浅析@ResponseBodyAdvice的理解以及实际应用
一、@ResponseBodyAdvice的理解
1、ResponseBodyAdvice接口类 —— 其描述大致解释下：
允许在执行{@code@ResponseBody}或{@code ResponseEntity}控制器方法之后，但在使用{@code HttpMessageConverter}编写主体之前自定义响应。
实现可以直接用{@code RequestMappingHandlerAdapter}和{@code exceptionhandleexceptionresolver}注册，或者更可能用{@code@ControllerAdvice}注释，在这种情况下，它们将被两者自动检测。
/**
* Allows customizing the response after the execution of an {@code @ResponseBody}
* or a {@code ResponseEntity} controller method but before the body is written
* with an {@code HttpMessageConverter}.
*
* Implementations may be registered directly with
* {@code RequestMappingHandlerAdapter} and {@code ExceptionHandlerExceptionResolver}
* or more likely annotated with {@code @ControllerAdvice} in which case they
* will be auto-detected by both.*/
public interface ResponseBodyAdvice<T> {
/**
* Whether this component supports the given controller method return type
* and the selected {@code HttpMessageConverter} type.
* @param returnType the return type
* @param converterType the selected converter type
* @return {@code true} if {@link #beforeBodyWrite} should be invoked;
* {@code false} otherwise
*/
boolean supports(MethodParameter returnType, Class<? extends HttpMessageConverter<?>> converterType);
/**
* Invoked after an {@code HttpMessageConverter} is selected and just before
* its write method is invoked.
* @param body the body to be written
* @param returnType the return type of the controller method
* @param selectedContentType the content type selected through content negotiation
* @param selectedConverterType the converter type selected to write to the response
* @param request the current request
* @param response the current response
* @return the body that was passed in or a modified (possibly new) instance
*/
T beforeBodyWrite(T body, MethodParameter returnType, MediaType selectedContentType,
Class<? extends HttpMessageConverter<?>> selectedConverterType,
ServerHttpRequest request, ServerHttpResponse response);
}
2、个人理解：
ResponseBodyAdvice 接口是在 Controller 执行 return 之后，在 response 返回给客户端之前，执行的对 response 的一些处理，可以实现对 response 数据的一些统一封装或者加密等操作。
该接口一共有两个方法：
（1）supports —— 判断是否要执行beforeBodyWrite方法，true为执行，false不执行 —— 通过supports方法，我们可以选择哪些类或哪些方法要对response进行处理，其余的则不处理。
（2）beforeBodyWrite —— 对 response 处理的具体执行方法。
二、实例
有一个Controller类，返回参数为OutputObject，我们通过ResponseBodyAdvice，对该类的所有方法返回的OutputObject中的部分数据进行统一加密处理。
// 对响应报文统一处理，对bean内容进行加密
@Component
//声明该类要处理的包路径
@ControllerAdvice("com.cmos.edcreg.web.controller")
public class ResponseAdvice implements ResponseBodyAdvice {
private final Logger logger = LoggerFactory.getLogger(ResponseAdvice.class);
// 对response处理的具体方法
@Override
public Object beforeBodyWrite(Object arg0, MethodParameter arg1,
MediaType arg2, Class arg3, ServerHttpRequest arg4,
ServerHttpResponse arg5) {
OutputObject out = new OutputObject();
try {
//arg0转换为OutputObject类型
ObjectMapper objectMapper=new ObjectMapper();
out = objectMapper.readValue(org.json.JSONObject.valueToString(arg0), OutputObject.class);
//获取加密密钥
String oldEncryptKey = out.getBean().get("oldEncryptKey");
//获取加密字符串
DesSpecial des = new DesSpecial();
String encryptData = des.strEnc(JSON.toJSONString(out.getBean()), oldEncryptKey, null, null);
//封装数据（清除原来数据，放入加密数据）
out.getBean().clear();
out.getBean().put("data", encryptData);
return out;
} catch (Exception e) {
logger.error("返回报文处理出错", e);
out.setReturnCode(ReturnInfoEnums.PROCESS_ERROR.getCode());
out.setReturnMessage(ReturnInfoEnums.PROCESS_ERROR.getMessage());
return out;
}
}
/* 选择哪些类，或哪些方法需要走beforeBodyWrite
* 从arg0中可以获取方法名和类名
* arg0.getMethod().getDeclaringClass().getName()为获取方法名
*/
@Override
public boolean supports(MethodParameter arg0, Class arg1) {
return "com.cmos.edcreg.web.controller.GdH5AppointmentActiveVideoNewController".equals(arg0.getMethod().getDeclaringClass().getName());
}
}
三、在spring项目开发过程中的应用场景
对controller层返回值进行修改增强处理。比如返回值5，需要封装成：{"code":"0","data":5,,"msg":"success"} 格式返回前端
1、controller层业务代码
@RestController //此注解包含@ResponseBody注解
@RequestMapping("/mp")
public class ResponseBodyAdviceController {
@RequestMapping(value = "/hello", method = RequestMethod.GET)
public int hello() {
return 5;
}
}
2、实现ResponseBodyAdvice接口的切面类
/**
*此注解针对controller层的类做增强功能，即对加了@RestController注解的类进行处理
*/
@ControllerAdvice(annotations = RestController.class)
public class RestResultWrapper implements ResponseBodyAdvice<Object> {
@Override
public boolean supports(MethodParameter returnType, Class<? extends HttpMessageConverter<?>> converterType) {
return true;
}
@Override
public Object beforeBodyWrite(Object body, MethodParameter returnType, MediaType selectedContentType, Class<? extends HttpMessageConverter<?>> selectedConverterType, ServerHttpRequest request,
ServerHttpResponse response) {
//定义一个统一的返回类
RestResult responseResult = new RestResult( "0", body, "success");
//如果handler处理类的返回类型是String（即控制层的返回值类型），为了保证一致性，这里需要将ResponseResult转回去
if(body instanceof String) {
return JSON.toJSONString(responseResult);
}
//封装后的数据返回到前端页面
return JSONObject.toJSON(responseResult);
}
}
3、返回公共类的创建
// 统一返回Rest风格的数据结构
public class RestResult<T> implements Serializable {
private String code = "2000";
// 成功时返回的数据，失败时返回具体的异常信息
private T data;
// 请求失败返回的提示信息，给前端进行页面展示的信息
private String message ;
public RestResult() {
}
@Override
public String toString() {
return "RestResult{" +
"code='" + code + '\'' +
", data=" + data +
", message=" + message +
'}';
}
public RestResult(String code, T data, String message) {
this.code = code;
this.data = data;
this.message = message;
}
}
