Code sharing of MongoDB usage guide in Java

MongoDB is a very popular NoSQL database today. This article introduces how to use MongoDB's Java driver to operate MongoDB.

1. Introduce the MongoDB Java Driver package

If the Java project that needs to operate MongoDB is a Maven project, you can add the following configuration to the dependencies.

<dependencies>
    <dependency>
        <groupId>org.mongodb</groupId>
        <artifactId>mongo-java-driver</artifactId>
        <version>2.13.2</version>
    </dependency>
</dependencies>

Or use it by directly downloading the jar package, download address: mongo-java-driver-2.13.2.jar.

For detailed information on how to introduce the MongoDB jar package, please refer to the official documentation.

2. Connect to MongoDB

You can use MongoClient to connect to MongoDB. The usage of MongoClient is as follows:

MongoClient mongoClient = new MongoClient("localhost", 27017);
DB db = mongoClient.getDB("mydb");

above The code connects to the MongoDB service on localhost:27017 and specifies to use the mydb database. After connecting, you can perform further operations on this database.

It should be pointed out that MongoClient is thread safe and can share the same MongoClient in a multi-process environment. Generally speaking, in an application, you only need to generate a global MongoClient instance, and then use this instance in other places in the program.

3. Authentication

You can use multiple methods to authenticate connections. Two methods are introduced below.

1. Method 1: The

createCredential

method of the MongoCredentialMongoCredential class can specify the authentication user name, password, and database used, and Returns a MongoCredentialobject. The method is declared as follows:

static MongoCredential createCredential(String userName, String database, char[] password)

For example,

MongoCredential credential = MongoCredential.createCredential("user", "mydb", "password".toCharArray();

The above creates a MongoCredential object with the user name user, password password, and database mydb.

The generated MongoCredential object will be used as the parameter of the MongoClient constructor function. Since the MongoClient constructor is of <a href="http://www.php.cn/wiki/1059.html" target="_blank">List</a><MongoCredential> type, it needs to be constructed into a List first and then passed. A complete authentication example is as follows:

MongoCredential credential = MongoCredential.createCredential("user", "mydb", "password".toCharArray()); 
ServerAddress serverAddress = new ServerAddress("localhost", 27017); 
MongoClient mongoClient = new MongoClient(serverAddress, Arrays.asList(credential)); 
DB db = mongoClient.getDB("mydb");

2. Method 2: MongoClientURI

You can also use MongoClientURI to complete MongoDB authentication, which represents a URI object. The constructor of MongoClientURI accepts a string of type String. The format of this string is as follows:

mongodb://[username:password@]host1[:port1][,host2[:port2],…[,hostN[:portN]]][/[database][?options]]

The generated MongoClientURI object is used as MongoClientThe parameters of the constructor, the complete authentication example is as follows:

String sURI = String.format("mongodb://%s:%s@%s:%d/%s", "user", "password", "localhost", 27017, "mydb"); 
MongoClientURI uri = new MongoClientURI(sURI); 
MongoClient mongoClient = new MongoClient(uri); 
DB db = mongoClient.getDB("mydb");

4. Obtain a collection

DBCollection coll = db.getCollection("mycol");

Then you can operate on the specified collection, for example, insert, Delete , search, update documents, etc.

5. Insert document

For example, a document is represented by Json as follows,

{ “name”: “mongo”, “info”: { “ver”: “3.0” } }

now needs to be inserted into the collection mycol. To insert into a collection, a document can be constructed using BasicDB<a href="http://www.php.cn/wiki/60.html" target="_blank">Object</a>.

BasicDBObject doc = new BasicDBObject("name", "mongo").append("info", new BasicDBObject("ver", "3.0"));
coll.insert(doc);

6. Find documents

1. Find a document that meets the conditions through findOne

You can find a document that meets the conditions through findOne. For example, for the mycol collection above, executing the following command:

DBObject myDoc = coll.findOne();
System.out.println(myDoc);

will output the first document in the mycol collection. You can also find a document that meets the search conditions by specifying the search parameters of findOne.

2. Find all documents that meet the conditions through find

find is used to find documents that meet the conditions. It returns a DBCursor object, through Traverse the DBCursor object to obtain all documents that meet the search conditions.
For explanation and testing, we first insert a batch of documents in the following format

{ “i”: value }

for (int i=0; i < 100; i++) {
    coll.insert(new BasicDBObject("i", i));
}

findUsage examples are as follows:

DBCursor cursor = coll.find();
try {
   while(cursor.hasNext()) {
       System.out.println(cursor.next());
   }
} finally {
   cursor.close();
}

will Output all documents in the mycol collection.

You can also specify the search conditions, for example:

BasicDBObject query = new BasicDBObject("i", 71);

DBCursor cursor = coll.find(query);

try {
   while(cursor.hasNext()) {
       System.out.println(cursor.next());
   }
} finally {
   cursor.close();
}

For the case where the search conditions include $operator, for example, the following mongo shell command:

db.coll.find({i: {$gte: 50}});

You can use DBObject to generate search conditions,

// find all where i >= 50
BasicDBObject query = new BasicDBObject("i", new BasicDBObject("$gte", 50));

DBCursor cursor = coll.find(query);
try {
    while (cursor.hasNext()) {
        System.out.println(cursor.next());
    }
} finally {
    cursor.close();
}

7. Update the document

BasicDBObject query = new BasicDBObject("i", 70);
BasicDBObject up = new BasicDBObject("$set", new BasicDBObject("i", 100));
coll.update(query, up);

The above statement updates the document with i=70 to the value of i equal to 100.

与我们常用的更新文档的mongo语句一样，DBCollection还包含了save，findAndModify等更新文档的方法，其使用方法在此不再赘述，可以参考API说明文档即可。

八、删除文档

可以通过生成一个DBObject对象来删除指定的文档，例如：

BasicDBObject query = new BasicDBObject("i", 71);
coll.remove(query);

上面的语句删除i为71的文档。

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