How Java connects to MongoDB databases and creates and queries documents

To connect to the MongoDB database, you first need to install MongoDB and start the MongoDB service. You can install and start according to the guidelines provided on the official MongoDB website. The following is the complete sample code for connecting to the MongoDB database using Java: import com.mongodb.MongoClient; import com.mongodb.MongoClientURI; import com.mongodb.client.MongoCollection; import com.mongodb.client.MongoDatabase; import org.bson.Document; public class MongoDBExample { public static void main(String[] args) { //MongoDB Connection URI String connectionString = "mongodb://localhost:27017"; //Connect to MongoDB database MongoClient mongoClient = new MongoClient(new MongoClientURI(connectionString)); //Select Database MongoDatabase database = mongoClient.getDatabase("mydb"); //Select Collection MongoCollection<Document> collection = database.getCollection("mycollection"); //Create Document Document document = new Document("name", "John") .append("age", 30) .append("city", "New York"); //Insert Document collection.insertOne(document); //Query Document Document query = new Document("name", "John"); Document result = collection.find(query).first(); System.out.println(result); //Close MongoDB connection mongoClient.close(); } } In the above code, MongoDB's Java driver dependency library is used. You can add the following Maven dependencies in the 'pom. xml' file: <dependency> <groupId>org.mongodb</groupId> <artifactId>mongodb-driver-sync</artifactId> <version>4.4.4</version> </dependency> In the code, the MongoDB connection URI was first created, specifying the host and port number of MongoDB. Then, the MongoClient object was created using this URI. Next, we selected the database and collection, and created a document. Finally, the document was inserted into the collection and queried. Please replace the URI, database name, and collection name according to the actual situation, and use the API provided by MongoDB for operations as needed. The following is a sample MongoDB document: json { "_id": ObjectId("605f8e5b8bddf835ea3e129c"), "name": "John", "age": 30, "city": "New York" } This is a document that contains fields such as' name ',' age ', and' city '`_ The 'id' field is a unique identifier automatically generated by MongoDB. I hope this sample code can help you.