用RestHighLevelClient来设置es字段返回字符数

要设置返回的字段字符数，可以使用source filtering和field collapsing来实现。以下是一个例子：

RestHighLevelClient client = new RestHighLevelClient(
        RestClient.builder(new HttpHost("localhost", 9200, "http")));

// 设置source filtering
SearchSourceBuilder sourceBuilder = new SearchSourceBuilder();
sourceBuilder.fetchSource(new String[]{"title", "content"}, new String[]{"content"});

// 设置field collapsing
CollapseBuilder collapseBuilder = new CollapseBuilder("title");

// 设置请求
SearchRequest searchRequest = new SearchRequest("my_index");
searchRequest.source(sourceBuilder);
searchRequest.collapse(collapseBuilder);

// 执行请求
SearchResponse searchResponse = client.search(searchRequest, RequestOptions.DEFAULT);

// 处理结果
SearchHits hits = searchResponse.getHits();
for (SearchHit hit : hits) {
    String title = hit.getField("title").getValue();
    String content = hit.getField("content").getValue();
    System.out.println("Title: " + title);
    System.out.println("Content: " + content.substring(0, Math.min(100, content.length())));
}

在这个例子中，我们设置了source filtering，只返回title和content字段的内容。同时，我们也设置了field collapsing，按照title字段进行折叠。在结果处理中，我们使用getValue()方法获取字段的值，然后截取了content字段的前100个字符。