Dubbo的SPI机制介绍以及Adaptive实例

这篇文章主要讲解了"Dubbo的SPI机制介绍以及Adaptive实例"，文中的讲解内容简单清晰，易于学习与理解，下面请大家跟着小编的思路慢慢深入，一起来研究和学习"Dubbo的SPI机制介绍以及Adaptive实例"吧！

1、Dubbo的@Adaptive例子

@SPI("dubbo")public interface AdaptiveExt {    @Adaptive    // 单元测试方法4的注解为@Adaptive({"t"})    String echo(String msg, URL url);}

public class DubboAdaptiveExt implements AdaptiveExt {    @Override    public String echo(String msg, URL url) {        return "dubbo";    }}public class SpringCloudAdaptiveExt implements AdaptiveExt {    @Override    public String echo(String msg, URL url) {        return "spring cloud";    }}// 单元测试3中加上@Adaptive注解,其余不加@Adaptivepublic class ThriftAdaptiveExt implements AdaptiveExt {    @Override    public String echo(String msg, URL url) {        return "thrift";    }}

同时应当在resources目录下新建META-INF/dubbo文件夹,新建com.alibaba.dubbo.demo.provider.adaptive.AdaptiveExt,即接口的全限定名文件,文件内容为:

dubbo=com.alibaba.dubbo.demo.provider.adaptive.impl.DubboAdaptiveExtcloud=com.alibaba.dubbo.demo.provider.adaptive.impl.SpringCloudAdaptiveExtthrift=com.alibaba.dubbo.demo.provider.adaptive.impl.ThriftAdaptiveExt

下面是4个单元测试用例。观察4个测试用例的输出结果,我们可以得出以下结论:

1. 从测试3可以看出,若实现类加了@Adaptive注解,则它优先级最高,getAdaptiveExtension()创建的就是该类的实例

2. 从测试1看出,若SP注解上有值,且url参数中无值,并且没有类标注@Adaptive注解,则创建dubbo的key对应的类的实例

3. 从测试4看出,若方法上有注解@Adpative({"t"}),则URL中应当配上该参数t=cloud,创建cloud对应的实例

4. 从测试2看出,方法有注解@Adaptive,同时URL配置的是默认参数,该参数时通过AdaptiveExt通过转小写生成(adaptive.ext=cloud),则创建的就是cloud对应类的实例,可以看出,其实测试2和4类似,只要URL中有参数并且配置正确,则忽略@SPI注解上的值

所以可以得出优先级: @Adaptive标注的类 > URL参数 > @SPI注解中的值

/** * SPI上有注解,@SPI("dubbo"),url无参数,没有类上添加@Adaptive注解,方法@Adaptive注解上无参数,输出dubbo */@Testpublic void test1(){    ExtensionLoader loader = ExtensionLoader.getExtensionLoader(AdaptiveExt.class);    AdaptiveExt adaptiveExtension = loader.getAdaptiveExtension();    URL url = URL.valueOf("test://localhost/test");    System.out.println(adaptiveExtension.echo("d", url));}

/** * SPI上有注解,@SPI("dubbo"),URL中也有具体的值,输出spring cloud,注意这里对方法标注有@Adaptive注解,但是该注解没有值 */@Testpublic void test2(){    ExtensionLoader loader = ExtensionLoader.getExtensionLoader(AdaptiveExt.class);    AdaptiveExt adaptiveExtension = loader.getAdaptiveExtension();    URL url = URL.valueOf("test://localhost/test?adaptive.ext=cloud");    System.out.println(adaptiveExtension.echo("d", url));}

/** * SPI上有注解,@SPI("dubbo"),URL中也有具体的值,ThriftAdaptiveExt实现类上面有@Adaptive注解,输出thrift */@Testpublic void test3(){    ExtensionLoader loader = ExtensionLoader.getExtensionLoader(AdaptiveExt.class);    AdaptiveExt adaptiveExtension = loader.getAdaptiveExtension();    URL url = URL.valueOf("test://localhost/test?adaptive.ext=cloud");    System.out.println(adaptiveExtension.echo("d", url));}

/** * SPI上有注解,@SPI("dubbo"),URL中也有具体的值,接口方法中加上注解@Adaptive({"t"}),各个实现类上面没有 * @Adaptive注解,输出spring cloud */@Testpublic void test4(){    ExtensionLoader loader = ExtensionLoader.getExtensionLoader(AdaptiveExt.class);    AdaptiveExt adaptiveExtension = loader.getAdaptiveExtension();    URL url = URL.valueOf("test://localhost/test?t=cloud");    System.out.println(adaptiveExtension.echo("d", url));}

2、Dubbo的@Adaptive自适应拓展机制源码分析

2.1、测试用例1

首先先分析测试用例对应的源码,其余几种情况都差不多,1种情况分析透彻了,其余几种自然就清楚了.

// SPI上有注解,@SPI("dubbo"),url无参数,没有类上添加@Adaptive注解,方法@Adaptive注解上无参数,输出dubbo@Testpublic void test1(){    ExtensionLoader loader = ExtensionLoader.getExtensionLoader(AdaptiveExt.class);    AdaptiveExt adaptiveExtension = loader.getAdaptiveExtension();    URL url = URL.valueOf("test://localhost/test");    System.out.println(adaptiveExtension.echo("d", url));}

public T getAdaptiveExtension() {    Object instance = cachedAdaptiveInstance.get();    if (instance == null) {        if (createAdaptiveInstanceError == null) {            synchronized (cachedAdaptiveInstance) {                instance = cachedAdaptiveInstance.get();                if (instance == null) {                    try {                        // 创建自适应拓展代理类对象并放入缓存                        instance = createAdaptiveExtension();                        cachedAdaptiveInstance.set(instance);                    } catch (Throwable t) {                        // 抛异常                    }                }            }        } else {            // 抛异常        }    }    return (T) instance;}

private T createAdaptiveExtension() {    try {        // 分为3步:1是创建自适应拓展代理类Class对象,2是通过反射创建对象,3是给创建的对象按需依赖注入        return injectExtension((T) getAdaptiveExtensionClass().newInstance());    } catch (Exception e) {        // 抛异常    }}private Class getAdaptiveExtensionClass() {    // 从默认目录中加载标注了@SPI注解的实现类    getExtensionClasses();    // 如果有标注了@Adaptive注解实现类,那么cachedAdaptiveClass不为空,直接返回    if (cachedAdaptiveClass != null) {        return cachedAdaptiveClass;    }    // 创建自适应拓展代理类class文件    return cachedAdaptiveClass = createAdaptiveExtensionClass();}

private Class createAdaptiveExtensionClass() {    // code就是保存了创建的class字符串数据    String code = createAdaptiveExtensionClassCode();    ClassLoader classLoader = findClassLoader();    Compiler compiler = ExtensionLoader.getExtensionLoader(Compiler.class).getAdaptiveExtension();    return compiler.compile(code, classLoader);}

private String createAdaptiveExtensionClassCode() {    // 用来存放生成的代理类class文件    StringBuilder codeBuilder = new StringBuilder();    // 遍历标注有@SPI注解的接口的所有方法,这里分析的是com.alibaba.dubbo.demo.provider.adaptive.AdaptiveExt    Method[] methods = type.getMethods();    // 这些方法中应当致至少有一个方法被@Adaptive注解标注,否则不需要生成自适应代理类,直接抛出异常    boolean hasAdaptiveAnnotation = false;    for (Method m : methods) {        if (m.isAnnotationPresent(Adaptive.class)) {            hasAdaptiveAnnotation = true;            break;        }    }    // no need to generate adaptive class since there's no adaptive method found.    if (!hasAdaptiveAnnotation)        // 抛异常    // 生成包信息,形如package com.alibaba.dubbo.demo.provider.adaptive;    codeBuilder.append("package ").append(type.getPackage().getName()).append(";");    // 生成导包信息,形如import com.alibaba.dubbo.common.extension.ExtensionLoader;    codeBuilder.append("\nimport ").append(ExtensionLoader.class.getName()).append(";");    // 生成类名,形如public class AdaptiveExt$Adaptive     //                             implements com.alibaba.dubbo.demo.provider.adaptive.AdaptiveExt {    codeBuilder.append("\npublic class ").append(type.getSimpleName()).append("$Adaptive").                                 append(" implements ").append(type.getCanonicalName()).append(" {");    // 遍历所有方法,为SPI接口的所有方法生成代理方法    for (Method method : methods) {        // 方法返回值、参数、抛出异常        Class rt = method.getReturnType();        Class[] pts = method.getParameterTypes();        Class[] ets = method.getExceptionTypes();        // 获取方法上的Adaptive注解,如果方法上没有该注解,直接为该方法抛出异常        Adaptive adaptiveAnnotation = method.getAnnotation(Adaptive.class);        StringBuilder code = new StringBuilder(512);        if (adaptiveAnnotation == null) {            code.append("throw new UnsupportedOperationException(\"method ")                    .append(method.toString()).append(" of interface ")                    .append(type.getName()).append(" is not adaptive method!\");");        } else {            // urlTypeIndex用来记录URL这个参数在第几个参数位置上,这里String echo(String msg, URL url);            // 在位置1上            int urlTypeIndex = -1;            for (int i = 0; i < pts.length; ++i) {                if (pts[i].equals(URL.class)) {                    urlTypeIndex = i;                    break;                }            }            // 找到了URL参数            if (urlTypeIndex != -1) {                // 空指针检查                // s形如:if (arg1 == null) throw new IllegalArgumentException("url == null");                String s = String.format("\nif (arg%d == null)                               throw new IllegalArgumentException(\"url == null\");",urlTypeIndex);                code.append(s);                // s形如:com.alibaba.dubbo.common.URL url = arg1;                s = String.format("\n%s url = arg%d;", URL.class.getName(), urlTypeIndex);                code.append(s);            }            // 没找到,暂不分析,TODO            // 获取方法上的Adaptive注解的值,@Adaptive({"t"}),这里是t            String[] value = adaptiveAnnotation.value();            // 如果@Adaptive注解没有值,对应第二种测试情况,从接口名生成从url中获取参数的key,            // key为adaptive.ext,获取参数为url.getParameter("adaptive.ext", "dubbo")            // 因为第二种情况URL中传递了adaptive.ext这个参数,            // 所以String extName = url.getParameter("t", "dubbo");中获取的是cloud            if (value.length == 0) {                char[] charArray = type.getSimpleName().toCharArray();                StringBuilder sb = new StringBuilder(128);                for (int i = 0; i < charArray.length; i++) {                    if (Character.isUpperCase(charArray[i])) {                        if (i != 0) {                            sb.append(".");                        }                        sb.append(Character.toLowerCase(charArray[i]));                    } else {                        sb.append(charArray[i]);                    }                }                value = new String[]{sb.toString()};            }            // hasInvocation 暂不分析,TODO                                    // defaultExtName是dubbo,cachedDefaultName = names[0],这个值是@SPI("dubbo")里的            String defaultExtName = cachedDefaultName;            String getNameCode = null;            for (int i = value.length - 1; i >= 0; --i) {                if (i == value.length - 1) {                    if (null != defaultExtName) {                        if (!"protocol".equals(value[i]))                            if (hasInvocation)                                getNameCode =                                      String.format("url.getMethodParameter(methodName,                                                    \"%s\", \"%s\")", value[i], defaultExtName);                            else                                // 形如:url.getParameter("t", "dubbo");                                // 理解就是看url中有没有传t参数,传了就以url中为准,否则就取                                // @SPI("dubbo")中的为默认值                                getNameCode = String.format("url.getParameter(\"%s\", \"%s\")",                                                                      value[i], defaultExtName);                        else                            getNameCode = String.format("( url.getProtocol() == null ?                                                \"%s\" : url.getProtocol() )", defaultExtName);                    }                                       else {                        if (!"protocol".equals(value[i]))                            if (hasInvocation)                                getNameCode = String.format("url.getMethodParameter(methodName,                                                    \"%s\", \"%s\")", value[i], defaultExtName);                            else                                getNameCode = String.format("url.getParameter(\"%s\")", value[i]);                        else                            getNameCode = "url.getProtocol()";                    }                } else {                    if (!"protocol".equals(value[i]))                        if (hasInvocation)                            getNameCode = String.format("url.getMethodParameter(methodName,                                                      \"%s\", \"%s\")", value[i], defaultExtName);                        else                            getNameCode = String.format("url.getParameter(\"%s\", %s)",                                                                           value[i], getNameCode);                    else                        getNameCode = String.format("url.getProtocol() == null ?                                                          (%s) : url.getProtocol()", getNameCode);                }            }            // 形如:String extName = url.getParameter("t", "dubbo");            // 这个extName就是要为@SPI标注的接口生成哪个代理类            code.append("\nString extName = ").append(getNameCode).append(";");            // check extName == null?            // 形如:if (extName == null)  throw new IllegalStateException("...");            String s = String.format("\nif(extName == null) " +                            "throw new IllegalStateException(\"Fail to get extension(%s)                                  name from url(\" + url.toString() + \") use keys(%s)\");",                                                         type.getName(), Arrays.toString(value));            code.append(s);            // AdaptiveExt extension = (AdaptiveExt)            //       ExtensionLoader.getExtensionLoader(AdaptiveExt.class).getExtension(extName);            s = String.format("\n%s extension = (% 0) {                codeBuilder.append(", ");            }            codeBuilder.append(pts[i].getCanonicalName());            codeBuilder.append(" ");            codeBuilder.append("arg").append(i);        }        codeBuilder.append(")");        // 异常        if (ets.length > 0) {            codeBuilder.append(" throws ");            for (int i = 0; i < ets.length; i++) {                if (i > 0) {                    codeBuilder.append(", ");                }                codeBuilder.append(ets[i].getCanonicalName());            }        }        codeBuilder.append(" {");        codeBuilder.append(code.toString());        codeBuilder.append("\n}");    }    codeBuilder.append("\n}");    if (logger.isDebugEnabled()) {        logger.debug(codeBuilder.toString());    }    return codeBuilder.toString();}

通过这一系列代码,Dubbo就为AdaptiveExt根据@SPI的注解值dubbo生成了一个自适应拓展代理类,类代码如下:

package com.alibaba.dubbo.demo.provider.adaptive;import com.alibaba.dubbo.common.extension.ExtensionLoader;public class AdaptiveExt$Adaptive implements com.alibaba.dubbo.demo.provider.adaptive.AdaptiveExt {    public java.lang.String echo(java.lang.String arg0, com.alibaba.dubbo.common.URL arg1) {        if (arg1 == null)             throw new IllegalArgumentException("url == null");        com.alibaba.dubbo.common.URL url = arg1;        // 核心,通过上面的分析我们知道,并没有配置t参数,所以URL取不到t参数,则以默认值dubbo代替,而dubbo就是        // @SPI注解的值,adaptiveExtension.echo("d", url),执行这句代码时,adaptiveExtension实际上是        // AdaptiveExt$Adaptive的实例对象,因此会走到它的echo方法中        String extName = url.getParameter("t", "dubbo");        if (extName == null)            throw new IllegalStateException("Fail to get extension(AdaptiveExt) name                                                  from url(" + url.toString() + ") use keys([t])");        // 为了排版布局,使用了简写AdaptiveExt.class,但是应当知道这里应当是全限定名        // 这里面根据extName去获取Adaptive实例对象,获取的是dubbo的key对应的DubboAdaptiveExt实例对象        com.alibaba.dubbo.demo.provider.adaptive.AdaptiveExt extension =                           (com.alibaba.dubbo.demo.provider.adaptive.AdaptiveExt)                                     ExtensionLoader.getExtensionLoader(AdaptiveExt.class).                                                                           getExtension(extName);        // 所以会走DubboAdaptiveExt的echo方法,输出dubbo        return extension.echo(arg0, arg1);    }}

2.2、测试用例2和4

分析完了测试用例1,再来分析2和4就简单多了,看代码.归纳起来就是,如果方法上配置了@Adaptive,就将接口名转小写(adaptive.ext),去URL中取这个参数对应的值,即url.getParameter("adaptive.ext", "dubbo")的值作为extName,生成的也是extName对应的类.如果方法上配置了@Adaptive({"t"}),则以url.getParameter("t", "dubbo")这种方式去取值作为extName.

// 获取方法上的Adaptive注解的值,@Adaptive({"t"}),这里是tString[] value = adaptiveAnnotation.value();// 如果@Adaptive注解没有值,对应第二种测试情况,从接口名生成从url中获取参数的key,key为adaptive.ext,获取参数// 为url.getParameter("adaptive.ext", "dubbo")// 因为第二种情况URL中传递了adaptive.ext这个参数,所以String extName = url.getParameter("t", "dubbo");中获取的是cloudif (value.length == 0) {    char[] charArray = type.getSimpleName().toCharArray();    StringBuilder sb = new StringBuilder(128);    for (int i = 0; i < charArray.length; i++) {        if (Character.isUpperCase(charArray[i])) {            if (i != 0) {                sb.append(".");            }            sb.append(Character.toLowerCase(charArray[i]));        } else {            sb.append(charArray[i]);        }    }    value = new String[]{sb.toString()};}

// defaultExtName是dubbo,cachedDefaultName = names[0],这个值是@SPI("dubbo")里的String defaultExtName = cachedDefaultName;String getNameCode = null;for (int i = value.length - 1; i >= 0; --i) {    if (i == value.length - 1) {        if (null != defaultExtName) {            if (!"protocol".equals(value[i]))                if (hasInvocation)                    // 删除部分代码                else                    // 形如:url.getParameter("t", "dubbo");                    // 理解就是看url中有没有传t参数,传了就以url中为准,否则就取@SPI("dubbo")中的为默认值                    getNameCode = String.format("url.getParameter(\"%s\", \"%s\")", value[i], defaultExtName);            else                // 删除部分代码        } else {            // 删除部分代码        }    } }// 形如:String extName = url.getParameter("t", "dubbo");// 这个extName就是要为@SPI标注的接口生成哪个代理类code.append("\nString extName = ").append(getNameCode).append(";");

2.3、测试用例3

接下来分析测试用例3,即ThriftAdaptiveExt类上面标注了@Adaptive注解,前面也说过,它的优先级最高,下面看代码.

 private Class getAdaptiveExtensionClass() {    // 1.从默认目录中加载标注了@SPI注解的实现类    getExtensionClasses();    // 2.如果有标注了@Adaptive注解实现类,那么cachedAdaptiveClass不为空,直接返回    if (cachedAdaptiveClass != null) {        return cachedAdaptiveClass;    }    // 3.创建自适应拓展代理类class文件    return cachedAdaptiveClass = createAdaptiveExtensionClass();}

前面我们分析没有类上面标注@Adaptive注解时,dubbo需要根据配置情况为接口生成自适应拓展代理类,也就是上述对应的步骤3代码.但是当有类标注了@Adaptive注解时,情况就不一样了.看上面步骤1getExtensionClasses()会走到下面loadClass方法,当解析到ThriftAdaptiveExt类时,发现它满足clazz.isAnnotationPresent(Adaptive.class)条件,因此cachedAdaptiveClass = clazz被缓存起来,不会再走后面的逻辑.这样当走步骤2时,直接返回cachedAdaptiveClass.那么dubbo为AdaptiveExt接口生成的自适应拓展就是ThriftAdaptiveExt.

private void loadClass(Map> extensionClasses, java.net.URL resourceURL,                                    Class clazz, String name) throws NoSuchMethodException {    // 判断clazz是否为标注了@Adaptive注解,后面分析    if (clazz.isAnnotationPresent(Adaptive.class)) {        if (cachedAdaptiveClass == null) {            cachedAdaptiveClass = clazz;        } else if (!cachedAdaptiveClass.equals(clazz)) {            throw new IllegalStateException("More than 1 adaptive class found: "                    + cachedAdaptiveClass.getClass().getName()                    + ", " + clazz.getClass().getName());        }    }    // 删除无关代码}

感谢各位的阅读，以上就是"Dubbo的SPI机制介绍以及Adaptive实例"的内容了，经过本文的学习后，相信大家对Dubbo的SPI机制介绍以及Adaptive实例这一问题有了更深刻的体会，具体使用情况还需要大家实践验证。这里是，小编将为大家推送更多相关知识点的文章，欢迎关注！