What is service class in java

Java 9 Modules — Creating Services and Service Providers

In Java 9, we can develop Services and Service Providers as modules. A service module declares that it uses one or more interfaces whose implementations will be provided at run time by some provider modules. A provider module declares what implementations of service interfaces it provides.

We still have the option to deploying service providers on the class path (check out this example ).

Deploying Services and Service Providers as modules

The Service Module

Let’s say we have a service interface com.service.api.AnInterface. To declare this interface as service provider interface (SPI), we will use the «uses» clause in module-info.java:

The Service Provider Module

A service provider will use «provides .. with» clause to declare what service interface it intends to use (by using provides keyword) and what implementation of the interface it wants to expose (by using with keyword).

module com.service.provider

We don’t have to specify the service implementation in a file under the resource directory META-INF/services. (Without modules, we still have to do that).

The Client Application using the Service

Client application should be unaware of the provider implementation at compile time. We can deploy any providers during runtime via ‘module-path’.

Discovering the Service implementations

We still need to use ServiceLoader#load(AnInterface.class) to discover service implementation instances. This is typically done in service API module itself.

Let’s see a complete example to understand how to do that.

Example

In this example, we will create very simple service API module ‘msg.service.api’ which ‘uses’ a service interface to display a message. The example Provider will implement the interface and will show the message in a Java Swing dialog. We will also create a third project which will require the service interface and will have the provider deployed during runtime via module path.

The Service API

msg.service.api/src/msg/service/MsgService.java

package msg.service; import java.util.ArrayList; import java.util.List; import java.util.ServiceLoader; public interface MsgService < static ListgetInstances() < ServiceLoaderservices = ServiceLoader.load(MsgService.class); List list = new ArrayList<>(); services.iterator().forEachRemaining(list::add); return list; > void showMessage(String msg); >

msg.service.api/src/module-info.java

D:\java-modules\java-service-loader-example\msg.service.api>"tree /A /F"
| 
\---src 
| module-info.java 
| 
\---msg 
\---service 
MsgService.java 

D:\java-modules\java-service-loader-example\msg.service.api>javac -d out src/module-info.java src/msg/service/MsgService.java

D:\java-modules\java-service-loader-example\msg.service.api>jar --create --file msg-service.jar -C out .

Now we have following files:

D:\java-modules\java-service-loader-example\msg.service.api>"tree /A /F"
| msg-service.jar
| 
+---out
| | module-info.class
| | 
| \---msg
| \---service
| MsgService.class
| 
\---src 
| module-info.java 
| 
\---msg 
\---service 
MsgService.java 

The Service Provider

msg.service.provider.swing/src/msg/provider/swing/MsgServiceImpl.java

package msg.provider.swing; import msg.service.MsgService; import javax.swing.*; public class MsgServiceImpl implements MsgService < @Override public void showMessage(String msg) < JOptionPane.showMessageDialog(null, msg); >>

msg.service.provider.swing/src/module-info.java

module msg.service.provider.swing

Above module is also requiring ‘java.desktop’ which contains javax.swing.

Following is the directory structure of the provider project:

D:\java-modules\java-service-loader-example/msg.service.provider.swing>"tree /A /F"
| 
\---src 
| module-info.java 
| 
\---msg 
\---provider 
\---swing 
MsgServiceImpl.java 

Copying msg-lib.jar(the service API) to msg.service.provider.swing/lib, so that we can compile the provider classes:

D:\java-modules\java-service-loader-example\msg.service.provider.swing>mkdir lib

D:\java-modules\java-service-loader-example\msg.service.provider.swing>copy ..\msg.service.api\msg-service.jar lib\msg-service.jar 
1 file(s) copied.

D:\java-modules\java-service-loader-example\msg.service.provider.swing>"tree /A /F"
| 
+---lib
| msg-service.jar
| 
\---src 
| module-info.java 
| 
\---msg 
\---provider 
\---swing 
MsgServiceImpl.java 

D:\java-modules\java-service-loader-example\msg.service.provider.swing>javac -d out --module-path lib src/module-info.java src/msg/provider/swing/MsgServiceImpl.java

D:\java-modules\java-service-loader-example\msg.service.provider.swing>jar --create --file msg-service-swing.jar -C out .

D:\java-modules\java-service-loader-example\msg.service.provider.swing>"tree /A /F"
| msg-service-swing.jar
| 
+---lib
| msg-service.jar
| 
+---out
| | module-info.class
| | 
| \---msg
| \---provider
| \---swing
| MsgServiceImpl.class
| 
\---src 
| module-info.java 
| 
\---msg 
\---provider 
\---swing 
MsgServiceImpl.java 

The Service Client Application

my-app/src/com/logicbig/AppMain.java

package com.logicbig; import msg.service.MsgService; import java.util.List; public class AppMain < public static void main(String[] args) < ListmsgServices = MsgService.getInstances(); for (MsgService msgService : msgServices) < msgService.showMessage("A test message"); >> >

my-app/src/module-info.java

D:\java-modules\java-service-loader-example/my-app>"tree /A /F"
| 
\---src 
| module-info.java 
| 
\---com 
\---logicbig 
AppMain.java 

Copying msg-lib.jar (Service API) to my-app/lib/msg-lib.jar

D:\java-modules\java-service-loader-example\my-app>mkdir lib

D:\java-modules\java-service-loader-example\my-app>copy ..\msg.service.api\msg-service.jar lib\msg-service.jar 
1 file(s) copied.

Copying msg-service-swing.jar (the provider) to my-app/lib/msg-service-swing.jar:

D:\java-modules\java-service-loader-example\my-app>copy ..\msg.service.provider.swing\msg-service-swing.jar lib\msg-service-swing.jar 
1 file(s) copied.

D:\java-modules\java-service-loader-example\my-app>"tree /A /F"
| 
+---lib
| msg-service-swing.jar
| msg-service.jar
| 
\---src 
| module-info.java 
| 
\---com 
\---logicbig 
AppMain.java 

D:\java-modules\java-service-loader-example\my-app>javac -d out --module-path lib src/module-info.java src/com/logicbig/AppMain.java

D:\java-modules\java-service-loader-example\my-app> java —module-path out;lib —module my.app/com.logicbig.AppMain

Example Project

Dependencies and Technologies Used:

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Service class java example

In Java, a service is defined by a set of interfaces and classes. The service contains an interface or an abstract class that defines the functionality provided by the service. There are multiple implementations for a service and they are called as service providers.

What is a service class in programming?

A service class is a named group of work within a workload with similar performance goals, resource requirements, or business importance. You must define at least one service class. You can define up to 100 service classes.

What is the purpose of a service class?

A Service class is used by a client to interact with some functionality in your application. Usually it is public, and has some business meaning. For example, a TicketingService class might allow you to buyTicket, sellTicket and so on.

What is @service annotation in Java?

@Service. This annotation is used on a class. @Service marks a Java class that performs some service, such as executing business logic, performing calculations, and calling external APIs. This annotation is a specialized form of the @Component annotation intended to be used in the service layer.

How does a Java service work?

So, a Java web service receives a HTTP request as an input, and generates a structured XML/JSON as an output. A request is parsed, then what needs to be done is defined based on the parameters, and a response is generated.

What is difference between DAO and service?

The definition of a DAO is a company that operates without any human involvement. The difference between the two is that a DAO does not have labor while a service has human labor. The difference between DAO and service is that a DAO is an organization without a central manager.

What is @service and @component in Spring?

@Component is a generic stereotype for any Spring-managed component. @Service annotates classes at the service layer. @Repository annotates classes at the persistence layer, which will act as a database repository.

Can we use @service instead of @repository?

According to documentaion @Repository , @Service , @Controller are all synonyms. They all are just specializations of @Component annotation. So, generally, they can be used one instead of other.

How do you name a service class?

There is no «special» convention for naming service classes. They are classes so they should be a noun(s) in singular form in CamelCase: Customer , Company , Employee , UserService , WrapperManager , FileStream , etc.

What is a service in code?

With computer software, a service is software that performs automated tasks, responds to hardware events, or listens for data requests from other software. In a user’s operating system, these services are often loaded automatically at startup, and run in the background, without user interaction.

What is a service in JavaScript?

A Service worker is basically a script (JavaScript file) that runs in background and assists in offline first web application development.

What is the difference between helper and service?

Service able to serve some clients, and often this is a SOA specific entity. Helper provides a set of methods which commonly are pure functions.

What is the use of service class in spring boot?

It is used to mark the class as a service provider. So overall @Service annotation is used with classes that provide some business functionalities. Spring context will autodetect these classes when annotation-based configuration and classpath scanning is used. Add the spring-context dependency in your pom.

What are helper classes in Java?

Helper Class is a Java class which includes basic error handling, some helper functions etc. Helper class contains functions that help in assisting the program. This Class intends to give quick implementation of basic functions such that programmers do not have to implement again and again.

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