ControllerAdvice ResponseBodyAdvice failed to enclose a String response - rest

Question

Not sure why, but when an endpoint return a String, the ResponseBodyAdvice always throws a Casting exception. Any other data type such as Long, List worked as desired, only the String data got exception. Any suggestion on how to fix this issue?
#RestController
public class AppController {
private static Logger logger = LogManager.getLogger(AppController.class);
#RequestMapping(path = "/hello",
method = GET)
public String hello() {
logger.info("... AppController.hello()");
return "hello, world!";
}
#RequestMapping(path = "/timestamp",
method = GET)
public long timestamp() {
logger.info("... AppController.timestamp()");
return System.currentTimeMillis();
}
}
here is the adviser:
#ControllerAdvice
public class ResponseAdviser implements ResponseBodyAdvice<Object> {
private static Logger logger = LogManager.getLogger(ResponseAdviser.class);
#Override
public boolean supports(MethodParameter returnType,
Class<? extends HttpMessageConverter<?>> converterType) {
logger.trace("... ResponseAdviser.supports()");
return true;
}
#Override
public Object beforeBodyWrite(Object body,
MethodParameter returnType,
MediaType selectedContentType,
Class<? extends HttpMessageConverter<?>> selectedConverterType,
ServerHttpRequest request,
ServerHttpResponse response) {
logger.info("... ResponseAdviser.beforeBodyWrite()");
Response resp = new Response();
resp.setData(body);
return resp;
}
}
And the Reponse class is basically, adding a timestamp and enclose endpoint returned data
#Data
public class Response {
private Date timestamp;
private Object data;
public Response() {
this.timestamp = new Date();
}
}
Here is the stack trace:
Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is java.lang.ClassCastException: org.phan.message.Response cannot be cast to java.lang.String] with root cause
java.lang.ClassCastException: org.phan.message.Response cannot be cast to java.lang.String
at org.springframework.http.converter.StringHttpMessageConverter.getContentLength(StringHttpMessageConverter.java:41) ~[spring-web-4.3.8.RELEASE.jar:4.3.8.RELEASE]
at org.springframework.http.converter.AbstractHttpMessageConverter.addDefaultHeaders(AbstractHttpMessageConverter.java:260) ~[spring-web-4.3.8.RELEASE.jar:4.3.8.RELEASE]
at org.springframework.http.converter.AbstractHttpMessageConverter.write(AbstractHttpMessageConverter.java:205) ~[spring-web-4.3.8.RELEASE.jar:4.3.8.RELEASE]
at org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:247) ~[spring-webmvc-4.3.8.RELEASE.jar:4.3.8.RELEASE]
at org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor.handleReturnValue(RequestResponseBodyMethodProcessor.java:174) ~[spring-webmvc-4.3.8.RELEASE.jar:4.3.8.RELEASE]
at org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite.handleReturnValue(HandlerMethodReturnValueHandlerComposite.java:81) ~[spring-web-4.3.8.RELEASE.jar:4.3.8.RELEASE]
at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:113) ~[spring-webmvc-4.3.8.RELEASE.jar:4.3.8.RELEASE]
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:827) ~[spring-webmvc-4.3.8.RELEASE.jar:4.3.8.RELEASE]
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:738) ~[spring-webmvc-4.3.8.RELEASE.jar:4.3.8.RELEASE]
at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85) ~[spring-webmvc-4.3.8.RELEASE.jar:4.3.8.RELEASE]
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:963) ~[spring-webmvc-4.3.8.RELEASE.jar:4.3.8.RELEASE]
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:897) ~[spring-webmvc-4.3.8.RELEASE.jar:4.3.8.RELEASE]
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970) ~[spring-webmvc-4.3.8.RELEASE.jar:4.3.8.RELEASE]
at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861) ~[spring-webmvc-4.3.8.RELEASE.jar:4.3.8.RELEASE]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:635) ~[tomcat-embed-core-8.5.14.jar:8.5.14]
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846) ~[spring-webmvc-4.3.8.RELEASE.jar:4.3.8.RELEASE]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:742) ~[tomcat-embed-core-8.5.14.jar:8.5.14]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-8.5.14.jar:8.5.14]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.14.jar:8.5.14]
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) ~[tomcat-embed-websocket-8.5.14.jar:8.5.14]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.14.jar:8.5.14]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.14.jar:8.5.14]
at org.springframework.boot.web.filter.ApplicationContextHeaderFilter.doFilterInternal(ApplicationContextHeaderFilter.java:55) ~[spring-boot-1.5.3.RELEASE.jar:1.5.3.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-4.3.8.RELEASE.jar:4.3.8.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.14.jar:8.5.14]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.14.jar:8.5.14]
at org.springframework.boot.actuate.trace.WebRequestTraceFilter.doFilterInternal(WebRequestTraceFilter.java:110) ~[spring-boot-actuator-1.5.3.RELEASE.jar:1.5.3.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-4.3.8.RELEASE.jar:4.3.8.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.14.jar:8.5.14]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.14.jar:8.5.14]
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:197) ~[spring-web-4.3.8.RELEASE.jar:4.3.8.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-4.3.8.RELEASE.jar:4.3.8.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.14.jar:8.5.14]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.14.jar:8.5.14]
at org.springframework.boot.actuate.autoconfigure.MetricsFilter.doFilterInternal(MetricsFilter.java:106) ~[spring-boot-actuator-1.5.3.RELEASE.jar:1.5.3.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-4.3.8.RELEASE.jar:4.3.8.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.14.jar:8.5.14]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.14.jar:8.5.14]
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:198) ~[tomcat-embed-core-8.5.14.jar:8.5.14]
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) [tomcat-embed-core-8.5.14.jar:8.5.14]
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:478) [tomcat-embed-core-8.5.14.jar:8.5.14]
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140) [tomcat-embed-core-8.5.14.jar:8.5.14]
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:80) [tomcat-embed-core-8.5.14.jar:8.5.14]
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87) [tomcat-embed-core-8.5.14.jar:8.5.14]
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342) [tomcat-embed-core-8.5.14.jar:8.5.14]
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:799) [tomcat-embed-core-8.5.14.jar:8.5.14]
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) [tomcat-embed-core-8.5.14.jar:8.5.14]
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:861) [tomcat-embed-core-8.5.14.jar:8.5.14]
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1455) [tomcat-embed-core-8.5.14.jar:8.5.14]
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-8.5.14.jar:8.5.14]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [na:1.8.0_121]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [na:1.8.0_121]
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-8.5.14.jar:8.5.14]
at java.lang.Thread.run(Thread.java:745) [na:1.8.0_121]

Answer 1

You can try this code below:
#Configuration
public class WebConfig extends WebMvcConfigurerAdapter {
#Override
public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
super.configureMessageConverters(converters);
converters.add(0, new MappingJackson2HttpMessageConverter());
}
}

Answer 2

Reason:
The root cause of ClassCastException thrown is that you convert the response type from String to Response in the method ResponseAdviser.beforeBodyWrite.
When your return type of a controller request method is String, the HttpMessageConverter instance used to convert the return value is StringHttpMessageConverter.
The sequence of converters to use when processing your return value of a controller method is like this:
ByteArrayHttpMessageConverter cannot process String return type.
As we know, before write and flush the response, ContentLength should be calculated(when add http headers). The implements of StringHttpMessageConverter.getContentLength is like this:
We can see, the type of input parameter str is String, but actually, the response type has already been modified to Response. So the ClassCastException thrown.
Solution:
Tell spring framework, don't use StringHttpMessageConverter to process String return type in controller method. You just need to add a MappingJackson2HttpMessageConverter in front of StringHttpMessageConverter.
sample code:
#Configuration
public class WebMvcConfiguration implements WebMvcConfigurer {
#Override
public void configureMessageConverters(List<HttpMessageConverter<?>>
converters) {
WebMvcConfigurer.super.configureMessageConverters(converters);
converters.add(0, new MappingJackson2HttpMessageConverter());
}
}
Why MappingJackson2HttpMessageConverter won't throw the ClassCastException? Just take a look at the implements(in its super class AbstractJackson2HttpMessageConverter):
The type of input parameter object is Object, so it can process both String and Response.

Answer 3

In the ResponseBodyAdvice class, add the beforeBodyWrite method:
#Override
public Object beforeBodyWrite(Object body, MethodParameter returnType,
MediaType selectedContentType, Class<? extends HttpMessageConverter<?>> selectedConverterType,
ServerHttpRequest request, ServerHttpResponse response) {
...
Response resp = new Response();
resp.setData(body);
//返回值body为String类型时
if (body != null && body instanceof String) {
try {
response.getHeaders().setContentType(MediaType.APPLICATION_JSON_UTF8);
return objectMapper.writeValueAsString(resp);
} catch (JsonProcessingException e) {
log.error(e.getMessage(), e);
throw new RuntimeException(e.getMessage(), e);
}
}
...
}

Answer 4

Since you are using the #RestController annotation to identify your rest endpoint, if you would like to attach an Advice to it you have to use the #RestControllerAdvice annotation designed for rest endpoints.

Answer 5

This error occurs because the return type of beforeBodyWrite method and your requestmapping method should be same. You may try always return the Response in your controller...
All other types like fastJson or javabean have no errors except String. So I write additional code to handle String types. You can overwrite the Response's toString(), and if the coming type is String then you return Response.toString(). This may solve your problem

Answer 6

I recommend using the following code, override the extendMessageConverters method and remove the converters which instance of StringHttpMessageConverter class, as you don't need them at all.
By the way, If you choose to override configureMessageConverters method as your solution, it will work, but in the meantime, the properties you put in application.yml will not have any effects cause the default configuration method(which can load the properties by file) will not execute.
#Configuration
public class RestfulResponseConfigurer implements WebMvcConfigurer {
#Override
public void extendMessageConverters(List<HttpMessageConverter<?>> converters) {
converters.removeIf(httpMessageConverter -> httpMessageConverter instanceof StringHttpMessageConverter);
}
}