每个ExtensionLoader实例只负责加载一个特定扩展点实现
每个扩展点对应最多只有一个ExtensionLoader实例
对于每个扩展点实现，最多只会有一个实例
一个扩展点实现可以对应多个名称(逗号分隔)
每个扩展点最多只能有一个被AdaptiveExtension
每个扩展点可以有多个可自动激活的扩展点实现(使用@Activate注解)
由于每个扩展点实现最多只有一个实例，因此扩展点实现应保证线程安全
如果扩展点有多个Wrapper，那么最终其执行的顺序不确定(内部使用ConcurrentHashSet存储)
getExtension方法：
public T getExtension(String name) {
if (name == null || name.length() == 0)
throw new IllegalArgumentException("Extension name == null");
if ("true".equals(name)) {
return getDefaultExtension();
}
// 先从缓存获取
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) {
// 构建instance
instance = createExtension(name);
holder.set(instance);
}
}
}
return (T) instance;
}createExtension方法：
private T createExtension(String name) {
// 获取class文件
Class<?> clazz = getExtensionClasses().get(name);
if (clazz == null) {
throw findException(name);
}
try {
// 线程缓存获取
T instance = (T) EXTENSION_INSTANCES.get(clazz);
if (instance == null) {
// 反射构建对象
EXTENSION_INSTANCES.putIfAbsent(clazz, clazz.newInstance());
instance = (T) EXTENSION_INSTANCES.get(clazz);
}
// IOC填充对象
injectExtension(instance);
Set<Class<?>> wrapperClasses = cachedWrapperClasses;
// AOP切片实现
if (wrapperClasses != null && !wrapperClasses.isEmpty()) {
// 通过含参的构造方法将SPI实例（根据指定名字创建好的）注入进去
// 注入成功并创建好实例之后会把这个组装好的Wrapper实例返回
// 这样循环到下一个Wrapper类时其实注入的是上一个Wrapper类实例
// 这样导致先注入的后执行
for (Class<?> wrapperClass : wrapperClasses) {
instance = injectExtension((T) wrapperClass.getConstructor(type).newInstance(instance));
}
}
// 返回构建好的实力
return instance;
} catch (Throwable t) {
throw new IllegalStateException("Extension instance(name: " + name + ", class: " +
type + ") could not be instantiated: " + t.getMessage(), t);
}
}injectExtension方法：
private T injectExtension(T instance) {
try {
if (objectFactory != null) {
// 遍历目标类上的所有方法
for (Method method : instance.getClass().getMethods()) {
// 检查方法是否已set 开头，且方法只有一个参数，且方法访问级别是public
if (method.getName().startsWith("set")
&& method.getParameterTypes().length == 1
&& Modifier.isPublic(method.getModifiers())) {
/**
* Check {@link DisableInject} to see if we need auto injection for this property
*/
// 如果方法有 DisableInject 注解修饰，则忽略
if (method.getAnnotation(DisableInject.class) != null) {
continue;
}
// 获取 setter 方法参数类型
Class<?> pt = method.getParameterTypes()[0];
if (ReflectUtils.isPrimitives(pt)) {
continue;
}
try {
// 获取属性名，比如 setName 方法对应属性名 name
String property = method.getName().length() > 3 ? method.getName().substring(3, 4).toLowerCase() + method.getName().substring(4) : "";
// 从 ObjectFactory 中获取依赖对象
Object object = objectFactory.getExtension(pt, property);
if (object != null) {
// 通过反射调用 setter 方法设置依赖
method.invoke(instance, object);
}
} catch (Exception e) {
logger.error("Failed to inject via method " + method.getName()
+ " of interface " + type.getName() + ": " + e.getMessage(), e);
}
}
}
}
} catch (Exception e) {
logger.error(e.getMessage(), e);
}
return instance;
}getExtensionClasses方法：
private Map<String, Class<?>> getExtensionClasses() {
Map<String, Class<?>> classes = cachedClasses.get();
// 先从缓存获取，没有就去加载
if (classes == null) {
synchronized (cachedClasses) {
classes = cachedClasses.get();
if (classes == null) {
classes = loadExtensionClasses();
cachedClasses.set(classes);
}
}
}
return classes;
}loadExtensionClasses方法：
private Map<String, Class<?>> loadExtensionClasses() {
// 加载默认的实现
final SPI defaultAnnotation = type.getAnnotation(SPI.class);
if (defaultAnnotation != null) {
String value = defaultAnnotation.value();
if ((value = value.trim()).length() > 0) {
String[] names = NAME_SEPARATOR.split(value);
// 默认实现只能一个
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];
}
}
// 从META-INF/dubbo/internal/、META-INF/dubbo/、META-INF/services/ 这三个指定的文件夹加加载此类型的实现类
Map<String, Class<?>> extensionClasses = new HashMap<String, Class<?>>();
loadDirectory(extensionClasses, DUBBO_INTERNAL_DIRECTORY);
loadDirectory(extensionClasses, DUBBO_DIRECTORY);
loadDirectory(extensionClasses, SERVICES_DIRECTORY);
return extensionClasses;
}loadDirectory方法：
private void loadDirectory(Map<String, Class<?>> extensionClasses, String dir) {
String fileName = dir + type.getName();
try {
Enumeration<java.net.URL> urls;
ClassLoader classLoader = findClassLoader();
// 根据文件名加载所有的同名文件
if (classLoader != null) {
urls = classLoader.getResources(fileName);
} else {
urls = ClassLoader.getSystemResources(fileName);
}
if (urls != null) {
while (urls.hasMoreElements()) {
java.net.URL resourceURL = urls.nextElement();
// 加载文件里的资源
loadResource(extensionClasses, classLoader, resourceURL);
}
}
} catch (Throwable t) {
logger.error("Exception when load extension class(interface: " +
type + ", description file: " + fileName + ").", t);
}
}loadResource方法：
private void loadResource(Map<String, Class<?>> extensionClasses, ClassLoader classLoader, java.net.URL resourceURL) {
try {
BufferedReader reader = new BufferedReader(new InputStreamReader(resourceURL.openStream(), "utf-8"));
try {
String line;
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;
// 根据 = 分割
int i = line.indexOf('=');
if (i > 0) {
name = line.substring(0, i).trim();
line = line.substring(i + 1).trim();
}
if (line.length() > 0) {
// 根据读取的内容 使用Class.forName加载对应类
loadClass(extensionClasses, resourceURL, Class.forName(line, true, classLoader), name);
}
} catch (Throwable t) {
IllegalStateException e = new IllegalStateException("Failed to load extension class(interface: " + type + ", class line: " + line + ") in " + resourceURL + ", cause: " + t.getMessage(), t);
exceptions.put(line, e);
}
}
}
} finally {
reader.close();
}
} catch (Throwable t) {
logger.error("Exception when load extension class(interface: " +
type + ", class file: " + resourceURL + ") in " + resourceURL, t);
}
}loadClass方法：
private void loadClass(Map<String, Class<?>> extensionClasses, java.net.URL resourceURL, Class<?> clazz, String name) throws NoSuchMethodException {
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) { // 如果类被Adaptive修饰，设置cachedAdaptiveClass缓存
cachedAdaptiveClass = clazz;
} else if (!cachedAdaptiveClass.equals(clazz)) {
throw new IllegalStateException("More than 1 adaptive class found: "
+ cachedAdaptiveClass.getClass().getName()
+ ", " + clazz.getClass().getName());
}
} else if (isWrapperClass(clazz)) { // 如果是wrapper类，设置wrapper的缓存
Set<Class<?>> wrappers = cachedWrapperClasses;
if (wrappers == null) {
cachedWrapperClasses = new ConcurrentHashSet<Class<?>>();
wrappers = cachedWrapperClasses;
}
wrappers.add(clazz);
} else { // 普通的spi实现类
clazz.getConstructor();
if (name == null || name.length() == 0) {
name = findAnnotationName(clazz);
if (name.length() == 0) {
throw new IllegalStateException("No such extension name for the class " + clazz.getName() + " in the config " + resourceURL);
}
}
String[] names = NAME_SEPARATOR.split(name);
if (names != null && names.length > 0) {
Activate activate = clazz.getAnnotation(Activate.class);
if (activate != null) { //如果有activate 加入缓存 如果对应多个名字 只会采用第一个名字
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) { // 将名字->类加入缓存
extensionClasses.put(n, clazz);
} else if (c != clazz) {
throw new IllegalStateException("Duplicate extension " + type.getName() + " name " + n + " on " + c.getName() + " and " + clazz.getName());
}
}
}
}
}///
///
getAdaptiveExtension方法：
public T getAdaptiveExtension() {
Object instance = cachedAdaptiveInstance.get();
// 双重检查 加锁创建缓存
if (instance == null) {
if (createAdaptiveInstanceError == null) {
synchronized (cachedAdaptiveInstance) {
instance = cachedAdaptiveInstance.get();
if (instance == null) {
try {
// 缓存没有 创建
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;
}createAdaptiveExtension方法：
// 调用 getAdaptiveExtensionClass 方法获取自适应拓展 Class 对象
// 通过反射进行实例化
// 调用injectExtension方法向拓展实例中注入依赖
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方法：
private Class<?> getAdaptiveExtensionClass() {
// 先获取此type的所有实现类的class
getExtensionClasses();
if (cachedAdaptiveClass != null) { //如果有 Adaptive修饰的实现类 直接返回
return cachedAdaptiveClass;
}
// 构建代理类
return cachedAdaptiveClass = createAdaptiveExtensionClass();
}createAdaptiveExtensionClass方法：
private Class<?> createAdaptiveExtensionClass() {
// 生成代理类的代码
String code = createAdaptiveExtensionClassCode();
ClassLoader classLoader = findClassLoader();
com.alibaba.dubbo.common.compiler.Compiler compiler = ExtensionLoader.getExtensionLoader(com.alibaba.dubbo.common.compiler.Compiler.class).getAdaptiveExtension();
// 使用javassist 编译为class
return compiler.compile(code, classLoader);
}createAdaptiveExtensionClassCode方法：
private String createAdaptiveExtensionClassCode() {
StringBuilder codeBuilder = new StringBuilder();
Method[] methods = type.getMethods();
boolean hasAdaptiveAnnotation = false;
// 第一部分
// 如果没有Adaptive修饰方法会抛异常
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)
throw new IllegalStateException("No adaptive method on extension " + type.getName() + ", refuse to create the adaptive class!");
// 第二部分
// 生成package、import等代码
codeBuilder.append("package ").append(type.getPackage().getName()).append(";");
codeBuilder.append("\nimport ").append(ExtensionLoader.class.getName()).append(";");
codeBuilder.append("\npublic class ").append(type.getSimpleName()).append("$Adaptive").append(" implements ").append(type.getCanonicalName()).append(" {");
//第三部分
// 如果Adaptive没有修饰方法，此代理类不会构建具体的方法
// Adaptive修饰的方法必须参数含有URL或者某个参数有getURL方法
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;
}
}
// found parameter in URL type
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);
}
// did not find parameter in URL type
else {
String attribMethod = null;
// find URL getter method
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 adaptive 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);
}
// 第四部分
// 生成类对应的名字
String[] value = adaptiveAnnotation.value();
// value is not set, use the value generated from class name as the key
if (value.length == 0) { // 如果注解没有给出名字 就用类名用.拼接 eg: CatST --> cat.s.t
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()};
}
// Invocation参数处理
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);
// 第五部分 生成返回类型
// return statement
if (!rt.equals(void.class)) {
code.append("\nreturn ");
}
// 第六部分 生成拓展加载与目标方法调用逻辑 大致逻辑就是根据获取到的name获取对应的实现类，然后调用实现类的方法
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(");");
}
codeBuilder.append("\npublic ").append(rt.getCanonicalName()).append(" ").append(method.getName()).append("(");
for (int i = 0; i < pts.length; i++) {
if (i > 0) {
codeBuilder.append(", ");
}
codeBuilder.append(pts[i].getCanonicalName());
codeBuilder.append(" ");
codeBuilder.append("arg").append(i);
}
codeBuilder.append(")");
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();
}
///
///
getActivateExtension方法：
public List<T> getActivateExtension(URL url, String[] values, String group) {
List<T> exts = new ArrayList<T>();
List<String> names = values == null ? new ArrayList<String>(0) : Arrays.asList(values);
if (!names.contains(Constants.REMOVE_VALUE_PREFIX + Constants.DEFAULT_KEY)) {
getExtensionClasses();
for (Map.Entry<String, Activate> entry : cachedActivates.entrySet()) {
String name = entry.getKey();
Activate activate = entry.getValue();
// 根据group过滤
if (isMatchGroup(group, activate.group())) {
T ext = getExtension(name);
if (!names.contains(name) // 防止重复加入 下面就是根据指定name寻找对应的实现类
&& !names.contains(Constants.REMOVE_VALUE_PREFIX + name)
&& isActive(activate, url)) { // 检测value和url 如果类上的Activate(value={"bigKey"},group = "q") 制定了value,那么url中如果不含有此key的参数就匹配不上
exts.add(ext);
}
}
}
Collections.sort(exts, ActivateComparator.COMPARATOR);
}
List<T> usrs = new ArrayList<T>();
// 根据name寻找实现类
for (int i = 0; i < names.size(); i++) {
String name = names.get(i);
if (!name.startsWith(Constants.REMOVE_VALUE_PREFIX)
&& !names.contains(Constants.REMOVE_VALUE_PREFIX + name)) {
if (Constants.DEFAULT_KEY.equals(name)) {
if (!usrs.isEmpty()) {
exts.addAll(0, usrs);
usrs.clear();
}
} else {
T ext = getExtension(name);
usrs.add(ext);
}
}
}
if (!usrs.isEmpty()) {
exts.addAll(usrs);
}
return exts;
}
////
https://www.jianshu.com/u/ee989c623747https://blog.csdn.net/yuansha...
https://blog.csdn.net/qq_3521...
**粗体** _斜体_ [链接](http://example.com) `代码` - 列表 > 引用。你还可以使用@来通知其他用户。