一.參考
dubbo啓動，使用spi動態擴展的地方參考之前寫的<dubbo源碼之啓動、導出服務>
二.架構
1.每個接口或者ExtensionFactory都對應一個ExtensionLoader。對接口主要有四步操作:
(1).獲取接口的ExtensionLoader.
(2).從擴展文件中讀取對應接口的所有實現類
(3).創建優先級最高，真正使用的類的實例
(4).注入這個類的屬性,通過setxxx方法.
2.從優先級看,@Adaptive類 > url 路徑 > @Spi的值.
3.@Adaptive用在方法上時，key是url的參數名，通過這個參數名的取值判斷用哪個實現類.
@Activate用於配置不同實現類的分組，組內的優先級.
三.源碼細節
(一).Protocol接口加載
測試代碼是ServiceConfig的成員protocl,初始化代碼爲
Protocol protocol = ExtensionLoader.getExtensionLoader(Protocol.class).getAdaptiveExtension();
加載dubbo的Protocol接口的ExtensionLoader.
1.ExtensionLoader#getExtensionLoader()方法,入參爲Protocol接口。代碼如下:
public static <T> ExtensionLoader<T> getExtensionLoader(Class<T> type) {
//接口不能爲空
if (type == null)
throw new IllegalArgumentException("Extension type == null");
//傳入type必須是接口
if (!type.isInterface()) {
throw new IllegalArgumentException("Extension type(" + type + ") is not interface!");
}
//接口必須帶有@spi註解
if (!withExtensionAnnotation(type)) {
throw new IllegalArgumentException("Extension type(" + type +
") is not extension, because WITHOUT @" + SPI.class.getSimpleName() + " Annotation!");
}
//在緩存ExtensionLoader#EXTENSION_LOADERS是否已經有loader了，沒有再創建
ExtensionLoader<T> loader = (ExtensionLoader<T>) EXTENSION_LOADERS.get(type);
if (loader == null) {
//創建ExtensionLoader,操作都在構造方法裏面.構造方法在下面代碼.
EXTENSION_LOADERS.putIfAbsent(type, new ExtensionLoader<T>(type));
loader = (ExtensionLoader<T>) EXTENSION_LOADERS.get(type);
}
return loader;
}
private ExtensionLoader(Class<?> type) {
this.type = type;
//第一次使用ExtensionLoader,先創建ExtensionFactory接口工廠的ExtensionLoader.
//然後調用ExtensionLoader#getAdaptiveExtension()獲取ExtensionFactory的實例.
objectFactory = (type == ExtensionFactory.class ? null : ExtensionLoader.getExtensionLoader(ExtensionFactory.class).getAdaptiveExtension());
}
2.獲取擴展接口的實例
入口ExtensionLoader#getAdaptiveExtension().
public T getAdaptiveExtension() {
//雙重校驗
Object instance = cachedAdaptiveInstance.get();
if (instance == null) {
if (createAdaptiveInstanceError == null) {
synchronized (cachedAdaptiveInstance) {
instance = cachedAdaptiveInstance.get();
if (instance == null) {
try {
//創建接口擴展的實際實例對象，代碼在下面
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;
}
創建擴展接口的實例
入口 ExtensionLoader#createAdaptiveExtension
private T createAdaptiveExtension() {
try {
/* 先調用getAdaptiveExtensionClass()獲取接口實際使用的實現類，代碼如下.
再調用newInstance()創建這個實現類的對象
最後調用injectExtension()對這個對象的屬性進行注入.
對於Protocol接口,這裏創建動態生成的Protocol$Adaptive類的實例 */
return injectExtension((T) getAdaptiveExtensionClass().newInstance());
} catch (Exception e) {
throw new IllegalStateException("Can not create adaptive extension " + type + ", cause: " + e.getMessage(), e);
}
}
獲取接口的擴展類
入口ExtensionLoader#getAdaptiveExtensionClass()
private Class<?> getAdaptiveExtensionClass() {
//獲取擴展類
getExtensionClasses();
if (cachedAdaptiveClass != null) {
//如果有帶Adaptive註解的,優先返回有帶Adaptive註解的實現類
return cachedAdaptiveClass;
}
//Protocol接口的實現類沒有@Adaptive註解的，進到這裏,在後面6處分析
return cachedAdaptiveClass = createAdaptiveExtensionClass();
}
方法ExtensionLoader#getExtensionClasses()獲取接口的所有實現類
private Map<String, Class<?>> getExtensionClasses() {
Map<String, Class<?>> classes = cachedClasses.get();
if (classes == null) {
synchronized (cachedClasses) {
classes = cachedClasses.get();
if (classes == null) {
//讀取擴展接口文件,加載,代碼在下面
classes = loadExtensionClasses();
//對於ExtensionFactory,這裏有兩個,SpiExtensionFactory和SpringExtensionFactory.
cachedClasses.set(classes);
}
}
}
return classes;
}
3.讀取spi文件的接口的所有的實現類
如果是protocol協議,這裏能獲取到{RegistryProtocol,InjvmProtocol,ThriftProtocol,DubboProtocol,MockProtocol,HttpProtocol,RedisProtocol,RmiProtocol}八個實現類,默認使用DubboProtocol.
入口是ExtensionLoader#loadExtensionClasses()
private Map<String, Class<?>> loadExtensionClasses() {
//獲取接口的spi註解,比如ExtensionFactory,Protocol
final SPI defaultAnnotation = type.getAnnotation(SPI.class);
if (defaultAnnotation != null) {
//獲取擴展默認加載哪個實現類.
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<?>>();
//加載META-INF/dubbo/internal/目錄下的擴展文件
loadFile(extensionClasses, DUBBO_INTERNAL_DIRECTORY);
//加載META-INF/dubbo/目錄下的擴展文件
loadFile(extensionClasses, DUBBO_DIRECTORY);
//加載META-INF/services/目錄下的擴展文件
loadFile(extensionClasses, SERVICES_DIRECTORY);
return extensionClasses;
}
讀取文件,入口是ExtensionLoader#loadFile().加載到的實現類都放到extensionClasses.key是別名，value是實現類.
private void loadFile(Map<String, Class<?>> extensionClasses, String dir) {
//格式是META-INF/dubbo/internal/com.alibaba.dubbo.common.extension.ExtensionFactory
//目錄名+接口路徑文件名
String fileName = dir + type.getName();
try {
Enumeration<java.net.URL> urls;
//調用ExtensionLoader.class.getClassLoader()獲取ClassLoader
ClassLoader classLoader = findClassLoader();
if (classLoader != null) {
//獲取文件路徑的url格式
urls = classLoader.getResources(fileName);
} else {
urls = ClassLoader.getSystemResources(fileName);
}
if (urls != null) {
//遍歷所有文件路徑的url
while (urls.hasMoreElements()) {
/* 接口文件的本地磁盤路徑file:/xxx/dubbo-config/xxx/internal/xxx.ExtensionFactory格式 */
java.net.URL url = urls.nextElement();
try {
BufferedReader reader = new BufferedReader(new InputStreamReader(url.openStream(), "utf-8"));
try {
/* 一行行遍歷接口文件,對於ExtensionFactory接口，在dubbo-config只有下面一行 spring=com.alibaba.dubbo.config.spring.extension.SpringExtensionFactory
在dubbo-common下面有adaptive=com.alibaba.dubbo.common.extension.factory.AdaptiveExtensionFactory
spi=com.alibaba.dubbo.common.extension.factory.SpiExtensionFactory兩行 */
String line = null;
while ((line = reader.readLine()) != null) {
// 切分#號隔開
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) {
//取出name別名部分
name = line.substring(0, i).trim();
//接口實現類賦值給line，這裏是SpringExtensionFactory類全路徑
line = line.substring(i + 1).trim();
}
if (line.length() > 0) {
//創建實現類的Class對象
Class<?> clazz = Class.forName(line, true, classLoader);
//判斷實現類是否是該接口的
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.");
}
//實現類上是否有Adaptive註解
if (clazz.isAnnotationPresent(Adaptive.class)) {
if (cachedAdaptiveClass == null) {
//有Adaptive註解的放到成員cachedAdaptiveClass裏面,這個優先級最高
cachedAdaptiveClass = clazz;
} else if (!cachedAdaptiveClass.equals(clazz)) {
throw new IllegalStateException("More than 1 adaptive class found: "
+ cachedAdaptiveClass.getClass().getName()
+ ", " + clazz.getClass().getName());
}
} else {
try {
//實現類是否有參數爲本接口類型的構造方法，這樣後面可以把多個實現類鏈接起來
clazz.getConstructor(type);
Set<Class<?>> wrappers = cachedWrapperClasses;
if (wrappers == null) {
cachedWrapperClasses = new ConcurrentHashSet<Class<?>>();
wrappers = cachedWrapperClasses;
}
wrappers.add(clazz);
} catch (NoSuchMethodException e) {
//實現類是否有無參構造方法
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);
}
}
}
//做正則表達式匹配name,對於SpringExtensionFactory,這裏是spring
String[] names = NAME_SEPARATOR.split(name);
if (names != null && names.length > 0) {
Activate activate = clazz.getAnnotation(Activate.class);
if (activate != null) {
//如果實現類有Activate註解，加入cachedActivates緩存.
cachedActivates.put(names[0], activate);
}
for (String n : names) {
if (!cachedNames.containsKey(clazz)) {
//加入已經解析的名稱緩存cachedNames
cachedNames.put(clazz, n);
}
Class<?> c = extensionClasses.get(n);
if (c == null) {
//加入已經解析過得接口拓展類緩存
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) {
...
}
}
} // end of while read lines
} finally {
//關閉讀文件句柄
reader.close();
}
} catch (Throwable t) {
...
}
} // end of while urls
}
} catch (Throwable t) {
...
}
}
4.創建接口的實現類的對象,以ExtensionFactory爲例，實現類是AdaptiveExtensionFactory，它的優先級最高，帶有@Adaptive註解.代碼如下:
public AdaptiveExtensionFactory() {
//進到這裏，可以從緩存直接拿到了，因爲是調用ExtensionLoader.getExtensionLoader(ExtensionFactory.class)纔到這裏
ExtensionLoader<ExtensionFactory> loader = ExtensionLoader.getExtensionLoader(ExtensionFactory.class);
List<ExtensionFactory> list = new ArrayList<ExtensionFactory>();
//遍歷所有ExtensionFactory接口的實現類,這裏與兩個,spi和spring
for (String name : loader.getSupportedExtensions()) {
/* 創建所有ExtensionFactory接口實現類的對象，這裏先去創建SpiExtensionFactory類的對象,然後調用ExtensionLoader#injectExtension()方法注入對象 */
list.add(loader.getExtension(name));
}
factories = Collections.unmodifiableList(list);
}
ExtensionLoader#getExtension()調用ExtensionLoader#createExtension()完成操作.代碼如下:
比如傳入的name是"spi",
private T createExtension(String name) {
//獲取"spi"的實現類SpiExtensionFactory
Class<?> clazz = getExtensionClasses().get(name);
if (clazz == null) {
throw findException(name);
}
try {
T instance = (T) EXTENSION_INSTANCES.get(clazz);
//第一次獲取爲空
if (instance == null) {
//創建實現類的對象,比如創建SpiExtensionFactory類的對象
EXTENSION_INSTANCES.putIfAbsent(clazz, (T) clazz.newInstance());
instance = (T) EXTENSION_INSTANCES.get(clazz);
}
//對對象進行注入,比如對SpiExtensionFactory對象進行注入，主要是調用它的setxxx方法.
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);
}
}
5.ioc，注入對象屬性
private T injectExtension(T instance) {
try {
if (objectFactory != null) {
for (Method method : instance.getClass().getMethods()) {
//只處理setxxx()方法,方法參數只有一個
if (method.getName().startsWith("set")
&& method.getParameterTypes().length == 1
&& Modifier.isPublic(method.getModifiers())) {
//獲取要注入的方法的參數類型
Class<?> pt = method.getParameterTypes()[0];
try {
String property = method.getName().length() > 3 ? method.getName().substring(3, 4).toLowerCase() + method.getName().substring(4) : "";
/* 調用ExtensionFactory#getExtension()獲取要注入的參數的對象實例,property是參數名,主要是去容器中獲取bean的實例對象，比如spring的singleObjects*/
Object object = objectFactory.getExtension(pt, property);
if (object != null) {
//調用setxxx()方法注入參數對象
method.invoke(instance, object);
}
} catch (Exception e) {
logger.error("fail to inject via method " + method.getName()
+ " of interface " + type.getName() + ": " + e.getMessage(), e);
}
}
}
}
} catch (Exception e) {
logger.error(e.getMessage(), e);
}
return instance;
}
6.創建自適應的擴展類，在接口的多個實現類中選一個.
從前面的2調用過來，比如Protocol接口
private Class<?> createAdaptiveExtensionClass() {
//代碼在下面分析,Protocol這裏返回Protocol$Adaptive類的實現代碼字串
String code = createAdaptiveExtensionClassCode();
//獲取當前類的ClassLoader
ClassLoader classLoader = findClassLoader();
//獲取Compiler接口的實現類JavassistCompiler
com.alibaba.dubbo.common.compiler.Compiler compiler = ExtensionLoader.getExtensionLoader(com.alibaba.dubbo.common.compiler.Compiler.class).getAdaptiveExtension();
//調用Compiler接口的實現類JavassistCompiler把上面的字符串代碼編譯成Class
return compiler.compile(code, classLoader);
}
創建擴展類的字符串代碼最後生成的字符串如下圖,
代碼如下:
private String createAdaptiveExtensionClassCode() {
StringBuilder codeBuidler = new StringBuilder();
//獲取接口內部的類，比如Protocol接口的類
Method[] methods = type.getMethods();
boolean hasAdaptiveAnnotation = false;
//遍歷所有方法，判斷是否有帶@Adaptive註解的方法
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.
//所有類都沒有adaptive方法，則拋出異常
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() + "$Adaptive" + " implements " + type.getCanonicalName() + " {");
for (Method method : methods) {
//返回值類型
Class<?> rt = method.getReturnType();
//參數類型
Class<?>[] pts = method.getParameterTypes();
//方法拋出的異常類型
Class<?>[] ets = method.getExceptionTypes();
//獲取方法上的Adaptive註解
Adaptive adaptiveAnnotation = method.getAnnotation(Adaptive.class);
StringBuilder code = new StringBuilder(512);
if (adaptiveAnnotation == null) {
//沒有Adaptive註解
code.append("throw new UnsupportedOperationException(\"method ")
.append(method.toString()).append(" of interface ")
.append(type.getName()).append(" is not adaptive method!\");");
} else {
//有Adaptive註解的
int urlTypeIndex = -1;
//取出參數類型是url的參數位置索引
for (int i = 0; i < pts.length; ++i) {
if (pts[i].equals(URL.class)) {
urlTypeIndex = i;
break;
}
}
// found parameter in URL type
if (urlTypeIndex != -1) {
//參數中有url類型的
// 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);
}
// did not find parameter in URL type
else {
//參數中沒有url類型的,比如Protocol#export(Invoker invoker).沒有url參數,帶有@Adaptive註解,返回Exporter
String attribMethod = null;
// find URL getter method
//遍歷所有參數
LBL_PTS:
for (int i = 0; i < pts.length; ++i) {
Method[] ms = pts[i].getMethods();
//比如獲取到Invoker類型的參數,遍歷Invoker的所有成員方法
//找到一個getxxx方法，返回值是URL類型,記下方法名.
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;
}
}
}
...
}
//獲取方法上@Adaptive註解的value值
String[] value = adaptiveAnnotation.value();
// value is not set, use the value generated from class name as the key
if (value.length == 0) {
//沒有值的話，默認取dubbo接口的名稱,比如protocol
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()};
}
//獲取方法的所有參數，看是否有Invocation類型.
boolean hasInvocation = false;
for (int i = 0; i < pts.length; ++i) {
if (pts[i].getName().equals("com.alibaba.dubbo.rpc.Invocation")) {
...
}
}
//獲取接口的默認擴展的實現名
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);
}
}
...
}
...
}
codeBuidler.append("\n}");
return codeBuidler.toString();
}