读Dubbo源码，学习SPI

核心类

ExtensionLoader

使用方法

1. 定义接口，使用@SPI标记

@SPI("impl1")
public interface SimpleExt { // @Adaptive example, do not specify a explicit key. @Adaptive String echo(URL url, String s); @Adaptive({"key1", "key2"}) String yell(URL url, String s); // no @Adaptive String bang(URL url, int i); } @SPI("impl1") public interface UseProtocolKeyExt { // protocol key is the second @Adaptive({"key1", "protocol"}) String echo(URL url, String s); // protocol key is the first @Adaptive({"protocol", "key2"}) String yell(URL url, String s); } 

2. 扩展类

• SimpleExt.java

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"; } } 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"; } } 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"; } } 

---

• UseProtocolKeyExt.java

public class UseProtocolKeyExtImpl1 implements UseProtocolKeyExt { public String echo(URL url, String s) { return "Ext3Impl1-echo"; } public String yell(URL url, String s) { return "Ext3Impl1-yell"; } } public class UseProtocolKeyExtImpl2 implements UseProtocolKeyExt { public String echo(URL url, String s) { return "Ext3Impl2-echo"; } public String yell(URL url, String s) { return "Ext3Impl2-yell"; } } public class UseProtocolKeyExtImpl3 implements UseProtocolKeyExt { public String echo(URL url, String s) { return "Ext3Impl3-echo"; } public String yell(URL url, String s) { return "Ext3Impl3-yell"; } } 

3.SPI资源路径

• 路径-> META-INFO/dubbo/interal/{@SPI注解的全限定名}

com.alibaba.dubbo.common.extensionloader.ext1.SimpleExt com.alibaba.dubbo.common.extensionloader.ext3.UseProtocolKeyExt

• 实现类配置

  • com.alibaba.dubbo.common.extensionloader.ext1.SimpleExt

  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

  • com.alibaba.dubbo.common.extensionloader.ext3.UseProtocolKeyExt

  impl1=com.alibaba.dubbo.common.extensionloader.ext3.impl.UseProtocolKeyExtImpl1 impl2=com.alibaba.dubbo.common.extensionloader.ext3.impl.UseProtocolKeyExtImpl2 impl3=com.alibaba.dubbo.common.extensionloader.ext3.impl.UseProtocolKeyExtImpl3

4.测试方法

• SimpleExt.java

    @Test
    public void test_getAdaptiveExtension_defaultAdaptiveKey() throws Exception {
        {
            // #1
            SimpleExt ext = ExtensionLoader.getExtensionLoader(SimpleExt.class).getAdaptiveExtension();

            Map<String, String> map = new HashMap<String, String>(); URL url = new URL("p1", "1.2.3.4", 1010, "path1", map); // #2 String echo = ext.echo(url, "haha"); assertEquals("Ext1Impl1-echo", echo); } { #3 SimpleExt ext = ExtensionLoader.getExtensionLoader(SimpleExt.class).getAdaptiveExtension(); Map<String, String> map = new HashMap<String, String>(); map.put("simple.ext", "impl2"); URL url = new URL("p1", "1.2.3.4", 1010, "path1", map); #4 String echo = ext.echo(url, "haha"); assertEquals("Ext1Impl2-echo", echo); } } 

• #1.该方法执行后会通过ExtensionLoader.createAdaptiveExtensionClassCode生成一个代理类对象ext，见附录1
• #2.1 ext中有一行：String extName = url.getParameter("simple.ext", "impl1"); (key,defaultValue) ，其中key：simple.ext是接口名称SimpleExt去驼峰加. 构成，原因在于echo方法没有@Adaptive注解没有传入参数；defaultValue根据接口@SPI值impl1生成。
• #2.2 url中map为空，extName取传入的默认值impl1
• #2.3 ext中有一行 com.alibaba.dubbo.common.extensionloader.ext1.SimpleExt extension = (com.alibaba.dubbo.common.extensionloader.ext1.SimpleExt)ExtensionLoader.getExtensionLoader(com.alibaba.dubbo.common.extensionloader.ext1.SimpleExt.class).getExtension(extName); 根据extName扩展名去寻找真正需要的扩展实现类。此时extName是impl1，那么真正执行的echo就是impl1代表的SimpleExtImpl1实例
• #3同#1
• #4.1 url中map为("simple.ext", "impl2")
• #4.2 通过String extName = url.getParameter("simple.ext", "impl1")；获得extName为impl2
• #4.3 此时extName是impl2，那么真正执行的echo就是impl2代表的SimpleExtImpl2实例

    @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); #5 String echo = ext.yell(url, "haha"); assertEquals("Ext1Impl2-yell", echo); #6 url = url.addParameter("key1", "impl3"); // note: URL is value's type echo = ext.yell(url, "haha"); assertEquals("Ext1Impl3-yell", echo); } 

• #5.1 因为yell方法上@Adaptive注解有参数{"key1", "key2"}，那么ext生成的代理方法中获取extName代码为：String extName = url.getParameter("key1",url.getParameter("key2", "impl1"));
• #5.2 url中map为("key2", "impl2")，第一轮判后extName是impl2，第二轮判断后extName为impl2
• #5.3 此时extName是impl2，那么真正执行的echo就是impl2代表的SimpleExtImpl2实例
• #6.1 url中map为("key2", "impl2")("key1", "impl3") ,第一轮判后extName是impl2，第二轮判断后extName为impl3
• #6.2 此时extName是impl3，那么真正执行的echo就是impl3代表的SimpleExtImpl3实例
• 参数判断顺序与参数定义顺序相反

    @Test
    public void test_getAdaptiveExtension_protocolKey() throws Exception {
        #1
        UseProtocolKeyExt ext = ExtensionLoader.getExtensionLoader(UseProtocolKeyExt.class).getAdaptiveExtension(); { #2 String echo = ext.echo(URL.valueOf("1.2.3.4:20880"), "s"); assertEquals("Ext3Impl1-echo", echo); // default value #3 Map<String, String> map = new HashMap<String, String>(); URL url = new URL("impl3", "1.2.3.4", 1010, "path1", map); echo = ext.echo(url, "s"); assertEquals("Ext3Impl3-echo", echo); // use 2nd key, protocol #4 url = url.addParameter("key1", "impl2"); echo = ext.echo(url, "s"); assertEquals("Ext3Impl2-echo", echo); // use 1st key, key1 } 

• #1.该方法执行后会通过ExtensionLoader.createAdaptiveExtensionClassCode生成一个代理类对象ext，见附录2
• #2.1 echo方法@Adaptive注解中有值({"key1", "protocol"})，且其中一个为protocol，在ext中extName判断方法为url.getParameter("key1", (url.getProtocol() == null ? "impl1" : url.getProtocol()));
• #2.2 url中未指定protocol，同时map为null，判断后extName为默认值impl1
• #2.3 此时extName是impl1，那么真正执行的echo就是impl1代表的UseProtocolKeyExtImpl1实例
• #3.1 此时url的protocol为impl3，extName为impl3
• #3.2 此时extName是impl3，那么真正执行的echo就是impl3代表的UseProtocolKeyExtImpl3实例
• #4.1 此时url的proto是impl3，map("key1", "impl2")，extName是impl2
• #4.2 此时extName是impl2，那么真正执行的echo就是impl2代表的UseProtocolKeyExtImpl2实例

        {
    
            Map<String, String> map = new HashMap<String, String>();
            URL url = new URL(null, "1.2.3.4", 1010, "path1", map); #5 String yell = ext.yell(url, "s"); assertEquals("Ext3Impl1-yell", yell); // default value #6 url = url.addParameter("key2", "impl2"); // use 2nd key, key2 yell = ext.yell(url, "s"); assertEquals("Ext3Impl2-yell", yell); #7 url = url.setProtocol("impl3"); // use 1st key, protocol yell = ext.yell(url, "d"); assertEquals("Ext3Impl3-yell", yell); } } 

• #5.1 yell方法@Adaptive注解中有值({"protocol", "key1"})，且其中一个为protocol，在ext中extName判断方法为url.getProtocol() == null ? (url.getParameter( "key2", "impl1" ) ) : url.getProtocol()
• #5.2 url中未指定protocol，同时map为null，判断后extName为默认值impl1
• #5.3 此时extName是impl1，那么真正执行的echo就是impl1代表的UseProtocolKeyExtImpl1实例
• #6.1 此时map("key2", "impl2"),extName为impl2
• #6.2 此时extName是impl2，那么真正执行的echo就是impl2代表的UseProtocolKeyExtImpl2实例
• #7.1 此时url的proto是impl3，map("key1", "impl2")，extName是impl3
• #7.2 此时extName是impl3，那么真正执行的echo就是impl3代表的UseProtocolKeyExtImpl3实例

附录1

package com.alibaba.dubbo.common.extensionloader.ext1;

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


public class SimpleExt$Adaptive implements com.alibaba.dubbo.common.extensionloader.ext1.SimpleExt { public java.lang.String echo(com.alibaba.dubbo.common.URL arg0, java.lang.String arg1) { if (arg0 == null) { throw new IllegalArgumentException("url == null"); } com.alibaba.dubbo.common.URL url = arg0; String extName = url.getParameter("simple.ext", "impl1"); if (extName == null) { throw new IllegalStateException( "Fail to get extension(com.alibaba.dubbo.common.extensionloader.ext1.SimpleExt) name from url(" + url.toString() + ") use keys([simple.ext])"); } com.alibaba.dubbo.common.extensionloader.ext1.SimpleExt extension = (com.alibaba.dubbo.common.extensionloader.ext1.SimpleExt) ExtensionLoader.getExtensionLoader(com.alibaba.dubbo.common.extensionloader.ext1.SimpleExt.class) .getExtension(extName); return (extension.echo(arg0, arg1)); } public java.lang.String yell(com.alibaba.dubbo.common.URL arg0, java.lang.String arg1) { if (arg0 == null) { throw new IllegalArgumentException("url == null"); } com.alibaba.dubbo.common.URL url = arg0; String extName = url.getParameter("key1", url.getParameter("key2", "impl1")); if (extName == null) { throw new IllegalStateException( "Fail to get extension(com.alibaba.dubbo.common.extensionloader.ext1.SimpleExt) name from url(" + url.toString() + ") use keys([key1, key2])"); } com.alibaba.dubbo.common.extensionloader.ext1.SimpleExt extension = (com.alibaba.dubbo.common.extensionloader.ext1.SimpleExt) ExtensionLoader.getExtensionLoader(com.alibaba.dubbo.common.extensionloader.ext1.SimpleExt.class) .getExtension(extName); return (extension.yell(arg0, arg1)); } public java.lang.String bang(com.alibaba.dubbo.common.URL arg0, int arg1) { throw new UnsupportedOperationException( "method public abstract java.lang.String com.alibaba.dubbo.common.extensionloader.ext1.SimpleExt.bang(com.alibaba.dubbo.common.URL,int) of interface com.alibaba.dubbo.common.extensionloader.ext1.SimpleExt is not adaptive method!"); } } 

附录2

package com.alibaba.dubbo.common.extensionloader.ext3;
import com.alibaba.dubbo.common.extension.ExtensionLoader;
public class UseProtocolKeyExt$Adaptive implements com.alibaba.dubbo.common.extensionloader.ext3.UseProtocolKeyExt {
	public java.lang.String echo( com.alibaba.dubbo.common.URL arg0, java.lang.String arg1 )
	{
		if ( arg0 == null )
			throw new IllegalArgumentException( "url == null" ); com.alibaba.dubbo.common.URL url = arg0; String extName = url.getParameter( "key1", (url.getProtocol() == null ? "impl1" : url.getProtocol() ) ); if ( extName == null ) throw new IllegalStateException( "Fail to get extension(com.alibaba.dubbo.common.extensionloader.ext3.UseProtocolKeyExt) name from url(" + url.toString() + ") use keys([key1, protocol])" ); com.alibaba.dubbo.common.extensionloader.ext3.UseProtocolKeyExt extension = (com.alibaba.dubbo.common.extensionloader.ext3.UseProtocolKeyExt)ExtensionLoader.getExtensionLoader( com.alibaba.dubbo.common.extensionloader.ext3.UseProtocolKeyExt.class ).getExtension( extName ); return(extension.echo( arg0, arg1 ) ); } public java.lang.String yell( com.alibaba.dubbo.common.URL arg0, java.lang.String arg1 ) { if ( arg0 == null ) throw new IllegalArgumentException( "url == null" ); com.alibaba.dubbo.common.URL url = arg0; String extName = url.getProtocol() == null ? (url.getParameter( "key2", "impl1" ) ) : url.getProtocol(); if ( extName == null ) throw new IllegalStateException( "Fail to get extension(com.alibaba.dubbo.common.extensionloader.ext3.UseProtocolKeyExt) name from url(" + url.toString() + ") use keys([protocol, key2])" ); com.alibaba.dubbo.common.extensionloader.ext3.UseProtocolKeyExt extension = (com.alibaba.dubbo.common.extensionloader.ext3.UseProtocolKeyExt)ExtensionLoader. getExtensionLoader( com.alibaba.dubbo.common.extensionloader.ext3.UseProtocolKeyExt.class ).getExtension( extName ); return(extension.yell( arg0, arg1 ) ); } }