一、复杂查询
Java可以通过使用MongoDB的Java驱动程序来执行各种类型的复杂查询。以下是一些常见的查询操作及其对应的Java代码示例：
1、查询单个文档：
MongoClient mongoClient = new MongoClient("localhost", 27017);
MongoDatabase database = mongoClient.getDatabase("mydb");
MongoCollection collection = database.getCollection("mycollection");
Document document = collection.find(eq("name", "John")).first();
System.out.println(document.toJson()); 2、查询多个文档：
MongoClient mongoClient = new MongoClient("localhost", 27017);
MongoDatabase database = mongoClient.getDatabase("mydb");
MongoCollection collection = database.getCollection("mycollection");
FindIterable documents = collection.find(gt("age", 18));
for (Document document : documents) {
System.out.println(document.toJson());
} 3、查询嵌套文档：
MongoClient mongoClient = new MongoClient("localhost", 27017);
MongoDatabase database = mongoClient.getDatabase("mydb");
MongoCollection collection = database.getCollection("mycollection");
Document query = new Document("address.city", "New York");
FindIterable documents = collection.find(query);
for (Document document : documents) {
System.out.println(document.toJson());
} 4、查询数组字段：
MongoClient mongoClient = new MongoClient("localhost", 27017);
MongoDatabase database = mongoClient.getDatabase("mydb");
MongoCollection collection = database.getCollection("mycollection");
Document query = new Document("tags", "technology");
FindIterable documents = collection.find(query);
for (Document document : documents) {
System.out.println(document.toJson());
} 二、聚合操作
Java可以使用MongoDB的聚合管道来执行复杂的聚合操作。以下是一些常见的聚合操作及其对应的Java代码示例：
1、简单聚合：
MongoClient mongoClient = new MongoClient("localhost", 27017);
MongoDatabase database = mongoClient.getDatabase("mydb");
MongoCollection collection = database.getCollection("mycollection");
List pipeline = Arrays.asList(
new Document("$match", new Document("status", "A")),
new Document("$group", new Document("_id", "$category").append("count", new Document("$sum", 1)))
);
AggregateIterable result = collection.aggregate(pipeline);
for (Document document : result) {
System.out.println(document.toJson());
} 2、聚合计算：
MongoClient mongoClient = new MongoClient("localhost", 27017);
MongoDatabase database = mongoClient.getDatabase("mydb");
MongoCollection collection = database.getCollection("mycollection");
List pipeline = Arrays.asList(
new Document("$group", new Document("_id", null).append("total", new Document("$sum", "$amount"))),
new Document("$project", new Document("_id", 0).append("total", 1))
);
AggregateIterable result = collection.aggregate(pipeline);
for (Document document : result) {
System.out.println(document.toJson());
} 3、聚合排序：
MongoClient mongoClient = new MongoClient("localhost", 27017);
MongoDatabase database = mongoClient.getDatabase("mydb");
MongoCollection collection = database.getCollection("mycollection");
List pipeline = Arrays.asList(
new Document("$group", new Document("_id", "$category").append("total", new Document("$sum", "$amount"))),
new Document("$sort", new Document("total", -1))
);
AggregateIterable result = collection.aggregate(pipeline);
for (Document document : result) {
System.out.println(document.toJson());
} 使用Java在MongoDB数据库中实现复杂查询和聚合操作可以帮助开发人员更好地处理和分析数据。通过使用MongoDB的Java驱动程序，可以轻松执行各种类型的查询操作，包括单个文档查询、多个文档查询、嵌套文档查询和数组字段查询。此外，使用MongoDB的聚合管道可以执行复杂的聚合操作，包括简单聚合、聚合计算和聚合排序等。通过学习和应用这些技术，开发人员可以充分利用Java和MongoDB的强大功能，构建高效可靠的数据处理和分析系统。
