|
8 | 8 |
|
9 | 9 | ### 1. @SPI注解 |
10 | 10 |
|
| 11 | +在Dubbo中某个接口被@SPI注解修饰时，就表示该接口是扩展接口，在前文中提到的SimpleExt就是由@SPI注解修饰，因而SimpleExt这个接口表示的就是一个扩展点接口。 |
| 12 | + |
| 13 | +另外在@SPI注解的value值指定了扩展点默认的实现类名，例如SimpleExt注解由@SPI("impl1")修饰，则表示它的实现类名为：SimpleExtImpl1，查看SPI的配置文件可证： |
| 14 | + |
| 15 | +``` |
| 16 | +# Comment 1 |
| 17 | +impl1=org.apache.dubbo.common.extension.ext1.impl.SimpleExtImpl1#Hello World |
| 18 | +impl2=org.apache.dubbo.common.extension.ext1.impl.SimpleExtImpl2 # Comment 2 |
| 19 | + impl3=org.apache.dubbo.common.extension.ext1.impl.SimpleExtImpl3 # with head space |
| 20 | +``` |
| 21 | + |
| 22 | +Dubbo通过ExtensionLoader去加载上述SPI配置文件，然后读取到@SPI("impl1")接口的扩展点实现类为SimpleExtImpl1，随后通过getExtension()方法获取扩展点实现类的对象，那么Dubbo是如何处理@SPI注解的呢？ |
| 23 | + |
| 24 | +Dubbo SPI的核心逻辑几乎都封装在ExtensionLoader之中，ExtensionLoader存放于dubbo-common模块的extension保重，功能类似于JDK SPI中的java.util.ServiceLoader。 |
| 25 | + |
| 26 | +下面展示了ExtensionLoader最常用的使用方式： |
| 27 | +``` |
| 28 | +SimpleExt ext = getExtensionLoader(SimpleExt.class).getDefaultExtension(); |
| 29 | +``` |
| 30 | + |
| 31 | + |
| 32 | + |
11 | 33 | ### 2. @Adaptive注解 |
12 | 34 |
|
13 | 35 | AdaptiveExtensionFactory 不实现任何具体的功能，而是用来适配 ExtensionFactory 的 SpiExtensionFactory 和 SpringExtensionFactory 这两种实现。AdaptiveExtensionFactory 会根据运行时的一些状态来选择具体调用 ExtensionFactory 的哪个实现。 |
14 | 36 |
|
15 | 37 | AdaptiveExtensionFactory会根据运行时状态来决定给ExtensionFactory赋值哪个实现，例如在Dubbo源码本地，使用的是SpiExtensionFactory这个类，而如果 |
16 | 38 | 是在Spring环境的话，则会使用SpringExtensionFactory这种实现。适配核心逻辑在AdaptiveExtensionFactory的构造方法里。 |
| 39 | + |
| 40 | +``` |
| 41 | + private Class<?> getAdaptiveExtensionClass() { |
| 42 | + // 获取扩展点实现类，如果缓存中没有则去扫描SPI文件，扫描到扩展点实现类后则存入cachedClasses缓存中 |
| 43 | + getExtensionClasses(); // ------------------------ ① |
| 44 | + if (cachedAdaptiveClass != null) { |
| 45 | + return cachedAdaptiveClass; |
| 46 | + } |
| 47 | + return cachedAdaptiveClass = createAdaptiveExtensionClass(); |
| 48 | + } |
| 49 | +
|
| 50 | + ... 省略 |
| 51 | +
|
| 52 | + private void loadClass(Map<String, Class<?>> extensionClasses, java.net.URL resourceURL, Class<?> clazz, String name, |
| 53 | + boolean overridden) throws NoSuchMethodException { |
| 54 | + if (!type.isAssignableFrom(clazz)) { |
| 55 | + throw new IllegalStateException("Error occurred when loading extension class (interface: " + |
| 56 | + type + ", class line: " + clazz.getName() + "), class " |
| 57 | + + clazz.getName() + " is not subtype of interface."); |
| 58 | + } |
| 59 | + // 如果加载的扩展点实现类中有@Adaptive注解修饰，则将该类缓存到cachedAdaptiveClass缓存中 |
| 60 | + // 而如果对于有@Adaptive修饰的接口，并且修饰在了方法上，没有@Adaptive注解修饰的扩展点实现类的话，则会通过Javassist生成代理代码，生成对于的自适应逻辑 |
| 61 | + if (clazz.isAnnotationPresent(Adaptive.class)) { |
| 62 | + cacheAdaptiveClass(clazz, overridden); // ------------------------ ② |
| 63 | + } else if (isWrapperClass(clazz)) { // 判断是否是包装类，判断依据是：该扩展实现类是否包含拷贝构造函数（即构造函数只有一个参数且为扩展接口类型） |
| 64 | + cacheWrapperClass(clazz); |
| 65 | + } else { |
| 66 | + clazz.getConstructor(); |
| 67 | + if (StringUtils.isEmpty(name)) { |
| 68 | + name = findAnnotationName(clazz); |
| 69 | + if (name.length() == 0) { |
| 70 | + throw new IllegalStateException("No such extension name for the class " + clazz.getName() + " in the config " + resourceURL); |
| 71 | + } |
| 72 | + } |
| 73 | +
|
| 74 | + String[] names = NAME_SEPARATOR.split(name); |
| 75 | + if (ArrayUtils.isNotEmpty(names)) { |
| 76 | + cacheActivateClass(clazz, names[0]); |
| 77 | + for (String n : names) { |
| 78 | + cacheName(clazz, n); |
| 79 | + saveInExtensionClass(extensionClasses, clazz, n, overridden); |
| 80 | + } |
| 81 | + } |
| 82 | + } |
| 83 | + } |
| 84 | +``` |
| 85 | + |
| 86 | +在①中会去加载扩展点实现类，然后将所有的扩展点都加载然后缓存到对应的缓存中，当程序走到了②时，会判断扩展点实现类是否有@Adaptive注解修饰，如果有的话就会将其实现类缓存到cachedAdaptiveClass中；否则在①中判断到cachedAdaptiveClass中没有缓存的实现类，就表示没有@Adaptive修饰 |
| 87 | +的扩展点实现类，就会去通过Javassist来生成代理代码，即生成对于的Xxx@Adaptive代码。 |
| 88 | + |
| 89 | +``` |
| 90 | +package org.apache.dubbo.common.extension.ext1; |
| 91 | +
|
| 92 | +import org.apache.dubbo.common.extension.ExtensionLoader; |
| 93 | +
|
| 94 | +
|
| 95 | +public class SimpleExt$Adaptive implements org.apache.dubbo.common.extension.ext1.SimpleExt { |
| 96 | + public java.lang.String bang(org.apache.dubbo.common.URL arg0, int arg1) { |
| 97 | + throw new UnsupportedOperationException( |
| 98 | + "The method public abstract java.lang.String org.apache.dubbo.common.extension.ext1.SimpleExt.bang(org.apache.dubbo.common.URL,int) of interface org.apache.dubbo.common.extension.ext1.SimpleExt is not adaptive method!"); |
| 99 | + } |
| 100 | +
|
| 101 | + public java.lang.String echo(org.apache.dubbo.common.URL arg0, |
| 102 | + java.lang.String arg1) { |
| 103 | + if (arg0 == null) { |
| 104 | + throw new IllegalArgumentException("url == null"); |
| 105 | + } |
| 106 | +
|
| 107 | + org.apache.dubbo.common.URL url = arg0; |
| 108 | + String extName = url.getParameter("simple.ext", "impl1"); |
| 109 | +
|
| 110 | + if (extName == null) { |
| 111 | + throw new IllegalStateException( |
| 112 | + "Failed to get extension (org.apache.dubbo.common.extension.ext1.SimpleExt) name from url (" + |
| 113 | + url.toString() + ") use keys([simple.ext])"); |
| 114 | + } |
| 115 | +
|
| 116 | + org.apache.dubbo.common.extension.ext1.SimpleExt extension = (org.apache.dubbo.common.extension.ext1.SimpleExt) ExtensionLoader.getExtensionLoader(org.apache.dubbo.common.extension.ext1.SimpleExt.class) |
| 117 | + .getExtension(extName); |
| 118 | +
|
| 119 | + return extension.echo(arg0, arg1); |
| 120 | + } |
| 121 | +
|
| 122 | + public java.lang.String yell(org.apache.dubbo.common.URL arg0, |
| 123 | + java.lang.String arg1) { |
| 124 | + if (arg0 == null) { |
| 125 | + throw new IllegalArgumentException("url == null"); |
| 126 | + } |
| 127 | +
|
| 128 | + org.apache.dubbo.common.URL url = arg0; |
| 129 | + String extName = url.getParameter("key1", |
| 130 | + url.getParameter("key2", "impl1")); |
| 131 | +
|
| 132 | + if (extName == null) { |
| 133 | + throw new IllegalStateException( |
| 134 | + "Failed to get extension (org.apache.dubbo.common.extension.ext1.SimpleExt) name from url (" + |
| 135 | + url.toString() + ") use keys([key1, key2])"); |
| 136 | + } |
| 137 | +
|
| 138 | + org.apache.dubbo.common.extension.ext1.SimpleExt extension = (org.apache.dubbo.common.extension.ext1.SimpleExt) ExtensionLoader.getExtensionLoader(org.apache.dubbo.common.extension.ext1.SimpleExt.class) |
| 139 | + .getExtension(extName); |
| 140 | +
|
| 141 | + return extension.yell(arg0, arg1); |
| 142 | + } |
| 143 | +} |
| 144 | +``` |
| 145 | + |
| 146 | + |
17 | 147 | ### 3. @Activate注解 |
18 | 148 |
|
19 | 149 |
|
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