筆記簡述
本學習筆記主要是介紹了SPI的使用以及原理，dubbo是如何實現自身的SPI，dubbo如何使用的可以看Dubbo 簡要介紹和使用 學習（一）
更多內容可看[目錄]Dubbo 源碼學習
目錄
Dubbo SPI 源碼學習 & admin安裝（二）
1、SPI
1.1、Java SPI DEMO
1.2、Java SPI 源碼實現
2、Dubbo SPI 配置
3、Dubbo SPI 使用 & 源碼學習
3.1、 Protocol 獲取
3.2、SPI配置文件解析
4、dubbo-admin 安裝使用
1、SPI
在dubbo中包含了很多組件，各種組件又有不同的協議使得存在多種實現，而且在開發中都是推薦針對接口編程，那就存在一個問題了，如何選擇合適的實現類呢？解決方案就是SPI
SPI的全名為Service Provider Interface，提供類似于插拔式的實現類選擇能力。在java中使用的類是java.util.ServiceLoader，然后在META-INF/services/創建的具體文件中寫上具體的實現類的類名稱，就可以實現具體的類，在早期的JDBC中，必須得通過Class.forName("xxx")這種硬編碼的方式去生成對應類的實例，但是現在可以直接通過SPI達到同樣的目的
1.1、Java SPI DEMO
public interface Search {
void print();
}
public class FileSearch implements Search {
@Override
public void print() {
System.out.println("==== A ====");
}
}
public class SpiTest {
public static void main(String[] args){
ServiceLoader<Search> serviceLoader = ServiceLoader.load(Search.class);
Iterator<Search> it = serviceLoader.iterator();
while (it.hasNext()){
Search printImpl = it.next();
printImpl.print();
}
}
}
spi.Search
spi.FileSearch
spi.WebSearch
image
如上圖，需要在資源文件的根目錄創建一個META-INF.services的文件夾，新建一個Search接口完整路徑的文件，本例子是spi.Search，里面填入實現類的類全程。如下圖，確實調用了兩個具體的實例，迭代分別執行。
image
1.2、Java SPI 源碼實現
如下圖，首先獲取到fullName數據，然后調用getResource獲取該文件內的資源
image
private Iterator<String> parse(Class<?> service, URL u)
throws ServiceConfigurationError
{
InputStream in = null;
BufferedReader r = null;
ArrayList<String> names = new ArrayList<>();
try {
in = u.openStream();
r = new BufferedReader(new InputStreamReader(in, "utf-8"));
int lc = 1;
while ((lc = parseLine(service, u, r, lc, names)) >= 0);
} catch (IOException x) {
fail(service, "Error reading configuration file", x);
} finally {
try {
if (r != null) r.close();
if (in != null) in.close();
} catch (IOException y) {
fail(service, "Error closing configuration file", y);
}
}
return names.iterator();
}
然后解析文件內的內容，存入到一個ArrayList中，并返回其迭代器（后面肯定還差一步就是實例化）
image
很明顯了，在獲取到類信息，直接調用newInstance方法完成實例化操作
同時根據newInstance也可以知道對外提供的spi的實現類不能有自定義的構造函數
2、Dubbo SPI 配置
dubbo的spi和java自帶的spi稍有區別，如上述的demo中，是在文件中寫入什么實現類，就會去實現，如果需要獲取其中的一個，則需要循環迭代獲取處理，而在dubbo中則采用了類似kv對的樣式，在具體使用的時候則通過相關想法即可獲取，而且獲取的文件路徑也不一致
ExtensionLoader 類文件
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/";
如上述代碼片段可知，dubbo是支持從META-INF/dubbo/,META-INF/dubbo/internal/以及META-INF/services/三個文件夾的路徑去獲取spi配置
image
例如com.alibaba.dubbo.rpc.Protocol 文件內容
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
不過觀察上述文件會發現，HttpProtocol是沒有對應的k值，那就是說無法通過kv對獲取到其協議實現類
后面通過源碼可以發現，如果沒有對應的name的時候，dubbo會通過findAnnotationName方法獲取一個可用的name
3、Dubbo SPI 使用 & 源碼學習
通過獲取協議的代碼來分析下具體的操作過程
3.1、 Protocol 獲取
Protocol protocol = ExtensionLoader.getExtensionLoader(Protocol.class).getAdaptiveExtension();
public static <T> ExtensionLoader<T> getExtensionLoader(Class<T> type) {
// 靜態方法，意味著可以直接通過類調用
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);
// 從map中獲取該類型的ExtensionLoader數據
if (loader == null) {
EXTENSION_LOADERS.putIfAbsent(type, new ExtensionLoader<T>(type));
// 如果沒有則，創建一個新的ExtensionLoader對象，并且以該類型存儲
loader = (ExtensionLoader<T>) EXTENSION_LOADERS.get(type);
// 再從map中獲取
// 這里這樣做的原因就是為了防止并發的問題，而且map本是也是個ConcurrentHashMap
}
return loader;
}
private ExtensionLoader(Class<?> type) {
this.type = type;
objectFactory = (type == ExtensionFactory.class ? null : ExtensionLoader.getExtensionLoader(ExtensionFactory.class).getAdaptiveExtension());
}
// 傳入的type是Protocol.class，所以需要獲取ExtensionFactory.class最合適的實現類
public T getAdaptiveExtension() {
Object instance = cachedAdaptiveInstance.get();
if (instance == null) {
if(createAdaptiveInstanceError == null) {
synchronized (cachedAdaptiveInstance) {
instance = cachedAdaptiveInstance.get();
if (instance == null) {
try {
instance = createAdaptiveExtension();
// 創建對象，也是需要關注的函數
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());
// (T) getAdaptiveExtensionClass().newInstance() 創建一個具體的實例對象
// getAdaptiveExtensionClass() 生成相關的class
// injectExtension 往該對象中注入數據
} catch (Exception e) {
throw new IllegalStateException("Can not create adaptive extenstion " + type + ", cause: " + e.getMessage(), e);
}
}
private Class<?> getAdaptiveExtensionClass() {
getExtensionClasses();
// 通過加載SPI配置，獲取到需要的所有的實現類存儲到map中
// 通過可能會去修改cachedAdaptiveClass數據，具體原因在spi配置文件解析中分析
if (cachedAdaptiveClass != null) {
return cachedAdaptiveClass;
}
return cachedAdaptiveClass = createAdaptiveExtensionClass();
}
private Class<?> createAdaptiveExtensionClass() {
String code = createAdaptiveExtensionClassCode();
// 動態生成需要的代碼內容字符串
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);
// 編譯，生成相應的類
}
如下代碼Protocol$Adpative 整個的類就是通過createAdaptiveExtensionClassCode()方法生成的一個大字符串
public class Protocol$Adpative implements com.alibaba.dubbo.rpc.Protocol {
public void destroy() {throw new UnsupportedOperationException("method public abstract void com.alibaba.dubbo.rpc.Protocol.destroy() of interface com.alibaba.dubbo.rpc.Protocol is not adaptive method!");
}
public int getDefaultPort() {throw new UnsupportedOperationException("method public abstract int com.alibaba.dubbo.rpc.Protocol.getDefaultPort() of interface com.alibaba.dubbo.rpc.Protocol is not adaptive method!");
}
public com.alibaba.dubbo.rpc.Exporter export(com.alibaba.dubbo.rpc.Invoker arg0) throws com.alibaba.dubbo.rpc.RpcException {
// 暴露遠程服務，傳入的參數是invoke對象
if (arg0 == null) throw new IllegalArgumentException("com.alibaba.dubbo.rpc.Invoker argument == null");
if (arg0.getUrl() == null) throw new IllegalArgumentException("com.alibaba.dubbo.rpc.Invoker argument getUrl() == null");
com.alibaba.dubbo.common.URL url = arg0.getUrl();
String extName = ( url.getProtocol() == null ? "dubbo" : url.getProtocol() );
// 如果沒有具體協議，則使用dubbo協議
if(extName == null) throw new IllegalStateException("Fail to get extension(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.export(arg0);
}
public com.alibaba.dubbo.rpc.Invoker refer(java.lang.Class arg0, com.alibaba.dubbo.common.URL arg1) throws com.alibaba.dubbo.rpc.RpcException {
// 引用遠程對象，生成相對應的遠程invoke對象
if (arg1 == null) throw new IllegalArgumentException("url == null");
com.alibaba.dubbo.common.URL url = arg1;
String extName = ( url.getProtocol() == null ? "dubbo" : url.getProtocol() );
if(extName == null) throw new IllegalStateException("Fail to get extension(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);
}
}
到現在可以認為是最上面的獲取protocol的方法Protocol protocol = ExtensionLoader.getExtensionLoader(Protocol.class).getAdaptiveExtension()返回了一個代碼拼接而成然后編譯操作的實現類Protocol$Adpative
可是得到具體的實現呢？在com.alibaba.dubbo.rpc.Protocol extension = (com.alibaba.dubbo.rpc.Protocol)ExtensionLoader.getExtensionLoader(com.alibaba.dubbo.rpc.Protocol.class).getExtension(extName)這個代碼中，當然這個是有在具體的暴露服務或者引用遠程服務才被調用執行的。
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);
}
// 無論是否真有數據，在cachedInstances存儲的是一個具體的Holder對象
Object instance = holder.get();
if (instance == null) {
synchronized (holder) {
instance = holder.get();
if (instance == null) {
instance = createExtension(name);
// 創建對象
holder.set(instance);
}
}
}
return (T) instance;
}
private T createExtension(String name) {
Class<?> clazz = getExtensionClasses().get(name);
// 獲取具體的實現類的類
if (clazz == null) {
throw findException(name);
}
try {
T instance = (T) EXTENSION_INSTANCES.get(clazz);
if (instance == null) {
EXTENSION_INSTANCES.putIfAbsent(clazz, (T) clazz.newInstance());
// clazz.newInstance 才是真正創建對象的操作
instance = (T) EXTENSION_INSTANCES.get(clazz);
}
injectExtension(instance);
// 往實例中反射注入參數
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);
}
}
到這一步就可以認為是dubbo的spi加載整個的過程完成了，整個鏈路有些長，需要好好的梳理一下
3.2、SPI配置文件解析
上文3.1說到getExtensionClasses完成對spi文件的解析
private Map<String, Class<?>> loadExtensionClasses() {
final SPI defaultAnnotation = type.getAnnotation(SPI.class);
// 查看該類是否存在SPI注解信息
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];
// 設置默認的名稱，如果注解的值經過切割，發現超過1個的數據，則同樣會認為錯誤
}
}
Map<String, Class<?>> extensionClasses = new HashMap<String, Class<?>>();
loadFile(extensionClasses, DUBBO_INTERNAL_DIRECTORY);
// 加載文件
loadFile(extensionClasses, DUBBO_DIRECTORY);
loadFile(extensionClasses, SERVICES_DIRECTORY);
return extensionClasses;
}
private void loadFile(Map<String, Class<?>> extensionClasses, String dir) {
String fileName = dir + type.getName();
// type.getName就是類名稱，和java的類似
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('=');
// 對k=v這樣的格式進行分割操作，分別獲取
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)) {
// 如果獲取的類包含了Adaptive注解
if(cachedAdaptiveClass == null) {
cachedAdaptiveClass = clazz;
} else if (! cachedAdaptiveClass.equals(clazz)) {
// 已經存在了該數據，現在又出現了，則拋出異常
throw new IllegalStateException("More than 1 adaptive class found: "
+ cachedAdaptiveClass.getClass().getName()
+ ", " + clazz.getClass().getName());
}
} else { // 不包含Adaptive注解信息
try {
clazz.getConstructor(type);
// 查看構造函數是否包含了type的類型參數
// 如果不存在，則拋出NoSuchMethodException異常
Set<Class<?>> wrappers = cachedWrapperClasses;
if (wrappers == null) {
cachedWrapperClasses = new ConcurrentHashSet<Class<?>>();
wrappers = cachedWrapperClasses;
}
wrappers.add(clazz);
// 往wrappers中添加該類
} catch (NoSuchMethodException e) {
clazz.getConstructor();
if (name == null || name.length() == 0) {
// 沒用名字的那種，也就是不存在k=v這種樣式
// 例如上面的HttpProtocol
name = findAnnotationName(clazz);
// 查看該類是否存在注解
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);
// 可能存在多個，切割開
if (names != null && names.length > 0) {
Activate activate = clazz.getAnnotation(Activate.class);
if (activate != null) {
// 如果類存在Activate的注解信息
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);
// 往容器中填充該鍵值對信息，k和v
} else if (c != clazz) {
// 存在多個同名擴展類，則拋出異常信息
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);
}
}
這樣完成了對spi配置文件的整個的掃描過程了
4、dubbo-admin 安裝使用
在上一節中利用dubbo-admin查看了服務提供方和服務調用方，現在就來簡要的介紹下如何在本地跑起來admin，先從github拉取代碼incubator-dubbo-ops到本地，在maven環境下，依賴maven-tomcat插件啟動，并沒有打包成war包丟到Tomcat下啟動
添加注冊組信息
dubbo-admin.xml 文件添加注冊組信息
<dubbo:registry client="curator" address="${dubbo.registry.address}" group="${dubbo.register.group}" check="false" file="false"/>
對應的配置文件信息，添加組的具體內容
dubbo.properties
dubbo.registry.address=zookeeper://127.0.0.1:2182
dubbo.register.group=dubbo-demo
dubbo.admin.root.password=root // root用戶的密碼是root
dubbo.admin.guest.password=guest // guest用戶的密碼是guest
添加Tomcat插件運行
在pom.xml文件內添加如下代碼
<build>
<plugins>
<plugin>
<groupId>org.apache.tomcat.maven</groupId>
<artifactId>tomcat7-maven-plugin</artifactId>
<version>2.2</version>
<configuration>
<uriEncoding>UTF-8</uriEncoding>
<port>8112</port>
<path>/</path>
</configuration>
</plugin>
</plugins>
</build>
接下來就可以使用mvn tomcat7:run -Dport=8112或者IDEA 的maven工具直接啟動
image
在瀏覽器輸入127.0.0.1:8112，輸入賬戶名和秘密（分別都是root），就進入到admin后臺頁面
image
