Dubbo源码解析之服务发现

1.从配置入手

xml形式引入一个dubbo服务配置如下：

<dubbo:reference id="demoService" interface="com.doubeier.dubbo.common.infterface.DemoService" />

根据之前所说内容，我们去DubboNamespaceHandler中查看该标签的解析情况：

registerBeanDefinitionParser("reference", new DubboBeanDefinitionParser(ReferenceBean.class, false));

然后，我们去看一下ReferenceBean的定义

public class ReferenceBean<T> extends ReferenceConfig<T> implements FactoryBean, ApplicationContextAware, InitializingBean, DisposableBean

对于spring bean生命周期相关的内容，这里都不再过多说明，这里直接关注重点方法，也就是getObject方法

2.从getObject开始入手

getObject方法是FactoryBean接口中定义的一个方法，FactoryBean是一种特殊的bean，从spring容器中获取FactoryBean对应的bean是，若是直接以beanName获取，会回去到对应getObject返回的对象，若加上"&"进行获取，则会获取到对应的FactoryBean的实例对象。下面我们来看一看ReferenceBean中的getObject方法：

    @Override
    public Object getObject() throws Exception {
        return get();
    }

再往下，其get方法是再其父类中定义的，也就是ReferenceConfig类中：

    public synchronized T get() {
        if (destroyed) {
            throw new IllegalStateException("Already destroyed!");
        }
        if (ref == null) {
            init();
        }
        return ref;
    }

很容易的看出，关键的方法就是init方法，向下追一下：

    private void init() {
    	//若已经初始化过，直接返回，避免重复初始化
        if (initialized) {
            return;
        }
        initialized = true;
        //接口全名检查
        if (interfaceName == null || interfaceName.length() == 0) {
            throw new IllegalStateException("<dubbo:reference interface=\"\" /> interface not allow null!");
        }
        
        //检测 consumer 变量是否为空，为空则创建
        checkDefault();
        appendProperties(this);
        if (getGeneric() == null && getConsumer() != null) {
            setGeneric(getConsumer().getGeneric());
        }
        if (ProtocolUtils.isGeneric(getGeneric())) {
            interfaceClass = GenericService.class;
        } else {
            try {
            	//加载对应class
                interfaceClass = Class.forName(interfaceName, true, Thread.currentThread()
                        .getContextClassLoader());
            } catch (ClassNotFoundException e) {
                throw new IllegalStateException(e.getMessage(), e);
            }
            checkInterfaceAndMethods(interfaceClass, methods);
        }
        //从系统变量中获取与接口名对应的属性值
        String resolve = System.getProperty(interfaceName);
        String resolveFile = null;
        if (resolve == null || resolve.length() == 0) {
        	//从系统属性中获取解析文件路径
            resolveFile = System.getProperty("dubbo.resolve.file");
            if (resolveFile == null || resolveFile.length() == 0) {
            	//从指定位置加载配置文件
                File userResolveFile = new File(new File(System.getProperty("user.home")), "dubbo-resolve.properties");
                if (userResolveFile.exists()) {
                	//获取文件绝对路径
                    resolveFile = userResolveFile.getAbsolutePath();
                }
            }
            if (resolveFile != null && resolveFile.length() > 0) {
                Properties properties = new Properties();
                FileInputStream fis = null;
                try {
                    fis = new FileInputStream(new File(resolveFile));
                    //加载文件配置
                    properties.load(fis);
                } catch (IOException e) {
                    throw new IllegalStateException("Unload " + resolveFile + ", cause: " + e.getMessage(), e);
                } finally {
                    try {
                        if (null != fis) fis.close();
                    } catch (IOException e) {
                        logger.warn(e.getMessage(), e);
                    }
                }
                resolve = properties.getProperty(interfaceName);
            }
        }
        if (resolve != null && resolve.length() > 0) {
            url = resolve;
            if (logger.isWarnEnabled()) {
                if (resolveFile != null) {
                    logger.warn("Using default dubbo resolve file " + resolveFile + " replace " + interfaceName + "" + resolve + " to p2p invoke remote service.");
                } else {
                    logger.warn("Using -D" + interfaceName + "=" + resolve + " to p2p invoke remote service.");
                }
            }
        }
        if (consumer != null) {
            if (application == null) {
                application = consumer.getApplication();
            }
            if (module == null) {
                module = consumer.getModule();
            }
            if (registries == null) {
                registries = consumer.getRegistries();
            }
            if (monitor == null) {
                monitor = consumer.getMonitor();
            }
        }
        if (module != null) {
            if (registries == null) {
                registries = module.getRegistries();
            }
            if (monitor == null) {
                monitor = module.getMonitor();
            }
        }
        if (application != null) {
            if (registries == null) {
                registries = application.getRegistries();
            }
            if (monitor == null) {
                monitor = application.getMonitor();
            }
        }
        //一堆检查校验--
        checkApplication();
        checkStub(interfaceClass);
        checkMock(interfaceClass);
        
        //添加各种信息到map中  这里有side，版本信息，时间戳
        Map<String, String> map = new HashMap<String, String>();
        Map<Object, Object> attributes = new HashMap<Object, Object>();
        map.put(Constants.SIDE_KEY, Constants.CONSUMER_SIDE);
        map.put(Constants.DUBBO_VERSION_KEY, Version.getProtocolVersion());
        map.put(Constants.TIMESTAMP_KEY, String.valueOf(System.currentTimeMillis()));
        if (ConfigUtils.getPid() > 0) {
            map.put(Constants.PID_KEY, String.valueOf(ConfigUtils.getPid()));
        }
        if (!isGeneric()) {
            String revision = Version.getVersion(interfaceClass, version);
            if (revision != null && revision.length() > 0) {
                map.put("revision", revision);
            }

            //获取接口方法名称 添加到map中
            String[] methods = Wrapper.getWrapper(interfaceClass).getMethodNames();
            if (methods.length == 0) {
                logger.warn("NO method found in service interface " + interfaceClass.getName());
                map.put("methods", Constants.ANY_VALUE)