java如何从mongodb集合中获取最后日期（或最大日期），其中userName=currentUserName

我有以下格式的登录名集合：

{ "_id" : ObjectId("541d9aee784269c2e9f3c092"), "userName" : "dani", 
"loginDate" : ISODate("2020-01-22T21:08:28.994Z")},
{ "_id" : ObjectId("541d9aee7842sdfsdfsdddsf"), "userName" : "bar", 
"loginDate" : ISODate("2020-01-20T21:02:33.994Z")},
{ "_id" : ObjectId("541d9aee784dfgsdfgdfgdfg"), "userName" : "yacuv", 
"loginDate" : ISODate("2020-01-17T21:01:11.994Z")},
{ "_id" : ObjectId("541d9aee784dfgdfgdfgdfgd"), "userName" : "ran", 
"loginDate" : ISODate("2020-01-15T21:02:33.994Z")},
{ "_id" : ObjectId("541d9aee784269cvvchgfghh"), "userName" : "bar", 
"loginDate" : ISODate("2020-01-12T21:02:54.994Z")}}

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如何获取每个用户的最后输入日期？

假设集合名为“yoval”：

产生：

{ "_id" : "yacuv", "maxDate" : ISODate("2020-01-17T21:01:11.994Z") }
{ "_id" : "ran", "maxDate" : ISODate("2020-01-15T21:02:33.994Z") }
{ "_id" : "bar", "maxDate" : ISODate("2020-01-20T21:02:33.994Z") }
{ "_id" : "dani", "maxDate" : ISODate("2020-01-22T21:08:28.994Z") }

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请将代码放入代码块中。

{ "_id" : "yacuv", "maxDate" : ISODate("2020-01-17T21:01:11.994Z") }
{ "_id" : "ran", "maxDate" : ISODate("2020-01-15T21:02:33.994Z") }
{ "_id" : "bar", "maxDate" : ISODate("2020-01-20T21:02:33.994Z") }
{ "_id" : "dani", "maxDate" : ISODate("2020-01-22T21:08:28.994Z") }