以下是一个使用Elasticsearch的Java API实现包括0值的平均桶聚合的示例代码：

import org.elasticsearch.action.search.SearchResponse;
import org.elasticsearch.client.RequestOptions;
import org.elasticsearch.client.RestHighLevelClient;
import org.elasticsearch.common.unit.DistanceUnit;
import org.elasticsearch.index.query.QueryBuilders;
import org.elasticsearch.search.aggregations.AggregationBuilders;
import org.elasticsearch.search.aggregations.bucket.histogram.DateHistogramInterval;
import org.elasticsearch.search.aggregations.bucket.histogram.Histogram;
import org.elasticsearch.search.aggregations.metrics.Avg;
import org.elasticsearch.search.builder.SearchSourceBuilder;
import org.elasticsearch.search.sort.SortBuilders;
import org.elasticsearch.search.sort.SortOrder;

import java.io.IOException;

public class AverageBucketAggregationExample {

    public static void main(String[] args) {
        try (RestHighLevelClient client = new RestHighLevelClient()) {
            SearchSourceBuilder sourceBuilder = new SearchSourceBuilder();
            sourceBuilder.query(QueryBuilders.matchAllQuery());
            sourceBuilder.sort(SortBuilders.fieldSort("timestamp").order(SortOrder.ASC));

            Histogram histogramAgg = AggregationBuilders.histogram("timestamp_histogram")
                    .field("timestamp")
                    .interval(DateHistogramInterval.DAY)
                    .minDocCount(0) // 包括0值
                    .subAggregation(AggregationBuilders.avg("average_price").field("price"));

            sourceBuilder.aggregation(histogramAgg);

            SearchResponse response = client.search(sourceBuilder, RequestOptions.DEFAULT);

            Histogram agg = response.getAggregations().get("timestamp_histogram");
            for (Histogram.Bucket entry : agg.getBuckets()) {
                String key = entry.getKeyAsString();
                long docCount = entry.getDocCount();
                Avg averagePrice = entry.getAggregations().get("average_price");
                double avgPrice = averagePrice.getValue();
                System.out.println("Key: " + key + ", Doc Count: " + docCount + ", Average Price: " + avgPrice);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

在上述示例中，我们首先创建一个SearchSourceBuilder对象，配置查询条件和排序方式。然后，我们创建一个Histogram聚合，指定要聚合的字段(timestamp)、时间间隔(DateHistogramInterval)以及是否包括0值(minDocCount)。接下来，我们在Histogram聚合中创建一个Avg聚合，指定要计算平均值的字段(price)。最后，我们将Histogram聚合添加到SearchSourceBuilder中，并使用RestHighLevelClient执行查询。

在查询响应中，我们可以使用response.getAggregations().get("timestamp_histogram")获取Histogram聚合对象，然后遍历桶列表获取每个桶的键、文档计数和平均值。