MongoDB - Java

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在本节中，我们将学习如何设置 MongoDB 客户端。

安装

在您的 Java 程序中开始使用 MongoDB 之前，您需要确保机器上已安装 MongoDB 客户端和 Java。您可以查看 Java 教程，了解如何在您的机器上安装 Java。现在，让我们检查如何设置 MongoDB 客户端。

  • 您需要下载 jar 文件 **mongodb-driver-3.11.2.jar 及其依赖项 mongodb-driver-core-3.11.2.jar**。请确保下载这些 jar 文件的最新版本。

  • 您需要将下载的 jar 文件包含到您的类路径中。

连接到数据库

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

以下是连接到数据库的代码片段：

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

执行后，上述程序会给出以下输出。

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

创建集合

要创建集合，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"); 
   } 
}

编译后，上述程序会给出以下结果：

Connected to the database successfully 
Collection created successfully

获取/选择集合

要从数据库中获取/选择集合，使用 **com.mongodb.client.MongoDatabase** 类的 **getCollection()** 方法。

以下是获取/选择集合的程序：

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"); 
   }
}

编译后，上述程序会给出以下结果：

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

插入文档

要将文档插入 MongoDB，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", "https://tutorialspoint.com/mongodb/")
	.append("by", "tutorials point");
	
	//Inserting document into the collection
	collection.insertOne(document);
	System.out.println("Document inserted successfully");
}

编译后，上述程序会给出以下结果：

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

检索所有文档

要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，因此您需要迭代此游标。

以下是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", "https://tutorialspoint.com/mongodb/")
		.append("by", "tutorials point");
		Document document2 = new Document("title", "RethinkDB")
		.append("description", "database")
		.append("likes", 200)
		.append("url", "https://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++;
		}
	}
}

编译后，上述程序会给出以下结果：

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

更新文档

要更新集合中的文档，使用 **com.mongodb.client.MongoCollection** 类的 **updateOne()** 方法。

以下是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++; 
      }     
   }  
}

编译后，上述程序会给出以下结果：

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

删除文档

要从集合中删除文档，您需要使用 **com.mongodb.client.MongoCollection** 类的 **deleteOne()** 方法。

以下是删除文档的程序：

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++; 
      }       
   } 
}

编译后，上述程序会给出以下结果：

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

删除集合

要从数据库中删除集合，您需要使用 **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");
   } 
}

编译后，上述程序会给出以下结果：

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

列出所有集合

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

以下是列出数据库所有集合的程序：

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); 
      } 
   }
}

编译后，上述程序会给出以下结果：

Connected to the database successfully 
Collection created successfully 
myCollection 
myCollection1 
myCollection5

其余 MongoDB 方法 **save()、limit()、skip()、sort()** 等的工作方式与后续教程中解释的相同。

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