java - Spring @Component 在 @PostConstruct 完成之前可用

Question

我正在将 Spring Boot 2.0.3 用于 REST 应用程序。我的情况很奇怪。

我有这个界面:

public interface ConnectionPoolManager {

    public Connection getConnection(@NotNull String tenantId, boolean longTask);

    public DataSource getDataSource(@NotNull String tenantId, boolean longTask);
}

及其实现:

@Component
@Profile({"prod"})
public class ConnectionPoolManagerImpl implements ConnectionPoolManager {
    private Logger log = LogManager.getLogger();

    private Map<String, DataSource> dataSourceMap = new ConcurrentHashMap<String, DataSource>();


    private Map<String, DataSource> dataSourceLongConnectionsMap = new ConcurrentHashMap<String, DataSource>();

    private Map<String, String> tenantDatabaseInstanceMap = new ConcurrentHashMap<String, String>();

    @Autowired
    private TenantRestClient tenantRestClient;

    @Autowired
    private PasswordEncrypt passwordEncrypt;

    @Autowired
    private Environment env;

    @Autowired
    private DataSource primaryDataSource;

    /**
     * At application startup we cache connection to all DB instances
     */
    @PostConstruct
    public void init() {
        try {
            log.info("Caching datasource connections...");
            Set<String> databaseIds = tenantRestClient.findDatabaseInstanceIds();
            //Creating datasource and caching them for later
            databaseIds.forEach(s -> getLocalCache(false).put(s, createDataSource(s, false)));
            databaseIds.forEach(s -> getLocalCache(true).put(s, createDataSource(s, true)));
            log.info("Cached {} datasources", dataSourceMap.size());
        } catch (Exception e) {
            log.warn("Error trying to cache datasources.", e);
        }
    }

在这个类(class)中，我调用了tenantRestClient.findDatabaseInstanceIds()，但我遇到了问题。

@Component
public class TenantRestClient {
    private Logger log = LogManager.getLogger();

    @Autowired
    private RestTemplateBuilder restTemplateBuilder;

    private RestTemplate restTemplate;

    @PostConstruct
    public void init() {
        log.debug("------------INIT--------");
        restTemplate = restTemplateBuilder.build();
        log.debug("Post construct {} - {}", restTemplateBuilder, restTemplate);
        log.debug("------------INIT COMPLETED --------");
    }

  public Set<String> findDatabaseInstanceIds() {
           //my logic here

            ResponseEntity<Set<String>> response = restTemplate.exchange(uriBuilder.toUriString(), HttpMethod.GET, entity, new ParameterizedTypeReference<Set<String>>() {
            });

        }
    }

事实上，findDatabaseInstanceIds() 方法是在调用 init() 之前调用的。当然，然后我有一个 NullPointerException 因为restTemplate 是空的。bean tenantRestClient 已准备就绪，并且可以在调用 init() 方法之前调用方法，这怎么可能？

Answer 1

您需要创建一个带有 RestTemplate bean 的配置类，并将其 Autowiring 到您的类。

@Configuration
public class Config



@Bean
public RestTemplate restTemplate(){
  return restTemplateBuilder.build();

}

这将为您的项目创建restTemplate bean。如果您需要多个 RestTemplate，请查看@Qualifier。
现在您可以在类中 Autowiring RestTemplate。不需要PostConstruct

@Component
public class TenantRestClient {
    private Logger log = LogManager.getLogger();

    @Autowired
    private RestTemplate restTemplate;

    public Set<String> findDatabaseInstanceIds() {
           //my logic here

            ResponseEntity<Set<String>> response = restTemplate.exchange(uriBuilder.toUriString(), HttpMethod.GET, entity, new ParameterizedTypeReference<Set<String>>() {
            });

        }
    }