在2版本之前的版本,项目中有两个相同名字的bean是可以启动成功的,但是会有覆盖问题
但是在2.X版本的时候会报错:
could not be registered. A bean with that name has already been defined in class path resource
这时候解决办法可以在配置文件中添加:
spring.main.allow-bean-definition-overriding=true
/** 是否允许使用相同名称重新注册不同的bean实现. 默认是允许*/
private boolean allowBeanDefinitionOverriding = true;
/**
* Set whether it should be allowed to override bean definitions by registering
* a different definition with the same name, automatically replacing the former.
* If not, an exception will be thrown. This also applies to overriding aliases.
* <p>Default is "true".【这里明确说明了默认是true】
* @see #registerBeanDefinition
*/
public boolean isAllowBeanDefinitionOverriding() {
return this.allowBeanDefinitionOverriding;
}
@Override
public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
throws BeanDefinitionStoreException {
Assert.hasText(beanName, "Bean name must not be empty");
Assert.notNull(beanDefinition, "BeanDefinition must not be null");
if (beanDefinition instanceof AbstractBeanDefinition) {
try {
((AbstractBeanDefinition) beanDefinition).validate();
}
catch (BeanDefinitionValidationException ex) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
"Validation of bean definition failed", ex);
}
}
//bean加载到spring的工程中后,会存储在beanDefinitionMap中,key是bean的名称。
BeanDefinition existingDefinition = this.beanDefinitionMap.get(beanName);
if (existingDefinition != null) {//不为空,说明相同名称的bean已经存在了
if (!isAllowBeanDefinitionOverriding()) {//如果不允许相同名称的bean存在,则直接抛出异常
throw new BeanDefinitionOverrideException(beanName, beanDefinition, existingDefinition);
}
else if (existingDefinition.getRole() < beanDefinition.getRole()) {
// e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE
if (logger.isInfoEnabled()) {
logger.info("Overriding user-defined bean definition for bean '" + beanName +
"' with a framework-generated bean definition: replacing [" +
existingDefinition + "] with [" + beanDefinition + "]");
}
}
else if (!beanDefinition.equals(existingDefinition)) {
if (logger.isDebugEnabled()) {
logger.debug("Overriding bean definition for bean '" + beanName +
"' with a different definition: replacing [" + existingDefinition +
"] with [" + beanDefinition + "]");
}
}
else {
if (logger.isTraceEnabled()) {
logger.trace("Overriding bean definition for bean '" + beanName +
"' with an equivalent definition: replacing [" + existingDefinition +
"] with [" + beanDefinition + "]");
}
}
//可见,上面allowBeanDefinitionOverriding =true时,只是记录了一些日志,然后后来发现的这个bean,会覆盖之前老的bean。
this.beanDefinitionMap.put(beanName, beanDefinition);
}
else {
if (hasBeanCreationStarted()) {
// Cannot modify startup-time collection elements anymore (for stable iteration)
synchronized (this.beanDefinitionMap) {
this.beanDefinitionMap.put(beanName, beanDefinition);
List<String> updatedDefinitions = new ArrayList<>(this.beanDefinitionNames.size() + 1);
updatedDefinitions.addAll(this.beanDefinitionNames);
updatedDefinitions.add(beanName);
this.beanDefinitionNames = updatedDefinitions;
if (this.manualSingletonNames.contains(beanName)) {
Set<String> updatedSingletons = new LinkedHashSet<>(this.manualSingletonNames);
updatedSingletons.remove(beanName);
this.manualSingletonNames = updatedSingletons;
}
}
}
else {
// Still in startup registration phase
this.beanDefinitionMap.put(beanName, beanDefinition);
this.beanDefinitionNames.add(beanName);
this.manualSingletonNames.remove(beanName);
}
this.frozenBeanDefinitionNames = null;
}
if (existingDefinition != null || containsSingleton(beanName)) {
resetBeanDefinition(beanName);
}
}
上面贴出来的是spring的代码,而springboot2.X对这个参数又进行了二次封装,springboot中的allowBeanDefinitionOverriding是没有初始化默认值的,我们知道,java中的boolean类型不初始化时是false。
springboot中源代码:
在SpringApplication类中
public class SpringApplication {
...
//boolean没初始化,所以默认为false
private boolean allowBeanDefinitionOverriding;
...
private void prepareContext(ConfigurableApplicationContext context, ConfigurableEnvironment environment, SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments, Banner printedBanner) {
context.setEnvironment(environment);
this.postProcessApplicationContext(context);
this.applyInitializers(context);
listeners.contextPrepared(context);
if (this.logStartupInfo) {
this.logStartupInfo(context.getParent() == null);
this.logStartupProfileInfo(context);
}
ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
beanFactory.registerSingleton("springApplicationArguments", applicationArguments);
if (printedBanner != null) {
beanFactory.registerSingleton("springBootBanner", printedBanner);
}
//将false值传过去
if (beanFactory instanceof DefaultListableBeanFactory) {
((DefaultListableBeanFactory)beanFactory).setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);
}
if (this.lazyInitialization) {
context.addBeanFactoryPostProcessor(new LazyInitializationBeanFactoryPostProcessor());
}
Set<Object> sources = this.getAllSources();
Assert.notEmpty(sources, "Sources must not be empty");
this.load(context, sources.toArray(new Object[0]));
listeners.contextLoaded(context);
}
而在1.5.8版本中,SpringApplication中,没有allowBeanDefinitionOverriding属性,因此在prepareContext方法中也就没有对allowBeanDefinitionOverriding进行赋值为false,所以在springboot1.5.8版本中默认就是支持名称相同的bean的覆盖。