SpringBoot從零單排 ------初級入門篇

package com.objectman.springboot_study;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class SpringbootStudyApplication {

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

}

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(excludeFilters = {
        @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
        @Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
public @interface SpringBootApplication {

}

/**
 * Indicates that a class provides Spring Boot application
 * {@link Configuration @Configuration}. Can be used as an alternative to the Spring's
 * standard {@code @Configuration} annotation so that configuration can be found
 * automatically (for example in tests).
 * <p>
 * Application should only ever include <em>one</em> {@code @SpringBootConfiguration} and
 * most idiomatic Spring Boot applications will inherit it from
 * {@code @SpringBootApplication}.
 *
 * @author Phillip Webb
 * @since 1.4.0
 */
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Configuration
public @interface SpringBootConfiguration {
}

import com.objectman.springboot_study.User;
import org.springframework.boot.SpringBootConfiguration;
import org.springframework.context.annotation.Bean;

@SpringBootConfiguration
public class Configuration_Test {

    public Configuration_Test() {
        System.out.println("=====>>>>> Configuration_Test 容器啟動初始化");
    }

    @Bean
    public User createUser() {
        User user = new User();
        user.setUserName("Object Man");
        user.setAge(18);
        return user;
    }
}

@SpringBootApplication
public class SpringbootStudyApplication {

    public static void main(String[] args) {
        ConfigurableApplicationContext context = SpringApplication.run(SpringbootStudyApplication.class, args);
        User user = (User) context.getBean("createUser");
        System.out.println("使用者姓名為：" + user.getUserName() + "，今年" + user.getAge() + "歲了");
    }
}

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import(AutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {
    String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";
    Class<?>[] exclude() default {};
    String[] excludeName() default {};
}

public String[] selectImports(AnnotationMetadata annotationMetadata) {
        if (!isEnabled(annotationMetadata)) {
            return NO_IMPORTS;
        }
        //AutoConfigurationMetadataLoader是springboot autoconfigure載入AutoConfigurationMetadata的內部工具類
        AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader
                .loadMetadata(this.beanClassLoader);
        AutoConfigurationEntry autoConfigurationEntry = getAutoConfigurationEntry(
                autoConfigurationMetadata, annotationMetadata);
        return StringUtils.toStringArray(autoConfigurationEntry.getConfigurations());
    }

//定義一個路徑
    protected static final String PATH = "META-INF/"
            + "spring-autoconfigure-metadata.properties";

    public static AutoConfigurationMetadata loadMetadata(ClassLoader classLoader) {
        return loadMetadata(classLoader, PATH);
    }

    static AutoConfigurationMetadata loadMetadata(ClassLoader classLoader, String path) {
        try {
            //找到自動配置的屬性檔案
            Enumeration<URL> urls = (classLoader != null) ? classLoader.getResources(path)
                    : ClassLoader.getSystemResources(path);
            //建立一個properties物件，將所有配置檔案載入到properties物件中
            Properties properties = new Properties();
            while (urls.hasMoreElements()) {
                properties.putAll(PropertiesLoaderUtils
                        .loadProperties(new UrlResource(urls.nextElement())));
            }
            return loadMetadata(properties);
        }
        catch (IOException ex) {
            throw new IllegalArgumentException(
                    "Unable to load @ConditionalOnClass location [" + path + "]", ex);
        }
    }

public enum FilterType {

   ANNOTATION, //按照註解過濾

   ASSIGNABLE_TYPE, //按照給定的型別過濾

   ASPECTJ, //使用ASPECTJ表示式

   REGEX, //透過正則

   CUSTOM //自定義規則

}

<parent>
        <!-- 一個非常牛x的依賴，使用之後後面常用的依賴包可以不用寫version了 -->
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.1.RELEASE</version>
</parent>

<!-- WEB依賴包 -->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>

import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
/**
 * @RestController = @Controller + @ResponseBody
 *
 */
@RestController
public class HelloWorldController {
    /**
     * RequestMapping 將Http請求對映到方法上
     */
    @RequestMapping("/")
    public String HelloWorld() {
        return "Hello World";
    }
}