监视变化

changeStream.forEach(event -> System.out.println("Change observed: " + event));

/**
 * This file demonstrates how to open a change stream by using the Java driver.
 * It connects to a MongoDB deployment, accesses the "sample_mflix" database, and listens
 * to change events in the "movies" collection. The code uses a change stream with a pipeline
 * to only filter for "insert" and "update" events.
 */
package usage.examples;
import java.util.Arrays;
import java.util.List;
import org.bson.Document;
import org.bson.conversions.Bson;
import com.mongodb.client.ChangeStreamIterable;
import com.mongodb.client.MongoClient;
import com.mongodb.client.MongoClients;
import com.mongodb.client.MongoCollection;
import com.mongodb.client.MongoDatabase;
import com.mongodb.client.model.Filters;
import com.mongodb.client.model.changestream.FullDocument;
public class Watch {
    public static void main( String[] args ) {
        // Replace the uri string with your MongoDB deployment's connection string
        String uri = "<connection string uri>";
        try (MongoClient mongoClient = MongoClients.create(uri)) {
            MongoDatabase database = mongoClient.getDatabase("sample_mflix");
            MongoCollection<Document> collection = database.getCollection("movies");
            // Creates instructions to match insert and update operations
            List<Bson> pipeline = Arrays.asList(
                Aggregates.match(
                        Filters.in("operationType",
                                Arrays.asList("insert", "update"))));
            
            // Creates a change stream that receives change events for the specified operations
            ChangeStreamIterable<Document> changeStream = database.watch(pipeline)
                .fullDocument(FullDocument.UPDATE_LOOKUP);
           
            final int[] numberOfEvents = {0};
            // Prints a message each time the change stream receives a change event, until it receives two events
            changeStream.forEach(event -> {
            System.out.println("Received a change to the collection: " + event);
                if (++numberOfEvents[0] >= 2) {
                  System.exit(0);
                }
            });
        }
    }
}

// Performs CRUD operations to generate change events when run with the Watch application
package usage.examples;
import java.util.Arrays;
import org.bson.Document;
import org.bson.types.ObjectId;
import com.mongodb.MongoException;
import com.mongodb.client.MongoClient;
import com.mongodb.client.MongoClients;
import com.mongodb.client.MongoCollection;
import com.mongodb.client.MongoDatabase;
import com.mongodb.client.result.InsertOneResult;
public class WatchCompanion {
    public static void main(String[] args) {
        // Replace the uri string with your MongoDB deployment's connection string
        String uri = "<connection string uri>";
        try (MongoClient mongoClient = MongoClients.create(uri)) {
            MongoDatabase database = mongoClient.getDatabase("sample_mflix");
            MongoCollection<Document> collection = database.getCollection("movies");
            try {
                // Inserts a sample document into the "movies" collection and print its ID
                InsertOneResult insertResult = collection.insertOne(new Document("test", "sample movie document"));
                System.out.println("Success! Inserted document id: " + insertResult.getInsertedId());
                // Updates the sample document and prints the number of modified documents
                UpdateResult updateResult = collection.updateOne(new Document("test", "sample movie document"), Updates.set("field2", "sample movie document update"));
                System.out.println("Updated " + updateResult.getModifiedCount() + " document.");
                // Deletes the sample document and prints the number of deleted documents
                DeleteResult deleteResult = collection.deleteOne(new Document("field2", "sample movie document update"));
                System.out.println("Deleted " + deleteResult.getDeletedCount() + " document.");
            
            // Prints a message if any exceptions occur during the operations
            } catch (MongoException me) {
                System.err.println("Unable to insert, update, or replace due to an error: " + me);
            }
        }
    }
}