可以从application.properties读取变量

Question

我正在制作一个春季应用程序，其中我将数据发送到运动界。我有AccessKey和SecretKey存储在application.properties中。在服务实现类中，我使用这些变量，但是我会遇到一个错误，即访问密钥不能为null。 productererServiceImpl类：

public class ProducerServiceImpl extends ProducerService {

private static final Logger LOG = LoggerFactory.getLogger(ProducerServiceImpl.class);

@Value(value = "${aws.stream_name}")
private String streamName;

@Value(value = "${aws.region}")
private String awsRegion;

@Value(value = "${aws.access_key}")
private String awsAccessKey;

@Value(value = "${aws.secret_key}")
private String awsSecretKey;

private KinesisProducer kinesisProducer = null;
public ProducerServiceImpl() {
    this.kinesisProducer = getKinesisProducer();
}

private KinesisProducer getKinesisProducer() {
    if (kinesisProducer == null) {

        BasicAWSCredentials awsCreds = new BasicAWSCredentials(awsAccessKey, awsSecretKey);

        KinesisProducerConfiguration config = new KinesisProducerConfiguration();
        config.setRegion(awsRegion);
        config.setCredentialsProvider(new AWSStaticCredentialsProvider(awsCreds));
        config.setMaxConnections(1);
        config.setRequestTimeout(6000); // 6 seconds
        config.setRecordMaxBufferedTime(5000); // 5 seconds

        kinesisProducer = new KinesisProducer(config);
    }

    return kinesisProducer;
}

我认为原因是，因为在函数之后，构造函数被称为首先，而变量并未从@value分配值。

Answer 1

如果您在字段上使用@Value注释，则Spring将使用 field注入。这意味着它首先需要创建一个productererServiceimpl（通过调用构造函数）的实例，然后它将使用反射来初始化用@value>的那些字段。

因此，由于注入值之前，请调用您的构造函数，它们将是null。

有两个基本解决方案，一种是使用构造函数注入：

public class ProducerServiceImpl extends ProducerService {
    // ... Fields

    // Pass @Value as constructor parameters
    public ProducerServiceImpl(@Value(value = "${aws.access_key}") String awsAccessKey) {
        // Set the fields before calling getKinesisProducer()
        // If you only need the fields to create the producer, you could also just pass them as arguments to the getKinesisProducer() function
        this.awsAccessKey = awsAccessKey;
        this.kinesisProducer = getKinesisProducer();
    }

    // ...
}

另一个解决方案是等到春季初始化豆子。这可以通过将逻辑移至用@postConstruct and的方法来完成，

public class ProducerServiceImpl extends ProducerService {
    // ... Fields

    // Replace the constructor by a method annotated with @PostConstruct
    @PostConstruct
    public void initializeKinesisProducer() {
        this.kinesisProducer = getKinesisProducer();
    }

    // ...
}

---

但是，首选的解决方案是将整个keneissproducer设置移动到Spring配置类，并提供它是豆子。由于所有弹簧豆都是单胎，因此您可以摆脱该初始化代码。例如：

// Create a new @Configuration class
@Configuration
public class KinesisConfiguration {

    // Create a @Bean method to construct your KinesisProducer
    @Bean
    // Pass all @Value's as parameters
    public KinesisProducer kinesisProducer(@Value("${aws.access_key} String awsAccessKey) {
        BasicAWSCredentials awsCreds = new BasicAWSCredentials(awsAccessKey, awsSecretKey);         KinesisProducerConfiguration config = new KinesisProducerConfiguration();
        config.setRegion(awsRegion);
        config.setCredentialsProvider(new AWSStaticCredentialsProvider(awsCreds));
        config.setMaxConnections(1);
        config.setRequestTimeout(6000); // 6 seconds
        config.setRecordMaxBufferedTime(5000); // 5 seconds

        return new KinesisProducer(config);
    }
}

现在您可以删除服务中的所有代码并使用：

public class ProducerServiceImpl extends ProducerService { 
    // Inject your KinesisProducer, either through field injection or constructor injection
    @Autowired
    private KinesisProducer kinesisProducer;
}

Answer 2

我建议将您的@value配置属性使用@ConfigurationProperties将其注入构造函数。