为什么 messageConverter.fromMessage() 不转换数组列表？ java.lang.ClassCastException: java.lang.String 无法施放

Question

我想发送包含销售列表的 JMS 消息并通过 onMessage() 接收。据我所知，springframework.jms.support.converter.MessageConverter 应该起到转换或转换消息的作用，因此我不必创建 XSD 或额外的映射 classes。我的意思是，我期待下面的测试发送一条消息和 (SalesMessage) messageConverter.fromMessage(message) 足以转换和实例化 SalesMessage 的对象。

基本上，错误是java.lang.ClassCastException: java.lang.String cannot be cast to ...SalesMessage。

我的测试

AnnotationConfigApplicationContext context;
MyMessageSender ms;
JmsListenerEndpointRegistry bean;

@Before
public void setUpBeforeClass() throws Exception {

    context =  new AnnotationConfigApplicationContext(AppConfig.class);
    ms = context.getBean(MyMessageSender.class);
}

@Test
public void test2() {

    Sale s = new Sale("product_type", 1L);
    List<Sale> l = new ArrayList<Sale>();
    l.add(s);

    SalesMessage sm = new SalesMessage(l, 1);

    ms.sendMessage(sm.toString());

    bean = context.getBean(JmsListenerEndpointRegistry.class);
    for (MessageListenerContainer listenerContainer : bean.getListenerContainers()) {
        DefaultMessageListenerContainer container = (DefaultMessageListenerContainer) listenerContainer;
        container.shutdown();
    }

}

MyJmsListener

    @Component
    public class MyJmsListener {

         @Autowired
         private MessageConverter messageConverter;

        @JmsListener(destination = AppConfig.QUEUE_NAME)
        public void handleMessage(Message message) {
            try {
                System.out.println("received: "+message);
//this prints received: ActiveMQTextMessage {commandId = 5, ..., jmsXGroupFirstForConsumer = false, text = SalesMessage [sales=[Sale [product_type=produ...ssageType=1]}
                SalesMessage salesMessage = (SalesMessage) messageConverter.fromMessage(message); // <<< here is the focus of my question
                System.out.println("salesMessage: "+salesMessage);
            }
            catch(JMSException e) {
                 e.printStackTrace();
            }

        }
    }

Spring 配置

@Configuration
@ComponentScan
@EnableJms
public class AppConfig {
    public static final String QUEUE_NAME = "example.queue";

    @Bean
    public ConnectionFactory connectionFactory() {
        ConnectionFactory connectionFactory =
                new ActiveMQConnectionFactory("vm://localhost");
        return connectionFactory;
    }

    @Bean
    public JmsListenerContainerFactory jmsListenerContainerFactory() {
        DefaultJmsListenerContainerFactory factory =
                new DefaultJmsListenerContainerFactory();
        factory.setConnectionFactory(connectionFactory());
        //core poll size=4 threads and max poll size 8 threads
        factory.setConcurrency("4-8");
        return factory;
    }

    @Bean
    MessageConverter converter(){
        return new SimpleMessageConverter();
    }
}

销售消息class

public class SalesMessage  implements Serializable{
    List<Sale> sales = new ArrayList<Sale>();
    int messageType;
    //getters/setters/toString()

促销 class

public class Sale  implements Serializable{
    private String product_type;
    private Long value;
//getters/setters/toString()

正在发送消息

@Component
public class MyMessageSender {

    @Autowired
    private ConnectionFactory connectionFactory;
    private JmsTemplate jmsTemplate;

    @PostConstruct
    public void init() {
        this.jmsTemplate = new JmsTemplate(connectionFactory);
    }

    public void sendMessage(String message) {
        System.out.println("sending: " + message);
        jmsTemplate.send(AppConfig.QUEUE_NAME, new MessageCreator() {
            @Override
            public Message createMessage(Session session) throws JMSException {
                return session.createTextMessage(message);
            }
        });
    }
}

*** 已编辑 Spring 配置已更新

@Configuration
@ComponentScan
@EnableJms
public class AppConfig {
    public static final String QUEUE_NAME = "example.queue";

    @Bean
    public ConnectionFactory connectionFactory() {
        ConnectionFactory connectionFactory = new ActiveMQConnectionFactory("vm://localhost");
        return connectionFactory;
    }

    @Bean
    public JmsListenerContainerFactory jmsListenerContainerFactory() {
        DefaultJmsListenerContainerFactory factory = new DefaultJmsListenerContainerFactory();
        factory.setConnectionFactory(connectionFactory());
        // core poll size=4 threads and max poll size 8 threads
        factory.setConcurrency("4-8");
        return factory;
    }

    @Bean
    public MessageConverter jacksonJmsMessageConverter() {
        MappingJackson2MessageConverter converter = new MappingJackson2MessageConverter();
        converter.setTargetType(MessageType.TEXT);
        converter.setTypeIdPropertyName("_type");
        return converter;
    }

    @Bean
    public JmsTemplate jmsTemplate() {
        JmsTemplate template = new JmsTemplate();
        template.setMessageConverter(jacksonJmsMessageConverter());
        template.setConnectionFactory(connectionFactory());
        return template;
    }

*** 已编辑当我在 Listener 端打印消息时，我得到

received: ActiveMQObjectMessage {commandId = 5, responseRequired = true, messageId = ID:win10-cha-51561-1509914170598-4:2:1:1:1, originalDestination = null, originalTransactionId = null, producerId = ID:win10-cha-51561-1509914170598-4:2:1:1, destination = queue://example.queue, transactionId = null, expiration = 0, timestamp = 1509914232995, arrival = 0, brokerInTime = 1509914232995, brokerOutTime = 1509914233010, correlationId = null, replyTo = null, persistent = true, type = null, priority = 4, groupID = null, groupSequence = 0, targetConsumerId = null, compressed = false, userID = null, content = org.apache.activemq.util.ByteSequence@24f339bf, marshalledProperties = null, dataStructure = null, redeliveryCounter = 0, size = 1346, properties = null, readOnlyProperties = true, readOnlyBody = true, droppable = false, jmsXGroupFirstForConsumer = false}

和 SalesMessage salesMessage = (SalesMessage) messageConverter.fromMessage(message) 引发此异常

org.springframework.jms.support.converter.MessageConversionException: Could not find type id property [_type] on message [ID:win10-cha-51561-1509914170598-4:2:1:1:1] from destination [queue://example.queue]

在发送端，我打印消息

SalesMessage [sales=[Sale [product_type=product_type, value=1]], messageType=1]

并且，这是我更新的完整应用程序配置（我遵循提供的建议）

@Configuration
@ComponentScan
@EnableJms
public class AppConfig {
    public static final String QUEUE_NAME = "example.queue";

    @Bean
    public ConnectionFactory connectionFactory() {
        ConnectionFactory connectionFactory = new ActiveMQConnectionFactory("vm://localhost");
        return connectionFactory;
    }

    @Bean
    public JmsListenerContainerFactory jmsListenerContainerFactory() {
        DefaultJmsListenerContainerFactory factory = new DefaultJmsListenerContainerFactory();
        factory.setConnectionFactory(connectionFactory());
        factory.setConcurrency("4-8");
        factory.setMessageConverter(jacksonJmsMessageConverter());
        return factory;
    }

    @Bean 
    public MessageConverter jacksonJmsMessageConverter() {
        MappingJackson2MessageConverter converter = new MappingJackson2MessageConverter();
        converter.setTargetType(MessageType.TEXT);
        converter.setTypeIdPropertyName("_type");


        ObjectMapper objectMapper = new ObjectMapper();

        objectMapper.configure(MapperFeature.DEFAULT_VIEW_INCLUSION, false);
        objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);

        converter.setObjectMapper(objectMapper);
        return converter;
    }
}

而且，这是我在上次建议后发送消息的方式（重大变化是从 jmsTemplate.send 到 jmsTemplate.convertAndSend）：

@Component
public class MyMessageSender {

    @Autowired
    private ConnectionFactory connectionFactory;
    private JmsTemplate jmsTemplate;

    @PostConstruct
    public void init() {
        this.jmsTemplate = new JmsTemplate(connectionFactory);
    }

    public void sendMessage(SalesMessage  message) {
        System.out.println("sending: " + message);
        jmsTemplate.convertAndSend(AppConfig.QUEUE_NAME, message);
    }
}

*** 已编辑

Answer 1

我明白你在这里想做什么，你可能正在尝试遵循这个例子：

https://spring.io/guides/gs/messaging-jms/

但是，该示例是在 Spring Boot.我有一种预感，你没有使用 Spring 引导，因为那里没有 @SpringBootApplication 注释。

如果我是对的，您需要使用您定义为 bean 的 SimpleMessageConverter 明确调用 DefaultJmsListenerContainerFactory.setMessageConverter 方法。我敢打赌 Spring Boot 可能会自动为您执行此操作，但在您的实现中，您必须手动执行此操作。

所以，它应该看起来像：

 @Bean
    public JmsListenerContainerFactory jmsListenerContainerFactory() {
        DefaultJmsListenerContainerFactory factory =
                new DefaultJmsListenerContainerFactory();
        factory.setConnectionFactory(connectionFactory());
        factory.setMessageConverter(converter());
        factory.setConcurrency("4-8");
        return factory;
    }

您还需要确保您的对象是可序列化的，然后您可以对对象本身执行 jmsTemplate.send。转换器将为您进行必要的消息负载类型转换。

Answer 2

嗯？

ms.sendMessage(sm.toString());

java.lang.ClassCastException: java.lang.String cannot be cast to ...SalesMessage.

那是因为您发送的是 String (sm.toString()) 而不是 JSON 形式的 SalesMessage。

使用jmsTemplate.convertAnsSend(destinationName, sm).

监听器容器工厂也需要Jackson转换器。

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