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Environment Abstraction
The Environment
interface
is an abstraction integrated in the container that models two key
aspects of the application environment: profiles
and properties.
A profile is a named, logical group of bean definitions to be registered with the
container only if the given profile is active. Beans may be assigned to a profile
whether defined in XML or with annotations. The role of the Environment
object with
relation to profiles is in determining which profiles (if any) are currently active,
and which profiles (if any) should be active by default.
Properties play an important role in almost all applications and may originate from
a variety of sources: properties files, JVM system properties, system environment
variables, JNDI, servlet context parameters, ad-hoc Properties
objects, Map
objects, and so
on. The role of the Environment
object with relation to properties is to provide the
user with a convenient service interface for configuring property sources and resolving
properties from them.
Bean Definition Profiles
Bean definition profiles provide a mechanism in the core container that allows for registration of different beans in different environments. The word, “environment,” can mean different things to different users, and this feature can help with many use cases, including:
-
Working against an in-memory datasource in development versus looking up that same datasource from JNDI when in QA or production.
-
Registering monitoring infrastructure only when deploying an application into a performance environment.
-
Registering customized implementations of beans for customer A versus customer B deployments.
Consider the first use case in a practical application that requires a
DataSource
. In a test environment, the configuration might resemble the following:
-
Java
-
Kotlin
@Bean
public DataSource dataSource() {
return new EmbeddedDatabaseBuilder()
.setType(EmbeddedDatabaseType.HSQL)
.addScript("my-schema.sql")
.addScript("my-test-data.sql")
.build();
}
@Bean
fun dataSource(): DataSource {
return EmbeddedDatabaseBuilder()
.setType(EmbeddedDatabaseType.HSQL)
.addScript("my-schema.sql")
.addScript("my-test-data.sql")
.build()
}
Now consider how this application can be deployed into a QA or production
environment, assuming that the datasource for the application is registered
with the production application server’s JNDI directory. Our dataSource
bean
now looks like the following listing:
-
Java
-
Kotlin
@Bean(destroyMethod = "")
public DataSource dataSource() throws Exception {
Context ctx = new InitialContext();
return (DataSource) ctx.lookup("java:comp/env/jdbc/datasource");
}
@Bean(destroyMethod = "")
fun dataSource(): DataSource {
val ctx = InitialContext()
return ctx.lookup("java:comp/env/jdbc/datasource") as DataSource
}
The problem is how to switch between using these two variations based on the
current environment. Over time, Spring users have devised a number of ways to
get this done, usually relying on a combination of system environment variables
and XML <import/>
statements containing ${placeholder}
tokens that resolve
to the correct configuration file path depending on the value of an environment
variable. Bean definition profiles is a core container feature that provides a
solution to this problem.
If we generalize the use case shown in the preceding example of environment-specific bean definitions, we end up with the need to register certain bean definitions in certain contexts but not in others. You could say that you want to register a certain profile of bean definitions in situation A and a different profile in situation B. We start by updating our configuration to reflect this need.
Using @Profile
The @Profile
annotation lets you indicate that a component is eligible for registration
when one or more specified profiles are active. Using our preceding example, we
can rewrite the dataSource
configuration as follows:
-
Java
-
Kotlin
@Configuration
@Profile("development")
public class StandaloneDataConfig {
@Bean
public DataSource dataSource() {
return new EmbeddedDatabaseBuilder()
.setType(EmbeddedDatabaseType.HSQL)
.addScript("classpath:com/bank/config/sql/schema.sql")
.addScript("classpath:com/bank/config/sql/test-data.sql")
.build();
}
}
@Configuration
@Profile("development")
class StandaloneDataConfig {
@Bean
fun dataSource(): DataSource {
return EmbeddedDatabaseBuilder()
.setType(EmbeddedDatabaseType.HSQL)
.addScript("classpath:com/bank/config/sql/schema.sql")
.addScript("classpath:com/bank/config/sql/test-data.sql")
.build()
}
}
-
Java
-
Kotlin
@Configuration
@Profile("production")
public class JndiDataConfig {
@Bean(destroyMethod = "") (1)
public DataSource dataSource() throws Exception {
Context ctx = new InitialContext();
return (DataSource) ctx.lookup("java:comp/env/jdbc/datasource");
}
}
1 | @Bean(destroyMethod = "") disables default destroy method inference. |
@Configuration
@Profile("production")
class JndiDataConfig {
@Bean(destroyMethod = "") (1)
fun dataSource(): DataSource {
val ctx = InitialContext()
return ctx.lookup("java:comp/env/jdbc/datasource") as DataSource
}
}
1 | @Bean(destroyMethod = "") disables default destroy method inference. |
As mentioned earlier, with @Bean methods, you typically choose to use programmatic
JNDI lookups, by using either Spring’s JndiTemplate /JndiLocatorDelegate helpers or the
straight JNDI InitialContext usage shown earlier but not the JndiObjectFactoryBean
variant, which would force you to declare the return type as the FactoryBean type.
|
The profile string may contain a simple profile name (for example, production
) or a
profile expression. A profile expression allows for more complicated profile logic to be
expressed (for example, production & us-east
). The following operators are supported in
profile expressions:
-
!
: A logicalNOT
of the profile -
&
: A logicalAND
of the profiles -
|
: A logicalOR
of the profiles
You cannot mix the & and | operators without using parentheses. For example,
production & us-east | eu-central is not a valid expression. It must be expressed as
production & (us-east | eu-central) .
|
You can use @Profile
as a meta-annotation for the purpose
of creating a custom composed annotation. The following example defines a custom
@Production
annotation that you can use as a drop-in replacement for
@Profile("production")
:
-
Java
-
Kotlin
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Profile("production")
public @interface Production {
}
@Target(AnnotationTarget.CLASS)
@Retention(AnnotationRetention.RUNTIME)
@Profile("production")
annotation class Production
If a @Configuration class is marked with @Profile , all of the @Bean methods and
@Import annotations associated with that class are bypassed unless one or more of
the specified profiles are active. If a @Component or @Configuration class is marked
with @Profile({"p1", "p2"}) , that class is not registered or processed unless
profiles 'p1' or 'p2' have been activated. If a given profile is prefixed with the
NOT operator (! ), the annotated element is registered only if the profile is not
active. For example, given @Profile({"p1", "!p2"}) , registration will occur if profile
'p1' is active or if profile 'p2' is not active.
|
@Profile
can also be declared at the method level to include only one particular bean
of a configuration class (for example, for alternative variants of a particular bean), as
the following example shows:
-
Java
-
Kotlin
@Configuration
public class AppConfig {
@Bean("dataSource")
@Profile("development") (1)
public DataSource standaloneDataSource() {
return new EmbeddedDatabaseBuilder()
.setType(EmbeddedDatabaseType.HSQL)
.addScript("classpath:com/bank/config/sql/schema.sql")
.addScript("classpath:com/bank/config/sql/test-data.sql")
.build();
}
@Bean("dataSource")
@Profile("production") (2)
public DataSource jndiDataSource() throws Exception {
Context ctx = new InitialContext();
return (DataSource) ctx.lookup("java:comp/env/jdbc/datasource");
}
}
1 | The standaloneDataSource method is available only in the development profile. |
2 | The jndiDataSource method is available only in the production profile. |
@Configuration
class AppConfig {
@Bean("dataSource")
@Profile("development") (1)
fun standaloneDataSource(): DataSource {
return EmbeddedDatabaseBuilder()
.setType(EmbeddedDatabaseType.HSQL)
.addScript("classpath:com/bank/config/sql/schema.sql")
.addScript("classpath:com/bank/config/sql/test-data.sql")
.build()
}
@Bean("dataSource")
@Profile("production") (2)
fun jndiDataSource() =
InitialContext().lookup("java:comp/env/jdbc/datasource") as DataSource
}
1 | The standaloneDataSource method is available only in the development profile. |
2 | The jndiDataSource method is available only in the production profile. |
With If you want to define alternative beans with different profile conditions,
use distinct Java method names that point to the same bean name by using the |
XML Bean Definition Profiles
The XML counterpart is the profile
attribute of the <beans>
element. Our preceding sample
configuration can be rewritten in two XML files, as follows:
<beans profile="development"
xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:jdbc="http://www.springframework.org/schema/jdbc"
xsi:schemaLocation="...">
<jdbc:embedded-database id="dataSource">
<jdbc:script location="classpath:com/bank/config/sql/schema.sql"/>
<jdbc:script location="classpath:com/bank/config/sql/test-data.sql"/>
</jdbc:embedded-database>
</beans>
<beans profile="production"
xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:jee="http://www.springframework.org/schema/jee"
xsi:schemaLocation="...">
<jee:jndi-lookup id="dataSource" jndi-name="java:comp/env/jdbc/datasource"/>
</beans>
It is also possible to avoid that split and nest <beans/>
elements within the same file,
as the following example shows:
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:jdbc="http://www.springframework.org/schema/jdbc"
xmlns:jee="http://www.springframework.org/schema/jee"
xsi:schemaLocation="...">
<!-- other bean definitions -->
<beans profile="development">
<jdbc:embedded-database id="dataSource">
<jdbc:script location="classpath:com/bank/config/sql/schema.sql"/>
<jdbc:script location="classpath:com/bank/config/sql/test-data.sql"/>
</jdbc:embedded-database>
</beans>
<beans profile="production">
<jee:jndi-lookup id="dataSource" jndi-name="java:comp/env/jdbc/datasource"/>
</beans>
</beans>
The spring-bean.xsd
has been constrained to allow such elements only as the
last ones in the file. This should help provide flexibility without incurring
clutter in the XML files.
The XML counterpart does not support the profile expressions described earlier. It is possible,
however, to negate a profile by using the
In the preceding example, the |
Activating a Profile
Now that we have updated our configuration, we still need to instruct Spring which
profile is active. If we started our sample application right now, we would see
a NoSuchBeanDefinitionException
thrown, because the container could not find
the Spring bean named dataSource
.
Activating a profile can be done in several ways, but the most straightforward is to do
it programmatically against the Environment
API which is available through an
ApplicationContext
. The following example shows how to do so:
-
Java
-
Kotlin
AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();
ctx.getEnvironment().setActiveProfiles("development");
ctx.register(SomeConfig.class, StandaloneDataConfig.class, JndiDataConfig.class);
ctx.refresh();
val ctx = AnnotationConfigApplicationContext().apply {
environment.setActiveProfiles("development")
register(SomeConfig::class.java, StandaloneDataConfig::class.java, JndiDataConfig::class.java)
refresh()
}
In addition, you can also declaratively activate profiles through the
spring.profiles.active
property, which may be specified through system environment
variables, JVM system properties, servlet context parameters in web.xml
, or even as an
entry in JNDI (see PropertySource
Abstraction). In integration tests, active
profiles can be declared by using the @ActiveProfiles
annotation in the spring-test
module (see context configuration with environment profiles
).
Note that profiles are not an “either-or” proposition. You can activate multiple
profiles at once. Programmatically, you can provide multiple profile names to the
setActiveProfiles()
method, which accepts String…
varargs. The following example
activates multiple profiles:
-
Java
-
Kotlin
ctx.getEnvironment().setActiveProfiles("profile1", "profile2");
ctx.getEnvironment().setActiveProfiles("profile1", "profile2")
Declaratively, spring.profiles.active
may accept a comma-separated list of profile names,
as the following example shows:
-Dspring.profiles.active="profile1,profile2"
Default Profile
The default profile represents the profile that is enabled if no profile is active. Consider the following example:
-
Java
-
Kotlin
@Configuration
@Profile("default")
public class DefaultDataConfig {
@Bean
public DataSource dataSource() {
return new EmbeddedDatabaseBuilder()
.setType(EmbeddedDatabaseType.HSQL)
.addScript("classpath:com/bank/config/sql/schema.sql")
.build();
}
}
@Configuration
@Profile("default")
class DefaultDataConfig {
@Bean
fun dataSource(): DataSource {
return EmbeddedDatabaseBuilder()
.setType(EmbeddedDatabaseType.HSQL)
.addScript("classpath:com/bank/config/sql/schema.sql")
.build()
}
}
If no profile is active, the dataSource
is
created. You can see this as a way to provide a default definition for one or more
beans. If any profile is enabled, the default profile does not apply.
The name of the default profile is default
. You can change the name of
the default profile by using setDefaultProfiles()
on the Environment
or,
declaratively, by using the spring.profiles.default
property.
PropertySource
Abstraction
Spring’s Environment
abstraction provides search operations over a configurable
hierarchy of property sources. Consider the following listing:
-
Java
-
Kotlin
ApplicationContext ctx = new GenericApplicationContext();
Environment env = ctx.getEnvironment();
boolean containsMyProperty = env.containsProperty("my-property");
System.out.println("Does my environment contain the 'my-property' property? " + containsMyProperty);
val ctx = GenericApplicationContext()
val env = ctx.environment
val containsMyProperty = env.containsProperty("my-property")
println("Does my environment contain the 'my-property' property? $containsMyProperty")
In the preceding snippet, we see a high-level way of asking Spring whether the my-property
property is
defined for the current environment. To answer this question, the Environment
object performs
a search over a set of PropertySource
objects. A PropertySource
is a simple abstraction over any source of key-value pairs, and
Spring’s StandardEnvironment
is configured with two PropertySource objects — one representing the set of JVM system properties
(System.getProperties()
) and one representing the set of system environment variables
(System.getenv()
).
These default property sources are present for StandardEnvironment , for use in standalone
applications. StandardServletEnvironment
is populated with additional default property sources including servlet config, servlet
context parameters, and a JndiPropertySource
if JNDI is available.
|
Concretely, when you use the StandardEnvironment
, the call to env.containsProperty("my-property")
returns true if a my-property
system property or my-property
environment variable is present at
runtime.
The search performed is hierarchical. By default, system properties have precedence over
environment variables. So, if the For a common
|
Most importantly, the entire mechanism is configurable. Perhaps you have a custom source
of properties that you want to integrate into this search. To do so, implement
and instantiate your own PropertySource
and add it to the set of PropertySources
for the
current Environment
. The following example shows how to do so:
-
Java
-
Kotlin
ConfigurableApplicationContext ctx = new GenericApplicationContext();
MutablePropertySources sources = ctx.getEnvironment().getPropertySources();
sources.addFirst(new MyPropertySource());
val ctx = GenericApplicationContext()
val sources = ctx.environment.propertySources
sources.addFirst(MyPropertySource())
In the preceding code, MyPropertySource
has been added with highest precedence in the
search. If it contains a my-property
property, the property is detected and returned, in favor of
any my-property
property in any other PropertySource
. The
MutablePropertySources
API exposes a number of methods that allow for precise manipulation of the set of
property sources.
Using @PropertySource
The @PropertySource
annotation provides a convenient and declarative mechanism for adding a PropertySource
to Spring’s Environment
.
Given a file called app.properties
that contains the key-value pair testbean.name=myTestBean
,
the following @Configuration
class uses @PropertySource
in such a way that
a call to testBean.getName()
returns myTestBean
:
-
Java
-
Kotlin
@Configuration
@PropertySource("classpath:/com/myco/app.properties")
public class AppConfig {
@Autowired
Environment env;
@Bean
public TestBean testBean() {
TestBean testBean = new TestBean();
testBean.setName(env.getProperty("testbean.name"));
return testBean;
}
}
@Configuration
@PropertySource("classpath:/com/myco/app.properties")
class AppConfig {
@Autowired
private lateinit var env: Environment
@Bean
fun testBean() = TestBean().apply {
name = env.getProperty("testbean.name")!!
}
}
Any ${…}
placeholders present in a @PropertySource
resource location are
resolved against the set of property sources already registered against the
environment, as the following example shows:
-
Java
-
Kotlin
@Configuration
@PropertySource("classpath:/com/${my.placeholder:default/path}/app.properties")
public class AppConfig {
@Autowired
Environment env;
@Bean
public TestBean testBean() {
TestBean testBean = new TestBean();
testBean.setName(env.getProperty("testbean.name"));
return testBean;
}
}
@Configuration
@PropertySource("classpath:/com/\${my.placeholder:default/path}/app.properties")
class AppConfig {
@Autowired
private lateinit var env: Environment
@Bean
fun testBean() = TestBean().apply {
name = env.getProperty("testbean.name")!!
}
}
Assuming that my.placeholder
is present in one of the property sources already
registered (for example, system properties or environment variables), the placeholder is
resolved to the corresponding value. If not, then default/path
is used
as a default. If no default is specified and a property cannot be resolved, an
IllegalArgumentException
is thrown.
@PropertySource can be used as a repeatable annotation. @PropertySource
may also be used as a meta-annotation to create custom composed annotations with
attribute overrides.
|
Placeholder Resolution in Statements
Historically, the value of placeholders in elements could be resolved only against
JVM system properties or environment variables. This is no longer the case. Because
the Environment
abstraction is integrated throughout the container, it is easy to
route resolution of placeholders through it. This means that you may configure the
resolution process in any way you like. You can change the precedence of searching through
system properties and environment variables or remove them entirely. You can also add your
own property sources to the mix, as appropriate.
Concretely, the following statement works regardless of where the customer
property is defined, as long as it is available in the Environment
:
<beans>
<import resource="com/bank/service/${customer}-config.xml"/>
</beans>