无法创建池的初始连接，无法获取 JDBC 连接错误

Question

I have a Spring Boot data JPA application where I am creating two data sources. I am getting this error when my application is booting up.

1. org.apache.tomcat.jdbc.pool.ConnectionPool init
SEVERE: Unable to create initial connections of pool.
java.sql.SQLException
    at org.apache.tomcat.jdbc.pool.PooledConnection.connectUsingDriver(PooledConnection.java:253)
2. Caused by: java.lang.NullPointerException
    at java.lang.Class.forName0(Native Method)
    at java.lang.Class.forName(Class.java:348)
    at org.apache.tomcat.jdbc.pool.PooledConnection.connectUsingDriver(PooledConnection.java:245)
    ... 88 more

3. Jan 20, 2020 7:39:29 PM org.hibernate.engine.jdbc.spi.SqlExceptionHelper logExceptions
ERROR: null
[http-bio-8080-exec-1] ERROR org.springframework.boot.web.support.ErrorPageFilter - Forwarding to error page from request [/orderForDateTopK/1/2] due to exception [Could not open JPA EntityManager for transaction; nested exception is javax.persistence.PersistenceException: org.hibernate.exception.GenericJDBCException: Unable to acquire JDBC Connection]
org.springframework.transaction.CannotCreateTransactionException: Could not open JPA EntityManager for transaction; nested exception is javax.persistence.PersistenceException: org.hibernate.exception.GenericJDBCException: Unable to acquire JDBC Connection
    at org.springframework.orm.jpa.JpaTransactionManager.doBegin(JpaTransactionManager.java:431)
    at org.springframework.transaction.support.AbstractPlatformTransactionManager.getTransaction(AbstractPlatformTransactionManager.java:373)

4. Caused by: javax.persistence.PersistenceException: org.hibernate.exception.GenericJDBCException: Unable to acquire JDBC Connection
    at org.hibernate.jpa.spi.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1692)

5. Caused by: org.hibernate.exception.GenericJDBCException: Unable to acquire JDBC Connection

Answer 1

You're using Tomcat JDBC Connection Pool for your datasource, but in your application.properties you configured connection pool for Hikari datasource.

Your datasource is not instanced well, because of the connection pool settings.

your wrong configuration:

#HikariCP settings
spring.datasource.hikari.connection-timeout=60000
spring.datasource.hikari.maximum-pool-size=15
spring.datasource.hikari.minimum-idle=1

---

You have 2 solutions

1- Change your connection pool settings from hikari to tomcat

like so

spring.datasource.tomcat.initial-size=
spring.datasource.tomcat.max-wait=
spring.datasource.tomcat.max-active=
spring.datasource.tomcat.max-idle=
spring.datasource.tomcat.min-idle=
spring.datasource.tomcat.default-auto-commit=
//..

Some useful guide in this field:

Configuring a Tomcat Connection Pool

2- Use Hikari Connection Pool instead of tomcat (Change datasource connection pool)

Some useful guide in this field:

A Simple Guide to Connection Pooling in Java

Introduction to HikariCP