Springboot使用了ResponseBodyAdvice處理返回值異常？
在使用爲了在controller層中只關心我業務數據，而不去關心數據的形式。通常來講，在http接口響應的json數據時，我都回去設置一個響應碼code，描述msg，數據data。形式以下：java
public class ResponseResult implements Serializable{
private static final long serialVersionUID = 1638693422783183022L;
private String code;
private String msg;
private Object data;
public ResponseResult(CodeConstant codeConstant) {
this.code = codeConstant.getCode();
this.msg = codeConstant.getMsg();
}
public ResponseResult(CodeConstant codeConstant, Object data) {
this(codeConstant);
this.data = data;
}
}
而在controller層中，我只關心我想要返回的數據，也是上面響應實體的部分，我不想在controller中還要處理響應數據包裝這種重複無聊的工做。因此controller中我想要的形式是，我只返回我業務須要返回的數據，效果以下：web
@RestController
@RequestMapping("/auth")
@Slf4j
public class UserController {
@RequestMapping("test1")
public UserEntity test1() {
return new UserEntity();
}
@RequestMapping("test")
public String test2() {
return "12312";
}
}
因此爲了統一接口響應的報文，我現實了ResponseBodyAdvice接口，經過這個接口的實現類來統一處理報文spring
public class BaseGlobalResponseBodyAdvice implements ResponseBodyAdvice<Object> {
//這個方法表示對於哪些請求要執行beforeBodyWrite，返回true執行，返回false不執行
@Override
public boolean supports(MethodParameter methodParameter, Class aClass) {
return true;
}
//對於返回的對象若是不是最終對象ResponseResult，則選包裝一下
@Override
public Object beforeBodyWrite(Object o, MethodParameter methodParameter, MediaType mediaType,
Class aClass, ServerHttpRequest serverHttpRequest, ServerHttpResponse serverHttpResponse) {
if(!(o instanceof ResponseResult)) {
ResponseResult responseResult = new ResponseResult(CodeConstant.SUCCESS, o);
return responseResult;
}
return o;
}
}
然而在測試返回值是String類型的時候，程序拋出一個類轉換的異常：apache
java.lang.ClassCastException: com.jinhualun.moguhou.merchant.console.base.common.ResponseResult cannot be cast to java.lang.String at org.springframework.http.converter.StringHttpMessageConverter.getContentLength(StringHttpMessageConverter.java:41) ~[spring-web-4.3.10.RELEASE.jar:4.3.10.RELEASE] at org.springframework.http.converter.AbstractHttpMessageConverter.addDefaultHeaders(AbstractHttpMessageConverter.java:260) ~[spring-web-4.3.10.RELEASE.jar:4.3.10.RELEASE] at org.springframework.http.converter.AbstractHttpMessageConverter.write(AbstractHttpMessageConverter.java:205) ~[spring-web-4.3.10.RELEASE.jar:4.3.10.RELEASE] at org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:247) ~[spring-webmvc-4.3.10.RELEASE.jar:4.3.10.RELEASE] at org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor.handleReturnValue(RequestResponseBodyMethodProcessor.java:174) ~[spring-webmvc-4.3.10.RELEASE.jar:4.3.10.RELEASE] at org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite.handleReturnValue(HandlerMethodReturnValueHandlerComposite.java:81) ~[spring-web-4.3.10.RELEASE.jar:4.3.10.RELEASE] at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:113) ~[spring-webmvc-4.3.10.RELEASE.jar:4.3.10.RELEASE] at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:827) ~[spring-webmvc-4.3.10.RELEASE.jar:4.3.10.RELEASE] at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:738) ~[spring-webmvc-4.3.10.RELEASE.jar:4.3.10.RELEASE] at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85) ~[spring-webmvc-4.3.10.RELEASE.jar:4.3.10.RELEASE] at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:967) ~[spring-webmvc-4.3.10.RELEASE.jar:4.3.10.RELEASE] at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:901) ~[spring-webmvc-4.3.10.RELEASE.jar:4.3.10.RELEASE] at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970) [spring-webmvc-4.3.10.RELEASE.jar:4.3.10.RELEASE] at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861) [spring-webmvc-4.3.10.RELEASE.jar:4.3.10.RELEASE] at javax.servlet.http.HttpServlet.service(HttpServlet.java:635) [tomcat-embed-core-8.5.16.jar:8.5.16] at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846) [spring-webmvc-4.3.10.RELEASE.jar:4.3.10.RELEASE] at javax.servlet.http.HttpServlet.service(HttpServlet.java:742) [tomcat-embed-core-8.5.16.jar:8.5.16] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) [tomcat-embed-core-8.5.16.jar:8.5.16] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.16.jar:8.5.16] at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) [tomcat-embed-websocket-8.5.16.jar:8.5.16] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-8.5.16.jar:8.5.16] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.16.jar:8.5.16] at com.jinhualun.moguhou.merchant.console.base.filter.CorsFilter.doFilter(CorsFilter.java:47) [classes/:na] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-8.5.16.jar:8.5.16] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.16.jar:8.5.16] at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99) [spring-web-4.3.10.RELEASE.jar:4.3.10.RELEASE] at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.3.10.RELEASE.jar:4.3.10.RELEASE] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-8.5.16.jar:8.5.16] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.16.jar:8.5.16] at org.springframework.web.filter.HttpPutFormContentFilter.doFilterInternal(HttpPutFormContentFilter.java:105) [spring-web-4.3.10.RELEASE.jar:4.3.10.RELEASE] at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.3.10.RELEASE.jar:4.3.10.RELEASE] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-8.5.16.jar:8.5.16] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.16.jar:8.5.16] at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:81) [spring-web-4.3.10.RELEASE.jar:4.3.10.RELEASE] at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.3.10.RELEASE.jar:4.3.10.RELEASE] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-8.5.16.jar:8.5.16] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.16.jar:8.5.16] at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:197) [spring-web-4.3.10.RELEASE.jar:4.3.10.RELEASE] at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.3.10.RELEASE.jar:4.3.10.RELEASE] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-8.5.16.jar:8.5.16] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.16.jar:8.5.16] at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:198) [tomcat-embed-core-8.5.16.jar:8.5.16] at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) [tomcat-embed-core-8.5.16.jar:8.5.16] at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:478) [tomcat-embed-core-8.5.16.jar:8.5.16] at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140) [tomcat-embed-core-8.5.16.jar:8.5.16] at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:80) [tomcat-embed-core-8.5.16.jar:8.5.16] at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87) [tomcat-embed-core-8.5.16.jar:8.5.16] at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342) [tomcat-embed-core-8.5.16.jar:8.5.16] at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:799) [tomcat-embed-core-8.5.16.jar:8.5.16] at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) [tomcat-embed-core-8.5.16.jar:8.5.16] at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868) [tomcat-embed-core-8.5.16.jar:8.5.16] at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1455) [tomcat-embed-core-8.5.16.jar:8.5.16] at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-8.5.16.jar:8.5.16] at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [na:1.8.0_131] at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [na:1.8.0_131] at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-8.5.16.jar:8.5.16] at java.lang.Thread.run(Thread.java:748) [na:1.8.0_131]
後來通過debug發現這個跟MessageConverter有關係。Springmvc內部定義了九個不一樣的MessageConverter用來處理不一樣的返回值。在AbstractMessageConverterMethodProcessor類下面的writeWithMessageConverters方法能夠看出來，每一個MessageConverer是根據返回類型和媒體類型來選擇處理的MessageConverter的，下面是代碼片斷：json
if (selectedMediaType != null) {
selectedMediaType = selectedMediaType.removeQualityValue();
for (HttpMessageConverter<?> messageConverter : this.messageConverters) {
if (messageConverter instanceof GenericHttpMessageConverter) {
if (((GenericHttpMessageConverter) messageConverter).canWrite(
declaredType, valueType, selectedMediaType)) {
outputValue = (T) getAdvice().beforeBodyWrite(outputValue, returnType, selectedMediaType,
(Class<? extends HttpMessageConverter<?>>) messageConverter.getClass(),
inputMessage, outputMessage);
if (outputValue != null) {
addContentDispositionHeader(inputMessage, outputMessage);
((GenericHttpMessageConverter) messageConverter).write(
outputValue, declaredType, selectedMediaType, outputMessage);
if (logger.isDebugEnabled()) {
logger.debug("Written [" + outputValue + "] as \"" + selectedMediaType +
"\" using [" + messageConverter + "]");
}
}
return;
}
}
else if (messageConverter.canWrite(valueType, selectedMediaType)) {
outputValue = (T) getAdvice().beforeBodyWrite(outputValue, returnType, selectedMediaType,
(Class<? extends HttpMessageConverter<?>>) messageConverter.getClass(),
inputMessage, outputMessage);
if (outputValue != null) {
addContentDispositionHeader(inputMessage, outputMessage);
((HttpMessageConverter) messageConverter).write(outputValue, selectedMediaType, outputMessage);
if (logger.isDebugEnabled()) {
logger.debug("Written [" + outputValue + "] as \"" + selectedMediaType +
"\" using [" + messageConverter + "]");
}
}
return;
}
}
}
因此致使這個問題的緣由就是，controller層中返回的類型是String，可是在ResponseBodyAdvice實現類中，咱們把響應的類型修改爲了ResponseResult。這就致使了，上面的這段代碼在選擇處理MessageConverter的時候，依舊根據以前的String類型選擇對應String類型的StringMessageConverter。而在StringMessageConverter類型，他只接受String類型的返回類型，咱們在ResponseBodyAdvice中將返回值從String類型改爲ResponseResult類型以後，調用StringMessageConverter方法發生類型強轉。ReponseResult沒法轉換成String，發生類型轉換異常。tomcat
因此解決該異常最好的方式就是重寫StringMessageConverter方法，讓他能夠解決ResonseResult類型的轉化。後來我沒有用這種方式，我以爲這樣相對比較麻煩，因此換了一種思路，在ResponseBodyAdvice中作了針對String類型返回值的修改：websocket
public class BaseGlobalResponseBodyAdvice implements ResponseBodyAdvice<Object> {
//這個方法表示對於哪些請求要執行beforeBodyWrite，返回true執行，返回false不執行
@Override
public boolean supports(MethodParameter methodParameter, Class aClass) {
return true;
}
//對於返回的對象若是不是最終對象ResponseResult，則選包裝一下
@Override
public Object beforeBodyWrite(Object o, MethodParameter methodParameter, MediaType mediaType,
Class aClass, ServerHttpRequest serverHttpRequest, ServerHttpResponse serverHttpResponse) {
if(!(o instanceof ResponseResult)) {
ResponseResult responseResult = new ResponseResult(CodeConstant.SUCCESS, o);
//由於handler處理類的返回類型是String，爲了保證一致性，這裏須要將ResponseResult轉回去
if(o instanceof String) {
return JSON.toJSONString(responseResult);
}
return responseResult;
}
return o;
}
}
最終解決了這個問題。mvc
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