// @SpringBootApplication 整合了 @Configuration + @ComponentScan + @EnableAutoConfiguration，其会自动进行组件扫描与配置
@SpringBootApplication
public class FooApplication {

  public static void main(String[] args) {
    // Bootstrap the application
    SpringApplication.run(FooApplication.class, args);
  }
}

@Component
public class MyComponent {}

@Configuration
public class TestConfig {
    @Bean(name="helloClient")
    public HessianProxyFactoryBean helloClient() {
        HessianProxyFactoryBean factory = new HessianProxyFactoryBean();
        ...
        return factory;
    }
}

@Configuration
@ConditionalOnClass(DataSource.class)
public class MySQLAutoconfiguration {
  //...
}

@Bean
@ConditionalOnBean(name = "dataSource")
@ConditionalOnMissingBean
public LocalContainerEntityManagerFactoryBean entityManagerFactory() {
    LocalContainerEntityManagerFactoryBean em
      = new LocalContainerEntityManagerFactoryBean();
    ...
    return em;
}

@Bean
@ConditionalOnProperty(
  name = "usemysql",
  havingValue = "local")
@ConditionalOnMissingBean
public DataSource dataSource() {
    DriverManagerDataSource dataSource = new DriverManagerDataSource();
    ...
    return dataSource;
}

// Defining Condition that checks if the JdbcTemplate is available on the classpath
//
// Conditions are used by the auto-configuration mechanism of Spring Boot
// There are several configuration classes in the spring-boot-autoconfigure.jar
// which contribute to the configuration if specific conditions are met
public class JdbcTemplateCondition implements Condition {
  @Override
  public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
    try {
      context.getClassLoader().loadClass("org.springframework.jdbc.core.JdbcTemplate");
      return true;
    } catch (Exception e) {
      return false;
    }
  }
}

// Use a custom condition class to decide whether a Bean should be created or not
@Conditional(JdbcTemplateCondition.class)
public class MyService {
  ...
}

@PostConstruct
public void initAfterStartup() {
    ...
}

@PreDestroy
public void cleanupBeforeExit() {
    ...
}

@Bean(destroyMethod = "close")
public MyBean myBean(){...

@Component
public class CommandLineAppStartupRunner implements CommandLineRunner {
  private static final Logger logger = LoggerFactory.getLogger(
    CommandLineAppStartupRunner.class
  );

  @Override
  public void run(String... args) throws Exception {
    logger.info(
      "Application started with command-line arguments: {} . \n To kill this application, press Ctrl + C.",
      Arrays.toString(args)
    );
  }
}

@Component
public class AppStartupRunner implements ApplicationRunner {
  private static final Logger logger = LoggerFactory.getLogger(
    AppStartupRunner.class
  );

  @Override
  public void run(ApplicationArguments args) throws Exception {
    logger.info(
      "Your application started with option names : {}",
      args.getOptionNames()
    );
  }
}

# 在本地跑时，默认是 local，在其它环境跑时，要通过 -Dspring.profiles.active= 来指定
spring.profiles.active=local

// jdbc.mysql.url=jdbc:mysql://localhost:3306/sampledb

// 配置数据源
@Configuration
public class HikariDataSourceConfiguration {

    @Value("jdbc.mysql.url")
    public String url;
    ...
    @Bean
    public HikariDataSource dataSource() {
        HikariConfig hikariConfig = new HikariConfig();
        hikariConfig.setJdbcUrl(url);
        ...
        return new HikariDataSource(hikariConfig);
    }
}

@Configuration
@PropertySource("classpath:configprops.properties")
@ConfigurationProperties(prefix = "mail")
public class ConfigProperties {

    public static class Credentials {
        private String authMethod;
        private String username;
        private String password;

       // standard getters and setters
    }
    private String host;
    private int port;
    private String from;
    private Credentials credentials;
    private List<String> defaultRecipients;
    private Map<String, String> additionalHeaders;

    // standard getters and setters
}

// 使用的时候直接注入
@AutoWired
public ConfigProperties config;

#Simple properties
mail.host=mailer@mail.com
mail.port=9000
mail.from=mailer@mail.com

#List properties
mail.defaultRecipients[0]=admin@mail.com
mail.defaultRecipients[1]=owner@mail.com

#Map Properties
mail.additionalHeaders.redelivery=true
mail.additionalHeaders.secure=true

#Object properties
mail.credentials.username=john
mail.credentials.password=password
mail.credentials.authMethod=SHA1

@Length(max = 4, min = 1)
private String authMethod;

@RestController
@RequestMapping("/persons")
class PersonController {

  @GetMapping("/{id}")
  public Person getPerson(@PathVariable Long id) {
    // ...
  }

  @PostMapping
  @ResponseStatus(HttpStatus.CREATED)
  public void add(@RequestBody Person person) {
    // ...
  }
}

@GetMapping("/hello/{name}")
private String hello(@PathVariable(value = "name", required = true) String name){
    //...
}

@GetMapping("/name")
private ResponseEntity<?> queryPerson(@RequestParam(value = "query", required = false) String query) {
    // ...
}

public class Message {
  @NotNull
  private String title;

  @NotNull
  private String message;
// getters/setters/etc
}

@PostMapping
public ResponseEntity<?> createMessage(@Valid @RequestBody Message message) {
    // ...
}

public class InRangeValidator implements ConstraintValidator<InRange, Integer> {
  private int min;
  private int max;

  @Override
  public void initialize(InRange constraintAnnotation) {
    this.min = constraintAnnotation.min();
    this.max = constraintAnnotation.max();
  }

  @Override
  public boolean isValid(Integer value, ConstraintValidatorContext context) {
    return value == null || (value >= min && value <= max);
  }
}

// 扩展 InRange 接口，添加自定义属性
@Target({ ElementType.METHOD, ElementType.FIELD, ElementType.PARAMETER })
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Constraint(validatedBy = { InRangeValidator.class })
public @interface InRange {
  String message() default "Value is out of range";

  Class<?>[] groups() default {  };

  Class<? extends Payload>[] payload() default {  };

  int min() default Integer.MIN_VALUE;

  int max() default Integer.MAX_VALUE;
}

@NotNull(groups = {Existing.class, New.class})
@InRange(
    min=18,
    message = "User must be at least 18 years old",
    groups = {Existing.class, New.class}
)
private Integer age;

@ExceptionHandler
@ResponseStatus(HttpStatus.BAD_REQUEST)
public ErrorResponse handleException(MethodArgumentNotValidException exception) {

    String errorMsg = exception.getBindingResult().getFieldErrors().stream()
            .map(DefaultMessageSourceResolvable::getDefaultMessage)
            .findFirst()
            .orElse(exception.getMessage());

    return ErrorResponse.builder().message(errorMsg).build();
}

<appender name="ERROR-APPENDER"
          class="ch.qos.logback.core.rolling.RollingFileAppender">
    <file>${LOG_PATH}/common-error.log</file>
    <!-- Error 级别过滤 -->
    <filter class="ch.qos.logback.classic.filter.LevelFilter">
      <level>ERROR</level>
      <onMatch>ACCEPT</onMatch>
      <onMismatch>DENY</onMismatch>
  </filter>
    <encoder>
        <pattern>%d{yyyy-MM-dd HH:mm:ss.SSS} ${LOG_LEVEL_PATTERN:-%5p} - [%thread] : %m%n${LOG_EXCEPTION_CONVERSION_WORD:-%wEx}
        </pattern>
    </encoder>
    <rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy">
        <!-- 按天滚动，可根据实际量调整单位 -->
        <fileNamePattern>${LOG_PATH}/common-error.log.%d{yyyy-MM-dd}
        </fileNamePattern>
        <maxHistory>15</maxHistory>
    </rollingPolicy>
</appender>

<root level="INFO">
    <!-- root中增加Error输出配置 -->
    <appender-ref ref="ERROR-APPENDER" />
</root>

<logger name="testLog" level="INFO"
        additivity="false">
    <appender-ref ref="WORK_SHIFT_CORE_MONITOR_LOG" />
    <!-- 每个logger增加ERROR输出 -->
    <appender-ref ref="ERROR-APPENDER" />
</logger>

dependencies {
    compile("org.springframework.boot:spring-boot-starter-cache")
}

@Cacheable("books")
public Book getByIsbn(String isbn) {
    ...
}

// Testing classes in Spring Boot
@RunWith(SpringJUnit4ClassRunner.class)
// Load context via Spring Boot
@SpringApplicationConfiguration(classes = ReadinglistApplication.class)
@WebAppConfiguration
public class ReadinglistApplicationTests {

  // Test that the context successfully loads (the method can be empty -> the test will fail if the context cannot be loaded)
  @Test
  public void contextLoads() {}
}

// Integration test by loading Springs application context
// To to integration testing with Spring, all components of the application have to be configured and wired up.
// Instead of doing this by hand we can use Spring's SpringJUnit4ClassRunner.
// It helps load a Spring application context in JUnit-based application tests.
// This method with the @ContextConfiguration annotation doesn't apply extenal properites (application.properties) and logging
// @ContextConfiguration specifies how to load the application context: A configuraiton class is passed to it as a parameter
@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(classes = PlaylistConfiguration.class)
public class PlaylistServiceTests {
  @Autowired
  private PlaylistService playlistService;

  @Test
  public void testService() {
    Playlist playlist = playlistService.findByName("X-Mas Songs");
    assertEquals("X-Mas Songs", playlist.getName());
    assertEquals(12, playlist.countSongs());
  }
}

@SpringBootTest
@Transactional
class MySpec extends Specification {

  @Autowired
  MyRepository myRepo

  def "Persist an entity"() {
    given:
    MyEntity entity = new MyEntity()

    when:
    myRepo.saveAndFlush(entity)

    then:
    myRepo.count() == 1
  }

  def "Persist another entity"() {
    given:
    MyEntity entity = new MyEntity()

    when:
    myRepo.saveAndFlush(entity)

    then:
    myRepo.count() == 1
  }
}