Spring Cloud中使用Feign时，如果POST方法中Body放入了List,那么在默认情况下会出现异常。
报错日志
feign.codec.DecodeException: Error while extracting response for type [com.meatball.common.response.ResultMsg<java.util.List<java.lang.String>>] and content type [application/json;charset=UTF-8]; nested exception is org.springframework.http.converter.HttpMessageNotReadableException: JSON parse error: Cannot deserialize instance of `java.util.ArrayList` out of VALUE_STRING token; nested exception is com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize instance of `java.util.ArrayList` out of VALUE_STRING token
at [Source: (PushbackInputStream); line: 1, column: 153] (through reference chain: com.meatball.common.response.ResultMsg["data"])
at feign.SynchronousMethodHandler.decode(SynchronousMethodHandler.java:180)
at feign.SynchronousMethodHandler.executeAndDecode(SynchronousMethodHandler.java:140)
at feign.SynchronousMethodHandler.invoke(SynchronousMethodHandler.java:78)
at feign.ReflectiveFeign$FeignInvocationHandler.invoke(ReflectiveFeign.java:103)
at com.sun.proxy.$Proxy275.getMembers(Unknown Source)
at com.meatball.custom.service.impl.CustomCouponAsyncImpl.getMemberIds(CustomCouponAsyncImpl.java:219)
at com.meatball.custom.service.impl.CustomCouponAsyncImpl.sendCustomCouponAsync(CustomCouponAsyncImpl.java:104)
at com.meatball.custom.service.impl.CustomCouponAsyncImpl$$FastClassBySpringCGLIB$$917f5776.invoke(<generated>)
at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:218)
at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:749)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163)
at org.springframework.aop.aspectj.MethodInvocationProceedingJoinPoint.proceed(MethodInvocationProceedingJoinPoint.java:88)
at org.springframework.cloud.sleuth.instrument.async.TraceAsyncAspect.traceBackgroundThread(TraceAsyncAspect.java:67)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethodWithGivenArgs(AbstractAspectJAdvice.java:644)
at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethod(AbstractAspectJAdvice.java:633)
at org.springframework.aop.aspectj.AspectJAroundAdvice.invoke(AspectJAroundAdvice.java:70)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:93)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
at org.springframework.aop.interceptor.AsyncExecutionInterceptor.lambda$invoke$0(AsyncExecutionInterceptor.java:115)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
Caused by: org.springframework.web.client.RestClientException: Error while extracting response for type [com.meatball.common.response.ResultMsg<java.util.List<java.lang.String>>] and content type [application/json;charset=UTF-8]; nested exception is org.springframework.http.converter.HttpMessageNotReadableException: JSON parse error: Cannot deserialize instance of `java.util.ArrayList` out of VALUE_STRING token; nested exception is com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize instance of `java.util.ArrayList` out of VALUE_STRING token
at [Source: (PushbackInputStream); line: 1, column: 153] (through reference chain: com.meatball.common.response.ResultMsg["data"])
at org.springframework.web.client.HttpMessageConverterExtractor.extractData(HttpMessageConverterExtractor.java:117)
at org.springframework.cloud.openfeign.support.SpringDecoder.decode(SpringDecoder.java:59)
at org.springframework.cloud.openfeign.support.ResponseEntityDecoder.decode(ResponseEntityDecoder.java:62)
at feign.optionals.OptionalDecoder.decode(OptionalDecoder.java:36)
at feign.SynchronousMethodHandler.decode(SynchronousMethodHandler.java:176)
... 27 common frames omitted
Caused by: org.springframework.http.converter.HttpMessageNotReadableException: JSON parse error: Cannot deserialize instance of `java.util.ArrayList` out of VALUE_STRING token; nested exception is com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize instance of `java.util.ArrayList` out of VALUE_STRING token
at [Source: (PushbackInputStream); line: 1, column: 153] (through reference chain: com.meatball.common.response.ResultMsg["data"])
at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.readJavaType(AbstractJackson2HttpMessageConverter.java:245)
at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.read(AbstractJackson2HttpMessageConverter.java:227)
at org.springframework.web.client.HttpMessageConverterExtractor.extractData(HttpMessageConverterExtractor.java:102)
... 31 common frames omitted
Caused by: com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize instance of `java.util.ArrayList` out of VALUE_STRING token
at [Source: (PushbackInputStream); line: 1, column: 153] (through reference chain: com.meatball.common.response.ResultMsg["data"])
at com.fasterxml.jackson.databind.exc.MismatchedInputException.from(MismatchedInputException.java:63)
at com.fasterxml.jackson.databind.DeserializationContext.reportInputMismatch(DeserializationContext.java:1343)
at com.fasterxml.jackson.databind.DeserializationContext.handleUnexpectedToken(DeserializationContext.java:1139)
at com.fasterxml.jackson.databind.DeserializationContext.handleUnexpectedToken(DeserializationContext.java:1093)
at com.fasterxml.jackson.databind.deser.std.StringCollectionDeserializer.handleNonArray(StringCollectionDeserializer.java:270)
at com.fasterxml.jackson.databind.deser.std.StringCollectionDeserializer.deserialize(StringCollectionDeserializer.java:183)
at com.fasterxml.jackson.databind.deser.std.StringCollectionDeserializer.deserialize(StringCollectionDeserializer.java:173)
at com.fasterxml.jackson.databind.deser.std.StringCollectionDeserializer.deserialize(StringCollectionDeserializer.java:21)
at com.fasterxml.jackson.databind.deser.impl.MethodProperty.deserializeAndSet(MethodProperty.java:129)
at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:369)
at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:159)
at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4013)
at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3084)
at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.readJavaType(AbstractJackson2HttpMessageConverter.java:239)
... 33 common frames omitted
重点
Cannot deserialize instance of `java.util.ArrayList` out of VALUE_STRING token
原因
jackson的解析中，当遇见[时会进行List的解析。
// Ok: must point to START_ARRAY
if (!p.isExpectedStartArrayToken()) {
return handleNonArray(p, ctxt, result);
}
/**
* START_ARRAY is returned when encountering '['
* which signals starting of an Array value
*/
START_ARRAY("[", JsonTokenId.ID_START_ARRAY),
解决
方案1，重写ObjectMapper
mapper.configure(DeserializationFeature.ACCEPT_SINGLE_VALUE_AS_ARRAY, true);
方案2，Spring Boot可以通过配置文件
spring.jackson.deserialization.ACCEPT_SINGLE_VALUE_AS_ARRAY=true
方案3，针对字段可以加注解
@JsonFormat(with = JsonFormat.Feature.ACCEPT_SINGLE_VALUE_AS_ARRAY)
private List<String> data;
方案4，自定义解析器
比较麻烦，不推荐。
