Spring Batch - 使用带有列表列表的ItemWriter

问题描述

我们的处理器返回列表<？> （有效传递列表< List<？>> ）到我们的 ItemWriter 。

Our processor returns a List<?> (effectively passing a List<List<?>>) to our ItemWriter.

现在，我们发现 JdbcBatchItemWriter 未被编程为处理 item instanceof List 。我们还观察到处理项目instanceof List ;我们需要编写一个自定义 ItemSqlParameterSourceProvider 。

Now, we observed that the JdbcBatchItemWriter is not programmed to handle item instanceof List. We also observed to process item instanceof List; we need to write a custom ItemSqlParameterSourceProvider.

但令人遗憾的是，它返回 SqlParameterSource ，它只能处理一个项并且再次无法处理列表。

But the sad part is that it returns SqlParameterSource which can handle only one item and again not capable of handling a List.

那么，是否有人可以帮助我们了解如何处理 JdbcBatchItemWriter 中的列表列表？

So, can someone help us understand how to handle list of lists in the JdbcBatchItemWriter?

推荐答案

通常，设计模式为：

Reader -> reads something, returns ReadItem
Processor -> ingests ReadItem, returns ProcessedItem
Writer -> ingests List<ProcessedItem>

如果您的处理器返回 List< Object> ，那么你需要你的作家期望列表< List< Object>> 。

If your processor is returning List<Object>, then you need your Writer to expect List<List<Object>>.

你可以这样做将 JdbcBatchItemWriter 包装为ItemWriter中的委托，如下所示：

You could do this by wrapping your JdbcBatchItemWriter as a delegate in an ItemWriter that looks something like this:

public class ListUnpackingItemWriter<T> implements ItemWriter<List<T>>, ItemStream, InitializingBean {

    private ItemWriter<T> delegate;

    @Override
    public void write(final List<? extends List<T>> lists) throws Exception {
        final List<T> consolidatedList = new ArrayList<>();
        for (final List<T> list : lists) {
            consolidatedList.addAll(list);
        }
        delegate.write(consolidatedList);
    }

    @Override
    public void afterPropertiesSet() {
        Assert.notNull(delegate, "You must set a delegate!");
    }

    @Override
    public void open(ExecutionContext executionContext) {
        if (delegate instanceof ItemStream) {
            ((ItemStream) delegate).open(executionContext);
        }
    }

    @Override
    public void update(ExecutionContext executionContext) {
        if (delegate instanceof ItemStream) {
            ((ItemStream) delegate).update(executionContext);
        }
    }

    @Override
    public void close() {
        if (delegate instanceof ItemStream) {
            ((ItemStream) delegate).close();
        }
    }

    public void setDelegate(ItemWriter<T> delegate) {
        this.delegate = delegate;
    }

}

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