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Spring Boot

Requirements

• jdk 1.8+
• maven 3.0+ /gradle 2.3+
• for maven in pom.xml include parent as
  • org.springframework.boot spring-boot-starter-parent 1.4.1.RELEASE
• get the spring boot dependency
  • org.springframework.boot spring-boot-starter-web
• install spring boot plugin for maven
  • org.springframework.boot spring-boot-maven-plugin

what is spring boot maven plugin

• Spring boot maven plugin provides
  • it collects all jars in classpath and creates an uber jar. So you can easily execute your service and transport it
  • it searches for public static void main class to run from
  • it has a build in depedency resolver which will override dependencies to match dependencies compatible with spring boot. (This will override the dependency set by us, maybe a problem since we cannot be sure if spring overrode version we set)

what can i do with spring boot?

• Spring boot automatically configures embedded tomcat (servlet container)
• If you want jetty we can configure embedded jetty

Rest controller

@RestController
public class HelloController {

    @RequestMapping("/")
    public String index() {
        return "Greetings from Spring Boot!";
    }

}

• @RestController combines @Controller and @ResponseBody to give us back

SpringBootApplication

@SpringBootApplication
public class Application {

    public static void main(String[] args) {
        ApplicationContext ctx = SpringApplication.run(Application.class, args);

        System.out.println("Let's inspect the beans provided by Spring Boot:");

        String[] beanNames = ctx.getBeanDefinitionNames();
        Arrays.sort(beanNames);
        for (String beanName : beanNames) {
            System.out.println(beanName);
        }
    }

}

• Spring boot application combines @ComponentScan, @Configuration, @EnableSpringMvc ( if spring-webmvc is in classpath, This will setup the dispatcherServlet (Servlet over httpServlet following servelt spec to handle http request and dispatch web requests, provide mapping and handle exceptions) @EnableAutoConfiguration. (Do we really want component scan always?)
• Note there is no web.xml , instead @SpringBootApplication uses SpringApplication.run() to launch application. Its pure java. The deployment description is embedded into code and spring determines it. (maybe not recommended)

Unit tests

@RunWith(SpringRunner.class)
@SpringBootTest
@AutoConfigureMockMvc
public class HelloControllerTest {

    @Autowired
    private MockMvc mvc;

    @Test
    public void getHello() throws Exception {
        mvc.perform(MockMvcRequestBuilders.get("/").accept(MediaType.APPLICATION_JSON))
                .andExpect(status().isOk())
                .andExpect(content().string(equalTo("Greetings from Spring Boot!")));
    }
}

  <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>

• MockMvc it comes from spring test dependency. It sets builder classes to send http requests to dispatcher servlet. To Autowire mockMvc we need @SpringBootTest and @AutoConfigureMockMvc
• This just sends a fake http request to dispacther servlet.. above it is sending stuff to dispatcher servlet and then aserting the response
• note since we do not start the server , this is a unit test for resource
• drawback is lot of annotations

Integration tests

package hello;

import static org.hamcrest.Matchers.equalTo;
import static org.junit.Assert.assertThat;

import java.net.URL;

import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.context.embedded.LocalServerPort;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.boot.test.web.client.TestRestTemplate;
import org.springframework.http.ResponseEntity;
import org.springframework.test.context.junit4.SpringRunner;

@RunWith(SpringRunner.class)
@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
public class HelloControllerIT {

    @LocalServerPort
    private int port;

    private URL base;

    @Autowired
    private TestRestTemplate template;

    @Before
    public void setUp() throws Exception {
        this.base = new URL("http://localhost:" + port + "/");
    }

    @Test
    public void getHello() throws Exception {
        ResponseEntity<String> response = template.getForEntity(base.toString(),
                String.class);
        assertThat(response.getBody(), equalTo("Greetings from Spring Boot!"));
    }
}

• embedded server is started on random port, by arguments of annotation @SpringBootTest
• we can discover the port at runtime using @LocalServerPort annotation

Management end points by spring boot

<dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
</dependency>

• after adding the above dependency do the below

mvn package && java -jar target/gs-spring-boot-0.1.0.jar

• its easy to check health of app

curl localhost:8080/health

• add endpoints.shutdown.enabled=true to application.properties to enable /shutdown endpoint

spring-boot-starter links

spring boot starter

what is jmx

• jmx is java management extension. It has api to get monitoring and management information for java. We can use a jmx client and query programtically monitoring information.