Spring Boot starts writing a Start

When we use the SpringBoot project, we can introduce a SpringBoot Start dependency, which requires very little code, or no code to use the default configuration, and no more tedious configuration. Let’s write a start ourselves.

Create a New Maven project for Start

1. The POM file is as follows

<dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-dependencies</artifactId>
            <version>2.1.0. RELEASE</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>
    </dependencies>
</dependencyManagement>

<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-autoconfigure</artifactId>
        <scope>compile</scope>
    </dependency>

    <dependency>
        <groupId>org.projectlombok</groupId>
        <artifactId>lombok</artifactId>
        <version>1.18.6</version>
        <optional>true</optional>
        <scope>provided</scope>
    </dependency>

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

</dependencies>
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• Spring-boot-autoconfigure A core dependency for springboot automatic configuration
• Spring – the boot – starter – test test package
• Lombok dispenses with getters/setters and other simplified code

2. Demo code

DemoService:

public interface DemoService {

    String getMessage(a);

    Integer getCode(a);
}

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DemoServiceImpl:

public class DemoServiceImpl implements DemoService {

    @Override
    public String getMessage(a) {
        return "Hello!";
    }

    @Override
    public Integer getCode(a) {
        return 123; }}Copy the code

DemoAutoConfiguration:

@Configuration
public class DemoAutoConfiguration {

    @Bean
    @ConditionalOnMissingBean(DemoService.class)
    public DemoService demoService(a) {
        return newDemoServiceImpl(); }}Copy the code

• @Configuration Indicates that this class is a Configuration class
• ConditionalOnMissingBean(demoservice.class) ConditionalOnMissingBean(demoservice.class

Spingboot’s automatic annotations are mainly implemented with these conditional annotations. Check out the previous article:

Conditional notes for Spring Boot automatic configuration

Spring Boot automatic configuration @enable * and @import annotations

Spring Boot automatic configuration @enableAutoConfiguration

3. Have SpringBoot recognize code that is automatically configured

You need to create a new file meta-INF /spring.factories under Resources

org.springframework.boot.autoconfigure.EnableAutoConfiguration=com.jiuxian.DemoAutoConfiguration
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SpringBoot the annotations in @ EnableAutoConfiguration. At the time of launch will pass SpringFactoriesLoader loadFactoryNames method to get the spring. The factories Configuration class under file

4. The test class

• We need to package the main method of Application Run

@SpringBootApplication
public class StartDemoApplication {

    public static void main(String[] args) { SpringApplication.run(StartDemoApplication.class, args); }}Copy the code

• The test class

@RunWith(SpringRunner.class)
@SpringBootTest
public class StartDemoApplicationTests {

    @Resource
    private DemoService demoService;

    @Test
    public void test(a) {
        String message = demoService.getMessage();
        System.out.println(message);
        Assert.assertEquals("Hello!", message);

        Integer code = demoService.getCode();
        System.out.println(code);
        Assert.assertEquals(123, (int) code); }}Copy the code

If there is no StartDemoApplication class, the test class starts with an @SpringBootApplication failed to find error

2. Create a SpringBoot project

1. service

@Service
public class TestService {

    @Resource
    private DemoService demoService;

    public void message(a) {
        System.out.println("code:" + demoService.getCode());
        System.out.println("message:"+ demoService.getMessage()); }}Copy the code

2. test

    @Resource
    private TestService testService;

    @Test
    public void test(a) {
        testService.message();
    }

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Results:

code:123
message:Hello!
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3. Override the DemoService method

@Service
public class DemoServiceImpl implements DemoService {

    @Override
    public String getMessage(a) {
        return "Hello!";
    }

    @Override
    public Integer getCode(a) {
        return 123; }}Copy the code

4. The test results

code:123
message:Hello!
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This result is due to the @conditionAlonmissingBean (demoservice.class) annotation in the DemoService implementation class of the Start project, which is used by default if it does not exist

Third, Demo source code

GitHub source address