上一篇文章重點分析了 SPI 加載過程，但是中途遺漏了一個點，當 SPI 相關類中，沒有 @Adaptive 註解怎麼辦？
本文主要分析這一過程。
這一過程代碼組要在 ExtensionLoader 的 getAdaptiveExtensionClass 方法裏面。
AdaptiveClassCodeGenerator
這個類的構造方法有兩個參數，一個是SPI 對應的 type，以及這個type對應的默認值。
public AdaptiveClassCodeGenerator(Class<?> type, String defaultExtName) {
this.type = type;
this.defaultExtName = defaultExtName;
}
而後會調用 generate 去生成默認 type$Adaptive的一段代碼。
generate
該方法首先會判斷 type 類中是否有 @Adaptive 修飾的方法，沒有則會拋出異常。
下面先看代碼具體分析：
public String generate() {
// no need to generate adaptive class since there's no adaptive method found.
// 如果沒有 Adaptive 方法，那麼就不需要生成
if (!hasAdaptiveMethod()) {
throw new IllegalStateException("No adaptive method exist on extension " + type.getName() + ", refuse to create the adaptive class!");
}
// 創建一個 StringBuilder
StringBuilder code = new StringBuilder();
// 添加包名信息
code.append(generatePackageInfo());
// 創建引用
code.append(generateImports());
// 創建類聲明
code.append(generateClassDeclaration());
// 獲取所有方法
Method[] methods = type.getMethods();
// 爲每一個方法生成默認方法
for (Method method : methods) {
code.append(generateMethod(method));
}
// 加上最後大括號
code.append("}");
if (logger.isDebugEnabled()) {
logger.debug(code.toString());
}
return code.toString();
}
上面方法中，主要是拼湊初來一個Java 類。包括檢測包名合法性，包名信息，包引用，類聲明，以及具體類體即方法。
- 使用
hasAdaptiveMethod檢測是否有 @Adaptive方法 - 整個類中，
type不會爲空，因爲在使用ExtensionLoader時候，需要傳入一個type告訴ExtensionLoader去加載哪個類。 generatePackageInfo是生成包聲明信息。generateImports是用於引用包所需的引用。主要是org.apache.dubbo.common.extension.ExtensionLoader。generateClassDeclaration，即將public class %s$Adaptive implements %s {中%s替換爲type類型。generateMethod，即將SPI 中type中接口方法參數，主要目的是- 檢查參數，非法參數拋異常
- 調用方法
cachedDefaultName所對應的 SPI 類，並且執行相應方法
如果SPI中沒有指明默認的類，則會使用SPI中對應第一個作爲例子。
最後將返回製作好的String。
例子
有時候在debug時候，由於是動態生成的類，IDE 往往無法找到源碼，只能進入對應接口頁面，這裏給出一些type$Adaptive 對應的代碼，有需要可以直接查看。
Protocol$Adaptive
package org.apache.dubbo.rpc;
import org.apache.dubbo.common.extension.ExtensionLoader;
public class Protocol$Adaptive implements org.apache.dubbo.rpc.Protocol {
public org.apache.dubbo.rpc.Invoker refer(java.lang.Class arg0, org.apache.dubbo.common.URL arg1) throws org.apache.dubbo.rpc.RpcException {
if (arg1 == null) throw new IllegalArgumentException("url == null");
org.apache.dubbo.common.URL url = arg1;
String extName = ( url.getProtocol() == null ? "dubbo" : url.getProtocol() );
if(extName == null) throw new IllegalStateException("Failed to get extension (org.apache.dubbo.rpc.Protocol) name from url (" + url.toString() + ") use keys([protocol])");
org.apache.dubbo.rpc.Protocol extension = (org.apache.dubbo.rpc.Protocol)ExtensionLoader.getExtensionLoader(org.apache.dubbo.rpc.Protocol.class).getExtension(extName);
return extension.refer(arg0, arg1);
}
public org.apache.dubbo.rpc.Exporter export(org.apache.dubbo.rpc.Invoker arg0) throws org.apache.dubbo.rpc.RpcException {
if (arg0 == null) throw new IllegalArgumentException("org.apache.dubbo.rpc.Invoker argument == null");
if (arg0.getUrl() == null) throw new IllegalArgumentException("org.apache.dubbo.rpc.Invoker argument getUrl() == null");
org.apache.dubbo.common.URL url = arg0.getUrl();
String extName = ( url.getProtocol() == null ? "dubbo" : url.getProtocol() );
if(extName == null) throw new IllegalStateException("Failed to get extension (org.apache.dubbo.rpc.Protocol) name from url (" + url.toString() + ") use keys([protocol])");
org.apache.dubbo.rpc.Protocol extension = (org.apache.dubbo.rpc.Protocol)ExtensionLoader.getExtensionLoader(org.apache.dubbo.rpc.Protocol.class).getExtension(extName);
return extension.export(arg0);
}
public void destroy() {
throw new UnsupportedOperationException("The method public abstract void org.apache.dubbo.rpc.Protocol.destroy() of interface org.apache.dubbo.rpc.Protocol is not adaptive method!");
}
public int getDefaultPort() {
throw new UnsupportedOperationException("The method public abstract int org.apache.dubbo.rpc.Protocol.getDefaultPort() of interface org.apache.dubbo.rpc.Protocol is not adaptive method!");
}
}
Cluster$Adaptive
package org.apache.dubbo.rpc.cluster;
import org.apache.dubbo.common.extension.ExtensionLoader;
public class Cluster$Adaptive implements org.apache.dubbo.rpc.cluster.Cluster {
public org.apache.dubbo.rpc.Invoker join(org.apache.dubbo.rpc.cluster.Directory arg0) throws org.apache.dubbo.rpc.RpcException {
if (arg0 == null) throw new IllegalArgumentException("org.apache.dubbo.rpc.cluster.Directory argument == null");
if (arg0.getUrl() == null) throw new IllegalArgumentException("org.apache.dubbo.rpc.cluster.Directory argument getUrl() == null");
org.apache.dubbo.common.URL url = arg0.getUrl();
String extName = url.getParameter("cluster", "failover");
if(extName == null) throw new IllegalStateException("Failed to get extension (org.apache.dubbo.rpc.cluster.Cluster) name from url (" + url.toString() + ") use keys([cluster])");
org.apache.dubbo.rpc.cluster.Cluster extension = (org.apache.dubbo.rpc.cluster.Cluster)ExtensionLoader.getExtensionLoader(org.apache.dubbo.rpc.cluster.Cluster.class).getExtension(extName);
return extension.join(arg0);
}
}
ProxyFactory$Adaptive
package org.apache.dubbo.rpc;
import org.apache.dubbo.common.extension.ExtensionLoader;
public class ProxyFactory$Adaptive implements org.apache.dubbo.rpc.ProxyFactory {
public org.apache.dubbo.rpc.Invoker getInvoker(java.lang.Object arg0, java.lang.Class arg1, org.apache.dubbo.common.URL arg2) throws org.apache.dubbo.rpc.RpcException {
if (arg2 == null) throw new IllegalArgumentException("url == null");
org.apache.dubbo.common.URL url = arg2;
String extName = url.getParameter("proxy", "javassist");
if(extName == null) throw new IllegalStateException("Failed to get extension (org.apache.dubbo.rpc.ProxyFactory) name from url (" + url.toString() + ") use keys([proxy])");
org.apache.dubbo.rpc.ProxyFactory extension = (org.apache.dubbo.rpc.ProxyFactory)ExtensionLoader.getExtensionLoader(org.apache.dubbo.rpc.ProxyFactory.class).getExtension(extName);
return extension.getInvoker(arg0, arg1, arg2);
}
public java.lang.Object getProxy(org.apache.dubbo.rpc.Invoker arg0, boolean arg1) throws org.apache.dubbo.rpc.RpcException {
if (arg0 == null) throw new IllegalArgumentException("org.apache.dubbo.rpc.Invoker argument == null");
if (arg0.getUrl() == null) throw new IllegalArgumentException("org.apache.dubbo.rpc.Invoker argument getUrl() == null");
org.apache.dubbo.common.URL url = arg0.getUrl();
String extName = url.getParameter("proxy", "javassist");
if(extName == null) throw new IllegalStateException("Failed to get extension (org.apache.dubbo.rpc.ProxyFactory) name from url (" + url.toString() + ") use keys([proxy])");
org.apache.dubbo.rpc.ProxyFactory extension = (org.apache.dubbo.rpc.ProxyFactory)ExtensionLoader.getExtensionLoader(org.apache.dubbo.rpc.ProxyFactory.class).getExtension(extName);
return extension.getProxy(arg0, arg1);
}
public java.lang.Object getProxy(org.apache.dubbo.rpc.Invoker arg0) throws org.apache.dubbo.rpc.RpcException {
if (arg0 == null) throw new IllegalArgumentException("org.apache.dubbo.rpc.Invoker argument == null");
if (arg0.getUrl() == null) throw new IllegalArgumentException("org.apache.dubbo.rpc.Invoker argument getUrl() == null");
org.apache.dubbo.common.URL url = arg0.getUrl();
String extName = url.getParameter("proxy", "javassist");
if(extName == null) throw new IllegalStateException("Failed to get extension (org.apache.dubbo.rpc.ProxyFactory) name from url (" + url.toString() + ") use keys([proxy])");
org.apache.dubbo.rpc.ProxyFactory extension = (org.apache.dubbo.rpc.ProxyFactory)ExtensionLoader.getExtensionLoader(org.apache.dubbo.rpc.ProxyFactory.class).getExtension(extName);
return extension.getProxy(arg0);
}
}
ZookeeperTransporter$Adaptive
package org.apache.dubbo.remoting.zookeeper;
import org.apache.dubbo.common.extension.ExtensionLoader;
public class ZookeeperTransporter$Adaptive implements org.apache.dubbo.remoting.zookeeper.ZookeeperTransporter {
public org.apache.dubbo.remoting.zookeeper.ZookeeperClient connect(org.apache.dubbo.common.URL arg0) {
if (arg0 == null) throw new IllegalArgumentException("url == null");
org.apache.dubbo.common.URL url = arg0;
String extName = url.getParameter("client", url.getParameter("transporter", "curator"));
if(extName == null) throw new IllegalStateException("Failed to get extension (org.apache.dubbo.remoting.zookeeper.ZookeeperTransporter) name from url (" + url.toString() + ") use keys([client, transporter])");
org.apache.dubbo.remoting.zookeeper.ZookeeperTransporter extension = (org.apache.dubbo.remoting.zookeeper.ZookeeperTransporter)ExtensionLoader.getExtensionLoader(org.apache.dubbo.remoting.zookeeper.ZookeeperTransporter.class).getExtension(extName);
return extension.connect(arg0);
}
}
RegistryFactory$Adaptive
package org.apache.dubbo.registry;
import org.apache.dubbo.common.extension.ExtensionLoader;
public class RegistryFactory$Adaptive implements org.apache.dubbo.registry.RegistryFactory {
public org.apache.dubbo.registry.Registry getRegistry(org.apache.dubbo.common.URL arg0) {
if (arg0 == null) throw new IllegalArgumentException("url == null");
org.apache.dubbo.common.URL url = arg0;
String extName = ( url.getProtocol() == null ? "dubbo" : url.getProtocol() );
if(extName == null) throw new IllegalStateException("Failed to get extension (org.apache.dubbo.registry.RegistryFactory) name from url (" + url.toString() + ") use keys([protocol])");
org.apache.dubbo.registry.RegistryFactory extension = (org.apache.dubbo.registry.RegistryFactory)ExtensionLoader.getExtensionLoader(org.apache.dubbo.registry.RegistryFactory.class).getExtension(extName);
return extension.getRegistry(arg0);
}
}
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