开篇
这篇文章尝试分析dubbo中getAdaptiveExtension过程，且以ExtensionFactory作为例子进行分析。
在这篇文章中我们会了解ExtensionFactory的几个对象AdaptiveExtensionFactory、SpringExtensionFactory、SpiExtensionFactory的初始化过程，然后在这个过程中一窥getAdaptiveExtension的全貌。
引用例子
说明：
- ExtensionLoader的使用分两步走，先getExtensionLoader后getAdaptiveExtension。
- getExtensionLoader返回对应类的ExtensionLoader。
- getAdaptiveExtension返回对应类的AdaptiveExtension。
- Protocol会返回Protocol$Adaptive的扩展类.
public class ServiceConfig<T> extends AbstractServiceConfig {
private static final Protocol protocol = ExtensionLoader.getExtensionLoader(Protocol.class).getAdaptiveExtension();
}ExtensionLoader介绍
核心变量说明:
- EXTENSION_LOADERS保存ExtensionLoader所有的loader对象。
- DIRECTORY目录保存所有需要访问SPI文件的目录。
- cachedAdaptiveClass保存type对应的AdaptiveClass。
- cachedClasses保存type对应的cachedClasses。
- type需要加载的类，如ExtensionFactory.class或Protocol.class。
- objectFactory保存ExtensionFactory对象。
过程说明：
- getExtensionLoader内部最终都会执行ExtensionLoader.getExtensionLoader(ExtensionFactory.class)
.getAdaptiveExtension()。 - ExtensionLoader.getExtensionLoader(ExtensionFactory.class)生成type为ExtensionFactory的ExtensionLoader。
- getAdaptiveExtension()最终执行ExtensionFactory的ExtensionLoader的getAdaptiveExtension()方法。
public class ExtensionLoader<T> {
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/";
private static final Pattern NAME_SEPARATOR = Pattern.compile("\\s*[,]+\\s*");
private static final ConcurrentMap<Class<?>, ExtensionLoader<?>> EXTENSION_LOADERS = new ConcurrentHashMap<Class<?>, ExtensionLoader<?>>();
private static final ConcurrentMap<Class<?>, Object> EXTENSION_INSTANCES = new ConcurrentHashMap<Class<?>, Object>();
// ==============================
private final Class<?> type;
//todo objectFactory保存的是ExtensionFactory
private final ExtensionFactory objectFactory;
private final ConcurrentMap<Class<?>, String> cachedNames = new ConcurrentHashMap<Class<?>, String>();
private final Holder<Map<String, Class<?>>> cachedClasses = new Holder<Map<String, Class<?>>>();
private final Map<String, Activate> cachedActivates = new ConcurrentHashMap<String, Activate>();
private final ConcurrentMap<String, Holder<Object>> cachedInstances = new ConcurrentHashMap<String, Holder<Object>>();
private final Holder<Object> cachedAdaptiveInstance = new Holder<Object>();
private volatile Class<?> cachedAdaptiveClass = null;
private String cachedDefaultName;
private volatile Throwable createAdaptiveInstanceError;
private Set<Class<?>> cachedWrapperClasses;
private Map<String, IllegalStateException> exceptions = new ConcurrentHashMap<String, IllegalStateException>();
private ExtensionLoader(Class<?> type) {
this.type = type;
objectFactory = (type == ExtensionFactory.class ? null : ExtensionLoader.getExtensionLoader(ExtensionFactory.class).getAdaptiveExtension());
}
@SuppressWarnings("unchecked")
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;
}
}getAdaptiveExtension
说明:
- 按照getAdaptiveExtension => createAdaptiveExtension => getAdaptiveExtensionClass().newInstance()流程进行分析。
public class ExtensionLoader<T> {
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;
}
private T createAdaptiveExtension() {
try {
return injectExtension((T) getAdaptiveExtensionClass().newInstance());
} catch (Exception e) {
throw new IllegalStateException("Can not create adaptive extension " + type + ", cause: " + e.getMessage(), e);
}
}
}getAdaptiveExtensionClass
说明：
- 类加载按照getExtensionClasses => loadExtensionClasses => loadFile流程。
- getExtensionClasses会判断是否有缓存，没缓存则走loadExtensionClasses加载类。
- getAdaptiveExtensionClass会判断是否有缓存，有则返回cachedAdaptiveClass，没有走createAdaptiveExtensionClass流程。
- ExtensionFactory的对应的类型不会走createAdaptiveExtensionClass过程，但其他如创建Protocol.class的工程则会走createAdaptiveExtensionClass流程。
- ExtensionFactory的getAdaptiveExtensionClass()方法返回AdaptiveExtensionFactory。
public class ExtensionLoader<T> {
private Class<?> getAdaptiveExtensionClass() {
//todo 核心在于读取文件当中所有的类定义并将这些类进行加载
getExtensionClasses();
if (cachedAdaptiveClass != null) {
return cachedAdaptiveClass;
}
//todo 这里创建了cachedAdaptiveClass,直接通过编码创建的AdaptiveClass
return cachedAdaptiveClass = createAdaptiveExtensionClass();
}
private Map<String, Class<?>> getExtensionClasses() {
Map<String, Class<?>> classes = cachedClasses.get();
if (classes == null) {
synchronized (cachedClasses) {
classes = cachedClasses.get();
if (classes == null) {
//todo 这里也会加载文件
classes = loadExtensionClasses();
cachedClasses.set(classes);
}
}
}
return classes;
}
}loadExtensionClasses
说明：
- loadExtensionClasses的内部会通过loadFile加载对应SPI对应的资源文件。
- loadFile读取对应的SPI资源文件并按行解析。
- loadFile过程中会初始化cachedAdaptiveClass 、cachedActivates、cachedNames。
- ExtensionFactory的SPI文件中包含cachedAdaptiveClass为AdaptiveExtensionFactory。
- ExtensionFactory对应有cachedAdaptiveClass，所以不会走createAdaptiveExtensionClass过程。
文件名：
META-INF/dubbo/internal/com.alibaba.dubbo.common.extension.ExtensionFactory
文件内容
spring=com.alibaba.dubbo.config.spring.extension.SpringExtensionFactory
文件名：
META-INF/dubbo/internal/com.alibaba.dubbo.common.extension.ExtensionFactory
文件内容：
adaptive=com.alibaba.dubbo.common.extension.factory.AdaptiveExtensionFactory
spi=com.alibaba.dubbo.common.extension.factory.SpiExtensionFactorypublic class ExtensionLoader<T> {
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()
+ ": " + 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;
}
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)) {
//todo 这个地方创建了cachedAdaptiveClass
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);
}
}
}AdaptiveExtensionFactory
说明：
- ExtensionLoader的getAdaptiveExtensionClass().newInstance()会执行AdaptiveExtensionFactory构造函数。
- AdaptiveExtensionFactory构造函数通过ExtensionFactory的ExtensionLoader的getExtension获取扩展。
- 扩展包括的name主要是spring和spi
spring=com.alibaba.dubbo.config.spring.extension.SpringExtensionFactory
spi=com.alibaba.dubbo.common.extension.factory.SpiExtensionFactory
- 调用ExtensionFactory的ExtensionLoader的getExtension(name)去加载spring和spi的ExtensionFactory。
@Adaptive
public class AdaptiveExtensionFactory implements ExtensionFactory {
//todo 这里会保存SpiExtensionFactory和SpringExtensionFactory
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;
}
}说明：
- ExtensionLoader的获取扩展按照getExtension => createExtension => clazz.newInstance()执行。
- spring通过执行SpringExtensionFactory的构造函数生成ExtensionFactory对象。
- spi通过执行SpiExtensionFactory的构造函数生成ExtensionFactory对象。
public class ExtensionLoader<T> {
public Set<String> getSupportedExtensions() {
Map<String, Class<?>> clazzes = getExtensionClasses();
return Collections.unmodifiableSet(new TreeSet<>(clazzes.keySet()));
}
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;
}
public T getExtension(String name) {
if (name == null || name.length() == 0)
throw new IllegalArgumentException("Extension name == null");
if ("true".equals(name)) {
return getDefaultExtension();
}
Holder<Object> holder = cachedInstances.get(name);
if (holder == null) {
cachedInstances.putIfAbsent(name, new Holder<Object>());
holder = cachedInstances.get(name);
}
Object instance = holder.get();
if (instance == null) {
synchronized (holder) {
instance = holder.get();
if (instance == null) {
instance = createExtension(name);
holder.set(instance);
}
}
}
return (T) instance;
}
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);
}
//todo 这里会把set变量注入进去
injectExtension(instance);
//todo 这里会把两个wrapper函数进行包装,特别针对protocol协议来说更是这样子
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);
}
}
}总结
整个ExtensionFactory的加载扩展其实宏观分为以下几个步骤：
- 1、LoadFile加载ExtensionFactory对应的SPI文件及内容。
- 2、ExtensionFactory对应的AdaptiveExtensionFactory的对象实例化。
- 3、AdaptiveExtensionFactory构造函数内部初始化SpringExtensionFactory和SpiExtensionFactory。
