如何解决com.fasterxml.jackson.databind.exc.MismatchedInputException:无法从START_OBJECT令牌中反序列化java.lang.String实例
我使用Spring Boot和Rappitmq来实现两个不同应用程序之间的异步消息传递。当我仅将字符串作为消息内容交换时,这可以很好地工作。我还促进了波霍舞的交流。由于pojos蜂在不同的程序包中,所以序列化/反序列化过程失败。为了解决这个问题,我使用JacksonConverter使用json。正如我在订阅者服务“ application / json”的消息头中看到的那样,它起作用
要交换的模型(发布和订阅服务中相同):
public class Employee{
private Integer id;
private String firstName;
private String lastName;
private Double salary;
public Employee(@JsonProperty("id") Integer id,@JsonProperty("firstName") String firstName,@JsonProperty("lastName") String lastName,@JsonProperty("salary") Double salary) {
this.id = id;
this.firstName = firstName;
this.lastName = lastName;
this.salary = salary;
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
public Double getSalary() {
return salary;
}
public void setSalary(Double salary) {
this.salary = salary;
}
@Override
public String toString() {
return "{" +
"id=" + id +
",firstName='" + firstName + '\'' +
",lastName='" + lastName + '\'' +
",salary=" + salary +
'}';
}
Beans在发布者服务中使用Jackson2JsonConverter:
@SpringBootApplication
public class PublisherApplication {
public static void main(String[] args) {
SpringApplication.run(PublisherApplication.class,args);
}
@Bean
public Jackson2JsonMessageConverter producerMessageConverter(){
return new Jackson2JsonMessageConverter();
}
@Bean
public RabbitTemplate rabbitTemplate(final ConnectionFactory connectionFactory){
RabbitTemplate rabbitTemplate = new RabbitTemplate(connectionFactory);
rabbitTemplate.setMessageConverter(producerMessageConverter());
return rabbitTemplate;
}
}
发送消息:
@Override
public void sendEmployeeObject(Employee employee) throws JsonProcessingException {
rabbitTemplate.convertAndSend(RabbitMqConstants.EXCHANGE_NAME,"foo.bar.baz",employee);
}
}
订户配置:
@Configuration
public class EmployeeMessageSubscriberConfig {
@Bean
@Qualifier("employeeQueue")
Queue queue() {
return new Queue(RabbitMqConstants.EMPLOYEE_QUEUE,false);
}
@Bean
@Qualifier("employeeExchange")
TopicExchange exchange() {
return new TopicExchange(RabbitMqConstants.EXCHANGE_NAME);
}
@Bean
@Qualifier("employeeQueueExchangeBinding")
Binding binding(Queue queue,TopicExchange exchange) {
return BindingBuilder.bind(queue).to(exchange).with("foo.bar.#");
}
@Bean
public Jackson2JsonMessageConverter converter() {
return new Jackson2JsonMessageConverter();
}
}
侦听器方法:
@RabbitListener(queues = RabbitMqConstants.EMPLOYEE_QUEUE)
public void handleMessage(Employee employee) {
System.out.println("Received <" + employee.toString() + ">");
}
要测试它,我通过rest api将Employee对象发送到发布者服务。在这里,我只是将其原样传递给Rabbit。订户服务读取消息,然后将其打印到控制台。
问题: 订户服务将打印正确的值:
Received <{id=1,firstName='John',lastName='Doe',salary=1.5}>
但是我也得到了错误跟踪:
Caused by: com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize instance of `java.lang.String` out of START_OBJECT token
at [Source: (String)"{"id":1,"firstName":"John","lastName":"Doe","salary":1.5}"; line: 1,column: 1]
at com.fasterxml.jackson.databind.exc.MismatchedInputException.from(MismatchedInputException.java:59)
据我所知,订户看到传入的Json是ob类型的Object,但它尝试将其反序列化为String。
问题: 当跟踪显示似乎有错误时,为什么打印出正确的输出? 当我使用RestController时,传入的对象会自动映射到给定的Model。使用Rabbitmq时是否必须以某种方式将其连接起来?
编辑:
这就是我遵循的guide。
正如我在订户的标题中看到的那样,有一个字段headers={__TypeId__=com.publisher.model.Employee}
,所以我已经在两个应用程序中将Employee模型设置为一个具有相同名称的包。还是一样的错误。 (就像我预期的那样,因为与standardMessageConverter相反,包名称未用于序列化)
解决方法
很明显,您不能直接通过Java Bean接收消息。
尝试使用byte[] msg
或String msg
作为handleMessage()
方法的参数,并将其手动转换为Employee
bean。
如果要使用Java Bean接收消息,则配置会有所帮助。
@Configuration
public class RabbitMQConfig {
@Bean
public RabbitListenerContainerFactory<?> rabbitListenerContainerFactory(ConnectionFactory connectionFactory){
SimpleRabbitListenerContainerFactory factory = new SimpleRabbitListenerContainerFactory();
factory.setConnectionFactory(connectionFactory);
factory.setMessageConverter(new Jackson2JsonMessageConverter());
return factory;
}
}
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