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Dubbo的SPI实现

2017-12-05 00:11 134 查看
在Dubbo中,例如protocol的选择都是通过@SPI来实现的。

以ReferenceConfig获取相应配置的协议protocol作为扩展点为例子。

private static final Protocol refprotocol = ExtensionLoader.getExtensionLoader(Protocol.class).getAdaptiveExtension();

在ReferenceConfig当中,协议protocol的选择并没有在代码中显式地表现出来。可以看首先通过了将protocol的类作为参数传递给了ExtensionLoader的静态方法专门获得了针对这protocol这一类的ExtensionLoader作为第一步。可以看它的getExtensionLoader()方法。

public static <T> ExtensionLoader<T> getExtensionLoader(Class<T> type) {
if (type == null)
throw new IllegalArgumentException("Extension type == null");
if(!type.isInterface()) {
throw new IllegalArgumentException("Extension type(" + type + ") is not interface!");
}
if(!withExtensionAnnotation(type)) {
throw new IllegalArgumentException("Extension type(" + type +
") is not extension, because WITHOUT @" + SPI.class.getSimpleName() + " Annotation!");
}

ExtensionLoader<T> loader = (ExtensionLoader<T>) EXTENSION_LOADERS.get(type);
if (loader == null) {
EXTENSION_LOADERS.putIfAbsent(type, new ExtensionLoader<T>(type));
loader = (ExtensionLoader<T>) EXTENSION_LOADERS.get(type);
}
return loader;
}

在这个方法里如果传递进来的类型是空的或者并不是接口,都会抛出非法的参数异常,但是值得一提的是,如果传递的参数类型没有实现@SPI注解,也会抛出相应的参数异常。

private static <T> boolean withExtensionAnnotation(Class<T> type) {
return type.isAnnotationPresent(SPI.class);
}

也就是说,能够被ExtensionLoader所自动装配的接口类都要实现@SPI接口。

@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE})
public @interface SPI {

/**
* 缺省扩展点名。
*/
String value() default "";

}

@SPI只有一个参数可以配置,那就是value,用来选择默认的扩展点的配置。

例如Protocol类作为接口也实现了@SPI,默认的value为dubbo,也就是说明在dubbo框架中默认选用dubbo协议。

在getExtensionLoader()方法检验完作为参数传递进来的类type之后,就会尝试在以类和类对应得到ExtensionLoader作为键值对存储的map中取得对应的ExtensionLoader。如果没有取到,则需要重新调用ExtensionLoader类的构造方法来获得新的类所对应的ExtensionLoader。

ExtensionLoader的构造方法实现的相当简单。

private ExtensionLoader(Class<?> type) {
this.type = type;
objectFactory = (type == ExtensionFactory.class ? null : ExtensionLoader.getExtensionLoader(ExtensionFactory.class).getAdaptiveExtension());
}

只是将类型存储,而类工厂的创建也与在ReferenceConfig中获取Protocol的方式也几乎一模一样,可以等等回来看这里类工厂的获取。

在成功创建了ExtensionLoader之后,尝试将类与相应的ExtensionLoader放在map里以便在后面的情况下不用再调用相应的构造方法获取新的ExtensionLoader实例。

在ReferenceConfig中,成功获取了类接口Protocol所对应的ExtensionLoader之后,将会在后面调用getAdaptiveExtension()方法获取真正需要拿来使用的具体protocol扩展点适配类。

可以看到他的getAdaptiveExtension()方法。

public T getAdaptiveExtension() {
Object instance = cachedAdaptiveInstance.get();
if (instance == null) {
if(createAdaptiveInstanceError == null) {
synchronized (cachedAdaptiveInstance) {
instance = cachedAdaptiveInstance.get();
if (instance == null) {
try {
instance = createAdaptiveExtension();
cachedAdaptiveInstance.set(instance);
} catch (Throwable t) {
createAdaptiveInstanceError = t;
throw new IllegalStateException("fail to create adaptive instance: " + t.toString(), t);
}
}
}
}
else {
throw new IllegalStateException("fail to create adaptive instance: " + createAdaptiveInstanceError.toString(), createAdaptiveInstanceError);
}
}

return (T) instance;
}

如果之前已经调用过这个方法,也就可以直接返回所需要的扩展点了,但是如果是第一次,那么则会通过createAdaptiveExtension()方法获取新的扩展点。

private T createAdaptiveExtension() {
try {
return injectExtension((T) getAdaptiveExtensionClass().newInstance());
} catch (Exception e) {
throw new IllegalStateException("Can not create adaptive extenstion " + type + ", cause: " + e.getMessage(), e);
}
}

getAdaptiveExtensionClass()则首先会通过getExtensionClasses()方法获取扩展点的类们。

private Map<String, Class<?>> getExtensionClasses() {
Map<String, Class<?>> classes = cachedClasses.get();
if (classes == null) {
synchronized (cachedClasses) {
classes = cachedClasses.get();
if (classes == null) {
classes = loadExtensionClasses();
cachedClasses.set(classes);
}
}
}
return classes;
}
如果是第一次调用,则会通过loadExtensionClasses()方法加载所需要的扩展点的类。
private Map<String, Class<?>> loadExtensionClasses() {
final SPI defaultAnnotation = type.getAnnotation(SPI.class);
if(defaultAnnotation != null) {
String value = defaultAnnotation.value();
if(value != null && (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()
+ ":
f5e7
" + Arrays.toString(names));
}
if(names.length == 1) cachedDefaultName = names[0];
}
}

Map<String, Class<?>> extensionClasses = new HashMap<String, Class<?>>();
loadFile(extensionClasses, DUBBO_INTERNAL_DIRECTORY);
loadFile(extensionClasses, DUBBO_DIRECTORY);
loadFile(extensionClasses, SERVICES_DIRECTORY);
return extensionClasses;
}

在load方法中,首先会尝试获取ExtensionLoader所对应的类的@SPI中的value属性,如果存在,就则会将其默认扩展点的名字配在这里置为value的值。

之后会尝试在

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/";

下面三个目录中尝试寻找并读取配置文件对于扩展点类的配置。

一个默认的配置文件如这样所写。

registry=com.alibaba.dubbo.registry.integration.RegistryProtocol
filter=com.alibaba.dubbo.rpc.protocol.ProtocolFilterWrapper
listener=com.alibaba.dubbo.rpc.protocol.ProtocolListenerWrapper
mock=com.alibaba.dubbo.rpc.support.MockProtocol
injvm=com.alibaba.dubbo.rpc.protocol.injvm.InjvmProtocol
dubbo=com.alibaba.dubbo.rpc.protocol.dubbo.DubboProtocol
rmi=com.alibaba.dubbo.rpc.protocol.rmi.RmiProtocol
hessian=com.alibaba.dubbo.rpc.protocol.hessian.HessianProtocol
com.alibaba.dubbo.rpc.protocol.http.HttpProtocol
com.alibaba.dubbo.rpc.protocol.webservice.WebServiceProtocol
thrift=com.alibaba.dubbo.rpc.protocol.thrift.ThriftProtocol
memcached=memcom.alibaba.dubbo.rpc.protocol.memcached.MemcachedProtocol
redis=com.alibaba.dubbo.rpc.protocol.redis.RedisProtocol
从loadFile()方法看到对于配置文件的读取并处理。
private void loadFile(Map<String, Class<?>> extensionClasses, String dir) {
String fileName = dir + type.getName();
try {
Enumeration<java.net.URL> urls;
ClassLoader classLoader = findClassLoader();
if (classLoader != null) {
urls = classLoader.getResources(fileName);
} else {
urls = ClassLoader.getSystemResources(fileName);
}
if (urls != null) {
while (urls.hasMoreElements()) {
java.net.URL url = urls.nextElement();
try {
BufferedReader reader = new BufferedReader(new InputStreamReader(url.openStream(), "utf-8"));
try {
String line = null;
while ((line = reader.readLine()) != null) {
final int ci = line.indexOf('#');
if (ci >= 0) line = line.substring(0, ci);
line = line.trim();
if (line.length() > 0) {
try {
String name = null;
int i = line.indexOf('=');
if (i > 0) {
name = line.substring(0, i).trim();
line = line.substring(i + 1).trim();
}
if (line.length() > 0) {
Class<?> clazz = Class.forName(line, true, classLoader);
if (! type.isAssignableFrom(clazz)) {
throw new IllegalStateException("Error when load extension class(interface: " +
type + ", class line: " + clazz.getName() + "), class "
+ clazz.getName() + "is not subtype of interface.");
}
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());
}
} else {
try {
clazz.getConstructor(type);
Set<Class<?>> wrappers = cachedWrapperClasses;
if (wrappers == null) {
cachedWrapperClasses = new ConcurrentHashSet<Class<?>>();
wrappers = cachedWrapperClasses;
}
wrappers.add(clazz);
} catch (NoSuchMethodException e) {
clazz.getConstructor();
if (name == null || name.length() == 0) {
name = findAnnotationName(clazz);
if (name == null || name.length() == 0) {
if (clazz.getSimpleName().length() > type.getSimpleName().length()
&& clazz.getSimpleName().endsWith(type.getSimpleName())) {
name = clazz.getSimpleName().substring(0, clazz.getSimpleName().length() - type.getSimpleName().length()).toLowerCase();
} else {
throw new IllegalStateException("No such extension name for the class " + clazz.getName() + " in the config " + url);
}
}
}
String[] names = NAME_SEPARATOR.split(name);
if (names != null && names.length > 0) {
Activate activate = clazz.getAnnotation(Activate.class);
if (activate != null) {
cachedActivates.put(names[0], activate);
}
for (String n : names) {
if (! cachedNames.containsKey(clazz)) {
cachedNames.put(clazz, n);
}
Class<?> c = extensionClasses.get(n);
if (c == null) {
extensionClasses.put(n, clazz);
} else if (c != clazz) {
throw new IllegalStateException("Duplicate extension " + type.getName() + " name " + n + " on " + c.getName() + " and " + clazz.getName());
}
}
}
}
}
}
} catch (Throwable t) {
IllegalStateException e = new IllegalStateException("Failed to load extension class(interface: " + type + ", class line: " + line + ") in " + url + ", cause: " + t.getMessage(), t);
exceptions.put(line, e);
}
}
} // end of while read lines
} finally {
reader.close();
}
} catch (Throwable t) {
logger.error("Exception when load extension class(interface: " +
type + ", class file: " + url + ") in " + url, t);
}
} // end of while urls
}
} catch (Throwable t) {
logger.error("Exception when load extension class(interface: " +
type + ", description file: " + fileName + ").", t);
}
}

loadFile的过程代码很长,但思路依旧清晰。

之前可以看到,具体的配置文件以key/value的形式配置在文件里的。由此,这里的操作比较清晰。

当通过反射具体的通过类名获取类的结构时,首先判断是否实现了@Adaptive接口,如果实现了,则作为适配类来保存。否则,判断这个类是否有单独以ExtensionLoader所对应的类作为唯一参数的构造方法,如果有,则作为包装类存储在缓存里面,如果两者都没有,则会,通过判断是否有方法实现了@Active注解,如果有,则可以当作扩展点的具体实现类保存在缓存里面。

在加载完毕相应的扩展类之后,如果,在之前的类加载当中,并没有找到带有@Adaptive注解的适配类,则在得到缓存的类map之后就,就会通过createAdaptiveExtensionClass()方法动态生成适配类。

private Class<?> createAdaptiveExtensionClass() {
String code = createAdaptiveExtensionClassCode();
ClassLoader classLoader = findClassLoader();
com.alibaba.dubbo.common.compiler.Compiler compiler = ExtensionLoader.getExtensionLoader(com.alibaba.dubbo.common.compiler.Compiler.class).getAdaptiveExtension();
return compiler.compile(code, classLoader);
}

首先,就要通过createAdaptiveExtensionClassCode()生成适配类的字节码。

private String createAdaptiveExtensionClassCode() {
StringBuilder codeBuidler = new StringBuilder();
Method[] methods = type.getMethods();
boolean hasAdaptiveAnnotation = false;
for(Method m : methods) {
if(m.isAnnotationPresent(Adaptive.class)) {
hasAdaptiveAnnotation = true;
break;
}
}
// 完全没有Adaptive方法,则不需要生成Adaptive类
if(! hasAdaptiveAnnotation)
throw new IllegalStateException("No adaptive method on extension " + type.getName() + ", refuse to create the adaptive class!");

codeBuidler.append("package " + type.getPackage().getName() + ";");
codeBuidler.append("\nimport " + ExtensionLoader.class.getName() + ";");
codeBuidler.append("\npublic class " + type.getSimpleName() + "$Adpative" + " implements " + type.getCanonicalName() + " {");

for (Method method : methods) {
Class<?> rt = method.getReturnType();
Class<?>[] pts = method.getParameterTypes();
Class<?>[] ets = method.getExceptionTypes();

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 {
int urlTypeIndex = -1;
for (int i = 0; i < pts.length; ++i) {
if (pts[i].equals(URL.class)) {
urlTypeIndex = i;
break;
}
}
// 有类型为URL的参数
if (urlTypeIndex != -1) {
// Null Point check
String s = String.format("\nif (arg%d == null) throw new IllegalArgumentException(\"url == null\");",
urlTypeIndex);
code.append(s);

s = String.format("\n%s url = arg%d;", URL.class.getName(), urlTypeIndex);
code.append(s);
}
// 参数没有URL类型
else {
String attribMethod = null;

// 找到参数的URL属性
LBL_PTS:
for (int i = 0; i < pts.length; ++i) {
Method[] ms = pts[i].getMethods();
for (Method m : ms) {
String name = m.getName();
if ((name.startsWith("get") || name.length() > 3)
&& Modifier.isPublic(m.getModifiers())
&& !Modifier.isStatic(m.getModifiers())
&& m.getParameterTypes().length == 0
&& m.getReturnType() == URL.class) {
urlTypeIndex = i;
attribMethod = name;
break LBL_PTS;
}
}
}
if(attribMethod == null) {
throw new IllegalStateException("fail to create adative class for interface " + type.getName()
+ ": not found url parameter or url attribute in parameters of method " + method.getName());
}

// Null point check
String s = String.format("\nif (arg%d == null) throw new IllegalArgumentException(\"%s argument == null\");",
urlTypeIndex, pts[urlTypeIndex].getName());
code.append(s);
s = String.format("\nif (arg%d.%s() == null) throw new IllegalArgumentException(\"%s argument %s() == null\");",
urlTypeIndex, attribMethod, pts[urlTypeIndex].getName(), attribMethod);
code.append(s);

s = String.format("%s url = arg%d.%s();",URL.class.getName(), urlTypeIndex, attribMethod);
code.append(s);
}

String[] value = adaptiveAnnotation.value();
// 没有设置Key,则使用“扩展点接口名的点分隔 作为Key
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()};
}

boolean hasInvocation = false;
for (int i = 0; i < pts.length; ++i) {
if (pts[i].getName().equals("com.alibaba.dubbo.rpc.Invocation")) {
// Null Point check
String s = String.format("\nif (arg%d == null) throw new IllegalArgumentException(\"invocation == null\");", i);
code.append(s);
s = String.format("\nString methodName = arg%d.getMethodName();", i);
code.append(s);
hasInvocation = true;
break;
}
}

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
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);
}
}
code.append("\nString extName = ").append(getNameCode).append(";");
// check extName == null?
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);

s = String.format("\n%s extension = (%<s)%s.getExtensionLoader(%s.class).getExtension(extName);",
type.getName(), ExtensionLoader.class.getSimpleName(), type.getName());
code.append(s);

// return statement
if (!rt.equals(void.class)) {
code.append("\nreturn ");
}

s = String.format("extension.%s(", method.getName());
code.append(s);
for (int i = 0; i < pts.length; i++) {
if (i != 0)
code.append(", ");
code.append("arg").append(i);
}
code.append(");");
}

codeBuidler.append("\npublic " + rt.getCanonicalName() + " " + method.getName() + "(");
for (int i = 0; i < pts.length; i ++) {
if (i > 0) {
codeBuidler.append(", ");
}
codeBuidler.append(pts[i].getCanonicalName());
codeBuidler.append(" ");
codeBuidler.append("arg" + i);
}
codeBuidler.append(")");
if (ets.length > 0) {
codeBuidler.append(" throws ");
for (int i = 0; i < ets.length; i ++) {
if (i > 0) {
codeBuidler.append(", ");
}
codeBuidler.append(pts[i].getCanonicalName());
}
}
codeBuidler.append(" {");
codeBuidler.append(code.toString());
codeBuidler.append("\n}");
}
codeBuidler.append("\n}");
if (logger.isDebugEnabled()) {
logger.debug(codeBuidler.toString());
}
return codeBuidler.toString();
}

在这个方法,首先对应类型中是否有实现了@Adaptive注解的方法,如果有,则需要在下面实现适配类的字节码构造,否则就没有必要实现适配类了。

在所要产生对应的适配类里,实现的方法也是必须要实现了@Adaptive注解的方法,否则会在下面的方法中写为调用就抛出异常。

if (adaptiveAnnotation == null) {
code.append("throw new UnsupportedOperationException(\"method ")
.append(method.toString()).append(" of interface ")
.append(type.getName()).append(" is not adaptive method!\");");
}

在配置了相应的注解的方法里,参数如果不是dubbo中的URL数据结构,则会遍历参数类中的get方法寻找URL参数。

接下来,以实现了@Adaptive注解的refer方法为例子,会在适配类当中实现这样的refer()方法。

publiccom.alibaba.dubbo.rpc.Invoker refer(java.lang.Class arg0,
com.alibaba.dubbo.common.URLarg1) throws java.lang.Class {

if (arg1 == null)
throw newIllegalArgumentException("url == null");

com.alibaba.dubbo.common.URL url =arg1;

String extName = (url.getProtocol() == null ?"dubbo" : url.getProtocol());
if (extName == null)
thrownewIllegalStateException("Failtogetextension(com.alibaba.dubbo.rpc.Protocol)name from url("+ url.toString() + ") use keys([protocol])");

com.alibaba.dubbo.rpc.Protocol extension =(com.alibaba.dubbo.rpc.Protocol)  ExtensionLoader.getExtensionLoader(com.alibaba.dubbo.rpc.Protocol.class)
.getExtension(extName);
return extension.refer(arg0, arg1);
}
}


到这里,ExtensionLoader的实现可以说是一目了然了。而在这里,默认@SPI的value默认配置也在这里巧妙实现,如果选择了别的配置,也可以在这里通过传递进来的protocol通过getExtension()方法,获取别的配置在了之前配置文件并被加载进来的扩展类。

在getExtension()方法中会直接尝试获取扩展类的实例,如果此时相应的实例还没有别创建,则会通过createExtension()方法新创建新的实例。

private T createExtension(String name) {
Class<?> clazz = getExtensionClasses().get(name);
if (clazz == null) {
throw findException(name);
}
try {
T instance = (T) EXTENSION_INSTANCES.get(clazz);
if (instance == null) {
EXTENSION_INSTANCES.putIfAbsent(clazz, (T) clazz.newInstance());
instance = (T) EXTENSION_INSTANCES.get(clazz);
}
injectExtension(instance);
Set<Class<?>> wrapperClasses = cachedWrapperClasses;
if (wrapperClasses != null && wrapperClasses.size() > 0) {
for (Class<?> wrapperClass : wrapperClasses) {
instance = injectExtension((T) wrapperClass.getConstructor(type).newInstance(instance));
}
}
return instance;
} catch (Throwable t) {
throw new IllegalStateException("Extension instance(name: " + name + ", class: " +
type + ")  could not be instantiated: " + t.getMessage(), t);
}
}

在这个方法中,值得注意的是在通过构造方法得到新的实例之后,会通过injectExtension()方法从在一开始配置方法中配置的类工厂插入对所需要注入的类成员属性进行注入。然后如果在之前的文件加载类的过程中配置了包装类,则会在这里直接使用包装类对刚创建的实例进行包装,例如在protocolFilterWrapper的创建中,会为具体的protocol构造拦截器链。

回到适配类的字节码生成完毕之后,通过compiler的适配类,编译新的适配类字节码‘,从而动态获得适配类的实例。最后在通过类工厂注入完毕相应的成员之后,就得到了ReferenceConfig中的protocol的适配类。

并不是所有接口都需要动态生成相应的适配类。

以类工厂为例子,下面是默认的类工厂配置文件。

adaptive=com.alibaba.dubbo.common.extension.factory.AdaptiveExtensionFactory
spi=com.alibaba.dubbo.common.extension.factory.SpiExtensionFactory
spring=com.alibaba.dubbo.config.spring.extension.SpringExtensionFactory

在这里已经确认了适配类,也就不用动态的生成适配类。

@Adaptive
public class AdaptiveExtensionFactory implements ExtensionFactory {

private final List<ExtensionFactory> factories;

public AdaptiveExtensionFactory() {
ExtensionLoader<ExtensionFactory> loader = ExtensionLoader.getExtensionLoader(ExtensionFactory.class);
List<ExtensionFactory> list = new ArrayList<ExtensionFactory>();
for (String name : loader.getSupportedExtensions()) {
list.add(loader.getExtension(name));
}
factories = Collections.unmodifiableList(list);
}

public <T> T getExtension(Class<T> type, String name) {
for (ExtensionFactory factory : factories) {
T extension = factory.getExtension(type, name);
if (extension != null) {
return extension;
}
}
return null;
}

}


在其构造方法中,会已经主动将剩下的两者从loader中获取实例并保存,之后如果需要类工厂来给新的实例进行成员注入,将会直接在这里的getExtension()中依次获取具体的类工厂进行成员注入。
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