xml中的扫描过程
<?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 https://www.springframework.org/schema/context/spring-context.xsd" default-lazy-init="false"> <context:component-scan base-package="com.morris.spring.demo.service"/> </beans>
xml中使用自定义标签context实现，最终会调用到componentscanbeandefinitionparser.parse()方法进行解析。
componentscanbeandefinitionparser.parse()
// org.springframework.context.annotation.componentscanbeandefinitionparser#parse
public beandefinition parse(element element, parsercontext parsercontext) {
// 获得base-package指定的包名
string basepackage = element.getattribute(base_package_attribute);
basepackage = parsercontext.getreadercontext().getenvironment().resolveplaceholders(basepackage);
// base-package中可能有多个，用逗号分隔，转换为数组
string[] basepackages = stringutils.tokenizetostringarray(basepackage,
configurableapplicationcontext.config_location_delimiters);
// actually scan for bean definitions and register them.
// 创建扫描器
classpathbeandefinitionscanner scanner = configurescanner(parsercontext, element);
// 开始扫描
set<beandefinitionholder> beandefinitions = scanner.doscan(basepackages);
// 注册了一些组件
// configurationclasspostprocessor
// autowiredannotationbeanpostprocessor
// commonannotationbeanpostprocessor
// eventlistenermethodprocessor
// defaulteventlistenerfactory
registercomponents(parsercontext.getreadercontext(), beandefinitions, element);
return null;
}
componentscanbeandefinitionparser#configurescanner
创建扫描器classpathbeandefinitionscanner
protected classpathbeandefinitionscanner configurescanner(parsercontext parsercontext, element element) {
boolean usedefaultfilters = true;
if (element.hasattribute(use_default_filters_attribute)) {
usedefaultfilters = boolean.parseboolean(element.getattribute(use_default_filters_attribute));
}
// delegate bean definition registration to scanner class.
// classpathbeandefinitionscanner构造方法中添加了默认的includefilters为@component
classpathbeandefinitionscanner scanner = createscanner(parsercontext.getreadercontext(), usedefaultfilters);
scanner.setbeandefinitiondefaults(parsercontext.getdelegate().getbeandefinitiondefaults());
scanner.setautowirecandidatepatterns(parsercontext.getdelegate().getautowirecandidatepatterns());
if (element.hasattribute(resource_pattern_attribute)) {
scanner.setresourcepattern(element.getattribute(resource_pattern_attribute));
}
try {
parsebeannamegenerator(element, scanner);
}
catch (exception ex) {
parsercontext.getreadercontext().error(ex.getmessage(), parsercontext.extractsource(element), ex.getcause());
}
try {
parsescope(element, scanner);
}
catch (exception ex) {
parsercontext.getreadercontext().error(ex.getmessage(), parsercontext.extractsource(element), ex.getcause());
}
parsetypefilters(element, scanner, parsercontext);
return scanner;
}
怎么知道扫描哪些注解呢？
classpathbeandefinitionscanner构造方法中会注入默认的filter。
protected void registerdefaultfilters() {
// 只扫描@component注解了的类，而@sevice、@configuration、@controller等注解都被@component修饰
this.includefilters.add(new annotationtypefilter(component.class));
classloader cl = classpathscanningcandidatecomponentprovider.class.getclassloader();
try {
this.includefilters.add(new annotationtypefilter(
((class<? extends annotation>) classutils.forname("javax.annotation.managedbean", cl)), false));
logger.trace("jsr-250 'javax.annotation.managedbean' found and supported for component scanning");
}
catch (classnotfoundexception ex) {
// jsr-250 1.1 api (as included in java ee 6) not available - simply skip.
}
try {
this.includefilters.add(new annotationtypefilter(
((class<? extends annotation>) classutils.forname("javax.inject.named", cl)), false));
logger.trace("jsr-330 'javax.inject.named' annotation found and supported for component scanning");
}
catch (classnotfoundexception ex) {
// jsr-330 api not available - simply skip.
}
}
在源码中只会扫描@component注解，而@sevice、@configuration、@controller等注解都被@component修饰，最终都会被扫描到。
classpathbeandefinitionscanner#doscan
开始扫描：
// org.springframework.context.annotation.classpathbeandefinitionscanner#doscan
protected set<beandefinitionholder> doscan(string... basepackages) {
assert.notempty(basepackages, "at least one base package must be specified");
set<beandefinitionholder> beandefinitions = new linkedhashset<>();
for (string basepackage : basepackages) {
// 查找basepackage下所有被@component注解修饰了的类
set<beandefinition> candidates = findcandidatecomponents(basepackage);
for (beandefinition candidate : candidates) {
// 上面findcandidatecomponents只是为bd设置了几个属性，bd的其他属性并没有初始化，所以需要遍历一次初始化属性并注册到registry
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);
// 注册到registry
registerbeandefinition(definitionholder, this.registry);
}
}
}
return beandefinitions;
}
classpathscanningcandidatecomponentprovider#scancandidatecomponents
查找basepackage下所有被@component注解修饰了的类：
// org.springframework.context.annotation.classpathscanningcandidatecomponentprovider#scancandidatecomponents
private set<beandefinition> scancandidatecomponents(string basepackage) {
set<beandefinition> candidates = new linkedhashset<>();
try {
// basepackage=com.morris.spring..service
// packagesearchpath=classpath*:com/morris/spring/service/**/*.class
string packagesearchpath = resourcepatternresolver.classpath_all_url_prefix +
resolvebasepackage(basepackage) + '/' + this.resourcepattern;
// 获取basepackage下所有的class文件
resource[] resources = getresourcepatternresolver().getresources(packagesearchpath);
boolean traceenabled = logger.istraceenabled();
boolean debugenabled = logger.isdebugenabled();
for (resource resource : resources) {
if (traceenabled) {
logger.trace("scanning " + resource);
}
if (resource.isreadable()) {
try {
// 使用asm将class文件的内容封装为metadatareader对象
// 注意这里用的不是反射，反射会加载类，占用堆空间
metadatareader metadatareader = getmetadatareaderfactory().getmetadatareader(resource);
// 判断类是否包含@component注解
if (iscandidatecomponent(metadatareader)) {
// 封装为bd
scannedgenericbeandefinition sbd = new scannedgenericbeandefinition(metadatareader);
sbd.setsource(resource);
if (iscandidatecomponent(sbd)) {
if (debugenabled) {
logger.debug("identified candidate component class: " + resource);
}
candidates.add(sbd);
}
... ...
return candidates;
}
registerannotationconfigprocessors
注册了多种重要的组件：
public static set<beandefinitionholder> registerannotationconfigprocessors(
beandefinitionregistry registry, @nullable object source) {
defaultlistablebeanfactory beanfactory = unwrapdefaultlistablebeanfactory(registry);
if (beanfactory != null) {
if (!(beanfactory.getdependencycomparator() instanceof annotationawareordercomparator)) {
beanfactory.setdependencycomparator(annotationawareordercomparator.instance);
}
if (!(beanfactory.getautowirecandidateresolver() instanceof contextannotationautowirecandidateresolver)) {
beanfactory.setautowirecandidateresolver(new contextannotationautowirecandidateresolver());
}
}
set<beandefinitionholder> beandefs = new linkedhashset<>(8);
// beanfactorypostprocessor
if (!registry.containsbeandefinition(configuration_annotation_processor_bean_name)) {
rootbeandefinition def = new rootbeandefinition(configurationclasspostprocessor.class);
def.setsource(source);
beandefs.add(registerpostprocessor(registry, def, configuration_annotation_processor_bean_name));
}
// beanpostprocessor
if (!registry.containsbeandefinition(autowired_annotation_processor_bean_name)) {
rootbeandefinition def = new rootbeandefinition(autowiredannotationbeanpostprocessor.class);
def.setsource(source);
beandefs.add(registerpostprocessor(registry, def, autowired_annotation_processor_bean_name));
}
// check for jsr-250 support, and if present add the commonannotationbeanpostprocessor.
if (jsr250present && !registry.containsbeandefinition(common_annotation_processor_bean_name)) {
rootbeandefinition def = new rootbeandefinition(commonannotationbeanpostprocessor.class);
def.setsource(source);
beandefs.add(registerpostprocessor(registry, def, common_annotation_processor_bean_name));
}
// check for jpa support, and if present add the persistenceannotationbeanpostprocessor.
if (jpapresent && !registry.containsbeandefinition(persistence_annotation_processor_bean_name)) {
rootbeandefinition def = new rootbeandefinition();
try {
def.setbeanclass(classutils.forname(persistence_annotation_processor_class_name,
annotationconfigutils.class.getclassloader()));
}
catch (classnotfoundexception ex) {
throw new illegalstateexception(
"cannot load optional framework class: " + persistence_annotation_processor_class_name, ex);
}
def.setsource(source);
beandefs.add(registerpostprocessor(registry, def, persistence_annotation_processor_bean_name));
}
// beanfactorypostprocessor
if (!registry.containsbeandefinition(event_listener_processor_bean_name)) {
rootbeandefinition def = new rootbeandefinition(eventlistenermethodprocessor.class);
def.setsource(source);
beandefs.add(registerpostprocessor(registry, def, event_listener_processor_bean_name));
}
if (!registry.containsbeandefinition(event_listener_factory_bean_name)) {
rootbeandefinition def = new rootbeandefinition(defaulteventlistenerfactory.class);
def.setsource(source);
beandefs.add(registerpostprocessor(registry, def, event_listener_factory_bean_name));
}
return beandefs;
}
扫描的最终结果就是将类上面有@component注解的类构建为一个beandefinition中，spring容器中有两个集合来存放这些beandefinition：
- beandefinitionnames：list<string>，存放所有的beandefinition对应的name
- beandefinitionmap：map<string, beandefinition>，存放所有的beandefinition
注解的扫描过程
注解扫描的使用：
package com.morris.spring.demo.annotation;
import com.morris.spring.demo.service.cityservice;
import org.springframework.context.annotation.annotationconfigapplicationcontext;
import org.springframework.context.annotation.componentscan;
@componentscan("com.morris.spring.service")
public class componentscandemo {
public static void main(string[] args) {
annotationconfigapplicationcontext applicationcontext = new annotationconfigapplicationcontext(componentscandemo.class);
cityservice cityservice = applicationcontext.getbean(cityservice.class);
cityservice.city();
}
}
使用@componentscan注解指定包的扫描，扫描过程将由configurationclasspostprocessor#postprocessbeandefinitionregistry完成。
configurationclasspostprocessor#postprocessbeandefinitionregistry
public void postprocessbeandefinitionregistry(beandefinitionregistry registry) {
int registryid = system.identityhashcode(registry);
if (this.registriespostprocessed.contains(registryid)) {
throw new illegalstateexception(
"postprocessbeandefinitionregistry already called on this post-processor against " + registry);
}
if (this.factoriespostprocessed.contains(registryid)) {
throw new illegalstateexception(
"postprocessbeanfactory already called on this post-processor against " + registry);
}
this.registriespostprocessed.add(registryid);
// 重点
processconfigbeandefinitions(registry);
}
configurationclasspostprocessor#processconfigbeandefinitions
public void processconfigbeandefinitions(beandefinitionregistry registry) {
list<beandefinitionholder> configcandidates = new arraylist<>();
string[] candidatenames = registry.getbeandefinitionnames();
// 先收集有@configuration、@component、@componentscan、@import、@importresource、@bean的bd
for (string beanname : candidatenames) {
beandefinition beandef = registry.getbeandefinition(beanname);
if (beandef.getattribute(configurationclassutils.configuration_class_attribute) != null) {
if (logger.isdebugenabled()) {
logger.debug("bean definition has already been processed as a configuration class: " + beandef);
}
}
else if (configurationclassutils.checkconfigurationclasscandidate(beandef, this.metadatareaderfactory)) {
// 进来需要@component、@componentscan、@import、@importresource、@bean
configcandidates.add(new beandefinitionholder(beandef, beanname));
}
}
... ...
// parse each @configuration class
configurationclassparser parser = new configurationclassparser(
this.metadatareaderfactory, this.problemreporter, this.environment,
this.resourceloader, this.componentscanbeannamegenerator, registry);
set<beandefinitionholder> candidates = new linkedhashset<>(configcandidates);
set<configurationclass> alreadyparsed = new hashset<>(configcandidates.size());
do {
// 开始解析
parser.parse(candidates);
parser.validate();
configurationclassparser#doprocessconfigurationclass
protected final sourceclass doprocessconfigurationclass(
configurationclass configclass, sourceclass sourceclass, predicate<string> filter)
throws ioexception {
... ...
// process any @componentscan annotations
// 处理@componentscan注解，扫描包下带有@component的注解，与xml中自定义标签context:component-scan的扫描流程一致
set<annotationattributes> componentscans = annotationconfigutils.attributesforrepeatable(
sourceclass.getmetadata(), componentscans.class, componentscan.class);
if (!componentscans.isempty() &&
!this.conditionevaluator.shouldskip(sourceclass.getmetadata(), configurationphase.register_bean)) {
for (annotationattributes componentscan : componentscans) {
// the config class is annotated with @componentscan -> perform the scan immediately
set<beandefinitionholder> scannedbeandefinitions =
this.componentscanparser.parse(componentscan, sourceclass.getmetadata().getclassname());
// check the set of scanned definitions for any further config classes and parse recursively if needed
for (beandefinitionholder holder : scannedbeandefinitions) {
beandefinition bdcand = holder.getbeandefinition().getoriginatingbeandefinition();
if (bdcand == null) {
bdcand = holder.getbeandefinition();
}
// checkconfigurationclasscandidate这个里面会特殊处理@configutation为full
if (configurationclassutils.checkconfigurationclasscandidate(bdcand, this.metadatareaderfactory)) {
parse(bdcand.getbeanclassname(), holder.getbeanname());
}
}
}
}
... ...
return null;
}
componentscanannotationparser#parse
public set<beandefinitionholder> parse(annotationattributes componentscan, final string declaringclass) {
// 解析@componentscan注解，构建classpathbeandefinitionscanner
// 构建方法中会添加默认的includefilters为@component
classpathbeandefinitionscanner scanner = new classpathbeandefinitionscanner(this.registry,
componentscan.getboolean("usedefaultfilters"), this.environment, this.resourceloader);
class<? extends beannamegenerator> generatorclass = componentscan.getclass("namegenerator");
boolean useinheritedgenerator = (beannamegenerator.class == generatorclass);
scanner.setbeannamegenerator(useinheritedgenerator ? this.beannamegenerator :
beanutils.instantiateclass(generatorclass));
scopedproxymode scopedproxymode = componentscan.getenum("scopedproxy");
if (scopedproxymode != scopedproxymode.default) {
scanner.setscopedproxymode(scopedproxymode);
}
else {
class<? extends scopemetadataresolver> resolverclass = componentscan.getclass("scoperesolver");
scanner.setscopemetadataresolver(beanutils.instantiateclass(resolverclass));
}
scanner.setresourcepattern(componentscan.getstring("resourcepattern"));
for (annotationattributes filter : componentscan.getannotationarray("includefilters")) {
for (typefilter typefilter : typefiltersfor(filter)) {
scanner.addincludefilter(typefilter);
}
}
for (annotationattributes filter : componentscan.getannotationarray("excludefilters")) {
for (typefilter typefilter : typefiltersfor(filter)) {
scanner.addexcludefilter(typefilter);
}
}
boolean lazyinit = componentscan.getboolean("lazyinit");
if (lazyinit) {
scanner.getbeandefinitiondefaults().setlazyinit(true);
}
set<string> basepackages = new linkedhashset<>();
string[] basepackagesarray = componentscan.getstringarray("basepackages");
for (string pkg : basepackagesarray) {
string[] tokenized = stringutils.tokenizetostringarray(this.environment.resolveplaceholders(pkg),
configurableapplicationcontext.config_location_delimiters);
collections.addall(basepackages, tokenized);
}
for (class<?> clazz : componentscan.getclassarray("basepackageclasses")) {
basepackages.add(classutils.getpackagename(clazz));
}
if (basepackages.isempty()) {
basepackages.add(classutils.getpackagename(declaringclass));
}
scanner.addexcludefilter(new abstracttypehierarchytraversingfilter(false, false) {
@override
protected boolean matchclassname(string classname) {
return declaringclass.equals(classname);
}
});
// 开始扫描
return scanner.doscan(stringutils.tostringarray(basepackages));
}
可以发现注解的扫描最后会调用classpathbeandefinitionscanner#doscan()，与xml中的扫描是同一个方法。
总结
- xml的扫描过程发生在obtainfreshbeanfactory()，也就是创建beanfactory时，而注解的扫描过程发生在invokebeanfactorypostprocessors()。
- xml的扫描会在obtainfreshbeanfactory()时注入configurationclasspostprocessor，而注解的扫描是在创建annotationconfigapplicationcontext实例时注入configurationclasspostprocessor，如果xml扫描到的类带有@componentscan注解，那么还会继续在invokebeanfactorypostprocessors()阶段继续扫描。
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