elasticssearch提供了CompletionSuggester查询来实现自动补全功能。这个查询会匹配以用户输入内容开头的词条并返回。为了提高补全查询效率，对于文档中字段的类型有一些约束：
+ 查询类型必须是：completion
+ 字段内容是多个补全词条形成的数组
PUT /test2
{"mappings": {"properties": {"title":{"type": "completion" #创建字段类型的时候，只能是completion}}}
}POST /test2/_doc/1
{"title":["Sony", "WH-1000XM3"] #字段的内容是多词条形成的数组
}POST test2/_doc/2
{"title": ["SK-II", "PITERA"]
}
POST test2/_doc/3
{"title": ["Nintendo", "switch"]
}# 查询语法，自动补全
GET /test2/_search
{"suggest": {"titleSuggest": { #查询的名称"text": "So", #查询的内容"completion": { #查询补全的类型"field": "title", #字段类型"skip_duplicates": true, #跳过重复的词条"size": 10 #查询的大小}}}
}完成一个hotel酒店的es库创建：（创建了两个自定义的分词器）
PUT /hotel
{"settings": {"analysis": {"analyzer": {"text_anlyzer": {"tokenizer": "ik_max_word","filter": "py"},"completion_analyzer": {"tokenizer": "keyword","filter": "py"}},"filter": {"py": {"type": "pinyin","keep_full_pinyin": false,"keep_joined_full_pinyin": true,"keep_original": true,"limit_first_letter_length": 16,"remove_duplicated_term": true,"none_chinese_pinyin_tokenize": false}}}},"mappings": {"properties": {"id":{"type": "keyword"},"name":{"type": "text","analyzer": "text_anlyzer","search_analyzer": "ik_smart","copy_to": "all"},"address":{"type": "keyword","index": false},"price":{"type": "integer"},"score":{"type": "integer"},"brand":{"type": "keyword","copy_to": "all"},"city":{"type": "keyword"},"starName":{"type": "keyword"},"business":{"type": "keyword","copy_to": "all"},"location":{"type": "geo_point"},"pic":{"type": "keyword","index": false},"all":{"type": "text","analyzer": "text_anlyzer","search_analyzer": "ik_smart"},"suggestion":{"type": "completion","analyzer": "completion_analyzer","search_analyzer": "ik_smart" # 使用这个为了拼音和汉字都可以使用，而不只是拼音}}}
}java代码查询：
@Testpublic void completionTest() throws IOException {SearchRequest request = new SearchRequest("hotel");request.source().suggest(new SuggestBuilder().addSuggestion("suggestions",SuggestBuilders.completionSuggestion("suggestion").prefix("火").size(10).skipDuplicates(true)));SearchResponse response = client.search(request, RequestOptions.DEFAULT);Suggest suggest = response.getSuggest();CompletionSuggestion suggestions = suggest.getSuggestion("suggestions");List<CompletionSuggestion.Entry.Option> options = suggestions.getOptions();for (CompletionSuggestion.Entry.Option option : options) {String string = option.getText().string();System.out.println(string);}}