How to Start a Spring Boot Application Without Database Dependency?

Starting Spring Boot Application Without Database Dependency

When working with Spring Boot applications that utilize databases, encountering errors when the database is unavailable can be frustrating. To overcome this issue, the application should be configured to start successfully even if the database is not accessible.

Cause of the Original Error

The error encountered during the initial attempt to start the Spring Boot application without the database stems from Hibernate and its reliance on metadata from the database to determine the table structure and relationships. When the database is not available, Hibernate fails to obtain the necessary metadata, resulting in the error.

Solution: Configuring Spring Boot and Hibernate

To address this issue, configure the following properties in the application.yml file:

spring:
  datasource:
    continueOnError: true
    initialize: false
    initialSize: 0
    timeBetweenEvictionRunsMillis: 5000
    minEvictableIdleTimeMillis: 5000
    minIdle: 0

  jpa:
    show-sql: true
    hibernate:
      ddl-auto: none
      naming_strategy: org.hibernate.cfg.DefaultNamingStrategy
    properties:
      hibernate:
        dialect: org.hibernate.dialect.MySQL5Dialect
        hbm2ddl:
          auto: none
        temp:
          use_jdbc_metadata_defaults: false

• spring.datasource.continueOnError: This property tells Spring to continue starting the application even if there is an error initializing the data source.
• spring.datasource.initialize: This property specifies whether to initialize the data source on startup. Setting it to false means the data source will not be initialized until a connection is actually attempted.
• spring.datasource.initialSize: This property sets the initial number of connections to establish at startup. Setting it to 0 means no connections will be established at startup.
• spring.datasource.timeBetweenEvictionRunsMillis: This property determines how often (in milliseconds) the data source will check for idle connections to evict.
• spring.datasource.minEvictableIdleTimeMillis: This property sets the minimum amount of time (in milliseconds) an idle connection can remain in the pool before it is eligible for eviction.
• spring.datasource.minIdle: This property sets the minimum number of idle connections to keep in the pool.
• spring.jpa.hibernate.ddl-auto: This property sets the action Hibernate will take on the database schema. Setting it to none means no changes should be made to the database schema.
• spring.jpa.hibernate.dialect: This property specifies the Hibernate dialect to use. Using the appropriate dialect ensures that Hibernate generates SQL that is compatible with the database.
• spring.jpa.hibernate.properties.hibernate.temp.use_jdbc_metadata_defaults: This property specifies whether Hibernate should use JDBC metadata to determine the table structure and relationships. Setting it to false prevents Hibernate from relying on the database and instead uses the mapping annotations in the domain classes to define the entities.

Benefits of the Solution

By implementing these configurations, the Spring Boot application:

• Starts successfully even when the database is unavailable.
• Establishes connections on the fly when the database becomes available, eliminating the need for restarts.
• Gracefully handles database outages without affecting the running application.

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