format of application properties

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Application Properties support us to work in different environments. In this chapter, you are going to learn how to configure and specify the properties to a Spring Boot application.

Command Line Properties

Spring Boot application converts the command line properties into Spring Boot Environment properties. Command line properties take precedence over the other property sources. By default, Spring Boot uses the 8080 port number to start the Tomcat. Let us learn how change the port number by using command line properties.

Step 1 − After creating an executable JAR file, run it by using the command java –jar <JARFILE> .

Step 2 − Use the command given in the screenshot given below to change the port number for Spring Boot application by using command line properties.

Note − You can provide more than one application properties by using the delimiter −.

Properties File

Properties files are used to keep ‘N’ number of properties in a single file to run the application in a different environment. In Spring Boot, properties are kept in the application.properties file under the classpath.

The application.properties file is located in the src/main/resources directory. The code for sample application.properties file is given below −

Note that in the code shown above the Spring Boot application demoservice starts on the port 9090.

Spring Boot supports YAML based properties configurations to run the application. Instead of application.properties , we can use application.yml file. This YAML file also should be kept inside the classpath. The sample application.yml file is given below −

Externalized Properties

Instead of keeping the properties file under classpath, we can keep the properties in different location or path. While running the JAR file, we can specify the properties file path. You can use the following command to specify the location of properties file while running the JAR −

Use of @Value Annotation

The @Value annotation is used to read the environment or application property value in Java code. The syntax to read the property value is shown below −

Look at the following example that shows the syntax to read the spring.application.name property value in Java variable by using @Value annotation.

Observe the code given below for a better understanding −

Note − If the property is not found while running the application, Spring Boot throws the Illegal Argument exception as Could not resolve placeholder 'spring.application.name' in value "${spring.application.name}" .

To resolve the placeholder issue, we can set the default value for the property using thr syntax given below −

Spring Boot Active Profile

Spring Boot supports different properties based on the Spring active profile. For example, we can keep two separate files for development and production to run the Spring Boot application.

Spring active profile in application.properties

Let us understand how to have Spring active profile in application.properties. By default, application. properties will be used to run the Spring Boot application. If you want to use profile based properties, we can keep separate properties file for each profile as shown below −

application.properties

application-dev.properties

application-prod.properties

While running the JAR file, we need to specify the spring active profile based on each properties file. By default, Spring Boot application uses the application.properties file. The command to set the spring active profile is shown below −

You can see active profile name on the console log as shown below −

Now, Tomcat has started on the port 9090 (http) as shown below −

You can set the Production active profile as shown below −

Now, Tomcat started on the port 4431 (http) as shown below −

Spring active profile for application.yml

Let us understand how to keep Spring active profile for application.yml. We can keep the Spring active profile properties in the single application.yml file. No need to use the separate file like application.properties.

The following is an example code to keep the Spring active profiles in application.yml file. Note that the delimiter (---) is used to separate each profile in application.yml file.

To command to set development active profile is given below −

Now, Tomcat started on the port 9090 (http) as shown below −

The command to set Production active profile is given below −

This will start Tomcat on the port 4431 (http) as shown below:

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Spring Boot – Application Properties

As we already know Spring Boot is built on the top of the spring and contains all the features of spring. And is becoming a favorite of developers these days because it’s a rapid production-ready environment that enables the developers to directly focus on the logic instead of struggling with the configuration and set-up. In Spring Boot, whenever you create a new Spring Boot Application in spring starter, or inside an IDE (Eclipse or STS) a file is located inside the src/main/resources folder named as application.properties file which is shown in the below image as shown below as follows:

Geeks, now you must be wondering what does this file do? What are the major roles of this file during development? So in a spring boot application, application.properties file is used to write the application-related property into that file. This file contains the different configuration which is required to run the application in a different environment, and each environment will have a different property defined by it. Inside the application properties file, we define every type of property like changing the port, database connectivity, connection to the eureka server, and many more. Now let’s see some examples for better understanding.

Example 1: To Change the Port Number

Sometimes when you run your spring application you may encounter the following type of error

The error is Port 8989 was already in use. So in this case you may kill that process that is running on this port number or you may change your port number and rerun your application. So where do you have to change your port number? e.g in the application.properties file .

So as given in the above screenshot you can change your port number by the following line 

Example 2: To define the name of our application

To define the name of our application you can write the properties like this

So you can see this represents the property as key-value pair here, every key associated with a value also.

Example 3: Connecting with the MySQL Database

To connect with the MySQL Database you have to write a bunch of lines. You can write the properties like this

Example 4: Connecting with the H2 Database

H2 is an embedded, open-source, and in-memory database. It is a relational database management system written in Java. It is a client/server application. It is generally used in unit testing. It stores data in memory, not persist the data on disk. To connect with the H2 Database you have to write a bunch of lines. You can write the properties like this

Example 5: Connecting with the MongoDB Database

To connect with the MongoDB Database you have to write a bunch of lines. You can write the properties like this

Example 6: Connecting with the Eureka Server

Eureka Server is an application that holds information about all client-service applications. Every Microservice will register into the Eureka server and the Eureka server knows all the client applications running on each port and IP address. Eureka Server is also known as Discovery Server. You can write the properties like this

Example 7 : Connecting with the PostgreSQL

PostgreSQL is a free and open-source relational database management system. To connect with the PostgreSQL Database you have to write a bunch of lines. You can write the properties like this.

Note : The value written here is sample data. Please write the values as per your requirements. But the keys remain the same. 

application.yml/application.yaml file

The application.properties file is not that readable. So most of the time developers choose application.yml file over application.properties file. YAML is a superset of JSON, and as such is a very convenient format for specifying hierarchical configuration data. YAML is more readable and it is good for the developers to read/write configuration files. For example, let’s pick some of the properties files that we have explained above, and let’s write them in YAML format.

Case 1: Let’s pick above example 3 where we were connecting with the MySQL Database , the corresponding properties will be as follows:

Case 2: Let’s pick above example 6 where we were connecting with the Eureka Server, the corresponding properties will be as follows:

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