一、问题

本人是一名Spring小白，跟着黑马的课程学习Mongodb时出现了如下报错：

ERROR 18080 --- [           main] o.s.boot.SpringApplication               : Application run failed
org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'commentService': Unsatisfied dependency expressed through field 'commentRepository'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'commentRepository': Cannot resolve reference to bean 'mongoTemplate' while setting bean property 'mongoOperations'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'mongoTemplate' defined in class path resource [org/springframework/boot/autoconfigure/data/mongo/MongoDataAutoConfiguration.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.data.mongodb.core.MongoTemplate]: Factory method 'mongoTemplate' threw exception; nested exception is org.springframework.dao.DataAccessResourceFailureException: Timed out after 30000 ms while waiting to connect. Client view of cluster state is {type=UNKNOWN, servers=[{address=192.168.40.141:27017, type=UNKNOWN, state=CONNECTING, exception={com.mongodb.MongoSocketOpenException: Exception opening socket}, caused by {java.net.SocketTimeoutException: Connect timed out}}]; nested exception is com.mongodb.MongoTimeoutException: Timed out after 30000 ms while waiting to connect. Client view of cluster state is {type=UNKNOWN, servers=[{address=192.168.40.141:27017, type=UNKNOWN, state=CONNECTING, exception={com.mongodb.MongoSocketOpenException: Exception opening socket}, caused by {java.net.SocketTimeoutException: Connect timed out}}]

二、定位

观察上述报错的第二行，我发现主要问题有三个：

1. 创建Bean错误：UnsatisfiedDependencyException: Error creating bean with name 'commentService': Unsatisfied dependency expressed through field 'commentRepository';
2. 连接数据库超时：DataAccessResourceFailureException: Timed out after 30000 ms while waiting to connect.
3. 数据库中存在不同名字的索引：这个信息提示好像在另一行，我忘了保存了

经过问题定位，我发现之前我在userid字段上建立了名为userid_1的索引，而黑马的代码会对userid字段建立名为userid的索引，故冲突。下图是我之前建立的索引：

项目中建立索引的代码如下：

//添加了一个单字段的索引
@Indexed
private String userid;//发布人ID

三、解决

删除数据库中与项目中命名冲突的索引即可：

之后，代码可正确执行：