缘起
近期在写对于文档的扫描项目。想到 spring 的包扫描，觉得可以借鉴。
下面的内容就是和上面文章是一样的，主要是理解一下过程。
将来打算在项目中使用。
component-scan
Usage
- usage
对于扫描包配置的常见使用。
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context.xsd">
<!--There is usually no need to include the <context:annotation-config> element when using <context:component-scan>.-->
<context:component-scan base-package="com.ryo.spring.learn"/>
</beans>
- xsd
component-scan xsd 内容。(spring 4.2.6)
<xsd:element name="component-scan">
<xsd:annotation>
<xsd:documentation><![CDATA[
Scans the classpath for annotated components that will be auto-registered as
Spring beans. By default, the Spring-provided @Component, @Repository, @Service,
@Controller, @RestController, @ControllerAdvice, and @Configuration stereotypes
will be detected.
Note: This tag implies the effects of the 'annotation-config' tag, activating @Required,
@Autowired, @PostConstruct, @PreDestroy, @Resource, @PersistenceContext and @PersistenceUnit
annotations in the component classes, which is usually desired for autodetected components
(without external configuration). Turn off the 'annotation-config' attribute to deactivate
this default behavior, for example in order to use custom BeanPostProcessor definitions
for handling those annotations.
Note: You may use placeholders in package paths, but only resolved against system
properties (analogous to resource paths). A component scan results in new bean definitions
being registered; Spring's PropertySourcesPlaceholderConfigurer will apply to those bean
definitions just like to regular bean definitions, but it won't apply to the component
scan settings themselves.
See javadoc for org.springframework.context.annotation.ComponentScan for information
on code-based alternatives to bootstrapping component-scanning.
]]></xsd:documentation>
</xsd:annotation>
<!--...-->
</xsd:element>
Parser
- parser
下面这个类为对应的解释器。
/**
* Parser for the {@code <context:component-scan/>} element.
*
* @author Mark Fisher
* @author Ramnivas Laddad
* @author Juergen Hoeller
* @since 2.5
*/
public class ComponentScanBeanDefinitionParser implements BeanDefinitionParser{
}
解释器的核心方法：
@Override
public BeanDefinition parse(Element element, ParserContext parserContext) {
//1. 获取需要扫描的包
String basePackage = element.getAttribute(BASE_PACKAGE_ATTRIBUTE);
basePackage = parserContext.getReaderContext().getEnvironment().resolvePlaceholders(basePackage);
String[] basePackages = StringUtils.tokenizeToStringArray(basePackage,
ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);
//2. 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;
}
- doScan()
对指定包下面的 class 文件进行扫描并且注册。
/**
* 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) {
Set<BeanDefinition> candidates = findCandidateComponents(basePackage);
for (BeanDefinition candidate : candidates) {
//....
}
}
return beanDefinitions;
}
对于每个包扫描并且封装的方法为
- findCandidateComponents(basePackage)
将一些日志打印的代码暂时去除了，感觉写的不太利于阅读。
/**
* 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;
Resource[] resources = this.resourcePatternResolver.getResources(packageSearchPath);
for (Resource resource : resources) {
if (resource.isReadable()) {
try {
MetadataReader metadataReader = this.metadataReaderFactory.getMetadataReader(resource);
if (isCandidateComponent(metadataReader)) {
ScannedGenericBeanDefinition sbd = new ScannedGenericBeanDefinition(metadataReader);
sbd.setResource(resource);
sbd.setSource(resource);
if (isCandidateComponent(sbd)) {
candidates.add(sbd);
}
}
}
catch (Throwable ex) {
throw new BeanDefinitionStoreException(
"Failed to read candidate component class: " + resource, ex);
}
}
}
}
catch (IOException ex) {
throw new BeanDefinitionStoreException("I/O failure during classpath scanning", ex);
}
return candidates;
}
Desc
(1) 先根据 context:component-scan 中属性的 base-package="com.ryo.spring.learn" 配置转换为 classpath*:com/ryo/spring/learn/**/*.class，
并扫描对应下的 class 和 jar 文件并获取类对应的路径，返回 Resource;
实现代码
- PathMatchingResourcePatternResolver.java
@Override
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);
}
else {
// all class path resources with the given name
return findAllClassPathResources(locationPattern.substring(CLASSPATH_ALL_URL_PREFIX.length()));
}
}
else {
// Only look for a pattern after a prefix here
// (to not get fooled by a pattern symbol in a strange prefix).
int prefixEnd = locationPattern.indexOf(":") + 1;
if (getPathMatcher().isPattern(locationPattern.substring(prefixEnd))) {
// a file pattern
return findPathMatchingResources(locationPattern);
}
else {
// a single resource with the given name
return new Resource[] {getResourceLoader().getResource(locationPattern)};
}
}
}
/**
* Find all class location resources with the given location via the ClassLoader.
* Delegates to {@link #doFindAllClassPathResources(String)}.
* @param location the absolute path within the classpath
* @return the result as Resource array
* @throws IOException in case of I/O errors
* @see java.lang.ClassLoader#getResources
* @see #convertClassLoaderURL
*/
protected Resource[] findAllClassPathResources(String location) throws IOException {
String path = location;
if (path.startsWith("/")) {
path = path.substring(1);
}
Set<Resource> result = doFindAllClassPathResources(path);
if (logger.isDebugEnabled()) {
logger.debug("Resolved classpath location [" + location + "] to resources " + result);
}
return result.toArray(new Resource[result.size()]);
}
(2) 根据 <context:exclude-filter> 指定的不扫描包
直接对需要扫描的包或者不需要扫描的包进行校验。
/**
* 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;
}
(3) 封装成BeanDefinition放到队列里
ComponentScanBeanDefinitionParser.parse(…)
中下面的代码实现，跳过。
registerComponents(parserContext.getReaderContext(), beanDefinitions, element);
