Trying it Out

The example below demonstrates how to use configurable variables inside a Ballerina project.

Creating the Ballerina Package

Follow the steps below to create the Ballerina package.

  1. Execute the command below to create a Ballerina package.

     bal new userPortal
  2. Navigate to the created userPortal directory, and execute the command below to add a module.

     bal add users
  3. Replace the content of the main.bal file with the content below.

     import ballerina/io;
     import ballerina/log;
     import userPortal.users;
     configurable string url = ?;
     configurable int[] ports = [9090];
     public function main() {
        io:println("Page URL : ", url);
        io:println("Available ports : ", ports);
        io:println("Admin : ", users:getAdminUser());
        table<users:UserInfo> key(username) userTable = users:getUsers();
        io:println("Other users : ", userTable );
        if(userTable.length() > 2) {
            log:printError("Maximum number of users is 2");
  4. Copy the content below to the users.bal file.

     public type UserInfo record {|
        readonly string username;
        int age;
     public type UserTable table<UserInfo> key(username);
     configurable UserInfo admin = ?;
     configurable UserTable users = ?;
     public function getAdminUser() returns UserInfo {
         return admin;
     public function getUsers() returns UserTable {
         return users;
  5. Create a file named Config.toml with the content below in the package root directory to provide the values through the configuration file.

     url = ""
     ports = [9090, 9091, 9092]
     username = "Bob"
     age = 25
     username = "John"
     age = 56
     username = "Tom"
     age = 14
     username = "Anna"
     age = 27
     format = "json"

    Note: The values for the url and port variables are given without a module-name header as those variables are defined in the userPortal root module. Similarly, the admin and users variables are defined in a userPortal.users non-root module . Therefore, they are provided with the module-name prefix as userPortal.users. Also, the project uses a ballerina/log imported module, which contains a configurable variable format, which is configured in the Config.toml file. As ballerina/log is neither the root module nor from the root package, it is provided with its org-name and module-name as a ballerina.log prefix.

    The created package will have the structure below.

     └── userPortal
         ├── Ballerina.toml
         ├── Config.toml
         ├── main.bal
         └── modules
             └── users
                 └── users.bal

Running the Ballerina Package

Follow the steps below to run the Ballerina package you created above.

  1. Execute the command below to build an executable of the package.
     bal build

    The output will be as shown below.

     Compiling source
     Generating executable
  2. Execute the command below to run the program.

     bal run target/bin/userPortal.jar

    The output will be as shown below.

     Page URL :
     Available ports : [9090,9091,9092]
     Admin : {"username":"Bob","age":25}
     Other users : [{"username":"John","age":56},{"username":"Tom","age":14},{"username":"Anna","age":27}]
     {"time":"2021-05-25T14:01:27.948+05:30", "level":"ERROR", "module":"sample/userPortal", "message":"Maximum number of users is 2"}