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dubbo-compiler源码解析

勿忘初心2018-11-18 12:02

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1         ExtensionLoader<Protocol> loader = ExtensionLoader.getExtensionLoader(Protocol.class);
2         final Protocol dubboProtocol = loader.getExtension("dubbo");
3         final Protocol adaptiveExtension = loader.getAdaptiveExtension();

2.2 dubbo-spi源码解析讲了第一句,在第四章 dubbo内核之aop源码解析讲了第二句,本章来讲最后一句。

getAdaptiveExtension()层级结构:

1 ExtensionLoader<T>.getAdaptiveExtension()
2 --createAdaptiveExtension()
3 ----injectExtension(getAdaptiveExtensionClass())
4 ------getAdaptiveExtensionClass()
5 --------getExtensionClasses()//从spi文件中查找实现类上具有@Adaptive注解的类
6 ----------loadExtensionClasses()
7 ------------loadFile(Map<String, Class<?>> extensionClasses, String dir)
8 --------createAdaptiveExtensionClass()//如果从spi文件中没有找到实现类上具有@Adaptive注解的类,则动态创建类

这里最后执行到了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 构造代码串

createAdaptiveExtensionClassCode()方法中会判断如果一个类中没有@Adaptive注解的方法,则直接抛出IllegalStateException异常;否则,会为有@Adaptive注解的方法构造代码,而没有@Adaptive注解的方法直接抛出UnsupportedOperationException异常。

构造出的结果为:

 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 }

说明:

  • 该生成类在dubbo2.5.3中export和refer方法声明处的异常抛出是错的(在dubbo2.5.4改正了);
  • 类名在dubbo2.5.4之前(包含2.5.4)也是错的Protocol$Adpative,dubbo2.5.5改正了。

 

二 获取Compiler装饰类

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的默认值为javassist,根据上一节的经验,默认获取的Compiler接口的实现类将是META-INF/dubbo/internal/com.alibaba.dubbo.common.compiler.Compiler文件中的key为javassit的实现类。文件内容如下:

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

根据上一节对ExtensionFactory的getAdaptiveExtension()的讲解,我们最终获取到的Compiler的AdaptiveExtension将是com.alibaba.dubbo.common.compiler.support.AdaptiveCompiler。

来看源码,首先是获取ExtensionLoader<com.alibaba.dubbo.common.compiler.Compiler> loader,最终的loader包含如下属性:

  • Class<?> type = interface com.alibaba.dubbo.common.compiler.Compiler
  • ExtensionFactory objectFactory = AdaptiveExtensionFactory(适配类)
    • factories = [SpringExtensionFactory实例, SpiExtensionFactory实例]

之后,是loader.getAdaptiveExtension()。

在该方法中,首先会调用createAdaptiveExtension()创建实例,之后放入缓存,然后返回。

 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          * 获取ExtensionClasses和适配类
13          * 其中适配类cachedAdaptiveClass如果不存在,则需要使用createAdaptiveExtensionClass()进行创建.
14          */
15         getExtensionClasses();
16         if (cachedAdaptiveClass != null) {
17             return cachedAdaptiveClass;
18         }
19         return cachedAdaptiveClass = createAdaptiveExtensionClass();
20     }

在createAdaptiveExtension()中首先会调用getAdaptiveExtensionClass()获取ExtensionClasses和修饰类,之后将修饰类返回。根据META-INF/dubbo/internal/com.alibaba.dubbo.common.compiler.Compiler文件的内容,最后返回

  • 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

之后调用AdaptiveCompiler的无参构造器创建AdaptiveCompiler对象实例,然后执行injectExtension(T instance)(这里没起作用)为AdaptiveCompiler对象实例注入相应的属性(AdaptiveCompiler必须提供相应的setter方法),最后返回AdaptiveCompiler对象实例。

 

三 编译代码并加载为Class<?>对象

创建好AdaptiveCompiler对象实例之后,然后执行下面的方法。

Class<?> compile(String code, ClassLoader classLoader)

看一下AdaptiveCompiler全部源码:

 1 @Adaptive
 2 public class AdaptiveCompiler implements Compiler {
 3     private static volatile String DEFAULT_COMPILER;//默认的编译器的名字
 4 
 5     public static void setDefaultCompiler(String compiler) {
 6         DEFAULT_COMPILER = compiler;
 7     }
 8 
 9     /**
10      * 典型的动态代理,在代理类中,存放着真实对象,使用真实对象执行相应的方法
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);//获取名字为name的实现类的实例,在获取的过程中会完成IOC和AOP
18         } else {
19             compiler = loader.getDefaultExtension();//获取默认的JavassitCompiler,调用getExtension(cachedDefaultName)
20         }
21         return compiler.compile(code, classLoader);//根据获取到的实现类compiler实例,来执行真正的动态生成类的代码
22     }
23 }

这里执行的是compiler = loader.getDefaultExtension(),该方法不说了,就是调用了getExtension(cachedDefaultName)生成一个JavassistCompiler的实例。之后就是执行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 根据正则表达式从code中获取包名和类名,组成全类名
18      * 2 根据全类名使用Class.forName创建Class<?>,如果该类在jvm中存在,则成功,否则抛出ClassNotFoundException,
19      *   执行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 }

该方法会执行JavassistCompiler的Class<?> doCompile(String name, String source)方法了,在该方法中,使用正则表达式对传入的源码解析成属性方法等,并使用javassist的API创建Class<?>。

最后,该final Protocol adaptiveExtension = loader.getAdaptiveExtension();代码返回的adaptiveExtension = Protocol$Adaptive实例。

 

总结(再啰嗦一遍):

  • ExtensionLoader.getExtensionLoader(ExtensionFactory.class).getAdaptiveExtension()最终返回的是:AdaptiveExtensionFactory实例,其属性factories = [SpringExtensionFactory实例, SpiExtensionFactory实例]
  • 不管是获取哪一个SPI接口(除了ExtensionFactory.接口)的ExtensionLoader,最终一定会有一个objectFactory=上述的AdaptiveExtensionFactory实例
  • getAdaptiveExtension():作用就是获取一个装饰类或动态代理类的实例, 如果有@Adaptive注解的类,则直接返回该类的实例,否则返回一个动态代理类的实例(例如Protocol$Adaptive的实例),之后完成属性注入(dubbo-IOC),最后返回实例。
  • getExtension(String key):作用就是从extensionClasses(即指定SPI接口的没有@Adaptive的实现类)获取指定key的extensionClass,并且实例化,之后完成属性注入(dubbo-IOC),再之后完成dubbo-AOP,最后返回实例。


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