How to create multiple database connections for different databases in java

There are multiple ways you can achieve this:

1. If you are using any Java EE container which supports distributed transaction then you can use there functionality.
2. If you are with plain JDBC then you will have to maintain your own connection for every database. For JDBC:
   1. Provide all connection details
   2. Have an Facade which gives you desired object by calling a abstract generic DAO.
   3. Have a factory which creates dao based on connection.
3. Use ORM tools like Hibernate, where you can use configuration for multiple database. Tutorial.
4. If you are using Spring, then you can configure one datasource per database. Docs

Design Patterns:

• Facade Pattern - for hiding the complexity and multiple database usage.
• Factory - In case you manage the database connection yourself.
• Singleton - For datasources

As you have not tagged your question with any of this, hibernate, JPA, ORM, I assume you are dealing with plain JDBC.

Having said that, I suggest you to have a DAO layer to deal with underlying databases, and leave the connection details to specific implementations. You can configure your connection strings in some .properties files, lets say.

[Complement]

You can also make use of DAO factory, an implementation of Abstract Factory or Factory Method pattern, whichever suits here.

[Links]

• A very fine implementation of DAO and DAO Factory, by BalusC
• Core J2EE Patterns -- arguably dated but might provide some idea.

You can handle multiple connections easily using a ORM tool like Hibernate.. You can specify each connection in a separate configuration file and instantiate the required connection by getting a new session factory each time.

Other way would be to use datasource and JNDI : Java connecting to multiple databases

I think you can use a combination of Factory pattern and Singleton pattern for the purpose.