升级Spring Boot3时StreamBridge发送XML消息报空指针异常求助

问题场景 #

将项目升级至Spring Boot 3.0.3后，在@SpringBootTest测试中使用StreamBridge发送contentType为application/xml的消息时，触发如下空指针异常：

java.lang.NullPointerException: Cannot invoke "Object.getClass()" because "result" is null
at org.springframework.cloud.function.cloudevent.CloudEventsFunctionInvocationHelper.doPostProcessResult(CloudEventsFunctionInvocationHelper.java:138)
at org.springframework.cloud.function.cloudevent.CloudEventsFunctionInvocationHelper.postProcessResult(CloudEventsFunctionInvocationHelper.java:114)
at org.springframework.cloud.function.cloudevent.CloudEventsFunctionInvocationHelper.postProcessResult(CloudEventsFunctionInvocationHelper.java:48)
at org.springframework.cloud.stream.function.StreamBridge.send(StreamBridge.java:181)
at org.springframework.cloud.stream.function.StreamBridge.send(StreamBridge.java:144)
at org.springframework.cloud.stream.function.StreamBridge.send(StreamBridge.java:140)
at com.example.demo.DemoApplicationTests.shouldSendMessage(DemoApplicationTests.java:33)

通过start.spring.io创建全新项目仍可复现，核心配置如下：

build.gradle（简化版） #

plugins {
  id 'java'
  id 'org.springframework.boot' version '3.0.3'
  id 'io.spring.dependency-management' version '1.1.0'
}

ext {
  set('springCloudVersion', "2022.0.1")
}

dependencies {
  implementation 'org.springframework.boot:spring-boot-starter-amqp'
  implementation 'org.springframework.cloud:spring-cloud-stream'
  implementation 'org.springframework.cloud:spring-cloud-stream-binder-rabbit'
  testImplementation 'org.springframework.boot:spring-boot-starter-test'
  testImplementation 'org.springframework.amqp:spring-rabbit-test'
  testImplementation 'org.springframework.cloud:spring-cloud-stream-test-binder'
}

application.yml #

spring:
  cloud:
    stream:
      bindings:
        demo-out-0:
          destination: some.topic
          contentType: application.xml   # 移除该行后测试通过
      rabbit:
        bindings:
          demo-out-0:
            producer:
              routingKeyExpression: '''some.routing.key'''

测试代码 #

@SpringBootTest
@Import(TestChannelBinderConfiguration.class)
class DemoApplicationTests {

    @Autowired
    private StreamBridge streamBridge;

    @Autowired
    private OutputDestination outputDestination;

    @Test
    void shouldSendMessage() {
        var minimalXml = """
                <?xml version="1.0" encoding="iso-8859-1" standalone="yes" ?>
                <Config></Config>
                """;

        streamBridge.send("demo-out-0", MessageBuilder.withPayload(minimalXml).build());

        var actual = outputDestination.receive(1000, "some.topic");

        Assertions.assertThat(new String(actual.getPayload()))
                .isEqualTo(minimalXml);
    }
}

问题原因 #

1. CloudEvent转换逻辑触发失败：Spring Cloud Stream 2022.0.x（适配Spring Boot 3）版本中，CloudEventsFunctionInvocationHelper会对已配置contentType的消息尝试进行CloudEvent格式转换。当消息是纯字符串XML且项目中没有引入XML序列化/反序列化依赖（如Jackson XML模块）时，转换过程会返回null，后续代码直接调用null.getClass()导致空指针异常。
2. 版本差异导致行为变化：Spring Boot 3之前的版本中，CloudEvent转换逻辑不会强制对已指定contentType的消息执行转换，或对转换失败的场景处理更健壮，因此不会触发该异常。
3. 移除contentType配置后的行为：移除绑定配置中的contentType后，消息默认使用text/plain类型，不会触发XML相关的转换逻辑，因此测试可以正常通过。

临时解决方案 #

• 手动指定消息contentType：发送消息时覆盖绑定配置的类型，比如设置为text/plain：

  MessageBuilder.withPayload(minimalXml)
                .setHeader(MessageHeaders.CONTENT_TYPE, MediaType.TEXT_PLAIN_VALUE)
                .build()
  

• 添加XML序列化依赖：引入Jackson XML模块，让CloudEvent转换可以正常完成，比如在Gradle中添加：

  implementation 'com.fasterxml.jackson.dataformat:jackson-dataformat-xml'
  

• 禁用原生编码转换：配置生产者使用原生编码，跳过CloudEvent转换逻辑：

  spring:
    cloud:
      stream:
        function:
          bindings:
            demo-out-0:
              producer:
                use-native-encoding: true
  

内容的提问来源于stack exchange，提问作者Michiel