ElasticSearch里我明明指定了long，为什么却变成了keyword

　　背景
　　实体类定义属性id为Long类型，但在调用 spring-data-elasticsearch:3.2.10.RELEASE中的putMapping(Class)方法时却被转换成了keyword类型源码
　　查看putMapping方法，可以发现最终调用最下边的重载方法class ElasticsearchRestTemplate {   ...   @Override   public  boolean putMapping(Class clazz) {     return putMapping(clazz, buildMapping(clazz));   }    @Override   public  boolean putMapping(Class clazz, Object mapping) {     return putMapping(getPersistentEntityFor(clazz).getIndexName(), getPersistentEntityFor(clazz).getIndexType(),                       mapping);   }     @Override   public  boolean putMapping(String indexName, String type, Class clazz) {     return putMapping(indexName, type, buildMapping(clazz));   }     @Override   public boolean putMapping(String indexName, String type, Object mapping) {     Assert.notNull(indexName, ＂No index defined for putMapping()＂);     Assert.notNull(type, ＂No type defined for putMapping()＂);     PutMappingRequest request = new PutMappingRequest(indexName).type(type);     if (mapping instanceof String) {       request.source(String.valueOf(mapping), XContentType.JSON);     } else if (mapping instanceof Map) {       request.source((Map) mapping);     } else if (mapping instanceof XContentBuilder) {       request.source((XContentBuilder) mapping);     }     try {       return client.indices().putMapping(request, RequestOptions.DEFAULT).isAcknowledged();     } catch (IOException e) {       throw new ElasticsearchException(＂Failed to put mapping for ＂ + indexName, e);     }   }   ... } 复制代码
　　查看buildMapping方法，因为并没有定义外部mappingPath配置文件，所以走最下边的mappingBuilder.buildPropertyMapping(clazz)来进行解析出String类型的json文件abstract class AbstractElasticsearchTemplate {   ...   protected String buildMapping(Class<?> clazz) {     // load mapping specified in Mapping annotation if present     if (clazz.isAnnotationPresent(Mapping.class)) {       String mappingPath = clazz.getAnnotation(Mapping.class).mappingPath();       if (!StringUtils.isEmpty(mappingPath)) {         String mappings = ResourceUtil.readFileFromClasspath(mappingPath);         if (!StringUtils.isEmpty(mappings)) {           return mappings;         }       } else {         LOGGER.info(＂mappingPath in @Mapping has to be defined. Building mappings using @Field＂);       }     }       // build mapping from field annotations     try {       MappingBuilder mappingBuilder = new MappingBuilder(elasticsearchConverter);       return mappingBuilder.buildPropertyMapping(clazz);     } catch (Exception e) {       throw new ElasticsearchException(＂Failed to build mapping for ＂ + clazz.getSimpleName(), e);     }   }   ... } 复制代码
　　查看buildPropertyMapping方法class MappingBuilder {   ...   String buildPropertyMapping(Class<?> clazz) throws IOException {     // 提前解析出一些通用属性，比如indexName,indexType等等 		ElasticsearchPersistentEntity<?> entity = elasticsearchConverter.getMappingContext() 				.getRequiredPersistentEntity(clazz); 		// 构造一个json构造器，以indexType开始 		XContentBuilder builder = jsonBuilder().startObject().startObject(entity.getIndexType());  		// 添加dynamic template 		addDynamicTemplatesMapping(builder, entity);  		// 父子文档判断 		String parentType = entity.getParentType(); 		if (hasText(parentType)) { 			builder.startObject(FIELD_PARENT).field(FIELD_TYPE, parentType).endObject(); 		}  		// 属性解析开始标志properties 		builder.startObject(FIELD_PROPERTIES); 		// 具体的properties解析，为根对象非nested对象 		mapEntity(builder, entity, true, ＂＂, false, FieldType.Auto, null);  		builder.endObject() // FIELD_PROPERTIES 				.endObject() // indexType 				.endObject() // root object 				.close();  		return builder.getOutputStream().toString();   }      private void mapEntity(XContentBuilder builder, @Nullable ElasticsearchPersistentEntity entity, boolean isRootObject, 			String nestedObjectFieldName, boolean nestedOrObjectField, FieldType fieldType, 			@Nullable Field parentFieldAnnotation) throws IOException {  		boolean writeNestedProperties = !isRootObject && (isAnyPropertyAnnotatedWithField(entity) || nestedOrObjectField); 		if (writeNestedProperties) {  			String type = nestedOrObjectField ? fieldType.toString().toLowerCase() 					: FieldType.Object.toString().toLowerCase(); 			builder.startObject(nestedObjectFieldName).field(FIELD_TYPE, type);  			if (nestedOrObjectField && FieldType.Nested == fieldType && parentFieldAnnotation != null 					&& parentFieldAnnotation.includeInParent()) {  				builder.field(＂include_in_parent＂, parentFieldAnnotation.includeInParent()); 			}  			builder.startObject(FIELD_PROPERTIES); 		}     // 对象字段属性的解析 		if (entity != null) {  			entity.doWithProperties((PropertyHandler) property -> { 				try { 					if (property.isAnnotationPresent(Transient.class) || isInIgnoreFields(property, parentFieldAnnotation)) { 						return; 					}  					buildPropertyMapping(builder, isRootObject, property); 				} catch (IOException e) { 					logger.warn(＂error mapping property with name {}＂, property.getName(), e); 				} 			}); 		}  		if (writeNestedProperties) { 			builder.endObject().endObject(); 		} 	}   // 解析每个property的方法   private void buildPropertyMapping(XContentBuilder builder, boolean isRootObject, 			ElasticsearchPersistentProperty property) throws IOException {  		if (property.isAnnotationPresent(Mapping.class)) {  			String mappingPath = property.getRequiredAnnotation(Mapping.class).mappingPath(); 			if (!StringUtils.isEmpty(mappingPath)) {  				ClassPathResource mappings = new ClassPathResource(mappingPath); 				if (mappings.exists()) { 					builder.rawField(property.getFieldName(), mappings.getInputStream(), XContentType.JSON); 					return; 				} 			} 		} 		// geo标识 		boolean isGeoPointProperty = isGeoPointProperty(property);     // completion标识 		boolean isCompletionProperty = isCompletionProperty(property);     // nested object标识 		boolean isNestedOrObjectProperty = isNestedOrObjectProperty(property); 		// 属性上的Field注解 		Field fieldAnnotation = property.findAnnotation(Field.class); 		if (!isGeoPointProperty && !isCompletionProperty && property.isEntity() && hasRelevantAnnotation(property)) {  			if (fieldAnnotation == null) { 				return; 			}  			Iterator<? extends TypeInformation<?>> iterator = property.getPersistentEntityTypes().iterator(); 			ElasticsearchPersistentEntity<?> persistentEntity = iterator.hasNext() 					? elasticsearchConverter.getMappingContext().getPersistentEntity(iterator.next()) 					: null;  			mapEntity(builder, persistentEntity, false, property.getFieldName(), isNestedOrObjectProperty, 					fieldAnnotation.type(), fieldAnnotation);  			if (isNestedOrObjectProperty) { 				return; 			} 		}  		MultiField multiField = property.findAnnotation(MultiField.class);  		if (isGeoPointProperty) { 			applyGeoPointFieldMapping(builder, property); 			return; 		}  		if (isCompletionProperty) { 			CompletionField completionField = property.findAnnotation(CompletionField.class); 			applyCompletionFieldMapping(builder, property, completionField); 		} 		// 判断是否为id属性 		if (isRootObject && fieldAnnotation != null && property.isIdProperty()) { 			applyDefaultIdFieldMapping(builder, property); 		} else if (multiField != null) { 			addMultiFieldMapping(builder, property, multiField, isNestedOrObjectProperty); 		} else if (fieldAnnotation != null) { 			addSingleFieldMapping(builder, property, fieldAnnotation, isNestedOrObjectProperty); 		} 	}   ... } 复制代码
　　至此可以看到，只要fieldName为id或document就判定为是id属性，然后将type设置为keyword并且可被索引。疑问到这里解决class SimpleElasticsearchPersistentProperty {   ...   private static final List SUPPORTED_ID_PROPERTY_NAMES = Arrays.asList(＂id＂, ＂document＂);   public SimpleElasticsearchPersistentProperty(Property property,       PersistentEntity<?, ElasticsearchPersistentProperty> owner, SimpleTypeHolder simpleTypeHolder) {     ...     this.isId = super.isIdProperty() || SUPPORTED_ID_PROPERTY_NAMES.contains(getFieldName());     ...   }      @Override   public boolean isIdProperty() {     return isId;   }   private void applyDefaultIdFieldMapping(XContentBuilder builder, ElasticsearchPersistentProperty property)       throws IOException {       builder.startObject(property.getFieldName()).field(FIELD_TYPE, TYPE_VALUE_KEYWORD).field(FIELD_INDEX, true)         .endObject();   }   ... } 复制代码话外题
　　项目中使用的ElasticSearch实体类都是采取@Document指定indexName来操作的，但是索引和表都涉及到分库分表，所以又不能写死，然后就采取的SpEL配合ThreadLocal从上下文里set后get，其实Spring对elasticsearch操作类似于关系型数据库也封装的有一层Repository抽象，名为ElasticsearchRepository，我们可以直接定义实体类操作接口继承就可以完成对单索引的CRUD以及Page等操作，但这样有一个问题，那就是indexName无法动态去调整，所以就放弃了这种，改用更底层的RestHighLevelClient封装的ElasticSearchRestTemplate模版类，这样在面对分库分表时就可以手动去对每个Document进行set不同的indexName，跨索引查询时也可以指定多个，也可以直接指定索引的alias，需要注意的时，在进行更新时，只指定alias是不被允许的，需要手动查出符合条件的Document在进行索引的分组批量更新，即调用ElasticSearch的bulk api
　　在对ElasticSearch和数据库的一致性问题上，我是通过封装不同的方法来确保强一致性和最终一致性强一致性
　　类似插入、更新、删除等场景下，都是放在一个事务里，先操作数据库，再操作ElasticSearch，这样可以确保操作ElasticSearch失败时，数据库可以成功回滚。一般只运用于对数据实时性要求敏感的场景，并且数据量不大的情况，但即便这样还是会有至少1s的延迟，这里就涉及到ElasticSearch的刷盘策略问题上了，这里不展开研究最终一致性
　　批量的插入、更新这些操作，如果放在一个大事务里，对数据库也是一种压力，所以一般是分批操作数据库，另起一个线程池对事务提交进行监听，将数据库数据同步到ElasticSearch里，在同步成功后反转数据库的同步状态字段。为了确保万无一失，后台会启动一个定时扫描数据库同步字段的线程去定时扫描同步。这种一般适用于大数据量的场景。当然你也可以去监听MySQL的binlog日志来进行同步。