spring的扫描bean我们一般都会这么配：、
<context:component-scan base-package="com.dubbo.single"/>这样就可以扫描到，com/dubbo/single包下的所有bean，具体是源码是怎么操作的，我们看下源码，前面的源码我们就不做介绍了，如果有不懂bean是如何加载的再去搜集相关资料，我们直接从扫描开始介绍起。
当解析了xml文件后，会有一个BeanDefinitionParserDelegate类执行parseCustomElement方法，如下：
public BeanDefinition parseCustomElement(Element ele, BeanDefinition containingBd) {
String namespaceUri = getNamespaceURI(ele);
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));
}标粗的这句会根据你写在xml中的命名空间获取所有的转换类，并且在下面的parse方法中，看使用哪个parse类：
public BeanDefinition parse(Element element, ParserContext parserContext) {
return findParserForElement(element, parserContext).parse(element, parserContext);
}根据我们配置的
context
:component-scan ，用来解析的parse类是：ComponentScanBeanDefinitionParse类，执行它的parse方法：
public BeanDefinition parse(Element element, ParserContext parserContext) {
String[] basePackages = StringUtils.tokenizeToStringArray(element.getAttribute(BASE_PACKAGE_ATTRIBUTE),
ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);
// Actually scan for bean definitions and register them.
ClassPathBeanDefinitionScanner scanner = configureScanner(parserContext, element);
Set<BeanDefinitionHolder> beanDefinitions = scanner.doScan(basePackages);
registerComponents(parserContext.getReaderContext(), beanDefinitions, element);
return null;
}我们重点看下doScan方法：
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;
}我们看下标粗的findCandidateComponents(basePackage)方法：
public Set<BeanDefinition> findCandidateComponents(String basePackage) {
Set<BeanDefinition> candidates = new LinkedHashSet<BeanDefinition>();
try {
String packageSearchPath = ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX +
resolveBasePackage(basePackage) + "/" + this.resourcePattern;
Resource[] resources = this.resourcePatternResolver.getResources(packageSearchPath);上面标粗的getResources方法做了扫描：
public Resource[] getResources(String locationPattern) throws IOException {
return this.resourcePatternResolver.getResources(locationPattern);
}public Resource[] getResources(String locationPattern) throws IOException {
Assert.notNull(locationPattern, "Location pattern must not be null");
if (locationPattern.startsWith(CLASSPATH_ALL_URL_PREFIX)) {
// a class path resource (multiple resources for same name possible)
if (getPathMatcher().isPattern(locationPattern.substring(CLASSPATH_ALL_URL_PREFIX.length()))) {
// a class path resource pattern
return findPathMatchingResources(locationPattern);
}上面的if语句会判断如果路径是以“classpath*”开头则进入执行findPathMatchingResources方法.
String CLASSPATH_ALL_URL_PREFIX = "classpath*:";
protected Resource[] findPathMatchingResources(String locationPattern) throws IOException {
String rootDirPath = determineRootDir(locationPattern);
String subPattern = locationPattern.substring(rootDirPath.length());
Resource[] rootDirResources = getResources(rootDirPath);
Set<Resource> result = new LinkedHashSet<Resource>(16);
for (Resource rootDirResource : rootDirResources) {
rootDirResource = resolveRootDirResource(rootDirResource);
if (isJarResource(rootDirResource)) {
result.addAll(doFindPathMatchingJarResources(rootDirResource, subPattern));
}
else if (rootDirResource.getURL().getProtocol().startsWith(ResourceUtils.URL_PROTOCOL_VFS)) {
result.addAll(VfsResourceMatchingDelegate.findMatchingResources(rootDirResource, subPattern, getPathMatcher()));
}
else {
result.addAll(doFindPathMatchingFileResources(rootDirResource, subPattern));
}
}
if (logger.isDebugEnabled()) {
logger.debug("Resolved location pattern [" + locationPattern + "] to resources " + result);
}
return result.toArray(new Resource[result.size()]);
}最后会执行我们标粗的逐句doFindPathMatchingFileResources方法，举例说明，比如我们原来配置是
<context:component-scan base-package="com.dubbo.single"/>
rootDirResource为：“classpath*:com/dubbo/single/”，subPattern为：“**/*.class”，然后我们进入方法查看：
protected Set<Resource> doFindPathMatchingFileResources(Resource rootDirResource, String subPattern)
throws IOException {
File rootDir;
try {
rootDir = rootDirResource.getFile().getAbsoluteFile();
}
catch (IOException ex) {
if (logger.isWarnEnabled()) {
logger.warn("Cannot search for matching files underneath " + rootDirResource +
" because it does not correspond to a directory in the file system", ex);
}
return Collections.emptySet();
}
return doFindMatchingFileSystemResources(rootDir, subPattern);
}方法中获取绝对路径：rootDir如下：“D:\workspaces\dubbo-parent\dubbo-single\target\classes\com\dubbo\single”
protected Set<Resource> doFindMatchingFileSystemResources(File rootDir, String subPattern) throws IOException {
if (logger.isDebugEnabled()) {
logger.debug("Looking for matching resources in directory tree [" + rootDir.getPath() + "]");
}
Set<File> matchingFiles = retrieveMatchingFiles(rootDir, subPattern);
Set<Resource> result = new LinkedHashSet<Resource>(matchingFiles.size());
for (File file : matchingFiles) {
result.add(new FileSystemResource(file));
}
return result;
}再最后进入了PathMatchingResourcePatternResolver的doRetriesMatchingFiles进行了递归查询所有.class文件：
protected void doRetrieveMatchingFiles(String fullPattern, File dir, Set<File> result) throws IOException {
if (logger.isDebugEnabled()) {
logger.debug("Searching directory [" + dir.getAbsolutePath() +
"] for files matching pattern [" + fullPattern + "]");
}
File[] dirContents = dir.listFiles();
if (dirContents == null) {
if (logger.isWarnEnabled()) {
logger.warn("Could not retrieve contents of directory [" + dir.getAbsolutePath() + "]");
}
return;
}
for (File content : dirContents) {
String currPath = StringUtils.replace(content.getAbsolutePath(), File.separator, "/");
if (content.isDirectory() && getPathMatcher().matchStart(fullPattern, currPath + "/")) {
if (!content.canRead()) {
if (logger.isDebugEnabled()) {
logger.debug("Skipping subdirectory [" + dir.getAbsolutePath() +
"] because the application is not allowed to read the directory");
}
}
else {
doRetrieveMatchingFiles(fullPattern, content, result);
}
}
if (getPathMatcher().match(fullPattern, currPath)) {
result.add(content);
}
}
}最后将扫描拿到的bean进行注册。
注意接口类就算加了注解也不会被spring所加载，在这里会进行过滤：
在ClassPathScanningCandidateComponentProvider类的方法findCandidateComponents中，获取到bean集合后会执行此方法：
if (isCandidateComponent(sbd)) {
if (debugEnabled) {
logger.debug("Identified candidate component class: " + resource);
}
candidates.add(sbd);
}在此处会对接口类进行过滤。
