How to read value from properties using picocli and using it connect postgres

Question

I using picocli and i want build cli get data from database and send it to another service. So i config look like

object Student : Table("student") {
    val id = integer("student_id").autoIncrement().primaryKey()
    val name = varchar("name", 50)
    val grade = integer("grade")
}

class App() : Callable<Integer> {
    @CommandLine.Option(names = ["-ho", "--host"], description = arrayOf("Host database"), defaultValue = "localhost")
    var host: String? = null

    @CommandLine.Option(names = ["-p", "--port"], description = arrayOf("port database"), defaultValue = "5432")
    var port: String? = null

    @CommandLine.Option(names = ["-d", "--database"], description = arrayOf("database"), defaultValue = "postgres")
    var database: String? = null

    @CommandLine.Option(names = ["-u", "--username"], description = arrayOf("username of database"), defaultValue = "postgres")
    var username: String? = null

    @CommandLine.Option(names = ["-w", "--password"], description = arrayOf("password off database"), defaultValue = "password")
    var password: String? = null

    override fun call(): Integer {
       connectDB()
       createStudent()
       return Integer(0)
    }

    fun createStudent() {
        println("Begin create student")
        transaction {
            create(Student)
        }
        println("End create student")
    }

    fun connectDB() {
        try {
            Database.connect("jdbc:postgresql://${this.host}:${this.port}/${this.database}", "org.postgresql.Driver",this.username.toString(),this.password.toString())
            print("Connect db")
        } catch (e : Exception) {
            println("Connect db fail with error ${e.message}")
        }
    }
}

fun main(args: Array<String>) {
    val existCode = CommandLine(App()).execute(*args)
    System.exit(existCode);
}

When I execute, it connect successfully. But I don't want parse value from args. I want read from my file properties example : db.properties or db.yml. How to do do it?

I searched document picocli but I can't find anything it. So now I am using org.jetbrains.exposed:exposed crud to my postgres. Does it work together with picoli? Any suggested frameworks if when get data from database and send it to another api ? Thanks you so much

Answer 1

The requirements you mention are a common CLI design pattern: users can either specify values on the command line, or in a configuration file (or both, in which case the command line overrides the config file).

In picocli, the easiest way to achieve that is with a default provider: if the value is not specified on the command line, the value is obtained from this default provider.

Your default provider implementation could read from a properties file or a yaml file, this is completely up to you.

For example:

@Command(name = "db", defaultValueProvider = MyDefaultProvider.class)
class App() : Callable<Integer> {
   // ...
}

class MyDefaultProvider implements picocli.CommandLine.IDefaultValueProvider {
    public String defaultValue(ArgSpec argSpec) throws Exception {
        // read db.properties (or db.yml or something) from some location
        Properties defaultValues = readProperties();

        // return the default value for the argument
        if (argSpec.isOption()) {
            OptionSpec option = (OptionSpec) argSpec;
            return defaultValues.getProperty(option.longestName());
        }
    }

    private Properties readProperties() throws IOException {
        //...
    }
}

Picocli also provides a built-in PropertiesDefaultProvider implementation, which looks for a file named .${COMMAND-NAME}.properties in the user home directory, where ${COMMAND-NAME} is the name of the command. (In your example, the App class does not have a @Command(name = "xxx") annotation, you may want to add this if you choose to use the built-in PropertiesDefaultProvider.)