[Java知识库]关于Spring中ResponseBodyAdvice的使用

ResponseBodyAdvice可以在注解@ResponseBody将返回值处理成相应格式之前操作返回值。实现这个接口即可完成相应操作。可用于对response 数据的一些统一封装或者加密等操作

1 ResponseBodyAdvice的简介

ResponseBodyAdvice接口和之前记录的RequestBodyAdvice接口类似, RequestBodyAdvice是请求到Controller之前拦截,做相应的处理操作, 而ResponseBodyAdvice是对Controller返回的{@code @ResponseBody}or a {@code ResponseEntity} 后,{@code HttpMessageConverter} 类型转换之前拦截, 进行相应的处理操作后,再将结果返回给客户端.

ResponseBodyAdvice的源代码:

/**   数据的处理顺序向下
 * 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}.
 *
 * <p>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.
 *
 * @author Rossen Stoyanchev
 * @since 4.1
 * @param <T> the body type
 */
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   方法返回的类型
	 * @param converterType the selected converter type   参数类型装换
	 * @return {@code true} if {@link #beforeBodyWrite} should be invoked;
	 * {@code false} otherwise
	 * 返回 true 则下面 beforeBodyWrite方法被调用, 否则就不调用下述方法
	 */
	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
	 */
	@Nullable
	T beforeBodyWrite(@Nullable T body, MethodParameter returnType, MediaType selectedContentType,
			Class<? extends HttpMessageConverter<?>> selectedConverterType,
			ServerHttpRequest request, ServerHttpResponse response);

}

说明:

• supports方法: 判断是否要执行beforeBodyWrite方法,true为执行,false不执行. 通过该方法可以选择哪些类或那些方法的response要进行处理, 其他的不进行处理.
• beforeBodyWrite方法: 对response方法进行具体操作处理

{@code @ResponseBody} 返回响应体, 例如List集合

{@code ResponseEntity} 返回响应实体对象,例如User对象

2 ResponseBodyAdvice的使用

1 准备一个SpringBoot项目环境

2 添加一个响应拦截类

@ControllerAdvice
public class BaseResponseBodyAdvice implements ResponseBodyAdvice<Object> {


    @Override
    public boolean supports(MethodParameter returnType, Class converterType) {
        return true;
    }

    @Override
    public Object beforeBodyWrite(Object body, MethodParameter returnType,
            MediaType selectedContentType, Class selectedConverterType, ServerHttpRequest request,
            ServerHttpResponse response) {

        // 遇到feign接口之类的请求, 不应该再次包装,应该直接返回
        // 上述问题的解决方案: 可以在feign拦截器中,给feign请求头中添加一个标识字段, 表示是feign请求
        // 在此处拦截到feign标识字段, 则直接放行 返回body.

        System.out.println("响应拦截成功");

        if (body instanceof BaseResponse) {
            return body;
        } else if (body == null) {
            return BaseResponse.ok();
        } else {
            return BaseResponse.ok(body);
        }
    }
}

3 添加一个返回包装类

@Data
@AllArgsConstructor
@NoArgsConstructor
public class BaseResponse<T> {

    private T data;
    private int status = 200;
    private String message;
    private long srvTime = System.currentTimeMillis();

    public BaseResponse(String message) {
        this.message = message;
    }

    public BaseResponse<T> setData(T data) {
        this.data = data;
        return this;
    }

    public static <T> BaseResponse<T> ok() {
        return new BaseResponse<>("操作成功");
    }

    public static <T> BaseResponse<T> ok(T data) {
        return new BaseResponse<T>("操作成功").setData(data);
    }

}

4 添加控制类

@Controller
@RequestMapping("/hello")
public class HelloWorld {

    // 此处数据从数据库中查询, 案例中也可以使用伪数据代替
    @Autowired
    private UserMapper userMapper;

    // {@code ResponseEntity} 案列
    @GetMapping("/one")
    @ResponseBody
    public User one() {

        List<User> users = userMapper.selectAll();
        System.out.println(users.get(0));
        return users.get(0);
    }

    
    // {@code @ResponseBody}  案列
    @GetMapping("/list")
    @ResponseBody
    public List<User> list() {

        List<User> users = userMapper.selectAll();
        System.out.println(users);
        return users;
    }
}    

5 接口测试

浏览器访问: http://localhost:8080/hello/one

User(id=1, username=李子柒, phone=77777, icon=李子柒的头像, queryTime=Wed Oct 27 20:47:02 CST 2021)
响应拦截成功

浏览器访问: http://localhost:8080/hello/list

[User(id=1, username=李子柒, phone=77777, icon=李子柒的头像, queryTime=Wed Oct 27 20:46:58 CST 2021)]
响应拦截成功

ps: 如果直接响应字符串返回,则会报类型转换异常.