自定义复杂bean注册到spring

A依赖B, B依赖C,A和C是有spring创建，而B要自己去创建，并且像B的有很多，比如B的调用实际是一个RPC

在什么时机去装机B并能让spring找到这个依赖呢？spring的FactoryBean就可以解决（不是BeanFactory）

下面以 Retrofit 为例简单说明，类B的bean都是由retrofit创建(动态代理)

先声明一个 FactoryBean的实现

public class ServiceFactoryBean implements FactoryBean {


private Retrofit retrofit;

private Class serviceClass;

public void setServiceClass(Class serviceClass){
this.serviceClass = serviceClass;
    }

public void setRetrofit(Retrofit retrofit) {
this.retrofit = retrofit;
    }

@Override
public Object getObject() throws Exception {

return retrofit.create(this.serviceClass);
    }

@Override
public Class getObjectType() {
return serviceClass;
    }

@Override
public boolean isSingleton() {
return true;
    }
}

在spring进行bean定义处理的时候就把类B的bean在spring中注册一下（实现接口BeanDefinitionRegistryPostProcessor）

@Configuration
public class CustomBeanDefinitionRegistryPostProcessor implements BeanDefinitionRegistryPostProcessor {

@Autowired
    BeanNameGenerator beanNameGenerator;

@Override
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
        logger.info("Invoke Metho postProcessBeanDefinitionRegistry");

        Reflections reflections = new Reflections("com.myapp.api.service");
        Retrofit retrofit = retrofit();
        Set<Class<?>> annotated = reflections.getTypesAnnotatedWith(RetrofitService.class);
for (Class<?> serviceClass : annotated) {
for(Annotation annotation : serviceClass.getAnnotations()){
if (annotation instanceof RetrofitService){//自定义注解RetrofitService，都需要通过retrofit创建bean
                    RootBeanDefinition beanDefinition = new RootBeanDefinition();
                    beanDefinition.setBeanClass(ServiceFactoryBean.class);
                    beanDefinition.setLazyInit(true);
                    beanDefinition.getPropertyValues().addPropertyValue("retrofit", retrofit);
                    beanDefinition.getPropertyValues().addPropertyValue("serviceClass", serviceClass);
                    String beanName = this.beanNameGenerator.generateBeanName(beanDefinition, registry);
                    registry.registerBeanDefinition(beanName, beanDefinition);
                }
            }
        }
    }

public Retrofit retrofit() {

final String basic = Base64.encodeToString(token.getBytes());

final OkHttpClient okHttpClient = new OkHttpClient();
        okHttpClient.setReadTimeout(60, TimeUnit.SECONDS);
        okHttpClient.setConnectTimeout(60, TimeUnit.SECONDS);

        okHttpClient.interceptors().add(new Interceptor() {
@Override
public Response intercept(Interceptor.Chain chain) throws IOException {
                Request original = chain.request();

                Request.Builder requestBuilder = original.newBuilder()
                        .header("Authorization", basic)
                        .method(original.method(), original.body());

                Request request = requestBuilder.build();
return chain.proceed(request);
            }
        });

return new Retrofit.Builder()
                .baseUrl(baseUrl)
                .addConverterFactory(JacksonConverterFactory.create())
                .client(okHttpClient)
                .build();
    }

}

如自己定义的类B接口

@RetrofitService
public interface UserService {
@POST("/user/register")
    Call<Object> register(@Body User user);
}

为什么要用BeanDefinitionRegistryPostProcessor，可以看看org.springframework.context.support.AbstractApplicationContext#refresh

BeanFactory 它的职责包括：实例化、定位、配置应用程序中的对象及建立这些对象间的依赖。

FactoryBean 作用是产生其他bean实例getObjectType()

到此完成，需要用户的地方直接使用按照驼峰命名引用或使用注解Autowired

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自定义复杂bean注册到spring

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