今天想分享的是dubbo @service注解
原本是在研究dubbo-spring-boot 启动方式的，看着看着就钻入这个坑。废话不多说切入正题。
先上一张图在application.properties中的配置
application.properties
spring-boot-starter-dubbo插件，可以去搜索下，其中一个版本中的的
package io.dubbo.springboot;
import com.alibaba.dubbo.config.spring.AnnotationBean;
import org.springframework.beans.BeanUtils;
import org.springframework.context.ApplicationContextInitializer;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.core.env.Environment;
public class DubboConfigurationApplicationContextInitializer implements ApplicationContextInitializer<ConfigurableApplicationContext> {
@Override
public void initialize(ConfigurableApplicationContext applicationContext) {
Environment env = applicationContext.getEnvironment();
String scan = env.getProperty("spring.dubbo.scan");
if (scan != null) {
AnnotationBean scanner = BeanUtils.instantiate(AnnotationBean.class);
scanner.setPackage(scan);
scanner.setApplicationContext(applicationContext);
applicationContext.addBeanFactoryPostProcessor(scanner);
applicationContext.getBeanFactory().addBeanPostProcessor(scanner);
applicationContext.getBeanFactory().registerSingleton("annotationBean", scanner);
}
}
}
相信都看明白了，这里是通过配置中的scan路径去扫描dubbo接口的。
至于，何时执行这个initialize（）方法，是通过扫描spring.factories这个配置文件将DubboConfigurationApplicationContextInitializer无缝对接到spring中。
//待贴代码
定位到SpringFactoriesLoader下的
public static List<String> loadFactoryNames(Class<?> factoryClass, ClassLoader classLoader) {
String factoryClassName = factoryClass.getName();
try {
Enumeration<URL> urls = (classLoader != null ? classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :
ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));
List<String> result = new ArrayList<String>();
while (urls.hasMoreElements()) {
URL url = urls.nextElement();
Properties properties = PropertiesLoaderUtils.loadProperties(new UrlResource(url));
String factoryClassNames = properties.getProperty(factoryClassName);
result.addAll(Arrays.asList(StringUtils.commaDelimitedListToStringArray(factoryClassNames)));
}
return result;
}
catch (IOException ex) {
throw new IllegalArgumentException("Unable to load [" + factoryClass.getName() +
"] factories from location [" + FACTORIES_RESOURCE_LOCATION + "]", ex);
}
}
在AbstractApplicationContext下的refresh方法下的invokeBeanFactoryPostProcessors(beanFactory)中扫描指定包下的类，然后将类定义加载到registry（DefaultListableBeanFactory）下的beanDefinitionNames下。
再看如何扫描：定位到AnnotationBean下的postProcessBeanFactory
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory)
throws BeansException {
if (annotationPackage == null || annotationPackage.length() == 0) {
return;
}
if (beanFactory instanceof BeanDefinitionRegistry) {
try {
// init scanner
Class<?> scannerClass = ReflectUtils.forName("org.springframework.context.annotation.ClassPathBeanDefinitionScanner");
Object scanner = scannerClass.getConstructor(new Class<?>[] {BeanDefinitionRegistry.class, boolean.class}).newInstance(new Object[] {(BeanDefinitionRegistry) beanFactory, true});
// add filter
Class<?> filterClass = ReflectUtils.forName("org.springframework.core.type.filter.AnnotationTypeFilter");
Object filter = filterClass.getConstructor(Class.class).newInstance(Service.class);
Method addIncludeFilter = scannerClass.getMethod("addIncludeFilter", ReflectUtils.forName("org.springframework.core.type.filter.TypeFilter"));
addIncludeFilter.invoke(scanner, filter);
// scan packages
String[] packages = Constants.COMMA_SPLIT_PATTERN.split(annotationPackage);
Method scan = scannerClass.getMethod("scan", new Class<?>[]{String[].class});
scan.invoke(scanner, new Object[] {packages});
} catch (Throwable e) {
// spring 2.0
}
}
}
粗略一看应该是利用jdk反射ClassPathBeanDefinitionScanner和TypeFilter和AnnotationTypeFilter这几个类完成了扫描，过滤的功能。
打开ClassPathBeanDefinitionScanner定位到scan方法，在定位到doScan方法
static final String DEFAULT_RESOURCE_PATTERN = "**/*.class";
//////
protected Set<BeanDefinitionHolder> doScan(String... basePackages) {
Assert.notEmpty(basePackages, "At least one base package must be specified");
Set<BeanDefinitionHolder> beanDefinitions = new LinkedHashSet<BeanDefinitionHolder>();
for (String basePackage : basePackages) {
Set<BeanDefinition> candidates = findCandidateComponents(basePackage);
for (BeanDefinition candidate : candidates) {
ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(candidate);
candidate.setScope(scopeMetadata.getScopeName());
String beanName = this.beanNameGenerator.generateBeanName(candidate, this.registry);
if (candidate instanceof AbstractBeanDefinition) {
postProcessBeanDefinition((AbstractBeanDefinition) candidate, beanName);
}
if (candidate instanceof AnnotatedBeanDefinition) {
AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition) candidate);
}
if (checkCandidate(beanName, candidate)) {
BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName);
definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
beanDefinitions.add(definitionHolder);
registerBeanDefinition(definitionHolder, this.registry);
}
}
}
return beanDefinitions;
}
找到findCandidateComponents方法，细看：
String packageSearchPath = ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX +
resolveBasePackage(basePackage) + '/' + this.resourcePattern;
Resource[] resources = this.resourcePatternResolver.getResources(packageSearchPath);
boolean traceEnabled = logger.isTraceEnabled();
boolean debugEnabled = logger.isDebugEnabled();
for (Resource resource : resources) {
if (traceEnabled) {
logger.trace("Scanning " + resource);
}
if (resource.isReadable()) {
try {
MetadataReader metadataReader = this.metadataReaderFactory.getMetadataReader(resource);
if (isCandidateComponent(metadataReader)) {
ScannedGenericBeanDefinition sbd = new ScannedGenericBeanDefinition(metadataReader);
sbd.setResource(resource);
sbd.setSource(resource);
通过匹配寻找到报下的所有的class文件，找到类定义，然后将类定义加载到DefaultListableBeanFactory中
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