AsyncItemWriter - 将自定义 class 解包到 Future 时遇到 ClassCastException

Question

我正在编写一个 spring 批处理作业来读取一些数据并将其写入文件。数据被分成 3 个块，每个块在合并之前都需要写入一个单独的文件。读取和聚合工作正常。

但是，当异步编写器抛出错误时 -- java.lang.ClassCastException: class package.Custom cannot be cast to class java.util.concurrent.Future

我的自定义 DTO 似乎没有展开到 Future 对象中。这是我的删节代码

 @Bean
    public Step workerStep() throws Exception {
        return stepBuilderFactory.get(WORKER_BEAN)
                .<Custom, Custom>chunk(CHUNK_SIZE)
                .reader(reader(null))
                .writer(writer())
                .taskExecutor(threadPoolExecutor)
                .throttleLimit(THROTTLE_LIMIT)
                .build();
    }

    @Bean
    @StepScope
    public CustomReader reader(@Value("#{stepExecutionContext['currentMod']}") Long currentMod) {
        if ( ... some logic ... ) {
            return null;
        }
        return new CustomReader();
    }

    @Bean
    @StepScope
    public AsyncItemWriter writer() throws Exception {
        AsyncItemWriter<Custom> asyncItemWriter = new AsyncItemWriter<>();
        asyncItemWriter.setDelegate(delegateWriter(null));
        asyncItemWriter.afterPropertiesSet();
        return asyncItemWriter;
    }

    @Bean(destroyMethod=EMPTY)
    @StepScope
    public CustomWriter<Custom> delegateWriter(@Value("#{stepExecutionContext['currentMod']}") Long currentMod) {
        CustomWriter<Custom> customWriter = new CustomWriter<>();

        customWriter.setLineAggregator(new DelimitedLineAggregator<Custom>() {
            {
                setDelimiter(COMMA);
                setFieldExtractor(new BeanWrapperFieldExtractor<Custom>() {
                    {
                        setNames( ... get names logic ... );
                    }
                });
            }
        });

        customWriter.setResource(new FileSystemResource(name));
        
        // ... header call-back logic ...
        
        customWriter.setAppendAllowed(true);
        customWriter.setShouldDeleteIfEmpty(true);
        customWriter.setShouldDeleteIfExists(true);
        return customWriter;
    }

    @Bean
    public TaskExecutor taskExecutor() {
        return new SimpleAsyncTaskExecutor(THREAD_NAME_PREFIX);
    }

Answer 1

AsyncItemWriter 需要包裹在 Future 中的项目（参见 Javadoc), and this is typically done by an AsyncItemProcessor. The AsyncItemWriter and AsyncItemProcessor are used in conjunction to implement a fork/join scenario, see Asynchronous Processors 部分。

AsyncItemWriter - 将自定义 class 解包到 Future 时遇到 ClassCastException

AsyncItemWriter - Facing ClassCastException when unwrapping custom class into Future

java

spring-batch