Configuring Tomcat Connection pool and Hikari Connection pool in Spring Boot Application

One key component of spring boot starter dependencies is spring-boot-starter-data-JPA. This allows us to use JPA and work with production databases by using some popular JDBC connection pooling implementations, such as HikariCP or Tomcat JDBC Connection Pool.

Tomcat Connection Pooling

Spring Boot will look for HikariCP on the classpath and use it by default when present.

To configure a Tomcat JDBC connection pool instead of the default HikariCP, we'll exclude HikariCP from the spring-boot-starter-data-JPA dependency and add the tomcat-JDBC Maven dependency.

Maven (pom.xml)

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-jpa</artifactId>
    <exclusions>
        <exclusion>
            <groupId>com.zaxxer</groupId>
            <artifactId>HikariCP</artifactId>
        </exclusion>
    </exclusions>
</dependency>
<dependency>
    <groupId>org.apache.tomcat</groupId>
    <artifactId>tomcat-jdbc</artifactId>
</dependency>

Gradle (build.gradle)

implementation('org.springframework.boot:spring-boot-starter-data-jpa') {
    exclude group: 'com.zaxxer', module: 'HikariCP'
}
implementation('org.apache.tomcat:tomcat-jdbc')

For optimizing its performance we can add additional properties 

# initialSize is the number of initial connections 
# created when the pool is started
spring.datasource.tomcat.initial-size=10
# maxWait is the maximum number of milliseconds 
# that the pool waits to return a connection 
# before throwing an exception.
spring.datasource.tomcat.max-wait=15000
# maxActive is the maximum number of active 
# connections that the pool can allocate at 
# the same time.
spring.datasource.tomcat.max-active=40
#maxIdle is the maximum number of connections 
# that should remain in the pool at any time
spring.datasource.tomcat.max-idle=15
# minIdle is the minimum number of connections 
# that should remain in the pool at any time.
spring.datasource.tomcat.min-idle=8
# The defaultAutoCommit property is used to 
# configure the default autocommit state of 
# connections created by this pool.
spring.datasource.tomcat.default-auto-commit=true

Please notice that we've configured a few additional connection pooling properties, such as the pool's initial size, and the maximum and the minimum number of idle connections.

How to know which connection pool is used?

@SpringBootApplication
public class KnowledgefactorydemoApplication 
                           implements CommandLineRunner {
  
    @Autowired
    private DataSource dataSource;
    public static void main(String[] args) {
        SpringApplication.
                 run(KnowledgefactorydemoApplication.class, args);
    }
    @Override
    public void run(String...args) throws Exception {
        System.out.println("DATASOURCE = " + dataSource);
    }

Start  Spring boot application 

On the console system will print,
         "DATASOURCE = class org.apache.tomcat.jdbc.pool.DataSource"

Hikari Connection Pooling

Spring Boot will look for HikariCP on the classpath and use it by default when present

Maven (pom.xml)

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>

Gradle (build.gradle)

implementation('org.springframework.boot:spring-boot-starter-data-jpa')

One of Hikari's advantages over other DataSource implementations is the fact that it offers a lot of configuration parameters.

We can specify the values for these parameters by using the prefix spring.datasource.hikari and appending the name of the Hikari parameter:

For optimizing its performance we can add additional properties 

# maximum number of milliseconds that a client 
# will wait for a connection
spring.datasource.hikari.connection-timeout = 20000 
# minimum number of idle connections maintained 
# by HikariCP in a connection pool
spring.datasource.hikari.minimum-idle= 10 
# maximum pool size
spring.datasource.hikari.maximum-pool-size= 10 
# maximum idle time for connection
spring.datasource.hikari.idle-timeout=10000 
# maximum lifetime in milliseconds of 
# a connection in the pool after it is closed.
spring.datasource.hikari.max-lifetime= 1000 
#default auto-commit behavior.
spring.datasource.hikari.auto-commit =true 

How to know which connection pool is used?

@SpringBootApplication
public class KnowledgefactorydemoApplication 
                    implements CommandLineRunner {
    @Autowired
    private DataSource dataSource;
    public static void main(String[] args) {
        SpringApplication.
                run(KnowledgefactorydemoApplication.class, args);
    }
    @Override
    public void run(String...args) throws Exception {
        System.out.println("DATASOURCE = " + dataSource);
    }

Start  Spring boot application

At the console, the system will print,

"DATASOURCE = class com.zaxxer.hikari.HikariDataSource"

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