摘要：序本文主要聊聊中的注解。這里從獲取注解有個可以標注使用哪個，這里的就是尋找這個標識。推薦注解指定，然后的返回，讓它去尋找默認的自己應用里頭都默認定義一個給托管

本文主要聊聊spring中的async注解。

@EnableAsync(proxyTargetClass = true)
@Configuration
public class AsyncConfig implements AsyncConfigurer{

    private static final Logger LOGGER = LoggerFactory.getLogger(AsyncConfig.class);

    @Override
    public Executor getAsyncExecutor() {
        return null;
    }

    @Override
    public AsyncUncaughtExceptionHandler getAsyncUncaughtExceptionHandler() {
        return new AsyncUncaughtExceptionHandler() {
            @Override
            public void handleUncaughtException(Throwable throwable, Method method, Object... params) {
                LOGGER.error(throwable);
            }
        };
    }
}

這里討論一下getAsyncExecutor這里定義null的情況。
spring-context-4.3.9.RELEASE-sources.jar!/org/springframework/scheduling/annotation/AbstractAsyncConfiguration.java

@Configuration
public abstract class AbstractAsyncConfiguration implements ImportAware {

    protected AnnotationAttributes enableAsync;

    protected Executor executor;

    protected AsyncUncaughtExceptionHandler exceptionHandler;


    @Override
    public void setImportMetadata(AnnotationMetadata importMetadata) {
        this.enableAsync = AnnotationAttributes.fromMap(
                importMetadata.getAnnotationAttributes(EnableAsync.class.getName(), false));
        if (this.enableAsync == null) {
            throw new IllegalArgumentException(
                    "@EnableAsync is not present on importing class " + importMetadata.getClassName());
        }
    }

    /**
     * Collect any {@link AsyncConfigurer} beans through autowiring.
     */
    @Autowired(required = false)
    void setConfigurers(Collection configurers) {
        if (CollectionUtils.isEmpty(configurers)) {
            return;
        }
        if (configurers.size() > 1) {
            throw new IllegalStateException("Only one AsyncConfigurer may exist");
        }
        AsyncConfigurer configurer = configurers.iterator().next();
        this.executor = configurer.getAsyncExecutor();
        this.exceptionHandler = configurer.getAsyncUncaughtExceptionHandler();
    }

}

這里從AsyncConfigurer獲取executor

spring-aop-4.3.9.RELEASE-sources.jar!/org/springframework/aop/interceptor/AsyncExecutionInterceptor.java

/**
     * Intercept the given method invocation, submit the actual calling of the method to
     * the correct task executor and return immediately to the caller.
     * @param invocation the method to intercept and make asynchronous
     * @return {@link Future} if the original method returns {@code Future}; {@code null}
     * otherwise.
     */
    @Override
    public Object invoke(final MethodInvocation invocation) throws Throwable {
        Class targetClass = (invocation.getThis() != null ? AopUtils.getTargetClass(invocation.getThis()) : null);
        Method specificMethod = ClassUtils.getMostSpecificMethod(invocation.getMethod(), targetClass);
        final Method userDeclaredMethod = BridgeMethodResolver.findBridgedMethod(specificMethod);

        AsyncTaskExecutor executor = determineAsyncExecutor(userDeclaredMethod);
        if (executor == null) {
            throw new IllegalStateException(
                    "No executor specified and no default executor set on AsyncExecutionInterceptor either");
        }

        Callable