The Spring Framework provides extensive support for working with SQL databases. From
direct JDBC access using JdbcTemplate
to complete ‘object relational mapping’
technologies such as Hibernate. Spring Data provides an additional level of functionality,
creating Repository
implementations directly from interfaces and using conventions to
generate queries from your method names.
Java’s javax.sql.DataSource
interface provides a standard method of working with
database connections. Traditionally a DataSource uses a URL
along with some
credentials to establish a database connection.
It’s often convenient to develop applications using an in-memory embedded database. Obviously, in-memory databases do not provide persistent storage; you will need to populate your database when your application starts and be prepared to throw away data when your application ends.
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The ‘How-to’ section includes a section on how to initialize a database |
Spring Boot can auto-configure embedded H2, HSQL and Derby databases. You don’t need to provide any connection URLs, simply include a build dependency to the embedded database that you want to use.
For example, typical POM dependencies would be:
<dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-data-jpa</artifactId> </dependency> <dependency> <groupId>org.hsqldb</groupId> <artifactId>hsqldb</artifactId> <scope>runtime</scope> </dependency>
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If, for whatever reason, you do configure the connection URL for an embedded
database, care should be taken to ensure that the database’s automatic shutdown is
disabled. If you’re using H2 you should use |
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You need a dependency on |
Production database connections can also be auto-configured using a pooling DataSource
.
Here’s the algorithm for choosing a specific implementation:
DataSource
for its performance and concurrency, so if
that is available we always choose it.If you use the spring-boot-starter-jdbc
or spring-boot-starter-data-jpa
‘starter POMs’ you will automatically get a dependency to tomcat-jdbc
.
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You can bypass that algorithm completely and specify the connection pool to use via
the |
DataSource configuration is controlled by external configuration properties in
spring.datasource.*
. For example, you might declare the following section in
application.properties
:
spring.datasource.url=jdbc:mysql://localhost/test spring.datasource.username=dbuser spring.datasource.password=dbpass spring.datasource.driver-class-name=com.mysql.jdbc.Driver
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You often won’t need to specify the |
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For a pooling |
See DataSourceProperties
for more of the supported options. These are the standard options that work regardless of
the actual implementation. It is also possible to fine tune implementation-specific settings
using the spring.datasource.*
prefix, refer to the documentation of the connection pool
implementation you are using for more details.
For instance, if you are using the Tomcat connection pool you could customize many additional settings:
# Number of ms to wait before throwing an exception if no connection is available. spring.datasource.max-wait=10000 # Maximum number of active connections that can be allocated from this pool at the same time. spring.datasource.max-active=50 # Validate the connection before borrowing it from the pool. spring.datasource.test-on-borrow=true
If you are deploying your Spring Boot application to an Application Server you might want to configure and manage your DataSource using your Application Servers built-in features and access it using JNDI.
The spring.datasource.jndi-name
property can be used as an alternative to the
spring.datasource.url
, spring.datasource.username
and spring.datasource.password
properties to access the DataSource
from a specific JNDI location. For example, the
following section in application.properties
shows how you can access a JBoss AS defined
DataSource
:
spring.datasource.jndi-name=java:jboss/datasources/customers
Spring’s JdbcTemplate
and NamedParameterJdbcTemplate
classes are auto-configured and
you can @Autowire
them directly into your own beans:
import org.springframework.beans.factory.annotation.Autowired; import org.springframework.jdbc.core.JdbcTemplate; import org.springframework.stereotype.Component; @Component public class MyBean { private final JdbcTemplate jdbcTemplate; @Autowired public MyBean(JdbcTemplate jdbcTemplate) { this.jdbcTemplate = jdbcTemplate; } // ... }
The Java Persistence API is a standard technology that allows you to ‘map’ objects to
relational databases. The spring-boot-starter-data-jpa
POM provides a quick way to get
started. It provides the following key dependencies:
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We won’t go into too many details of JPA or Spring Data here. You can follow the ‘Accessing Data with JPA’ guide from spring.io and read the Spring Data JPA and Hibernate reference documentation. |
Traditionally, JPA ‘Entity’ classes are specified in a persistence.xml
file. With
Spring Boot this file is not necessary and instead ‘Entity Scanning’ is used. By default
all packages below your main configuration class (the one annotated with
@EnableAutoConfiguration
or @SpringBootApplication
) will be searched.
Any classes annotated with @Entity
, @Embeddable
or @MappedSuperclass
will be
considered. A typical entity class would look something like this:
package com.example.myapp.domain; import java.io.Serializable; import javax.persistence.*; @Entity public class City implements Serializable { @Id @GeneratedValue private Long id; @Column(nullable = false) private String name; @Column(nullable = false) private String state; // ... additional members, often include @OneToMany mappings protected City() { // no-args constructor required by JPA spec // this one is protected since it shouldn't be used directly } public City(String name, String state) { this.name = name; this.country = country; } public String getName() { return this.name; } public String getState() { return this.state; } // ... etc }
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You can customize entity scanning locations using the |
Spring Data JPA repositories are interfaces that you can define to access data. JPA
queries are created automatically from your method names. For example, a CityRepository
interface might declare a findAllByState(String state)
method to find all cities in a
given state.
For more complex queries you can annotate your method using Spring Data’s
Query
annotation.
Spring Data repositories usually extend from the
Repository
or
CrudRepository
interfaces.
If you are using auto-configuration, repositories will be searched from the package
containing your main configuration class (the one annotated with
@EnableAutoConfiguration
or @SpringBootApplication
) down.
Here is a typical Spring Data repository:
package com.example.myapp.domain; import org.springframework.data.domain.*; import org.springframework.data.repository.*; public interface CityRepository extends Repository<City, Long> { Page<City> findAll(Pageable pageable); City findByNameAndCountryAllIgnoringCase(String name, String country); }
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We have barely scratched the surface of Spring Data JPA. For complete details check their reference documentation. |
By default, JPA databases will be automatically created only if you use an embedded
database (H2, HSQL or Derby). You can explicitly configure JPA settings using
spring.jpa.*
properties. For example, to create and drop tables you can add the
following to your application.properties
.
spring.jpa.hibernate.ddl-auto=create-drop
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Hibernate’s own internal property name for this (if you happen to remember it
better) is |
spring.jpa.properties.hibernate.globally_quoted_identifiers=true
passes hibernate.globally_quoted_identifiers
to the Hibernate entity manager.
By default the DDL execution (or validation) is deferred until the ApplicationContext
has started. There is also a spring.jpa.generate-ddl
flag, but it is not used if
Hibernate autoconfig is active because the ddl-auto
settings are more fine-grained.
The H2 database provides a browser-based console that Spring Boot can auto-configure for you. The console will be auto-configured when the following conditions are met:
com.h2database:h2
is on the classpathTip | |
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If you are not using Spring Boot’s developer tools, but would still like to make use
of H2’s console, then you can do so by configuring the |
By default the console will be available at /h2-console
. You can customize the console’s
path using the spring.h2.console.path
property.
When Spring Security is on the classpath and basic auth is enabled, the H2 console will be automatically secured using basic auth. The following properties can be used to customize the security configuration:
security.user.role
security.basic.authorize-mode
security.basic.enabled