在spring2.5版本提供了注解的依赖注入功能，可以减少对xml配置。
主要使用的是
AnnotationConfigApplicationContext： 一个注解配置上下文
AutowiredAnnotationBeanPostProcessor： spring提供的用于这一目的的BeanPostProcessor实现，用来检查当前对象是否有@Autowired标注的依赖注入。 项目中除了使用@Autowired之外，还可以选择JSR250的一些注解例如@Resource大致和@Autowired相同。
CommonAnnotationBeanPostProcessor：JSR250也需要BeanPostProcessor，spring实现类了。
在spring配置文件中添加<context:annotation-config/>可以将这些processor添加到spring容器中。
另外使用注解的方式还需要一个classpath-scanning功能，使用这一功能只需要在配置文件中添加<context:component-scan base-package='com.xx.xx'>
@Component注解使用太宽泛，细分了@Controller,@Service等标注。 简单示例
@Component
public class AnnotationDemo { public void printInfo(){
System.out.println(this.getClass());
}
}
@Component
public class AnnotationDemo2 { public void printInfo(){
System.out.println(this.getClass());
}
}
测试类
@Test
public void testAnnotationInject(){
ApplicationContext context = new AnnotationConfigApplicationContext("org.lzyer.test");
//指定某些类
//ApplicationContext context = new AnnotationConfigApplicationContext(AnnotationDemo.class,AnnotationDemo2.class);
AnnotationDemo ad = context.getBean(AnnotationDemo.class);
AnnotationDemo2 ad2 = context.getBean(AnnotationDemo2.class);
ad.printInfo();
ad2.printInfo();
}
方式一为加载包下带注解的类。方式二是指定某些类。
运行结果：
class org.lzyer.test.AnnotationDemo
class org.lzyer.test.AnnotationDemo2
注入流程
/**
* Create a new AnnotationConfigApplicationContext, scanning for bean definitions
* in the given packages and automatically refreshing the context.
* @param basePackages the packages to check for annotated classes
*/
public AnnotationConfigApplicationContext(String... basePackages) {
this();
scan(basePackages);//扫描包
refresh();//调用AbstractApplicationContext中的refresh方法
}
/**
* Perform a scan within the specified base packages.
* @param basePackages the packages to check for annotated classes
* @return number of beans registered
*/
public int scan(String... basePackages) {
int beanCountAtScanStart = this.registry.getBeanDefinitionCount(); doScan(basePackages);//扫描 // Register annotation config processors, if necessary.
if (this.includeAnnotationConfig) {
AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);
} return (this.registry.getBeanDefinitionCount() - beanCountAtScanStart);
}
/**
* Perform a scan within the specified base packages,
* returning the registered bean definitions.
* <p>This method does <i>not</i> register an annotation config processor
* but rather leaves this up to the caller.
* @param basePackages the packages to check for annotated classes
* @return set of beans registered if any for tooling registration purposes (never {@code null})
*/
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) {//遍历所有的包
Set<BeanDefinition> candidates = findCandidateComponents(basePackage);//查找候选组件
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);//注册beandefinition
}
}
}
return beanDefinitions;
}
/**
* Scan the class path for candidate components.
* @param basePackage the package to check for annotated classes
* @return a corresponding Set of autodetected bean definitions
*/
public Set<BeanDefinition> findCandidateComponents(String basePackage) {
Set<BeanDefinition> candidates = new LinkedHashSet<BeanDefinition>();
try {
String packageSearchPath = ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX +
resolveBasePackage(basePackage) + "/" + this.resourcePattern;//补充路径
Resource[] resources = this.resourcePatternResolver.getResources(packageSearchPath);
boolean traceEnabled = logger.isTraceEnabled();
boolean debugEnabled = logger.isDebugEnabled();
for (Resource resource : resources) {//遍历Resource
if (traceEnabled) {
logger.trace("Scanning " + resource);
}
if (resource.isReadable()) {
try {//通过asm获取class，暂且不研究asm
MetadataReader metadataReader = this.metadataReaderFactory.getMetadataReader(resource);
if (isCandidateComponent(metadataReader)) {//判断是否为候选组件
ScannedGenericBeanDefinition sbd = new ScannedGenericBeanDefinition(metadataReader);
sbd.setResource(resource);
sbd.setSource(resource);
if (isCandidateComponent(sbd)) {//判断是否为候选组件
if (debugEnabled) {
logger.debug("Identified candidate component class: " + resource);
}
candidates.add(sbd);//添加候选组件
}
else {
if (debugEnabled) {
logger.debug("Ignored because not a concrete top-level class: " + resource);
}
}
}
else {
if (traceEnabled) {
logger.trace("Ignored because not matching any filter: " + resource);
}
}
}
catch (Throwable ex) {
throw new BeanDefinitionStoreException(
"Failed to read candidate component class: " + resource, ex);
}
}
else {
if (traceEnabled) {
logger.trace("Ignored because not readable: " + resource);
}
}
}
}
catch (IOException ex) {
throw new BeanDefinitionStoreException("I/O failure during classpath scanning", ex);
}
return candidates;
}
查看2个判断条件。
/**
* Determine whether the given bean definition qualifies as candidate.
* <p>The default implementation checks whether the class is concrete
* (i.e. not abstract and not an interface). Can be overridden in subclasses.
* @param beanDefinition the bean definition to check
* @return whether the bean definition qualifies as a candidate component
*/
protected boolean isCandidateComponent(AnnotatedBeanDefinition beanDefinition) {
return (beanDefinition.getMetadata().isConcrete() && beanDefinition.getMetadata().isIndependent());
}
进行匹配。
/**
* Determine whether the given class does not match any exclude filter
* and does match at least one include filter.
* @param metadataReader the ASM ClassReader for the class
* @return whether the class qualifies as a candidate component
*/
protected boolean isCandidateComponent(MetadataReader metadataReader) throws IOException {
for (TypeFilter tf : this.excludeFilters) {
if (tf.match(metadataReader, this.metadataReaderFactory)) {
return false;
}
}
for (TypeFilter tf : this.includeFilters) {
if (tf.match(metadataReader, this.metadataReaderFactory)) {
return isConditionMatch(metadataReader);
}
}
return false;
}
@Override
protected boolean matchSelf(MetadataReader metadataReader) {
AnnotationMetadata metadata = metadataReader.getAnnotationMetadata();
return metadata.hasAnnotation(this.annotationType.getName()) ||
(this.considerMetaAnnotations && metadata.hasMetaAnnotation(this.annotationType.getName()));
}
查看hasAnnotation和 hasMetaAnnotation方法。
@Override
public boolean hasAnnotation(String annotationType) {
return this.annotationSet.contains(annotationType);
} @Override
public boolean hasMetaAnnotation(String metaAnnotationType) {
Collection<Set<String>> allMetaTypes = this.metaAnnotationMap.values();
for (Set<String> metaTypes : allMetaTypes) {
if (metaTypes.contains(metaAnnotationType)) {
return true;
}
}
return false;
}
annotationSet包含的是注解，
metaAnnotationMap的key为注解，value是一个set。