Tmp

In Spring’s approach to building RESTful web services, HTTP requests are handled by a controller.

These components are identified by the @RestController annotation ( shorthand for including both @Controller and @ResponseBody)

The @GetMapping annotation ensures that HTTP GET requests to /greeting are mapped to the greeting() method.

There are companion annotations for other HTTP verbs (e.g. @PostMapping for POST). There is also a @RequestMapping annotation that they all derive from, and can serve as a synonym (e.g. @RequestMapping(method=GET)).

@RequestParam binds the value of the query string parameter name into the name parameter of the greeting() method. If the name parameter is absent in the request, the defaultValue of World is used.

A key difference between a traditional MVC controller and the RESTful web service controller is the way that the HTTP response body is created. Rather than relying on a view technology to perform server-side rendering of the greeting data to HTML, this RESTful web service controller populates and returns a Greeting object. The object data will be written directly to the HTTP response as JSON.

The Greeting object must be converted to JSON. Thanks to Spring’s HTTP message converter support, you need not do this conversion manually. Because Jackson 2 is on the classpath, Spring’s MappingJackson2HttpMessageConverter is automatically chosen to convert the Greeting instance to JSON.

@RestController
public class GreetingController {
    private static final String template="hello,%s!";
    private final AtomicLong counter=new AtomicLong();
    @GetMapping("/greeting")
    public Greeting greeting(@RequestParam(value = "name",defaultValue = "World")String name){
        return new Greeting(counter.incrementAndGet(),String.format(template,name));
    }
}

@Data
public class Greeting {
    private final long id;
    private final String content;
    public Greeting(long id, String content){
        this.id = id;
        this.content = content;
    }
}

@SpringBootApplication is a convenience annotation that adds all of the following:

• @Configuration: Tags the class as a source of bean definitions for the application context.
• @EnableAutoConfiguration: Tells Spring Boot to start adding beans based on classpath settings, other beans, and various property settings. For example, if spring-webmvc is on the classpath, this annotation flags the application as a web application and activates key behaviors, such as setting up a DispatcherServlet.
• @ComponentScan: Tells Spring to look for other components, configurations, and services in the com/example package, letting it find the controllers.

The main() method uses Spring Boot’s SpringApplication.run() method to launch an application.

There was not a single line of XML? There is no web.xml file, either. This web application is 100% pure Java and you did not have to deal with configuring any plumbing or infrastructure.

@SpringBootApplication
@RestController
public class LearnApplication {

	public static void main(String[] args) {
		SpringApplication.run(LearnApplication.class, args);
	}
}

Build an executable JAR

You can run the application from the command line with Gradle or Maven. You can also build a single executable JAR file that contains all the necessary dependencies, classes, and resources and run that. Building an executable jar makes it easy to ship, version, and deploy the service as an application throughout the development lifecycle, across different environments, and so forth.

If you use Gradle, you can run the application by using ./gradlew bootRun. Alternatively, you can build the JAR file by using ./gradlew build and then run the JAR file, as follows:

java -jar build/libs/gs-rest-service-0.1.0.jar

If you use Maven, you can run the application by using ./mvnw spring-boot:run. Alternatively, you can build the JAR file with ./mvnw clean package and then run the JAR file, as follows:

java -jar target/gs-rest-service-0.1.0.jar