I have one POJO class which read properties from application.yaml file in spring boot. Here I need to set default value to groupId(to get when not given) based on combination of topic value and another string.
private String topic;
#Value("${topic}_test")
private String groupId;
I tried this but getting error as
Could not resolve placeholder 'topic' in value "${topic}_test
I create a variable and tried to access it in #Value but failed.
Please provide any suggestion to access this
Default value
Let's say you have a property like this in your application.yml file
topic: myFavoriteTopic
The code below will assign the value "myFavoriteTopic" to variable groupId if Spring is able to load the property with key topic from application.yml. If it's not, it will assign the default value "my default topic".
#Value("${topic:my default topic}")
private String groupId;
To set null as the default value, use:
#Value("${topic:#{null}}")
To use an empty String as the default value, use:
#Value("${topic:}")
Get key name from a variable
In your code snippet you have a String topic variable. For the Spring framework, this variable is not used in the property value retrieval. When you do #Value("${topic}"), "topic" is the name of the key that Spring will look for in application.yml. The name of the key cannot be determined at runtime based on the value of a Java variable. The reason is that properties can be loaded before the class code executes.
_test suffix
Also in your code snippet, you use #Value("${topic}_test"). What Spring does in this case is to concatenate "_test" to the value retrieved for property key topic. In my first example, groupId would be assigned "myFavoriteTopic_test".
Related
I have a Spring Boot application, using Intellij, and am trying to use the #Value annotation in order to get an environment variable from my application.properties.
My application.properties looks like this
server.port=27019
web.entrance.id=63d284ec
Using debugger, I can see that the value of entranceId is successfully retrieved from application.properties, but the same variable is always null in the String.format and my WebUrl has the string 'null' in it and I don't understand why.
#RestController
public class Controller {
#Value(("${entrance.id}"))
private String entranceId;
String WebUrl = String.format("http://localhost:27019/%s", entranceId);
Can someone explain if there is some detail I'm missing why this happens?
Thank you
Your thinking is wrong. Spring will process the #Value after the object has been constructed, whereas your field is being initialized as soon as the class is being constructed (so during constructing).
Basically what Spring does
new Controller()
Detect #Value and with reflection set value
Any construction callbacks (like #PostConstruct).
Your field is being filled at step 1 not after step 2. At which point the #Value hasn't yet been processed.
If you want to set the value you need to do that in an #PostConstruct method or use constructor injection to construct the URL.
I am using #value annotation in spring boot to read a property
#Value(value = "${propName:#{null}}")
private String prop;
And based on if it is null or driving some logic in my code. In my dev environment I want to keep it null so I don't add it in that property file (application-dev.properties). But instead of getting it as null, it is reading the value from default application.properties file.
Yes, this is the correct behavior based on Spring's property resolution. If you want to override it in your dev profile, simply add the property to your application-dev.properties, leaving the value empty. This will result in an empty String, not null, which you can convert to null with something like this:
#Value("${#{some_property == \"\"}:#{null}}")
private String prop;
It is probably a good idea to explicitly define these properties and give them values that make sense. Otherwise, you'll likely revisit this code in a few months and wonder what the heck is causing xyz.
You can read up on Spring and the order with which it resolves properties here but generally, you'd want to define variables that apply to all environments in your application.[properties][yaml], and then override them in the environment-specific properties files. In this case, it kind of sounds like this is a flag that's on or off depending on if the dev environment is set; you might consider something like this.
#Value("${property_to_drive_behavior:false}"
private Boolean prop;
This will default to false, so you don't need to add it to any properties file. If you want it set, override it in the environment-specific properties file. Booleans can be set in properties files using either the explicit true or false keywords or the values or 0 for false, 1 for true.
By default, property values of external configuration sources (such as application.properties files) are always injected directly into your beans by using the #Value annotation.
One solution to your problem is moving the propName property from application.properties to application-{profile}.properties.
I've got many .yml files with properties for different projects. Configuration bean is the same for all of them but some of properties might be missing for some reason. The question is how to set default NULL value to field such as HashMap via #Value. So what I'm trying is:
#Value("${property.time:#{null}}")
private Integer time;
#Value("#{${property.map:#{null}}}")
private HashMap<String,String> map;
So for first field if property is missing in .yml file then Integer becomes null which is correct.
If there is no map in .yml file I'm trying to set it to null but getting Exception:
Caused by: org.springframework.expression.spel.SpelParseException: Expression [#{null}] #1: EL1043E: Unexpected token. Expected 'identifier' but was 'lcurly({)'
p.s. Cant use spring boot in project so trying to fix it with spring framework
You could set the default value as follow :
#Value("${some.key:10}")
private int myKey;
Here it will try to look for the some.key value in the corresponding .yml file, if it is missing it will use the default value.
In my application.properties file I would like to have an optional value. Such as spring.datasource.url=${value} but optional
Is this possible?
You can define a property as "optional" by giving it a default value where you inject it.
For example:
#Value("${spring.datasource.url:null}")
private String springDatasourceURL;
In my Spring Boot app's application.properties I have this definition:
someProp=${SOME_ENV_VARIABLE}
But this is an optional value only set in certain environments, I use it like this
#Value("${someProp:#{null}}")
private String someProp;
Surprisingly I get this error when the env. var doesn't exist
Could not resolve placeholder 'SOME_ENV_VARIABLE' in string value "${SOME_ENV_VARIABLE}"
I was expecting Spring to just set a blank value if not found in any PropertySource.
How to make it optional?
Provide a default value in the application.properties
someProp=${SOME_ENV_VARIABLE:#{null}}
When used like #Value("${someProp}), this will correctly evaluate to null. First, if SOME_ENV_VARIABLE is not found when application.properties is being processed, its value becomes the string literal "#{null}". Then, #Value evaluates someProp as a SpEL expression, which results in null. The actual value can be verified by looking at the property in the Environment bean.
This solution utilizes the default value syntax specified by the PlaceholderConfigurerSupport class
Default property values can be defined globally for each configurer
instance via the properties property, or on a property-by-property
basis using the default value separator which is ":" by default and
customizable via setValueSeparator(String).
and Spring SpEL expression templating.
From Spring Boot docs on externalized configuration
Finally, while you can write a SpEL expression in #Value, such
expressions are not processed from Application property files.
This work for me:
spring.datasource.url=jdbc:mysql://${DB_IP:localhost}:3306/app
spring.datasource.username=${SPRING_DATASOURCE_USERNAME:mylocaluser}
spring.datasource.password=${SPRING_DATASOURCE_PASSWORD:localpass}
Because this is probably interesting to others who come here, you can override any properties file w/ an env variable implicitly. Let's say you have property.
someapp.foo
Then you can define an env variable SOMEAPP_FOO (capital letters and . -> _ ) and spring will implicitly set the property from the env. variable.
Described further here: https://hughesadam87.medium.com/how-to-override-spring-properties-with-env-vars-82ee1db2ae78