Mongodb 简明教程

MongoDB - Java

第一章，我们将学习如何设置 MongoDB 客户端

Installation

在 Java 程序中使用 MongoDB 之前，需要确保在计算机上设置了 MongoDB 客户端和 Java。可以查看 Java 教程，了解如何安装 Java。现在，我们来了解如何设置 MongoDB 客户端。

需要下载 jar 文件 mongodb-driver-3.11.2.jar and its dependency mongodb-driver-core-3.11.2.jar. 。务必下载最新版本的 jar 文件。
你需要将下载的 jar 文件包括在自己的类路径中。

Connect to Database

要连接数据库，你需要指定数据库名称；如果数据库不存在，则 MongoDB 会自动创建它。

以下是连接数据库的代码片段：

import com.mongodb.client.MongoDatabase;
import com.mongodb.MongoClient;
import com.mongodb.MongoCredential;
public class ConnectToDB {

   public static void main( String args[] ) {

      // Creating a Mongo client
      MongoClient mongo = new MongoClient( "localhost" , 27017 );

      // Creating Credentials
      MongoCredential credential;
      credential = MongoCredential.createCredential("sampleUser", "myDb",
         "password".toCharArray());
      System.out.println("Connected to the database successfully");

      // Accessing the database
      MongoDatabase database = mongo.getDatabase("myDb");
      System.out.println("Credentials ::"+ credential);
   }
}

现在，让我们编译并运行上述程序来创建我们的数据库 myDb，如下所示。

$javac ConnectToDB.java
$java ConnectToDB

在执行上述程序时，您将得到以下输出。

Connected to the database successfully
Credentials ::MongoCredential{
   mechanism = null,
   userName = 'sampleUser',
   source = 'myDb',
   password = <hidden>,
   mechanismProperties = {}
}

Create a Collection

为了创建一个集合，使用 com.mongodb.client.MongoDatabase 类的 createCollection() 方法。

以下是创建集合的代码片段 −

import com.mongodb.client.MongoDatabase;
import com.mongodb.MongoClient;
import com.mongodb.MongoCredential;
public class CreatingCollection {

   public static void main( String args[] ) {

      // Creating a Mongo client
      MongoClient mongo = new MongoClient( "localhost" , 27017 );

      // Creating Credentials
      MongoCredential credential;
      credential = MongoCredential.createCredential("sampleUser", "myDb",
         "password".toCharArray());
      System.out.println("Connected to the database successfully");

      //Accessing the database
      MongoDatabase database = mongo.getDatabase("myDb");

      //Creating a collection
      database.createCollection("sampleCollection");
      System.out.println("Collection created successfully");
   }
}

在编译程序后，你会得到以下结果−

Connected to the database successfully
Collection created successfully

Getting/Selecting a Collection

为了从数据库中获取/选择一个集合，使用 com.mongodb.client.MongoDatabase 类的 getCollection() 方法。

以下是用于获取/选择一个集合的程序−

import com.mongodb.client.MongoCollection;
import com.mongodb.client.MongoDatabase;
import org.bson.Document;
import com.mongodb.MongoClient;
import com.mongodb.MongoCredential;
public class selectingCollection {

   public static void main( String args[] ) {

      // Creating a Mongo client
      MongoClient mongo = new MongoClient( "localhost" , 27017 );

      // Creating Credentials
      MongoCredential credential;
      credential = MongoCredential.createCredential("sampleUser", "myDb",
         "password".toCharArray());
      System.out.println("Connected to the database successfully");

      // Accessing the database
      MongoDatabase database = mongo.getDatabase("myDb");

      // Creating a collection
      System.out.println("Collection created successfully");
      // Retrieving a collection
      MongoCollection<Document> collection = database.getCollection("myCollection");
      System.out.println("Collection myCollection selected successfully");
   }
}

在编译程序后，你会得到以下结果−

Connected to the database successfully
Collection created successfully
Collection myCollection selected successfully

Insert a Document

为了向 MongoDB 中插入一个文档，使用 com.mongodb.client.MongoCollection 类的 insert() 方法。

以下是插入文档的代码片段：

import com.mongodb.client.MongoCollection;
import com.mongodb.client.MongoDatabase;
import org.bson.Document;
import com.mongodb.MongoClient;
public class InsertingDocument {
	public static void main( String args[] ) {

	// Creating a Mongo client
	MongoClient mongo = new MongoClient( "localhost" , 27017 );

	// Accessing the database
	MongoDatabase database = mongo.getDatabase("myDb");

	// Creating a collection
	database.createCollection("sampleCollection");
	System.out.println("Collection created successfully");

	// Retrieving a collection
	MongoCollection<Document> collection = database.getCollection("sampleCollection");
	System.out.println("Collection sampleCollection selected successfully");
	Document document = new Document("title", "MongoDB")
	.append("description", "database")
	.append("likes", 100)
	.append("url", "http://www.tutorialspoint.com/mongodb/")
	.append("by", "tutorials point");

	//Inserting document into the collection
	collection.insertOne(document);
	System.out.println("Document inserted successfully");
}

在编译程序后，你会得到以下结果−

Connected to the database successfully
Collection sampleCollection selected successfully
Document inserted successfully

Retrieve All Documents

为了从集合中选择所有文档，使用 com.mongodb.client.MongoCollection 类的 find() 方法。此方法返回一个游标，所以你需要遍历此游标。

以下是用于选择所有文档的程序−

import com.mongodb.client.FindIterable;
import com.mongodb.client.MongoCollection;
import com.mongodb.client.MongoDatabase;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import org.bson.Document;
import com.mongodb.MongoClient;
import com.mongodb.MongoCredential;
public class RetrievingAllDocuments {
	public static void main( String args[] ) {

		// Creating a Mongo client
		MongoClient mongo = new MongoClient( "localhost" , 27017 );

		// Creating Credentials
		MongoCredential credential;
		credential = MongoCredential.createCredential("sampleUser", "myDb", "password".toCharArray());
		System.out.println("Connected to the database successfully");

		// Accessing the database
		MongoDatabase database = mongo.getDatabase("myDb");

		// Retrieving a collection
		MongoCollection<Document> collection = database.getCollection("sampleCollection");
		System.out.println("Collection sampleCollection selected successfully");
		Document document1 = new Document("title", "MongoDB")
		.append("description", "database")
		.append("likes", 100)
		.append("url", "http://www.tutorialspoint.com/mongodb/")
		.append("by", "tutorials point");
		Document document2 = new Document("title", "RethinkDB")
		.append("description", "database")
		.append("likes", 200)
		.append("url", "http://www.tutorialspoint.com/rethinkdb/")
		.append("by", "tutorials point");
		List<Document> list = new ArrayList<Document>();
		list.add(document1);
		list.add(document2);
		collection.insertMany(list);
		// Getting the iterable object
		FindIterable<Document> iterDoc = collection.find();
		int i = 1;
		// Getting the iterator
		Iterator it = iterDoc.iterator();
		while (it.hasNext()) {
			System.out.println(it.next());
			i++;
		}
	}
}

在编译程序后，你会得到以下结果−

Connected to the database successfully
Collection sampleCollection selected successfully
Document{{_id=5dce4e9ff68a9c2449e197b2, title=MongoDB, description=database, likes=100, url=http://www.tutorialspoint.com/mongodb/, by=tutorials point}}
Document{{_id=5dce4e9ff68a9c2449e197b3, title=RethinkDB, description=database, likes=200, url=http://www.tutorialspoint.com/rethinkdb/, by=tutorials point}}

Update Document

为了从集合中更新一个文档，使用 com.mongodb.client.MongoCollection 类的 updateOne() 方法。

以下是用于选择第一个文档的程序−

import com.mongodb.client.FindIterable;
import com.mongodb.client.MongoCollection;
import com.mongodb.client.MongoDatabase;
import com.mongodb.client.model.Filters;
import com.mongodb.client.model.Updates;
import java.util.Iterator;
import org.bson.Document;
import com.mongodb.MongoClient;
import com.mongodb.MongoCredential;
public class UpdatingDocuments {

   public static void main( String args[] ) {

      // Creating a Mongo client
      MongoClient mongo = new MongoClient( "localhost" , 27017 );

      // Creating Credentials
      MongoCredential credential;
      credential = MongoCredential.createCredential("sampleUser", "myDb",
         "password".toCharArray());
      System.out.println("Connected to the database successfully");

      // Accessing the database
      MongoDatabase database = mongo.getDatabase("myDb");
      // Retrieving a collection
      MongoCollection<Document> collection = database.getCollection("sampleCollection");
      System.out.println("Collection myCollection selected successfully");
      collection.updateOne(Filters.eq("title", 1), Updates.set("likes", 150));
      System.out.println("Document update successfully...");

      // Retrieving the documents after updation
      // Getting the iterable object
      FindIterable<Document> iterDoc = collection.find();
      int i = 1;
      // Getting the iterator
      Iterator it = iterDoc.iterator();
      while (it.hasNext()) {
         System.out.println(it.next());
         i++;
      }
   }
}

在编译程序后，你会得到以下结果−

Connected to the database successfully
Collection myCollection selected successfully
Document update successfully...
Document{{_id=5dce4e9ff68a9c2449e197b2, title=MongoDB, description=database, likes=100, url=http://www.tutorialspoint.com/mongodb/, by=tutorials point}}
Document{{_id=5dce4e9ff68a9c2449e197b3, title=RethinkDB, description=database, likes=200, url=http://www.tutorialspoint.com/rethinkdb/, by=tutorials point}}

Delete a Document

为了从集合中删除一个文档，你需要使用 com.mongodb.client.MongoCollection 类的 deleteOne() 方法。

以下是用于删除一个文档的程序−

import com.mongodb.client.FindIterable;
import com.mongodb.client.MongoCollection;
import com.mongodb.client.MongoDatabase;
import com.mongodb.client.model.Filters;
import java.util.Iterator;
import org.bson.Document;
import com.mongodb.MongoClient;
import com.mongodb.MongoCredential;
public class DeletingDocuments {

   public static void main( String args[] ) {

      // Creating a Mongo client
      MongoClient mongo = new MongoClient( "localhost" , 27017 );

      // Creating Credentials
      MongoCredential credential;
      credential = MongoCredential.createCredential("sampleUser", "myDb",
         "password".toCharArray());
      System.out.println("Connected to the database successfully");

      // Accessing the database
      MongoDatabase database = mongo.getDatabase("myDb");
      // Retrieving a collection
      MongoCollection<Document> collection = database.getCollection("sampleCollection");
      System.out.println("Collection sampleCollection selected successfully");
      // Deleting the documents
      collection.deleteOne(Filters.eq("title", "MongoDB"));
      System.out.println("Document deleted successfully...");

      // Retrieving the documents after updation
      // Getting the iterable object
      FindIterable<Document> iterDoc = collection.find();
      int i = 1;
      // Getting the iterator
      Iterator it = iterDoc.iterator();
      while (it.hasNext()) {
         System.out.println(it.next());
         i++;
      }
   }
}

在编译程序后，你会得到以下结果−

Connected to the database successfully
Collection sampleCollection selected successfully
Document deleted successfully...
Document{{_id=5dce4e9ff68a9c2449e197b3, title=RethinkDB, description=database, likes=200, url=http://www.tutorialspoint.com/rethinkdb/, by=tutorials point}}

Dropping a Collection

为了从数据库中删除一个集合，你需要使用 com.mongodb.client.MongoCollection 类的 drop() 方法。

以下是删除集合的程序——

import com.mongodb.client.MongoCollection;
import com.mongodb.client.MongoDatabase;
import org.bson.Document;
import com.mongodb.MongoClient;
import com.mongodb.MongoCredential;
public class DropingCollection {

   public static void main( String args[] ) {
      // Creating a Mongo client
      MongoClient mongo = new MongoClient( "localhost" , 27017 );
      // Creating Credentials
      MongoCredential credential;
      credential = MongoCredential.createCredential("sampleUser", "myDb",
         "password".toCharArray());
      System.out.println("Connected to the database successfully");

      // Accessing the database
      MongoDatabase database = mongo.getDatabase("myDb");

      // Creating a collection
      System.out.println("Collections created successfully");
      // Retrieving a collection
      MongoCollection<Document> collection = database.getCollection("sampleCollection");
      // Dropping a Collection
      collection.drop();
      System.out.println("Collection dropped successfully");
   }
}

在编译程序后，你会得到以下结果−

Connected to the database successfully
Collection sampleCollection selected successfully
Collection dropped successfully

Listing All the Collections

若要列出数据库中的所有集合，则需要使用 com.mongodb.client.MongoDatabase 类的 listCollectionNames() 方法。

以下是列出数据库内所有集合的程序——

import com.mongodb.client.MongoDatabase;
import com.mongodb.MongoClient;
import com.mongodb.MongoCredential;
public class ListOfCollection {

   public static void main( String args[] ) {

      // Creating a Mongo client
      MongoClient mongo = new MongoClient( "localhost" , 27017 );
      // Creating Credentials
      MongoCredential credential;
      credential = MongoCredential.createCredential("sampleUser", "myDb",
         "password".toCharArray());
      System.out.println("Connected to the database successfully");

      // Accessing the database
      MongoDatabase database = mongo.getDatabase("myDb");
      System.out.println("Collection created successfully");
      for (String name : database.listCollectionNames()) {
         System.out.println(name);
      }
   }
}

在编译程序后，你会得到以下结果−

Connected to the database successfully
Collection created successfully
myCollection
myCollection1
myCollection5

其余的 MongoDB 方法 save(), limit(), skip(), sort() 等与后续教程中解释的相同。