1、Spring与Dubbo整合例子
public class Consumer {
public static void main(String[] args) {
ClassPathXmlApplicationContext context =
new ClassPathXmlApplicationContext(new String[]{"META-INF/spring/dubbo-demo-consumer.xml"});
context.start();
DemoService demoService = (DemoService) context.getBean("demoService");
while (true) {
try {
Thread.sleep(1000);
String hello = demoService.sayHello("world"); // call remote method
System.out.println(hello); // get result
} catch (Throwable throwable) {
throwable.printStackTrace();
}
}
}
}
public class Provider {
public static void main(String[] args) throws Exception {
System.setProperty("java.net.preferIPv4Stack", "true");
ClassPathXmlApplicationContext context =
new ClassPathXmlApplicationContext(new String[]{"META-INF/spring/dubbo-demo-provider.xml"});
context.start();
System.in.read();
}
}
2、Spring解析dubbo配置文件
先启动服务提供者，再启动消费者，发现控制台可以正常输出。下面分析一下Spring是如何解析dubbo的消费者和服务提供者的配置文件。Spring容器提供了IOC功能，可以替我们生成bean。通常，我们将bean的定义放在xml文件中，下面我们来分析一下Spring加载xml配置文件并生成bean的过程。Spring提供的容器可以分为两种：BeanFactory和ApplicationContext。其中BeanFactory是懒加载，也就是延迟初始化，它在你调用getBean时才会初始化这个bean，而ApplicationContext是初始化容器时就会加载非延迟初始化的bean。先简单概况下Spring容器生成bean的过程，首先通过loadBeanDefinition过程将bean的信息封装成一个个BeanDefinition，然后再根据这些BeanDefinition创建bean。下面看Spring解析Dubbo的配置文件并生成bean的过程。
//1、new ClassPathXmlApplicationContext时Spring容器初始化,此时会先调用loadBeanDefinition方法去加载解析xml配置文件
context = new ClassPathXmlApplicationContext(new String[]{"META-INF/spring/dubbo-demo-provider.xml"});
//2、加载配置文件最终会走到这里
protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
if (delegate.isDefaultNamespace(root)) {
NodeList nl = root.getChildNodes();
// 3、这里其实已经通过dom4j将xml文件解析成了Document,将xml中的一项一项配置解析成了一个个Node去读取处理.
for (int i = 0; i < nl.getLength(); i++) {
Node node = nl.item(i);
if (node instanceof Element) {
Element ele = (Element) node;
// 4、判断是否是Spring默认可以处理的Node.这里看下面截图，由于dubbo：application是dubbo中定义的，不属于Spring的命
//名空间管理.
if (delegate.isDefaultNamespace(ele)) {
parseDefaultElement(ele, delegate);
}
else {
delegate.parseCustomElement(ele);
}
}
}
}
else {
delegate.parseCustomElement(root);
}
}
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public BeanDefinition parseCustomElement(Element ele, BeanDefinition containingBd) {
//http://dubbo.apache.org/schema/dubbo
String namespaceUri = getNamespaceURI(ele);
//DubboNameSpaceHandler
NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);
if (handler == null) {
error("Unable to locate Spring NamespaceHandler for XML schema namespace [" + namespaceUri + "]", ele);
return null;
}
return handler.parse(ele, new ParserContext(this.readerContext, this, containingBd));
}
private static BeanDefinition parse(Element element, ParserContext parserContext, Class beanClass, boolean required) {
RootBeanDefinition beanDefinition = new RootBeanDefinition();
//class com.alibaba.dubbo.config.ApplicationConfig
beanDefinition.setBeanClass(beanClass);
beanDefinition.setLazyInit(false);
//解析id属性
String id = element.getAttribute("id");
if ((id == null || id.length() == 0) && required) {
String generatedBeanName = element.getAttribute("name");
if (generatedBeanName == null || generatedBeanName.length() == 0) {
if (ProtocolConfig.class.equals(beanClass)) {
generatedBeanName = "dubbo";
} else {
generatedBeanName = element.getAttribute("interface");
}
}
if (generatedBeanName == null || generatedBeanName.length() == 0) {
generatedBeanName = beanClass.getName();
}
id = generatedBeanName;
int counter = 2;
while (parserContext.getRegistry().containsBeanDefinition(id)) {
id = generatedBeanName + (counter++);
}
}
if (id != null && id.length() > 0) {
if (parserContext.getRegistry().containsBeanDefinition(id)) {
throw new IllegalStateException("Duplicate spring bean id " + id);
}
//注册BeanDefinition
parserContext.getRegistry().registerBeanDefinition(id, beanDefinition);
//将id属性放入beanDefinition中,后续getBean创建bean时就是根据这些属性来创建bean,这里创建的bean是ApplicationConfig
beanDefinition.getPropertyValues().addPropertyValue("id", id);
}
//删去一些代码，reference是解析得到的value值，可见这里将属性和属性值都放入了BeanDefinition
beanDefinition.getPropertyValues().addPropertyValue(property, reference);
return beanDefinition;
}
到这里就解析完了，Spring将xml中的application节点解析成一个BeanDefinition，并注册到Registry中，Registry就是一个Map。下面分析Spring创建这个ApplicationConfig的过程。
3、Spring创建ApplicationConfig
context = new ClassPathXmlApplicationContext(new String[]{"META-INF/spring/dubbo-demo-provider.xml"});
// Spring容器的初始化过程，new ClassPathXmlApplicationContext后会走到这里
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
prepareRefresh();
// 这里面就会执行上面的分析过程，调用loadBeanDefinition解析BeanDefinition
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
postProcessBeanFactory(beanFactory);
// Invoke factory processors registered as beans in the context.
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
registerBeanPostProcessors(beanFactory);
// Initialize message source for this context.
initMessageSource();
// Initialize event multicaster for this context.
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
onRefresh();
// Check for listener beans and register them.
registerListeners();
// Instantiate all remaining (non-lazy-init) singletons.可以看到Spring容器初始化的后面会初始化非延迟加载的bean，
//这里会走到下图的preInstantiasteSingletons方法
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
finishRefresh();
}
}
}
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//Spring创建bean最终会走到这里
protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args)
throws BeanCreationException {
// Instantiate the bean.
BeanWrapper instanceWrapper = null;
if (mbd.isSingleton()) {
instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
}
if (instanceWrapper == null) {
//删除一些无用代码,这里会调用反射创建bean,创建完仅是一个空的bean，属性还没有赋值
instanceWrapper = createBeanInstance(beanName, mbd, args);
}
final Object bean = (instanceWrapper != null ? instanceWrapper.getWrappedInstance() : null);
// Initialize the bean instance.
Object exposedObject = bean;
try {
//属性赋值,最终也是调用反射进行赋值
populateBean(beanName, mbd, instanceWrapper);
if (exposedObject != null) {
exposedObject = initializeBean(beanName, exposedObject, mbd);
}
}
return exposedObject;
}
protected void populateBean(String beanName, RootBeanDefinition mbd, BeanWrapper bw) {
// 这里的pvs就是之前解析配置文件得到BeanDefinition时，给BeanDefinition注入进去的
PropertyValues pvs = mbd.getPropertyValues();
// 删除一些代码，最终这里会调用反射赋值，跳来跳去有点复杂
applyPropertyValues(beanName, mbd, bw, pvs);
}
protected void addSingleton(String beanName, Object singletonObject) {
//最终创建完bean以后会将它保存起来(猜测，Spring容器初始化以后，非懒加载的bean已经以如下方式保存到Spring容器中了，后续通过
//@Autowired注解)来获取时就是从这里面获取，只是分析，还没有看源码)
synchronized (this.singletonObjects) {
this.singletonObjects.put(beanName, (singletonObject != null ? singletonObject : NULL_OBJECT));
this.singletonFactories.remove(beanName);
this.earlySingletonObjects.remove(beanName);
this.registeredSingletons.add(beanName);
}
}
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