SpringBoot中BeanPostProcessor注册

在使用SpringBoot集成shiro时，遇到过一个问题，shiro需要注册一个LifecycleBeanPostProcessor，用来调用内部的init()和destroy()方法。
一般在Configuration中注册：

@Configuration
public class SpringServiceConfig {
    @Autowired
    private SpringDataSourceConfig springDataSourceConfig;
    private SpringRedisConfig springRedisConfig;
    @Autowired
    public SpringServiceConfig(SpringRedisConfig springRedisConfig) {
        this.springRedisConfig = springRedisConfig;
    }
    //sessionManager securityManager realm...
    @Bean
    public LifecycleBeanPostProcessor lifecycleBeanPostProcessor() {
        return new LifecycleBeanPostProcessor();
    }
    @Bean
    @DependsOn({"lifecycleBeanPostProcessor"})
    public DefaultAdvisorAutoProxyCreator advisorAutoProxyCreator() {
        DefaultAdvisorAutoProxyCreator defaultAdvisorAutoProxyCreator = new DefaultAdvisorAutoProxyCreator();
        defaultAdvisorAutoProxyCreator.setProxyTargetClass(true);
        return defaultAdvisorAutoProxyCreator;
    }
}

在这个Configuration中，使用@Autowired注入会失败！
如果是在属性上使用：

1 2	@Autowired private SpringDataSourceConfig springDataSourceConfig;

使用时发现springDataSourceConfig为空；
如果用构造器注入：

private SpringRedisConfig springRedisConfig;
@Autowired
public SpringServiceConfig(SpringRedisConfig springRedisConfig) {
    this.springRedisConfig = springRedisConfig;
}

会报错：

1	No default constructor found;

网上搜索后找到答案，原因是LifecycleBeanPostProcessor集成了BeanPostProcessor，而在Spring声明周期中，BeanPostProcessor和BeanFactoryPostProcessor的初始化是优先于bean的初始化的：

因此，如果一个@Configuration标注的类中返回了BeanPostProcessor或者BeanFactoryPostProcessor，那么无法使用@Autowired进行注入。
@Bean注解的javadoc中也有说明：

BeanFactoryPostProcessor-returning @Bean methods

Special consideration must be taken for @Bean methods that return Spring BeanFactoryPostProcessor (BFPP) types. Because BFPP objects must be instantiated very early in the container lifecycle, they can interfere(干涉) with processing of annotations such as @Autowired, @Value, and @PostConstruct within @Configuration classes. To avoid these lifecycle issues, mark BFPP-returning @Bean methods as static. For example:
1
2
3
4
@Bean
public static PropertyPlaceholderConfigurer ppc() {
    // instantiate, configure and return ppc ...
}
By marking this method as static, it can be invoked without causing instantiation of its declaring @Configuration class, thus avoiding the above-mentioned lifecycle conflicts. Note however that static @Bean methods will not be enhanced for scoping and AOP semantics as mentioned above. This works out in BFPP cases, as they are not typically referenced by other @Bean methods. As a reminder, a WARN-level log message will be issued for any non-static @Bean methods having a return type assignable to BeanFactoryPostProcessor.

解决的方案javadoc中也说了，就是给返回BeanPostProcessor或者BeanFactoryPostProcessor的方法使用static修饰。
这样，调用该方法时，不需要实例化外层的容器。

@Bean
public static LifecycleBeanPostProcessor lifecycleBeanPostProcessor() {
    return new LifecycleBeanPostProcessor();
}

参考：
Spring Java based configuration with static method
Spring Bean的生命周期