CS5233 Components Models and Engineering

Transcription

1 CS5233 Components Models and Engineering - Komponententechnologien Master of Science (Informatik) Java Services Seite 1

2 Services Services Build-in technology Java 6 build-in technology to load services dynamically Service definition = interface A service is defined by a (statically known) interface Service implementation = class The service implementation = service provider a class that implements the interface - is loaded at run-time Naming / locating services Java 6 supports finding and loading the service implementation through the directory META-INF/services from the Java classpath Relevant class java.util.serviceloader Seite 2

3 Services / Service Loader Service Loader java.util.serviceloader<s> class new with Java 1.6 Intention: extend an application by providing a jar-file as part of the classpath or in an application-specific directory Java build-in component technology may be used as advanced class.forname or simple Java-build-in component technology Seite 3

4 Services / Service Loader Service Loader / static factory methods ServiceLoader<S> is used to load Implementations of a Service S Factory methods of class ServiceLoader : Each method creates a service loader ( loads a service loader ) using a different class loader static <S> ServiceLoader<S> load(class<s> service) loads using the current thread context loader static <S> ServiceLoader<S> load(class<s> service, ClassLoader loader) loads using the given class loader static <S> ServiceLoader<S> loadinstalled( Class<S> service) loads using the extension class loader Usage Example: ServiceLoader<MyService> myserviceloader = ServiceLoader.load(MyService.class); Seite 4

5 Services / Service Loader Service Loader / iterator an instance of ServiceLoader<S> implements Iterable<S> Iterator<S> iterator() iterates over Implementations of S A call of next loads and returns an instance of a service provider Usage Example: ServiceLoader<MyService> myserviceloader = ServiceLoader.load(MyService.class); for (MyService s : myserviceloader) { use s Seite 5

6 Services / Example Service and Service Provider Service A set of interfaces and/or abstract classes Service provider Implementation / concrete subclasses of the service package accountservice; Example of a Service: interface AccountService create Accounts using a certain fixed currency interface Account deposit / withdraw get balance as string with currency symbol import java.util.currency; public interface AccountService { currency of all accounts */ Currency getaccountcurrency(); /** create account */ Account createaccount(); package accountservice; public interface Account { /** Enter the given amount */ void deposit(int amount); /** Withdraw the given amount */ void withdraw(int amount); /** Get a String-representation of the balance */ String getbalance(); An AccountService is bound to a fixed currency. There may be several Services each one using its currency. Seite 6

7 Services / Example Service and Service Provider package euroaccountservice ; Example of a Service Provider This provider may provide euro accounts. import java.util.currency; import accountservice.*; public class EuroAccountService implements AccountService { static final Currency currency = Currency.getInstance("EUR"); public Account createaccount () { return new Account() { int balance = 0; public void deposit(int amount) { balance += amount; public void withdraw(int amount) { balance -= amount; public String getbalance() { return balance + " " + currency.getsymbol(); ; public Currency getaccountcurrency () { return currency; Seite 7

8 Services / Example Service user loads service providers, checks them for appropriateness, uses an appropriate one import java.util.currency; import java.util.serviceloader; import accountservice.account; import accountservice.accountservice; public class Test { public static void main(string[] args) { ServiceLoader<AccountService> accservices = ServiceLoader.load(AccountService.class); // search for an euro account service and use it for (AccountService as : accservices) { if (as.getaccountcurrency().equals(currency. getinstance ("EUR"))) { Account account = as.createaccount (); account.deposit(100); account.withdraw(5); System. out.println(account. getbalance()); Seite 8

9 Services / Example Create jar file with services implementation Jar file must contain implementation classes a directory called META-INF within META-INF a directory called services directory services must contain the name of the provider classes Example: euroaccountservice.euroaccountservice Content of file accountservice.accountservice jar cf accserviceimpl.jar META-INF euroaccountservice Command to create jar file jar -tf accserviceimpl.jar META-INF/ META-INF/MANIFEST.MF META-INF/services/ META-INF/services/accountService.AccountService euroaccountservice/ euroaccountservice/euroaccountservice$1.class euroaccountservice/euroaccountservice.class java -cp.:accserviceimpl.jar servicetest.test Seite 9 Command to show the content of the jar file running the application