Spring Boot应用程序无法启动，并显示错误“应用程序需要单个bean，但是找到了2个”

时间：2019-01-25 21:13:04

标签： java spring spring-boot mqtt

我正在使用spring-integration-mqtt依赖关系编写Spring Boot应用程序，其中我使用CommandLineRunner bean在应用程序启动时启动MQTTSubscriber。

但是，当我运行该应用程序时，出现以下错误：

Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
2019-01-26 01:48:40.386 ERROR 59171 --- [           main] o.s.b.d.LoggingFailureAnalysisReporter   : 
***************************
APPLICATION FAILED TO START
***************************
Description:
Field MessageListener in im.sma.mqtt.mqttclient.DemoApplication required a single bean, but 2 were found:
    - messageListener: defined in file [/Users/sma/sandbox/slidecab/mqtt/mqtt-client/target/classes/im/sma/mqtt/mqttclient/config/MessageListener.class]
    - integrationHeaderChannelRegistry: defined in null
Action:
Consider marking one of the beans as @Primary, updating the consumer to accept multiple beans, or using @Qualifier to identify the bean that should be consumed

我注意到当我从代码中删除以下部分时，错误消失了：

@Autowired
Runnable MessageListener;

@Bean
public CommandLineRunner schedulingRunner(TaskExecutor executor) {
    return new CommandLineRunner() {
        public void run(String... args) throws Exception {
            executor.execute(MessageListener);
        }
    };
}

这是我的DemoApplication类，发生错误：

@SpringBootApplication
public class DemoApplication extends SpringBootServletInitializer {
    @Autowired
    Runnable MessageListener;

    @Override
    protected SpringApplicationBuilder configure(SpringApplicationBuilder application) {
        return application.sources(DemoApplication.class);
    }

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }
    @Bean
    public CommandLineRunner schedulingRunner(TaskExecutor executor) {
        return new CommandLineRunner() {
            public void run(String... args) throws Exception {
                executor.execute(MessageListener);
            }
        };
    }
}

此外，我还具有以下AppConfig类来设置TaskExecutor：

@Component
public class AppConfig {

    @Bean
    @Primary
    public TaskExecutor taskExecutor() {
        return new SimpleAsyncTaskExecutor();
    }
}

这是无法自动装配的MessageListener bean：

@Component
public class MessageListener implements Runnable {

    @Autowired
    MQTTSubscriberBase subscriber;

    @Override
    public void run() {
        while(true) {
            subscriber.subscribeMessage("demoTopic2019");
        }

    }
}

此外，我还具有以下配置来设置MQTTSubscriber：

public abstract class MQTTConfig {
    protected final String broker = "localhost";
    protected final int qos = 2;
    protected Boolean hasSSL = false; /* By default SSL is disabled */
    protected Integer port = 1883; /* Default port */
    protected final String userName = "guest" ;//"testUserName";
    protected final String password = "guest";//"demoPassword";
    protected final String TCP = "tcp://";
    protected final String SSL = "ssl://";

    protected abstract void config(String broker, Integer port, Boolean ssl, Boolean withUserNamePass);

    protected abstract void config();
}

public interface MQTTSubscriberBase {
    public static final Logger logger = LoggerFactory.getLogger(MQTTSubscriberBase.class);

    public void subscribeMessage(String topic);
    public void disconnect();
}

@Component
public class MQTTSubscriber extends MQTTConfig implements MqttCallback, MQTTSubscriberBase {
    private String brokerUrl = null;
    private String colon = ":";
    private String clientId = "demoClient2";

    private MqttClient client = null;
    private MqttConnectOptions options = null;
    private MemoryPersistence persistence = null;

    private static final Logger logger = LoggerFactory.getLogger(MQTTSubscriber.class);

    public MQTTSubscriber() {
        this.config();
    }

    @Override
    public void connectionLost(Throwable cause) {
        logger.info("Connection lost");
    }

    @Override
    public void messageArrived(String topic, MqttMessage message) throws Exception {
        String time = new Timestamp(System.currentTimeMillis()).toString();
        System.out.println();
        System.out.println("********************************************************");
        System.out.println("Message arrived at " + time + "Topic: " + topic + " Message: " + new String(message.getPayload()));
        System.out.println("********************************************************");
        System.out.println();
    }

    @Override
    public void deliveryComplete(IMqttDeliveryToken token) {
        // Not required for subscriber
    }


    @Override
    public void subscribeMessage(String topic) {
        try {
            this.client.subscribe(topic, this.qos);
        } catch (MqttException exception) {
            logger.error("ERROR", exception);
        }
    }

    @Override
    public void disconnect() {
        try {
            this.client.disconnect();
        } catch (MqttException exception) {
            logger.error("ERROR: ", exception);
        }
    }


    @Override
    public void config(String broker, Integer port, Boolean ssl, Boolean withUserNamePass) {
        String protocol = this.TCP;
        if (true == ssl) {
            protocol = this.SSL;
        }

        this.brokerUrl = protocol + broker + this.colon + port;
        this.persistence = new MemoryPersistence();
        this.options = new MqttConnectOptions();

        try {
            this.client = new MqttClient(this.brokerUrl, clientId, persistence);
            this.options.setCleanSession(true);
            if (true == withUserNamePass) {
                if (this.password != null) {
                    this.options.setPassword(this.password.toCharArray());
                }
                if (this.userName != null) {
                    this.options.setUserName(this.userName);
                }
            }
            this.client.connect(this.options);
            this.client.setCallback(this);
        }
        catch(MqttException exception) {
            this.logger.error("ERROR ", exception);
        }
    }

    @Override
    public void config() {
        this.brokerUrl = this.TCP + this.broker + this.colon + this.port;
        this.persistence = new MemoryPersistence();
        this.options = new MqttConnectOptions();

        try {
            this.client = new MqttClient(brokerUrl, clientId, persistence);
            this.options.setCleanSession(true);
            this.client.connect(options);
            this.client.setCallback(this);
        }
        catch(MqttException exception) {
            logger.error("ERROR", exception);
        }
    }

}

这些是我正在使用的依赖项：

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.1.2.RELEASE</version>
    <relativePath/>
  </parent>
  <groupId>im.sma.mqtt</groupId>
  <artifactId>mqtt-client</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <name>demo</name>
  <description>Demo project for Spring Boot</description>
  <properties>
    <java.version>1.8</java.version>
  </properties>
  <dependencies>
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-websocket</artifactId>
    </dependency>
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-test</artifactId>
      <scope>test</scope>
    </dependency>
    <dependency>
      <groupId>org.springframework.integration</groupId>
      <artifactId>spring-integration-mqtt</artifactId>
      <version>5.1.2.RELEASE</version>
    </dependency>

  </dependencies>
  <build>
    <plugins>
      <plugin>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-maven-plugin</artifactId>
      </plugin>
    </plugins>
  </build>
</project>

为什么不能注入豆子，应该采取什么措施？

2 个答案:

答案 0 :(得分：2)

问题是您使用的是自动接线的通用接口，即Runnable。

由于这一点，似乎存在与Runnable接口匹配的两个bean：

  1. 一个是您自己创建的MessageListener类
  2. 另一个DefaultHeaderChannelRegistry，作为称为integrationHeaderChannelRegistry的bean公开。大概是因为您在类路径中集成了Spring而被公开。

问题是由于这个原因，Spring IoC容器无法弄清楚应该注入哪个bean，它提供了一些解决方案。

将其中一个bean标记为@Primary

这可以用于其中99％的方案中将使用其中一个bean的方案中。通过将MessageListener类标记为@Primary，在尝试注入它时将具有优先级，例如：

@Primary // Add this
@Component
public class MessageListener implements Runnable {
    // ...
}

更新消费者以接受多个bean

当您要引用所有Runnable bean时，此方案很有用。在您的情况下，这可能不是解决方案，但是在某些情况下，您可能希望获取特定类型的所有bean。为此，您可以执行以下操作：

@Autowired
private List<Runnable> runnables; // Change the type to List<Runnable>

使用@Qualifier标识bean

另一种可能性是使用@Qualifier指定要注入的bean的确切名称。您可以在messageListener或integrationHeaderChannelRegistry之间进行选择。例如：

@Autowired
@Qualifier("messageListener")
private Runnable mesageListener;

这可能是您提出的最佳解决方案。

我也想提供一些其他解决方案。

使用特定类型

如果将自动装配字段的类型更改为MessageListener，则不会混淆应该注入哪个bean，因为只有一个MessageListener类型的bean：

@Autowired
private MessageListener mesageListener;

不使用Spring集成库

到目前为止，您所显示的代码与Spring集成无关。如果您的唯一目标是设置MQTT客户端，则可能要考虑删除spring-integration-mqtt软件包，而改为使用像Eclipse Paho这样的简单MQTT客户端实现。

由于另一个Bean是由于您添加了spring-integration-mqtt库而被自动创建的，因此将其删除将停止导致该Bean的创建，这也将解决该问题。

答案 1 :(得分：0)

我的代码在这个问题上呆了一周，今天我发现了Juste，因为我给两个方法命名了相同的名称：

   @Bean(name = "sqlServer")
public DataSource sqlServerDataSource() {
    DriverManagerDataSource dataSource = new DriverManagerDataSource();
    dataSource.setDriverClassName(env.getProperty("spring.ds-sql.driverClassName"));
    dataSource.setUrl(env.getProperty("spring.ds-sql.url"));
    dataSource.setUsername(env.getProperty("spring.ds-sql.username"));
    dataSource.setPassword(env.getProperty("spring.ds-sql.password"));
    return dataSource;
}

@Bean(name = "sqlJdbc")
public JdbcTemplate sqlServerDataSource(@Qualifier("sqlServer") DataSource dsSqlServer) {
    return new JdbcTemplate(dsSqlServer);
}

希望这对有相同案件的人有所帮助。

祝你好运

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