Configuration
最近看源码时，经常看了下@Configuration(proxyBeanMethods = false)这样的配置，但从命名上看应该是与代理有关的，于是抽个时间了解了下
proxyBeanMethods
首先这个是@Configuration注解中的一个参数，我们都知道，@Configuration是Spring中的配置类，一般用来申明Bean，在默认情况下proxyBeanMethods为true
含义
从源码中可以看到对该参数的描述如下：
Specify whether @Bean methods should get proxied in order to enforce bean lifecycle behavior, e.g. to return shared singleton bean instances even in case of direct @Bean method calls in user code. This feature requires method interception, implemented through a runtime-generated CGLIB subclass which comes with limitations such as the configuration class and its methods not being allowed to declare final.
The default is true, allowing for 'inter-bean references' via direct method calls within the configuration class as well as for external calls to this configuration's @Bean methods, e.g. from another configuration class. If this is not needed since each of this particular configuration's @Bean methods is self-contained and designed as a plain factory method for container use, switch this flag to false in order to avoid CGLIB subclass processing.
Turning off bean method interception effectively processes @Bean methods individually like when declared on non-@Configuration classes, a.k.a. "@Bean Lite Mode" (see @Bean's javadoc). It is therefore behaviorally equivalent to removing the @Configuration stereotype.当直接在Configuration中直接通过方法，实现实例件的属性依赖时，IDEA会有这样一段提示：
Method annotated with @Bean is called directly in a @Configuration where proxyBeanMethods set to false. Set proxyBeanMethods to true or use dependency injection.示例
先通过下面的示例看下现象:
两个配置类，写法差不多，区别在与proxyBeanMethods的配置以及AnimalCage属性的注入方法。
@Configuration(proxyBeanMethods = false)
public class GenericConfiguration {
@Bean
public DogCage dogCage(){
return new DogCage();
}
@Bean
public AnimalCage animalEden(){
AnimalCage animalCage = new AnimalCage();
animalCage.addCage(dogCage());
return animalCage;
}
}
@Configuration(proxyBeanMethods = true)
public class ProxyConfiguration {
@Bean
public DogCage dogCage(){
return new DogCage();
}
@Bean
public AnimalCage animalEden(@Autowired List cages){
return new AnimalCage(cages);
}
}先看下GenericConfiguration配置的情况:
public class Tests {
@Autowired
private BeanFactory beanFactory;
@Autowired
private GenericConfiguration genericConfiguration;
@Autowired
private AnimalCage animalCage;
@Autowired
private DogCage dogCage;
@Test
public void runConfig() {
log.info("configuration: {}", genericConfiguration); // 原始对象类型
log.info("Configuration中的Bean: {}", genericConfiguration.dogCage() == genericConfiguration.dogCage()); // 两次结果不一样
log.info("容器中的Bnea: {}", beanFactory.getBean(DogCage.class) == beanFactory.getBean(DogCage.class));// 从Spring容器中取值都是一样的
animalCage.cages.forEach(cage -> {
if (cage instanceof DogCage) {
log.info("dogCage : {} ", cage == dogCage); // 和上面的对象不一致，非单例
}
});
}
}再看下ProxyConfiguration配置的情况:
public class Tests {
@Test
public void runConfig() {
log.info("configuration: {}", proxyConfiguration); // 1、CGLIB代理的对象
log.info("Configuration中的Bean: {}", proxyConfiguration.dogCage() == proxyConfiguration.dogCage()); // 2、两次结果相同
log.info("容器中的Bnea: {}", beanFactory.getBean(DogCage.class) == beanFactory.getBean(DogCage.class));// 3、从Spring容器中取值都是一样的
animalCage.cages.forEach(cage -> {
if (cage instanceof DogCage) {
log.info("dogCage : {} ", cage == dogCage); // 和上面的对象不一致，非单例
}
});
}
}会得到这样的现象：
Lite Full Mode
看到上面的现象后，我们有必要了解下Spring配置中的Lite和Full两种模式
lite模式包含：
- 被@Component修饰的类
- 通过@ComponentScan扫描的类
- 通过@Import导入的配置类
- 通过@ImportResource导入的Spring配置文件
- 没有任何Spring相关注解，类里面有@Bean修饰的方法
- 被@Configuration修饰，但proxyBeanMethods = false
full模式包含：
- 被@Configuration修饰，且属性proxyBeanMethods = true（默认）
full模式使用特性：
- full模式下的配置类会被Cglib代理生成代理类取代原始类型保存到在容器中
- full模式下的@Bean方法不能是private和final，因为方法会被重写
- 单例scope下不同@Bean方法可以互相引用，实现单实例的语义
lite模式使用特性：
- lite模式下的配置类不生成代理，原始类型进入容器
- lite模式下的@Bean方法可以是private和final
- 单例scope下不同@Bean方法引用时无法做到单例，通过@Bean方法生成的对象都是新的实例
结束语
@Configuration(proxyBeanMethods = false)的配置其实是Lite模式，这种模式下，配置类不会生成代理类，速度会更快，但是要注意，在配置类中的@Bean方法，不能用来实现单例级别的依赖。
