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1.比较重要的注解
@SPI:扩展点接口的标识 ：作用域在类上；
@Adaptive:为生成Adaptive实例提供参数，作用域在类或方法上；
Adatpive，字面意思是个适配，但其实是个代理，它的意思是适配合适的对象处理请求。类似jdk的动态代理，因为dubbo底层会大量使用反射，出于性能考虑会默认使用javassist字节码编译生成一个adaptive拦截所有请求，然后由它基于策略动态委派合适的provider进行处理。
SPI接口会动态编译出一个adaptive，用于适配provider处理请求。用户可以自己实现一个adaptive，只需要对某个provider打上@adaptive即可，例如Dubbo自身的AdaptiveExtensionFactory类。
对于默认编译生成Adaptive的方案，需要使用@Adaptive声明接口上的哪些方法是adaptive方法，没有被声明的方法如果被请求会抛出异常非adaptive方法的异常
@Activate：可以被框架中自动激活加载扩展，此Annotation用于配置扩展被自动激活加载条件。
Activate，看起来有点不好理解，它的意思是条件激活，用户通过group和value配置激活条件。被activate注解的扩展点在满足某种条件时会被激活，它一般用来配合filter和Invokelistener，声明他们的使用场景。
1.1 测试对象代码
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 | # 1 .声明SPI 默认为imp1 @SPI ( "impl1" ) public interface SimpleExt { // 没有使用key的@Adaptive ！ @Adaptive String echo(URL url, String s); @Adaptive ({ "key1" , "key2" }) String yell(URL url, String s); // 无@Adaptive ！ String bang(URL url, int i); } //实现类1 public class SimpleExtImpl1 implements SimpleExt { public String echo(URL url, String s) { return "Ext1Impl1-echo" ; } public String yell(URL url, String s) { return "Ext1Impl1-yell" ; } public String bang(URL url, int i) { return "bang1" ; } } //实现类2 public class SimpleExtImpl2 implements SimpleExt { public String echo(URL url, String s) { return "Ext1Impl2-echo" ; } public String yell(URL url, String s) { return "Ext1Impl2-yell" ; } public String bang(URL url, int i) { return "bang2" ; } } //实现类3 public class SimpleExtImpl3 implements SimpleExt { public String echo(URL url, String s) { return "Ext1Impl3-echo" ; } public String yell(URL url, String s) { return "Ext1Impl3-yell" ; } public String bang(URL url, int i) { return "bang3" ; } } |
1.2 配置文件com.alibaba.dubbo.common.extensionloader.ext1.SimpleExt
位置要放在如下位置
| 1 2 3 4 5 | private static final String SERVICES_DIRECTORY = "META-INF/services/" ; private static final String DUBBO_DIRECTORY = "META-INF/dubbo/" ; private static final String DUBBO_INTERNAL_DIRECTORY = DUBBO_DIRECTORY + "internal/" ; |
具体内容如下
| 1 2 3 4 | # Comment 1 impl1=com.alibaba.dubbo.common.extensionloader.ext1.impl.SimpleExtImpl1#Hello World impl2=com.alibaba.dubbo.common.extensionloader.ext1.impl.SimpleExtImpl2 # Comment 2 impl3=com.alibaba.dubbo.common.extensionloader.ext1.impl.SimpleExtImpl3 # with head space |
定义3个实现。
1.4 测试
| 1 2 3 4 5 6 7 8 | @Test public void test_getDefaultExtension() throws Exception { SimpleExt ext = ExtensionLoader.getExtensionLoader(SimpleExt. class ).getDefaultExtension(); assertThat(ext, instanceOf(SimpleExtImpl1. class )); String name = ExtensionLoader.getExtensionLoader(SimpleExt. class ).getDefaultExtensionName(); assertEquals( "impl1" , name); } |
由于@SPI("impl1")，定义了默认实现的名称为imp1.
| 1 2 3 4 5 | @Test public void test_getExtension() throws Exception { assertTrue(ExtensionLoader.getExtensionLoader(SimpleExt. class ).getExtension( "impl1" ) instanceof SimpleExtImpl1); assertTrue(ExtensionLoader.getExtensionLoader(SimpleExt. class ).getExtension( "impl2" ) instanceof SimpleExtImpl2); } |
getExtensionLoader(Class<T> type):根据类名，返回具体实现类。这些配置信息在META对应文件中配置。当然，也可以使用@Extention注解配置（只不过，这个注解已经废弃了）
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 | @Test public void test_getAdaptiveExtension_defaultAdaptiveKey() throws Exception { { SimpleExt ext = ExtensionLoader.getExtensionLoader(SimpleExt. class ).getAdaptiveExtension(); Map<String, String> map = new HashMap<String, String>(); //没有指定具体parameters参数，所以选用默认实现，最后返回impl1 URL url = new URL( "p1" , "1.2.3.4" , 1010 , "path1" , map); //如果不设置默认的SPI实现类，则报异常 //java.lang.IllegalStateException: Fail to get extension(com.alibaba.dubbo.common.extensionloader.ext1.SimpleExt) name from url(p1://1.2.3.4:1010/path1) use keys([simple.ext]) String echo = ext.echo(url, "haha" ); assertEquals( "Ext1Impl1-echo" , echo); } { SimpleExt ext = ExtensionLoader.getExtensionLoader(SimpleExt. class ).getAdaptiveExtension(); Map<String, String> map = new HashMap<String, String>(); map.put( "simple.ext" , "impl2" ); //手动在参数中配置impl2,参数为simple.ext URL url = new URL( "p1" , "1.2.3.4" , 1010 , "path1" , map); String echo = ext.echo(url, "haha" ); assertEquals( "Ext1Impl2-echo" , echo); } } |
@Adaptive 测试
由于 yell方法声明了，@Adaptive({"key1", "key2"})
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 | @Test public void test_getAdaptiveExtension_customizeAdaptiveKey() throws Exception { SimpleExt ext = ExtensionLoader.getExtensionLoader(SimpleExt. class ).getAdaptiveExtension(); Map<String, String> map = new HashMap<String, String>(); map.put( "key2" , "impl2" ); URL url = new URL( "p1" , "1.2.3.4" , 1010 , "path1" , map); String echo = ext.yell(url, "haha" ); assertEquals( "Ext1Impl2-yell" , echo); url = url.addParameter( "key1" , "impl3" ); // 注意： URL是值类型 echo = ext.yell(url, "haha" ); assertEquals( "Ext1Impl3-yell" , echo); } |
如果参数不是key1,key2,即使参数值输入impl1,impl2也是无意义的。
由于bang方法，没有被@Adaptive 修饰，所以以下代码，会报异常
ExtensionLoader.getExtensionLoader(SimpleExt.class).getAdaptiveExtension().bang(..);
of interface com.alibaba.dubbo.common.extensionloader.ext1.SimpleExt is not adaptive method!
2.@Activate注解
配置文件
| 1 2 3 4 5 | group=com.alibaba.dubbo.common.extensionloader.activate.impl.GroupActivateExtImpl value=com.alibaba.dubbo.common.extensionloader.activate.impl.ValueActivateExtImpl order1=com.alibaba.dubbo.common.extensionloader.activate.impl.OrderActivateExtImpl1 order2=com.alibaba.dubbo.common.extensionloader.activate.impl.OrderActivateExtImpl2 com.alibaba.dubbo.common.extensionloader.activate.impl.ActivateExt1Impl1 |
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 | @SPI ( "impl1" ) public interface ActivateExt1 { String echo(String msg); } @Activate (group = { "default_group" }) public class ActivateExt1Impl1 implements ActivateExt1 { public String echo(String msg) { return msg; } } @Activate (group = { "group1" , "group2" }) public class GroupActivateExtImpl implements ActivateExt1 { public String echo(String msg) { return msg; } } @Activate (order = 1 , group = { "order" }) public class OrderActivateExtImpl1 implements ActivateExt1 { public String echo(String msg) { return msg; } } @Activate (order = 2 , group = { "order" }) public class OrderActivateExtImpl2 implements ActivateExt1 { public String echo(String msg) { return msg; } } @Activate (value = { "value" }, group = { "value" }) public class ValueActivateExtImpl implements ActivateExt1 { public String echo(String msg) { return msg; } } |
2.2测试代码
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 | @Test public void testLoadActivateExtension() throws Exception { // test default URL url = URL.valueOf( "test://localhost/test" ); List<ActivateExt1> list = ExtensionLoader.getExtensionLoader(ActivateExt1. class ) .getActivateExtension(url, new String[]{}, "default_group" ); Assert.assertEquals( 1 , list.size()); Assert.assertTrue(list.get( 0 ).getClass() == ActivateExt1Impl1. class ); // test group // url = url.addParameter(Constants.GROUP_KEY, "group1"); list = ExtensionLoader.getExtensionLoader(ActivateExt1. class ) .getActivateExtension(url, new String[]{}, "group1" ); Assert.assertEquals( 1 , list.size()); Assert.assertTrue(list.get( 0 ).getClass() == GroupActivateExtImpl. class ); // test value url = url.removeParameter(Constants.GROUP_KEY); // url = url.addParameter(Constants.GROUP_KEY, "value"); url = url.addParameter( "value" , "value" ); list = ExtensionLoader.getExtensionLoader(ActivateExt1. class ) .getActivateExtension(url, new String[]{}, "value" ); Assert.assertEquals( 1 , list.size()); Assert.assertTrue(list.get( 0 ).getClass() == ValueActivateExtImpl. class ); // test order url = URL.valueOf( "test://localhost/test" ); // url = url.addParameter(Constants.GROUP_KEY, "order"); list = ExtensionLoader.getExtensionLoader(ActivateExt1. class ) .getActivateExtension(url, new String[]{}, "order" ); Assert.assertEquals( 2 , list.size()); Assert.assertTrue(list.get( 0 ).getClass() == OrderActivateExtImpl1. class ); Assert.assertTrue(list.get( 1 ).getClass() == OrderActivateExtImpl2. class ); } |
以上内容，是通过代码演练的方式，讲解了dubbo SPI机制的威力。
如果对底层实现感兴趣，可参看博客。本文转自 randy_shandong 51CTO博客，原文链接：http://blog.51cto.com/dba10g/1880962，如需转载请自行联系原作者