MongoDB: Caused by: java.net.ConnectException: Connection refused: no further information at java.base/sun.nio.ch.Net.pollConnect(Native Method)

>PROBLEM

Starting a project using Maven, JEE/Spring, and MongoDB driver (mongo-java-driver) throws the following exception:

...[cluster-ClusterId{value='62586e27f362ec2cd1336bda', description='null'}-localhost:27027] # INFO  # org.mongodb.driver.cluster # method: info # Exception in monitor thread while connecting to server localhost:27027

com.mongodb.MongoSocketOpenException: Exception opening socket

...

Caused by: java.net.ConnectException: Connection refused: no further information at java.base/sun.nio.ch.Net.pollConnect(Native Method)

>SOLUTION

Although connection refusal may have many causes, this post will treat one of them that maybe it is your issue.

The "mongo-java-driver" tries to start MongoDB connection automatically as soon as the application starts if it finds MongoDB's configuration in .properties or .yml files.

It happens when we start a project using this default feature but later we decide to customize it, and there is no need for this feature anymore.

So, just remove or comment on the lines in the configuration file. 

For instance, if .yml, do this:

spring:

profiles: prod

jpa:
database: default
#  data:
#    mongodb:
#      host: localhost
#      port: 27027
#      database: mydatabase

If .properties:

#spring.data.mongodb.host=localhost
#spring.data.mongodb.port=27017
#spring.data.mongodb.database=mydatabase

>ENV

SpriingBoot 2.X
Java 17
MongoDB 5

- pom.xml:

<dependency>

<groupId>org.springframework.data</groupId>

<artifactId>spring-data-mongodb</artifactId>

</dependency>

<dependency>

<groupId>org.springframework.boot</groupId>

<artifactId>spring-boot-starter-data-mongodb</artifactId>

</dependency>

<dependency>

<groupId>org.mongodb</groupId>

<artifactId>mongo-java-driver</artifactId>

<version>3.12.10</version>

</dependency>