关于 Spring 的全局处理，有两方面要说:
- 统一数据返回格式
- 统一异常处理
- 为了将两个问题说明清楚，将分两个章节分别说明，本章主要说第一点
有童鞋说，我们项目都做了这种处理，就是在每个 API 都单独工具类将返回值进行封装，但这种不够优雅；我想写最少的代码完成这件事，也许有童鞋说，加几个注解就解决问题了，说的没错，但这篇文章主要是为了说明为什么加了几个注解就解决问题了，目的是希望大家知其所以然。
为了更好的说明问题，本文先说明如何实现，然后再详细剖析实现原理(这很关键)
为什么要做统一数据返回格式
前后端分离是当今服务形式的主流，如何让前端小伙伴可以处理标准的 response JSON 数据结构都至关重要，为了让前端有更好的逻辑展示与页面交互处理，每一次 RESTful 请求都应该包含以下几个信息:
名称
描述
status
状态码，标识请求成功与否，如 [1:成功；-1:失败]
errorCode
错误码，给出明确错误码，更好的应对业务异常；请求成功该值可为空
errorMsg
错误消息，与错误码相对应，更具体的描述异常信息
resultBody
返回结果，通常是 Bean 对象对应的 JSON 数据, 通常为了应对不同返回值类型，将其声明为泛型类型 实现
通用返回值类定义
根据上面的描述，用 Java Bean 来体现这个结构就是这样:
@Data
public final class CommonResult<T> {
private int status = 1;
private String errorCode = "";
private String errorMsg = "";
private T resultBody;
public CommonResult() {
}
public CommonResult(T resultBody) {
SpringBoot RESTful API返回统一数据格式还不懂？
}
}
配置
没错，我们需要借助几个关键注
@EnableWebMvc
@Configuration
public class UnifiedReturnConfig {
@RestControllerAdvice("com.example.unifiedreturn.api")
static class CommonResultResponseAdvice implements ResponseBodyAdvice<Object>{
@Override
public boolean supports(MethodParameter methodParameter, Class<? extends HttpMessageConverter<?>> aClass) {
return true;
}
@Override
public Object beforeBodyWrite(Object body, MethodParameter methodParameter, MediaType mediaType, Class<? extends HttpMessageConverter<?>> aClass, ServerHttpRequest serverHttpRequest, ServerHttpResponse serverHttpResponse) {
if (body instanceof CommonResult){
return body;
}
return new CommonResult<Object>(body);
}
}
}
dy);
}
}
}
到这里就结束了，我们就可以纵情的写任何 RESTful API 了，所有的返回值都会有统一的 JSON
@RestController
@RequestMapping("/users")
public class UserController {
@GetMapping("")
public List<UserVo> getUserList(){
List<UserVo> userVoList = Lists.newArrayListWithCapacity(2);
userVoList.add(UserVo.builder().id(1L).name("一米八的一小伙").age(18).build());
userVoList.add(UserVo.builder().id(2L).name("tan").age(19).build());
return userVoList;
}
}
lder().id(2L).name("tan").age(19).build());
return userVoList;
}
}
}
@GetMapping("/{id}")
public UserVo getUserByName(@PathVariable Long id){
return UserVo.builder().id(1L).name("一米八的一小伙").age(18)
getUserByName(@PathVariable Long id){
return UserVo.builder().id(1L).name("一米八的一小伙").age(18).
e("一米八的一小伙").age(18).
@GetMapping("/testResponseEntity")
public ResponseEntity getUserByAge(){
return new ResponseEntity(UserVo.builder().id(1L).name("一米八的一小伙").age(18).build(), H
ty getUserByAge(){
return new ResponseEntity(UserVo.builder().id(1L).name("一米八的一小伙").age(18).build(), HttpStatus.OK);
}
d(), HttpStatus.OK);
}
打开浏览器输入地址测试: http://localhost:8080/users/testR
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Documented
@Import(DelegatingWebMvcConfiguration.class)
public
icy.RUNTIME)
@Target(ElementType.TYP
ME)
@Target(ElementType.TYPE)
@Doc
TYPE)
@Doc
@Configuration
public class DelegatingWebMvcConfiguration extends WebMvcConfigurationSupport {
...
}
引入了 DelegatingWebMvcConfiguration.class，那来看这个类吧:
@Configurat
@Bean
public RequestMappingHandlerAdapter requestMappingHandlerAdapter() {
RequestMappingHandlerAdapter adapter = createRequestMappingHandlerAdapter();
...
return adapter;
}
lic RequestMappingHandlerAdapte
public class RequestMappingHandlerAdapter extends AbstractHandlerMethodAdapter
implements BeanFactoryAware, InitializingBean {
...
}
RequestMappingHandlerAdapter 是每一次请求处理的关键，来看该类的定义:
public class RequestMappingHandlerAdapter extends AbstractHandle
@Override
public void afterPropertiesSet() {
// Do this first, it may add ResponseBody advice beans
initControllerAdviceCache();
if (this.argumentResolvers == null) {
List<HandlerMethodArgumentResolver> resolvers = getDefaultArgumentResolvers();
this.argumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
}
if (this.initBinderArgumentResolvers == null) {
List<HandlerMethodArgumentResolver> resolvers = getDefaultInitBinderArgumentResolvers();
this.initBinderArgumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
}
if (this.returnValueHandlers == null) {
List<HandlerMethodReturnValueHandler> handlers = getDefaultReturnValueHandlers();
this.returnValueHandlers = new HandlerMethodReturnValueHandlerCompos
ull) {
L
andlers(handle
ull) {
L
}
ull) {
L
private void initControllerAdviceCache() {
...
if (logger.isInfoEnabled()) {http://logger.info("Looking for @ControllerAdvice: " + getApplicationContext());
}
List<ControllerAdviceBean> beans = ControllerAdviceBean.findAnnotatedBeans(getApplicationContext());
AnnotationAwareOrderComparator.sort(beans);
List<Object> requestResponseBodyAdviceBeans = new ArrayList<Object>();
for (ControllerAdviceBean bean : beans) {
...
if (ResponseBodyAdvice.class.isAssignableFrom(bean.getBeanType())) {
requestRespon
(beans);
List<Object> requestRe
ns);
List<Object> requestResponseBodyAdviceBean
sponseBodyAdviceBean
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@ControllerAdvice
@Response
stResponseBodyAdviceBeans.add(bean);
stResponseBodyAdviceBeans.add(bean);
}
}
ceBeans.add(bean);
}
}
}
}
}
通过 ControllerAdviceBean 静态方法扫描
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@ControllerAdvice
@ResponseBo
@ControllerAdvice
@ResponseBody
public @interfa
eBody
public @interface RestControllerAd
ce RestControllerAd
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);
...
return;
}
}
nericHttpMessageConve
pro
{
outputValue = (T) getAdvice().bef
{
outputValue = (T) getAdvice().beforeBodyWrite(outputValue, retur
) getAdvice().beforeBodyWrite(outputValue, retur
class RequestResponseBodyAdviceChain implements RequestBodyAdvice, ResponseBodyAdvice<Object> {
@Override
public Object beforeBodyWrite(Object body, MethodParameter returnType, MediaType contentType,
Class<? extends HttpMessageConverter<?>> converterType,
ServerHttpRequest request, ServerHttpResponse response) {
return processBody(body, returnType, contentType, converterType, request, response);
}
@SuppressWarnings("unchecked")
private <T> Object processBody(Object body, MethodParameter returnType, MediaType contentType,
Class<? extends HttpMessageConverter<?>> converterType,
ServerHttpRequest request, ServerHttpResponse response) {
for (ResponseBodyAdvice<?> advice : getMatchingAdvice(returnType, ResponseBodyAdvice.class)) {
if (advice.supports(returnType, converterType)) {
body = ((ResponseBodyAdvice<T>) advice).beforeBodyWrite((T) body, returnType,
e,
ServerHttpRequest request, ServerHttpResponse response) {
for (ResponseBodyAdvice<?> advice : getMatchingAdvice(returnType, ResponseBodyAdvice.class)) {
if (advice.supports(returnType, converterType)) {
body = ((ResponseBodyAdvice<T>) advice).beforeBodyWrite((T) body, returnType,
contentType, converterType, reques
body, returnType,
contentType, converterType, request, response);
}
}
re
verterType, request, response);
}
}
return body;
}
}
);
}
}
return body;
}
}
}
@Override
public void handleReturnValue(Object returnValue, MethodParameter returnType,
ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
HandlerMethodReturnValueHandler handler = selectHandler(returnValue, returnType);
if (handler == null) {
throw new IllegalArgumentException("Unknown return value type: " + returnType.g
Value, MethodParameter returnType,
ModelAndViewContainer mavContaine
meter returnType,
ModelAndViewContainer mavContainer, NativeWebRequest webRequest)
iner, NativeWebRequest webRequest) throws Exception {
t) throws Exception {
HandlerMethodReturnVal
HandlerMethodReturnVal
@Override
public boolean supportsParameter(MethodParameter parameter
;
}
handler.handleReturnValue(returnValue, retur
;
}
handler.handleReturnValue(retu
;
}
handler.handleReturnValue(returnValue, returnType, mavContainer, webRequ
ue(returnValue, returnType, mavContainer, webRequ
@Override
public void handleReturnValue(Object returnValue, MethodParameter returnType,
ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
...
if (responseEntity instanceof ResponseEntity) {
int returnStatus = ((ResponseEntity<?>) responseEntity).getStatusCodeValue();
outputMessage.getServletResponse().setStatus(returnStatus);
if (returnStatus == 200) {
if (SAFE_METHODS.contains(inputMessage.getMethod())
&& isResourceNotModified(inputMessage, outputMessage)) {
// Ensure headers are flushed, no body should be written.
outputMessage.flush();
// Skip call to converters, as they may update the body.
return;
}
}
}
// Try even with null body. ResponseBodyAdvice could get involved.
writeWithMessageConverters(responseEntity.getBody()
od())
&& isResourceNotModified(inputMessage, outputMessage)) {
// Ensure headers are flushed, no body should be written.
outputMessage.flush();
// Skip call to converters, as they may update the body.
return;
}
}
}
// Try even with null body. ResponseBodyAdvice could get involved.
writeWithMessageConverters(responseEntity.getBody(), returnType, inputMessage, outputMessage);
// Ens
ty.getBody(), returnType, inputMessage, outputMessage);
// Ensure headers are flushed even i
);
// Ensure headers are flushed even if no body was written.
outp
ed even if no body was written.
outputMessage.flush();
}
.
outputMessage.flush();
}
该方法提取出 responseEntity.getBody()，并传递个 MessageConverter，然后再继续调用 beforeBodyWrite 方法，这才是真相!!!这是 RESTful API 正常返回内容的情况