里，对参数进行了包装，然后调用老的invoke方法，并将返回值进行解包后返回给Dubbo框架。这里Result.CompatibleResult、Invocation.CompatibleInvocation以及Invoker.CompatibleInvoker都用到了代理模式。 | ||
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| 感兴趣的同学可以详细看一下以下几个类： | ||
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| * com.alibaba.dubbo.rpc.Invocation | ||
| * com.alibaba.dubbo.rpc.Invoker | ||
| * com.alibaba.dubbo.rpc.Result | ||
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| ## 后续todo list | ||
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| 目前兼容包仅仅是对常见的API及SPI做了支持，列表如下： | ||
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| * com.alibaba.dubbo.rpc.Filter / Invocation / Invoker / Result / RpcContext / RpcException | ||
| * com.alibaba.dubbo.config.*Config | ||
| * com.alibaba.dubbo.config.annotation.Reference / Service | ||
| * com.alibaba.dubbo.config.spring.context.annotation.EnableDubbo | ||
| * com.alibaba.dubbo.common.Constants / URL | ||
| * com.alibaba.dubbo.common.extension.ExtensionFactory | ||
| * com.alibaba.dubbo.common.serialize.Serialization / ObjectInput / ObjectOutput | ||
| * com.alibaba.dubbo.cache.CacheFactory / Cache | ||
| * com.alibaba.dubbo.rpc.service.EchoService / GenericService | ||
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| 大家如果在试用的过程中发现有任何问题请及时提出；同时如果对其他扩展点有兼容需求，也请大家提出来，也非常欢迎大家自己解决并贡献出来。 |
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| Original file line number | Diff line number | Diff line change |
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@@ -3,7 +3,6 @@ title: 提前if判断帮助CPU分支预测 | |
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| # 优化技巧：提前if判断帮助CPU分支预测 | ||
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| ## 分支预测 | ||
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