@SpringBootApplication
public class Application {
    public static void main(String[] args) throws Exception {
        SpringApplication.run(Application.class, args);
    }
}

@SpringBootApplication
public class Application {
    ...

    @Bean
    WebMvcConfigurer createWebMvcConfigurer(@Autowired HandlerInterceptor[] interceptors) {
        return new WebMvcConfigurer() {
            @Override
            public void addResourceHandlers(ResourceHandlerRegistry registry) {
                // 映射路径`/static/`到classpath路径:
                registry.addResourceHandler("/static/**")
                        .addResourceLocations("classpath:/static/");
            }
        };
    }
}

@Controller
public class UserController {
    @GetMapping("/")
    public ModelAndView index(){
        return new ModelAndView("index.html");
    }
}

public interface StorageService {

    // 根据URI打开InputStream:
    InputStream openInputStream(String uri) throws IOException;

    // 根据扩展名+InputStream保存并返回URI:
    String store(String extName, InputStream input) throws IOException;
}

@Component
@Profile("default")
public class LocalStorageService implements StorageService { ...... }

@Component
@Profile("!default")
public class CloudStorageService implements StorageService { ...... }

@Autowired
StorageService storageService;

@Component
@ConditionalOnProperty(value = "storage.type", havingValue = "local", matchIfMissing = true)
public class LocalStorageService implements StorageService {
    ...
}

@Component
@ConditionalOnProperty(value = "storage.type", havingValue = "aws")
public class AwsStorageService implements StorageService {
    ...
}

@Component
@ConditionalOnProperty(value = "storage.type", havingValue = "aliyun")
public class AliyunStorageService implements StorageService {
    ...
}

@Component
public class FileUploader {
    @Value("${storage.local.max-size:102400}")
    int maxSize;

    ...
}

@Configuration
@ConfigurationProperties("storage.local") 
public class StorageConfiguration {
    private String rootDir;
    private int maxSize;
    private boolean allowEmpty;
    private List<String> allowTypes;

    // TODO: getters and setters
}

@Component
public class StorageService {
    final Logger logger = LoggerFactory.getLogger(getClass());

    @Autowired
    StorageConfiguration storageConfig;

    @PostConstruct
    public void init() {
        logger.info("Load configuration: root-dir = {}", storageConfig.getRootDir());
        logger.info("Load configuration: max-size = {}", storageConfig.getMaxSize());
        logger.info("Load configuration: allowed-types = {}", storageConfig.getAllowTypes());
    }
}

@SpringBootApplication
// 启动自动配置，但排除指定的自动配置:
@EnableAutoConfiguration(exclude = DataSourceAutoConfiguration.class)
public class Application {
    ...
}

public class MasterDataSourceConfiguration {
    @Bean("masterDataSourceProperties")
    @ConfigurationProperties("spring.datasource-master")
    DataSourceProperties dataSourceProperties() {
        return new DataSourceProperties();
    }

    @Bean("masterDataSource")
    DataSource dataSource(@Autowired @Qualifier("masterDataSourceProperties") DataSourceProperties props) {
        return props.initializeDataSourceBuilder().build();
    }
}

public class SlaveDataSourceConfiguration {
    @Bean("slaveDataSourceProperties")
    @ConfigurationProperties("spring.datasource-slave")
    DataSourceProperties dataSourceProperties() {
        return new DataSourceProperties();
    }

    @Bean("slaveDataSource")
    DataSource dataSource(@Autowired @Qualifier("slaveDataSourceProperties") DataSourceProperties props) {
        return props.initializeDataSourceBuilder().build();
    }

}

@SpringBootApplication
@EnableAutoConfiguration(exclude = DataSourceAutoConfiguration.class)
@Import({ MasterDataSourceConfiguration.class, SlaveDataSourceConfiguration.class})
public class Application {
    ...
}

class RoutingDataSource extends AbstractRoutingDataSource {
    @Override
    protected Object determineCurrentLookupKey() {
        // 从ThreadLocal中取出key:
        return RoutingDataSourceContext.getDataSourceRoutingKey();
    }
}

public class RoutingDataSourceConfiguration {
    @Primary
    @Bean
    DataSource dataSource(
            @Autowired @Qualifier("masterDataSource") DataSource masterDataSource,
            @Autowired @Qualifier("slaveDataSource") DataSource slaveDataSource) {
        var ds = new RoutingDataSource();
        // 关联两个DataSource:
        ds.setTargetDataSources(Map.of(
                "masterDataSource", masterDataSource,
                "slaveDataSource", slaveDataSource));
        // 默认使用masterDataSource:
        ds.setDefaultTargetDataSource(masterDataSource);
        return ds;
    }

    @Bean
    JdbcTemplate jdbcTemplate(@Autowired DataSource dataSource) {
        return new JdbcTemplate(dataSource);
    }

    @Bean
    DataSourceTransactionManager dataSourceTransactionManager(@Autowired DataSource dataSource) {
        return new DataSourceTransactionManager(dataSource);
    }
}

@Controller
public class UserController {
    @RoutingWithSlave // <-- 指示在此方法中使用slave数据库
    @GetMapping("/profile")
    public ModelAndView profile(HttpSession session) {
        ...
    }
}

@Aspect
@Component
public class RoutingAspect {
    @Around("@annotation(routingWithSlave)")
    public Object routingWithDataSource(ProceedingJoinPoint joinPoint, RoutingWithSlave routingWithSlave)
            throws Throwable {
        try (RoutingDataSourceContext ctx = new RoutingDataSourceContext(RoutingDataSourceContext.SLAVE_DATASOURCE)) {
            return joinPoint.proceed();
        }
    }
}

@Component
public class AuthFilterRegistrationBean extends FilterRegistrationBean<Filter> {
    @Autowired
    UserService userService;

    @Override
    public Filter getFilter() {
        setOrder(10);
        return new AuthFilter();
    }

    class AuthFilter implements Filter {
        ...
    }
}

@Component
public class ApiFilterRegistrationBean extends FilterRegistrationBean<Filter> {
    @PostConstruct
    public void init() {
        setOrder(20);
        setFilter(new ApiFilter());
        setUrlPatterns(List.of("/api/*"));
    }

    class ApiFilter implements Filter {
        ...
    }
}