6. Spring JDBC

Spring Cloud GCP adds integrations with Spring JDBC so you can run your MySQL or PostgreSQL databases in Google Cloud SQL using Spring JDBC, or other libraries that depend on it like Spring Data JPA.

The Cloud SQL support is provided by Spring Cloud GCP in the form of two Spring Boot starters, one for MySQL and another one for PostgreSQL. The role of the starters is to read configuration from properties and assume default settings so that user experience connecting to MySQL and PostgreSQL is as simple as possible.

Maven coordinates, using Spring Cloud GCP BOM:


Gradle coordinates:

dependencies {
    compile group: 'org.springframework.cloud', name: 'spring-cloud-gcp-starter-sql-mysql'
    compile group: 'org.springframework.cloud', name: 'spring-cloud-gcp-starter-sql-postgresql'

6.1 Prerequisites

In order to use the Spring Boot Starters for Google Cloud SQL, the Google Cloud SQL API must be enabled in your GCP project.

To do that, go to the API library page of the Google Cloud Console, search for "Cloud SQL API", click the first result and enable the API.


There are several similar "Cloud SQL" results. You must access the "Google Cloud SQL API" one and enable the API from there.

6.2 Spring Boot Starter for Google Cloud SQL

The Spring Boot Starters for Google Cloud SQL provide an auto-configured DataSource object. Coupled with Spring JDBC, it provides a JdbcTemplate object bean that allows for operations such as querying and modifying a database.

public List<Map<String, Object>> listUsers() {
    return jdbcTemplate.queryForList("SELECT * FROM user;");

You can rely on Spring Boot data source auto-configuration to configure a DataSource bean. In other words, properties like the SQL username, spring.datasource.username, and password, spring.datasource.password can be used. There is also some configuration specific to Google Cloud SQL:

Property name


Default value

Unused if specified property(ies)


Enables or disables Cloud SQL auto configuration




Name of the database to connect to.




A string containing a Google Cloud SQL instance’s project ID, region and name, each separated by a colon. For example, my-project-id:my-region:my-instance-name.




File system path to the Google OAuth2 credentials private key file. Used to authenticate and authorize new connections to a Google Cloud SQL instance.

Default credentials provided by the Spring GCP Boot starter



Base64-encoded contents of OAuth2 account private key in JSON format. Used to authenticate and authorize new connections to a Google Cloud SQL instance.

Default credentials provided by the Spring GCP Boot starter


6.2.1 DataSource creation flow

Based on the previous properties, the Spring Boot starter for Google Cloud SQL creates a CloudSqlJdbcInfoProvider object which is used to obtain an instance’s JDBC URL and driver class name. If you provide your own CloudSqlJdbcInfoProvider bean, it is used instead and the properties related to building the JDBC URL or driver class are ignored.

The DataSourceProperties object provided by Spring Boot Autoconfigure is mutated in order to use the JDBC URL and driver class names provided by CloudSqlJdbcInfoProvider, unless those values were provided in the properties. It is in the DataSourceProperties mutation step that the credentials factory is registered in a system property to be SqlCredentialFactory.

DataSource creation is delegated to Spring Boot. You can select the type of connection pool (e.g., Tomcat, HikariCP, etc.) by adding their dependency to the classpath.

Using the created DataSource in conjunction with Spring JDBC provides you with a fully configured and operational JdbcTemplate object that you can use to interact with your SQL database. You can connect to your database with as little as a database and instance names.

6.2.2 Troubleshooting tips

Connection issues

If you’re not able to connect to a database and see an endless loop of Connecting to Cloud SQL instance […​] on IP […​], it’s likely that exceptions are being thrown and logged at a level lower than your logger’s level. This may be the case with HikariCP, if your logger is set to INFO or higher level.

To see what’s going on in the background, you should add a logback.xml file to your application resources folder, that looks like this:

<?xml version="1.0" encoding="UTF-8"?>
  <include resource="org/springframework/boot/logging/logback/base.xml"/>
  <logger name="com.zaxxer.hikari.pool" level="DEBUG"/>

Errors like c.g.cloud.sql.core.SslSocketFactory : Re-throwing cached exception due to attempt to refresh instance information too soon after error

If you see a lot of errors like this in a loop and can’t connect to your database, this is usually a symptom that something isn’t right with the permissions of your credentials or the Google Cloud SQL API is not enabled. Verify that the Google Cloud SQL API is enabled in the Cloud Console and that your service account has the necessary IAM roles.

To find out what’s causing the issue, you can enable DEBUG logging level as mentioned above.

PostgreSQL: java.net.SocketException: already connected issue

We found this exception to be common if your Maven project’s parent is spring-boot version 1.5.x, or in any other circumstance that would cause the version of the org.postgresql:postgresql dependency to be an older one (e.g., 9.4.1212.jre7).

To fix this, re-declare the dependency in its correct version. For example, in Maven:


6.3 Samples

Available sample applications and codelabs: