Solving Tricky Problems With the Help of Groovy Closures

PricingService.groovy

class InventorySystem {

    boolean open(String token) {
        // open a socket connection to some back-end mainframe system
        println "opening connection to mainframe, token: ${token}"
        true
    }

    BigDecimal pricingLookup(String clientId, String itemUuid)
    {
        // call the back end system to get the price of an item for a particular client
        // send back a mock price as the result:
       100.00
    }
    
    boolean close() {
        // close the socket connection
        println "closing connection to mainframe"
    }
}

class AuthenticationProvider {

    String authenticateUser(String username, String password) {
        "validToken"
    }
}

class InventoryApiConnectionFactory {
 
       // these properties would ordinarily be injected
       def authenticationProvider = new AuthenticationProvider()
       String username  = "username"
       String password  = "password"
       
       def logError(String msg) { println msg } // simulated logger
 
    def withInventoryConnection(Closure c) {
        def authenticatedUserToken = authenticationProvider.authenticateUser(username, password)
        def connection = new InventorySystem()
        def isOpen = connection.open(authenticatedUserToken)
        try {
            if(isOpen) {
                c.call(connection)
            }
        } catch (any) {
            logError("Something went wrong: ${any.message}".toString())
            throw any
        } finally {
            connection.close()
        }
       
    }
 
}

class PricingService {

    // would be injected
    InventoryApiConnectionFactory fac = new InventoryApiConnectionFactory()

    def priceLookup(String clientId, String itemUUID) {
        
        fac.withInventoryConnection { connection ->
            connection.pricingLookup(clientId, itemUUID)
        }
    }
}

PricingService ps = new PricingService()

println ps.priceLookup("client1", "item-11-22-33")

InventoryApiConnectionFactory.withInventoryConnection takes a closure as an argument and manages the full lifecycle of the legacy mainframe connection while executing any method exposed by InventorySystem, in this case, pricingLookup. Generally, there would be a corpus of methods to choose from that execute against the back-end system that someone wrote an API for.