5.2 dubbo-compiler源碼解析
1 ExtensionLoader<Protocol> loader = ExtensionLoader.getExtensionLoader(Protocol.class); 2 final Protocol dubboProtocol = loader.getExtension("dubbo"); 3 final Protocol adaptiveExtension = loader.getAdaptiveExtension();
在2.2 dubbo-spi源碼解析講了第一句,在第四章 dubbo內核之aop源碼解析講了第二句,本章來講最後一句。
getAdaptiveExtension()層級結構:
1 ExtensionLoader<T>.getAdaptiveExtension() 2 --createAdaptiveExtension() 3 ----injectExtension(getAdaptiveExtensionClass()) 4 ------getAdaptiveExtensionClass() 5 --------getExtensionClasses()//從spi文件中查找實現類上具有@Adaptive註解的類 6 ----------loadExtensionClasses() 7 ------------loadFile(Map<String, Class<?>> extensionClasses, String dir)8 --------createAdaptiveExtensionClass()//如果從spi文件中沒有找到實現類上具有@Adaptive註解的類,則動態創建類
這裏最後執行到了createAdaptiveExtensionClass()方法。
1 private Class<?> createAdaptiveExtensionClass() { 2 String code = createAdaptiveExtensionClassCode(); 3 ClassLoader classLoader = findClassLoader();4 com.alibaba.dubbo.common.compiler.Compiler compiler = ExtensionLoader.getExtensionLoader(com.alibaba.dubbo.common.compiler.Compiler.class).getAdaptiveExtension(); 5 return compiler.compile(code, classLoader); 6 }
一 構造代碼串
createAdaptiveExtensionClassCode()方法中會判斷如果一個類中沒有@Adaptive註解的方法,則直接拋出IllegalStateException異常;否則,會為有@Adaptive註解的方法構造代碼,而沒有@Adaptive註解的方法直接拋出UnsupportedOperationException異常。
構造出的結果為:
1 package com.alibaba.dubbo.rpc; 2 3 import com.alibaba.dubbo.common.extension.ExtensionLoader; 4 5 public class Protocol$Adaptive implements com.alibaba.dubbo.rpc.Protocol { 6 public void destroy() { 7 throw new UnsupportedOperationException("method public abstract void com.alibaba.dubbo.rpc.Protocol.destroy() of interface com.alibaba.dubbo.rpc.Protocol is not adaptive method!"); 8 } 9 public int getDefaultPort() { 10 throw new UnsupportedOperationException("method public abstract int com.alibaba.dubbo.rpc.Protocol.getDefaultPort() of interface com.alibaba.dubbo.rpc.Protocol is not adaptive method!"); 11 } 12 public com.alibaba.dubbo.rpc.Invoker refer(java.lang.Class arg0, com.alibaba.dubbo.common.URL arg1) throws com.alibaba.dubbo.rpc.RpcException { 13 if (arg1 == null) 14 throw new IllegalArgumentException("url == null"); 15 com.alibaba.dubbo.common.URL url = arg1; 16 String extName = (url.getProtocol() == null ? "dubbo" : url.getProtocol()); 17 if(extName == null) 18 throw new IllegalStateException("Fail to get extension(com.alibaba.dubbo.rpc.Protocol) name from url(" + url.toString() + ") use keys([protocol])"); 19 com.alibaba.dubbo.rpc.Protocol extension = (com.alibaba.dubbo.rpc.Protocol)ExtensionLoader.getExtensionLoader(com.alibaba.dubbo.rpc.Protocol.class).getExtension(extName); 20 return extension.refer(arg0, arg1); 21 } 22 public com.alibaba.dubbo.rpc.Exporter export(com.alibaba.dubbo.rpc.Invoker arg0) throws com.alibaba.dubbo.rpc.RpcException { 23 if (arg0 == null) 24 throw new IllegalArgumentException("com.alibaba.dubbo.rpc.Invoker argument == null"); 25 if (arg0.getUrl() == null) 26 throw new IllegalArgumentException("com.alibaba.dubbo.rpc.Invoker argument getUrl() == null"); 27 com.alibaba.dubbo.common.URL url = arg0.getUrl(); 28 String extName = (url.getProtocol() == null ? "dubbo" : url.getProtocol()); 29 if(extName == null) 30 throw new IllegalStateException("Fail to get extension(com.alibaba.dubbo.rpc.Protocol) name from url(" + url.toString() + ") use keys([protocol])"); 31 com.alibaba.dubbo.rpc.Protocol extension = (com.alibaba.dubbo.rpc.Protocol)ExtensionLoader.getExtensionLoader(com.alibaba.dubbo.rpc.Protocol.class).getExtension(extName); 32 return extension.export(arg0); 33 } 34 }
說明:
- 該生成類在dubbo2.5.3中export和refer方法聲明處的異常拋出是錯的(在dubbo2.5.4改正了);
- 類名在dubbo2.5.4之前(包含2.5.4)也是錯的Protocol$Adpative,dubbo2.5.5改正了。
二 獲取Compiler裝飾類
com.alibaba.dubbo.common.compiler.Compiler compiler = ExtensionLoader.getExtensionLoader(com.alibaba.dubbo.common.compiler.Compiler.class).getAdaptiveExtension();
先看一下com.alibaba.dubbo.common.compiler.Compiler接口:
1 @SPI("javassist") 2 public interface Compiler { 3 Class<?> compile(String code, ClassLoader classLoader); 4 }
@SPI的默認值為javassist,根據上一節的經驗,默認獲取的Compiler接口的實現類將是META-INF/dubbo/internal/com.alibaba.dubbo.common.compiler.Compiler文件中的key為javassit的實現類。文件內容如下:
1 adaptive=com.alibaba.dubbo.common.compiler.support.AdaptiveCompiler 2 jdk=com.alibaba.dubbo.common.compiler.support.JdkCompiler 3 javassist=com.alibaba.dubbo.common.compiler.support.JavassistCompiler
根據上一節對ExtensionFactory的getAdaptiveExtension()的講解,我們最終獲取到的Compiler的AdaptiveExtension將是com.alibaba.dubbo.common.compiler.support.AdaptiveCompiler。
來看源碼,首先是獲取ExtensionLoader<com.alibaba.dubbo.common.compiler.Compiler> loader,最終的loader包含如下屬性:
- Class<?> type = interface com.alibaba.dubbo.common.compiler.Compiler
- ExtensionFactory objectFactory = AdaptiveExtensionFactory(適配類)
- factories = [SpringExtensionFactory實例, SpiExtensionFactory實例]
之後,是loader.getAdaptiveExtension()。
在該方法中,首先會調用createAdaptiveExtension()創建實例,之後放入緩存,然後返回。
1 private T createAdaptiveExtension() { 2 try { 3 return injectExtension((T) getAdaptiveExtensionClass().newInstance()); 4 } catch (Exception e) { 5 throw new IllegalStateException("Can not create adaptive extenstion " + type + ", cause: " + e.getMessage(), 6 e); 7 } 8 } 9 10 private Class<?> getAdaptiveExtensionClass() { 11 /** 12 * 獲取ExtensionClasses和適配類 13 * 其中適配類cachedAdaptiveClass如果不存在,則需要使用createAdaptiveExtensionClass()進行創建. 14 */ 15 getExtensionClasses(); 16 if (cachedAdaptiveClass != null) { 17 return cachedAdaptiveClass; 18 } 19 return cachedAdaptiveClass = createAdaptiveExtensionClass(); 20 }
在createAdaptiveExtension()中首先會調用getAdaptiveExtensionClass()獲取ExtensionClasses和修飾類,之後將修飾類返回。根據META-INF/dubbo/internal/com.alibaba.dubbo.common.compiler.Compiler文件的內容,最後返回
- ExtensionClasses
- "jdk" -> "class com.alibaba.dubbo.common.compiler.support.JdkCompiler"
- "javassist" -> "class com.alibaba.dubbo.common.compiler.support.JavassistCompiler"
- cachedAdaptiveClass=class com.alibaba.dubbo.common.compiler.support.AdaptiveCompiler
之後調用AdaptiveCompiler的無參構造器創建AdaptiveCompiler對象實例,然後執行injectExtension(T instance)(這裏沒起作用)為AdaptiveCompiler對象實例註入相應的屬性(AdaptiveCompiler必須提供相應的setter方法),最後返回AdaptiveCompiler對象實例。
三 編譯代碼並加載為Class<?>對象
創建好AdaptiveCompiler對象實例之後,然後執行下面的方法。
Class<?> compile(String code, ClassLoader classLoader)
看一下AdaptiveCompiler全部源碼:
1 @Adaptive 2 public class AdaptiveCompiler implements Compiler { 3 private static volatile String DEFAULT_COMPILER;//默認的編譯器的名字 4 5 public static void setDefaultCompiler(String compiler) { 6 DEFAULT_COMPILER = compiler; 7 } 8 9 /** 10 * 典型的動態代理,在代理類中,存放著真實對象,使用真實對象執行相應的方法 11 */ 12 public Class<?> compile(String code, ClassLoader classLoader) { 13 Compiler compiler; 14 ExtensionLoader<Compiler> loader = ExtensionLoader.getExtensionLoader(Compiler.class); 15 String name = DEFAULT_COMPILER; // copy reference 16 if (name != null && name.length() > 0) { 17 compiler = loader.getExtension(name);//獲取名字為name的實現類的實例,在獲取的過程中會完成IOC和AOP 18 } else { 19 compiler = loader.getDefaultExtension();//獲取默認的JavassitCompiler,調用getExtension(cachedDefaultName) 20 } 21 return compiler.compile(code, classLoader);//根據獲取到的實現類compiler實例,來執行真正的動態生成類的代碼 22 } 23 }
這裏執行的是compiler = loader.getDefaultExtension(),該方法不說了,就是調用了getExtension(cachedDefaultName)生成一個JavassistCompiler的實例。之後就是執行JavassistCompiler的compile(String code, ClassLoader classLoader)方法。
1 package com.alibaba.dubbo.common.compiler.support; 2 3 import com.alibaba.dubbo.common.compiler.Compiler; 4 import com.alibaba.dubbo.common.utils.ClassHelper; 5 6 import java.util.regex.Matcher; 7 import java.util.regex.Pattern; 8 9 /** 10 * Abstract compiler. (SPI, Prototype, ThreadSafe) 11 */ 12 public abstract class AbstractCompiler implements Compiler { 13 private static final Pattern PACKAGE_PATTERN = Pattern.compile("package\\s+([$_a-zA-Z][$_a-zA-Z0-9\\.]*);"); 14 private static final Pattern CLASS_PATTERN = Pattern.compile("class\\s+([$_a-zA-Z][$_a-zA-Z0-9]*)\\s+"); 15 16 /** 17 * 1 根據正則表達式從code中獲取包名和類名,組成全類名 18 * 2 根據全類名使用Class.forName創建Class<?>,如果該類在jvm中存在,則成功,否則拋出ClassNotFoundException, 19 * 執行doCompile方法。 20 */ 21 public Class<?> compile(String code, ClassLoader classLoader) { 22 code = code.trim(); 23 Matcher matcher = PACKAGE_PATTERN.matcher(code); 24 String pkg; 25 if (matcher.find()) { 26 pkg = matcher.group(1); 27 } else { 28 pkg = ""; 29 } 30 matcher = CLASS_PATTERN.matcher(code); 31 String cls; 32 if (matcher.find()) { 33 cls = matcher.group(1); 34 } else { 35 throw new IllegalArgumentException("No such class name in " + code); 36 } 37 String className = pkg != null && pkg.length() > 0 ? pkg + "." + cls : cls; 38 try { 39 return Class.forName(className, true, ClassHelper.getCallerClassLoader(getClass())); 40 } catch (ClassNotFoundException e) { 41 if (!code.endsWith("}")) { 42 throw new IllegalStateException("The java code not endsWith \"}\", code: \n" + code + "\n"); 43 } 44 try { 45 return doCompile(className, code); 46 } catch (RuntimeException t) { 47 throw t; 48 } catch (Throwable t) { 49 throw new IllegalStateException("Failed to compile class, cause: " + t.getMessage() + ", class: " + className + ", code: \n" + code + "\n, stack: " + ClassUtils.toString(t)); 50 } 51 } 52 } 53 54 protected abstract Class<?> doCompile(String name, String source) throws Throwable; 55 }
該方法會執行JavassistCompiler的Class<?> doCompile(String name, String source)方法了,在該方法中,使用正則表達式對傳入的源碼解析成屬性方法等,並使用javassist的API創建Class<?>。
最後,該final Protocol adaptiveExtension = loader.getAdaptiveExtension();代碼返回的adaptiveExtension = Protocol$Adaptive實例。
總結(再啰嗦一遍):
- ExtensionLoader.getExtensionLoader(ExtensionFactory.class).getAdaptiveExtension()最終返回的是:AdaptiveExtensionFactory實例,其屬性factories = [SpringExtensionFactory實例, SpiExtensionFactory實例]
- 不管是獲取哪一個SPI接口(除了ExtensionFactory.接口)的ExtensionLoader,最終一定會有一個objectFactory=上述的AdaptiveExtensionFactory實例
- getAdaptiveExtension():作用就是獲取一個裝飾類或動態代理類的實例, 如果有@Adaptive註解的類,則直接返回該類的實例,否則返回一個動態代理類的實例(例如Protocol$Adaptive的實例),之後完成屬性註入(dubbo-IOC),最後返回實例。
- getExtension(String key):作用就是從extensionClasses(即指定SPI接口的沒有@Adaptive的實現類)獲取指定key的extensionClass,並且實例化,之後完成屬性註入(dubbo-IOC),再之後完成dubbo-AOP,最後返回實例。
5.2 dubbo-compiler源碼解析