@ConfigurationProperties is used to bind all the properties in a properties file to a Java class annotated with @ConfigurationProperties. You can then use a Java object to access configuration properties defined in a properties file.
Earlier I have shared with you a tutorial on how to read application properties in Spring Boot RESTful Web Service application. In this tutorial you will learn how to map properties in a specific properties file to a Java object.
Application Properties File
Let’s assume we have the following application.properties file.
database.name = photo_app
database.url = jdbc:mysql://localhost:3306/${database.name}
database.username = "developer"
database.password = "12345678"
Please note that each property starts with a prefix “database”. It can be any other prefix but having a prefix helps to map all the properties that start with “database” to a Java object much easier.
Let’s learn how to map these properties to a Java object.
Using @ConfigurationProperties
To map the above properties to a Java object we will need to create a Java model class with class fields that match property key.
In the above application.properties file we have the following properties:
- database.name,
- database.url,
- database.username,
- database.password.
Each property has a prefix “database”. This prefix will need to be specified in a @ConfigurationProperties() annotation. Here is how to create a Java class:
@ConfigurationProperties("database")
public class DatabaseConfiguration {
private String name;
private String url;
private String username;
private String password;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getUrl() {
return url;
}
public void setUrl(String url) {
this.url = url;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
}
Now we can Autowire/Inject this class annotated with @ConfigurationProperties into our Controller class for example and be able to access values in application properties file.
@RestController
@RequestMapping(path="/users")
public class UsersController {
@Autowired
DatabaseConfiguration databaseConfiguration;
@GetMapping(path="/status/check")
public String getStatus()
{
return " Working with database name " + databaseConfiguration.getName();
}
}
Reading a Specific Properties File with @PropertySource
By default, @ConfigurationProperties will work with a default application.properties file in your Spring Boot Application. You can specify which configuration properties file to use by using a @PropertySource annotation.
For example, let’s assume we have the following configuration properties defined in a properties file called dbconfig.properties.
database.name = photo_app
database.url = jdbc:mysql://localhost:3306/${database.name}
database.username = "developer"
database.password = "12345678"
To map properties stored in a dbconfig.properties file we will create the following Java class. Please have a look at how the @PropertySource annotation is used.
@PropertySource("classpath:dbconfig.properties")
@ConfigurationProperties("database")
public class DatabaseConfiguration {
private String name;
private String url;
private String username;
private String password;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getUrl() {
return url;
}
public void setUrl(String url) {
this.url = url;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
}
Validating Properties
When using @ConfigurationProperties it is possible to validate the value of the property when it is being set. For example:
@NotEmpty – The annotated element must not be null nor empty,
@Min(5) – The annotated element must be a number whose value must be higher or equal to the specified minimum,
@Max(50) – The annotated element must be a number whose value must be lower or equal to the specified maximum,
@Length(max = 8, min = 16) – Validate that the string is between min and max included,
@Pattern(regexp = “[a-z-A-Z]*”, message = “Username can not contain invalid characters”) – The annotated {@code CharSequence} must match the specified regular expression,
@Email – The string has to be a well-formed email address.
And here is an example of how you would use validation annotations in our class:
@PropertySource("classpath:dbconfig.properties")
@ConfigurationProperties("database")
public class DatabaseConfiguration {
@Length(min=2, max=10)
private String name;
@NotEmpty
private String url;
@Length(min=5, max=10)
@Pattern(regexp = "[a-z-A-Z]*", message = "Username can not contain invalid characters")
private String username;
@Length(min=8, max=16)
private String password;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getUrl() {
return url;
}
public void setUrl(String url) {
this.url = url;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
}
I hope this tutorial was helpful for you. If you are interested to learn more about Spring Boot, have a look at the below list of video courses. One of them might be exactly what you are looking for.