1. 复现问题
今天在使用knife4j请求后端接口时，首次请求能够正常访问。
只是修改个参数值，就报出如下错误信息：
org.springframework.http.converter.HttpMessageNotReadableException: JSON parse error: Unexpected character ('"' (code 34)): was expecting comma to separate Object entries; nested exception is com.fasterxml.jackson.core.JsonParseException: Unexpected character ('"' (code 34)): was expecting comma to separate Object entries
at [Source: (PushbackInputStream); line: 6, column: 4]
at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.readJavaType(AbstractJackson2HttpMessageConverter.java:389)
at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.read(AbstractJackson2HttpMessageConverter.java:342)
at org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodArgumentResolver.readWithMessageConverters(AbstractMessageConverterMethodArgumentResolver.java:185)
at org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor.readWithMessageConverters(RequestResponseBodyMethodProcessor.java:158)
at org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor.resolveArgument(RequestResponseBodyMethodProcessor.java:131)
at org.springframework.web.method.support.HandlerMethodArgumentResolverComposite.resolveArgument(HandlerMethodArgumentResolverComposite.java:121)
at org.springframework.web.method.support.InvocableHandlerMethod.getMethodArgumentValues(InvocableHandlerMethod.java:170)
at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:137)
at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:106)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:894)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:808)
at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1063)
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:963)
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006)
......
......
Caused by: com.fasterxml.jackson.core.JsonParseException: Unexpected character ('"' (code 34)): was expecting comma to separate Object entries
at [Source: (PushbackInputStream); line: 6, column: 4]
at com.fasterxml.jackson.core.JsonParser._constructError(JsonParser.java:1840)
at com.fasterxml.jackson.core.base.ParserMinimalBase._reportError(ParserMinimalBase.java:712)
at com.fasterxml.jackson.core.base.ParserMinimalBase._reportUnexpectedChar(ParserMinimalBase.java:637)
at com.fasterxml.jackson.core.json.UTF8StreamJsonParser.nextFieldName(UTF8StreamJsonParser.java:1010)
at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:376)
at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:159)
at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4202)
at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3258)
at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.readJavaType(AbstractJackson2HttpMessageConverter.java:378)
... 67 more
2. 分析问题
Unexpected character ('"' (code 34)): was expecting comma to separate Object entries错误，来自ChatGPT的解释如下图：
也就是说，我的请求参数(json格式)有误，导致jackson无法解析这样的参数。
于是到接口请求的地方，查看我的请求参数，如下图所示：
若你不仔细看，你无法看到问题所在。
我是反复尝试了数字，才看到在"id": 1的地方，出现了问题，因为1后面没有加上逗号(英文的逗号)。
3. 解决问题
由于1后面没有加上逗号，只要在其后面加上逗号即可，如下图所示：
重新请求后端接口，即能正常访问，如下图所示：
在工作过程中，还是要仔细。不能因为一个点，浪费很长排查问题的时间。
4. 重要补充
4.1 knife4j的详细教程
插句题外话，关于knife4j的详细使用教程，可以参考博文：全网最全的Knife4j swaggerj介绍
