Controller层代码这么写，简洁又优雅！
码农突围
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2022-08-04 10:44
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说到 Controller，相信大家都不陌生，它可以很方便地对外提供数据接口。它的定位，我认为是「不可或缺的配角」。
说它不可或缺是因为无论是传统的三层架构还是现在的 COLA 架构，Controller 层依旧有一席之地，说明他的必要性。
说它是配角是因为 Controller 层的代码一般是不负责具体的逻辑业务逻辑实现，但是它负责接收和响应请求。
接收请求并解析参数
调用 Service 执行具体的业务代码（可能包含参数校验）
捕获业务逻辑异常做出反馈
业务逻辑执行成功做出响应
//DTO
@Data
public class TestDTO {
private Integer num;
private String type;
}
//Service
@Service
public class TestService {
public Double service(TestDTO testDTO) throws Exception {
if (testDTO.getNum() <= 0) {
throw new Exception("输入的数字需要大于0");
}
if (testDTO.getType().equals("square")) {
return Math.pow(testDTO.getNum(), 2);
}
if (testDTO.getType().equals("factorial")) {
double result = 1;
int num = testDTO.getNum();
while (num > 1) {
result = result * num;
num -= 1;
}
return result;
}
throw new Exception("未识别的算法");
}
}
//Controller
@RestController
public class TestController {
private TestService testService;
@PostMapping("/test")
public Double test(@RequestBody TestDTO testDTO) {
try {
Double result = this.testService.service(testDTO);
return result;
} catch (Exception e) {
throw new RuntimeException(e);
}
}
@Autowired
public DTOid setTestService(TestService testService) {
this.testService = testService;
}
}
参数校验过多地耦合了业务代码，违背单一职责原则
可能在多个业务中都抛出同一个异常，导致代码重复
各种异常反馈和成功响应格式不统一，接口对接不友好
| 统一返回结构
//定义返回数据结构
public interface IResult {
Integer getCode();
String getMessage();
}
//常用结果的枚举
public enum ResultEnum implements IResult {
SUCCESS(2001, "接口调用成功"),
VALIDATE_FAILED(2002, "参数校验失败"),
COMMON_FAILED(2003, "接口调用失败"),
FORBIDDEN(2004, "没有权限访问资源");
private Integer code;
private String message;
//省略get、set方法和构造方法
}
//统一返回数据结构
@Data
@NoArgsConstructor
@AllArgsConstructor
public class Result<T> {
private Integer code;
private String message;
private T data;
public static <T> Result<T> success(T data) {
return new Result<>(ResultEnum.SUCCESS.getCode(), ResultEnum.SUCCESS.getMessage(), data);
}
public static <T> Result<T> success(String message, T data) {
return new Result<>(ResultEnum.SUCCESS.getCode(), message, data);
}
public static Result<?> failed() {
return new Result<>(ResultEnum.COMMON_FAILED.getCode(), ResultEnum.COMMON_FAILED.getMessage(), null);
}
public static Result<?> failed(String message) {
return new Result<>(ResultEnum.COMMON_FAILED.getCode(), message, null);
}
public static Result<?> failed(IResult errorResult) {
return new Result<>(errorResult.getCode(), errorResult.getMessage(), null);
}
public static <T> Result<T> instance(Integer code, String message, T data) {
Result<T> result = new Result<>();
result.setCode(code);
result.setMessage(message);
result.setData(data);
return result;
}
}
| 统一包装处理
public interface ResponseBodyAdvice<T> {
boolean supports(MethodParameter returnType, Class<? extends HttpMessageConverter<?>> converterType);
@Nullable
T beforeBodyWrite(@Nullable T body, MethodParameter returnType, MediaType selectedContentType, Class<? extends HttpMessageConverter<?>> selectedConverterType, ServerHttpRequest request, ServerHttpResponse response);
}
supports：判断是否要交给 beforeBodyWrite 方法执行，ture：需要；false：不需要
beforeBodyWrite：对 response 进行具体的处理
// 如果引入了swagger或knife4j的文档生成组件，这里需要仅扫描自己项目的包，否则文档无法正常生成
@RestControllerAdvice(basePackages = "com.example.demo")
public class ResponseAdvice implements ResponseBodyAdvice<Object> {
@Override
public boolean supports(MethodParameter returnType, Class<? extends HttpMessageConverter<?>> converterType) {
// 如果不需要进行封装的，可以添加一些校验手段，比如添加标记排除的注解
return true;
}
@Override
public Object beforeBodyWrite(Object body, MethodParameter returnType, MediaType selectedContentType, Class<? extends HttpMessageConverter<?>> selectedConverterType, ServerHttpRequest request, ServerHttpResponse response) {
// 提供一定的灵活度，如果body已经被包装了，就不进行包装
if (body instanceof Result) {
return body;
}
return Result.success(body);
}
}
| 参数校验
①@PathVariable 和 @RequestParam 参数校验
@RestController(value = "prettyTestController")
@RequestMapping("/pretty")
public class TestController {
private TestService testService;
@GetMapping("/{num}")
public Integer detail(@PathVariable("num") @Min(1) @Max(20) Integer num) {
return num * num;
}
@GetMapping("/getByEmail")
public TestDTO getByAccount(@RequestParam @NotBlank @Email String email) {
TestDTO testDTO = new TestDTO();
testDTO.setEmail(email);
return testDTO;
}
@Autowired
public void setTestService(TestService prettyTestService) {
this.testService = prettyTestService;
}
}
校验原理
用于解析 @RequestBody 标注的参数
处理 @ResponseBody 标注方法的返回值
public class RequestResponseBodyMethodProcessor extends AbstractMessageConverterMethodProcessor {
/**
* Throws MethodArgumentNotValidException if validation fails.
* @throws HttpMessageNotReadableException if {@link RequestBody#required()}
* is {@code true} and there is no body content or if there is no suitable
* converter to read the content with.
*/
@Override
public Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {
parameter = parameter.nestedIfOptional();
//把请求数据封装成标注的DTO对象
Object arg = readWithMessageConverters(webRequest, parameter, parameter.getNestedGenericParameterType());
String name = Conventions.getVariableNameForParameter(parameter);
if (binderFactory != null) {
WebDataBinder binder = binderFactory.createBinder(webRequest, arg, name);
if (arg != null) {
//执行数据校验
validateIfApplicable(binder, parameter);
//如果校验不通过，就抛出MethodArgumentNotValidException异常
//如果我们不自己捕获，那么最终会由DefaultHandlerExceptionResolver捕获处理
if (binder.getBindingResult().hasErrors() && isBindExceptionRequired(binder, parameter)) {
throw new MethodArgumentNotValidException(parameter, binder.getBindingResult());
}
}
if (mavContainer != null) {
mavContainer.addAttribute(BindingResult.MODEL_KEY_PREFIX + name, binder.getBindingResult());
}
}
return adaptArgumentIfNecessary(arg, parameter);
}
}
public abstract class AbstractMessageConverterMethodArgumentResolver implements HandlerMethodArgumentResolver {
/**
* Validate the binding target if applicable.
* <p>The default implementation checks for {@code @javax.validation.Valid},
* Spring's {@link org.springframework.validation.annotation.Validated},
* and custom annotations whose name starts with "Valid".
* @param binder the DataBinder to be used
* @param parameter the method parameter descriptor
* @since 4.1.5
* @see #isBindExceptionRequired
*/
protected void validateIfApplicable(WebDataBinder binder, MethodParameter parameter) {
//获取参数上的所有注解
Annotation[] annotations = parameter.getParameterAnnotations();
for (Annotation ann : annotations) {
//如果注解中包含了@Valid、@Validated或者是名字以Valid开头的注解就进行参数校验
Object[] validationHints = ValidationAnnotationUtils.determineValidationHints(ann);
if (validationHints != null) {
//实际校验逻辑，最终会调用Hibernate Validator执行真正的校验
//所以Spring Validation是对Hibernate Validation的二次封装
binder.validate(validationHints);
break;
}
}
}
}
②@RequestBody 参数校验
//DTO
@Data
public class TestDTO {
@NotBlank
private String userName;
@NotBlank
@Length(min = 6, max = 20)
private String password;
@NotNull
private String email;
}
//Controller
@RestController(value = "prettyTestController")
@RequestMapping("/pretty")
public class TestController {
private TestService testService;
@PostMapping("/test-validation")
public void testValidation(@RequestBody @Validated TestDTO testDTO) {
this.testService.save(testDTO);
}
@Autowired
public void setTestService(TestService testService) {
this.testService = testService;
}
}
校验原理
public class MethodValidationPostProcessor extends AbstractBeanFactoryAwareAdvisingPostProcessor implements InitializingBean {
//指定了创建切面的Bean的注解
private Class<? extends Annotation> validatedAnnotationType = Validated.class;
@Override
public void afterPropertiesSet() {
//为所有@Validated标注的Bean创建切面
Pointcut pointcut = new AnnotationMatchingPointcut(this.validatedAnnotationType, true);
//创建Advisor进行增强
this.advisor = new DefaultPointcutAdvisor(pointcut, createMethodValidationAdvice(this.validator));
}
//创建Advice，本质就是一个方法拦截器
protected Advice createMethodValidationAdvice(@Nullable Validator validator) {
return (validator != null ? new MethodValidationInterceptor(validator) : new MethodValidationInterceptor());
}
}
public class MethodValidationInterceptor implements MethodInterceptor {
@Override
public Object invoke(MethodInvocation invocation) throws Throwable {
//无需增强的方法，直接跳过
if (isFactoryBeanMetadataMethod(invocation.getMethod())) {
return invocation.proceed();
}
Class<?>[] groups = determineValidationGroups(invocation);
ExecutableValidator execVal = this.validator.forExecutables();
Method methodToValidate = invocation.getMethod();
Set<ConstraintViolation<Object>> result;
try {
//方法入参校验，最终还是委托给Hibernate Validator来校验
//所以Spring Validation是对Hibernate Validation的二次封装
result = execVal.validateParameters(
invocation.getThis(), methodToValidate, invocation.getArguments(), groups);
}
catch (IllegalArgumentException ex) {
...
}
//校验不通过抛出ConstraintViolationException异常
if (!result.isEmpty()) {
throw new ConstraintViolationException(result);
}
//Controller方法调用
Object returnValue = invocation.proceed();
//下面是对返回值做校验，流程和上面大概一样
result = execVal.validateReturnValue(invocation.getThis(), methodToValidate, returnValue, groups);
if (!result.isEmpty()) {
throw new ConstraintViolationException(result);
}
return returnValue;
}
}
③自定义校验规则
自定义注解类，定义错误信息和一些其他需要的内容
注解校验器，定义判定规则
//自定义注解类
@Target({ElementType.METHOD, ElementType.FIELD, ElementType.ANNOTATION_TYPE, ElementType.CONSTRUCTOR, ElementType.PARAMETER})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Constraint(validatedBy = MobileValidator.class)
public @interface Mobile {
/**
* 是否允许为空
*/
boolean required() default true;
/**
* 校验不通过返回的提示信息
*/
String message() default "不是一个手机号码格式";
/**
* Constraint要求的属性，用于分组校验和扩展，留空就好
*/
Class<?>[] groups() default {};
Class<? extends Payload>[] payload() default {};
}
//注解校验器
public class MobileValidator implements ConstraintValidator<Mobile, CharSequence> {
private boolean required = false;
private final Pattern pattern = Pattern.compile("^1[34578][0-9]{9}$"); // 验证手机号
/**
* 在验证开始前调用注解里的方法，从而获取到一些注解里的参数
*
* @param constraintAnnotation annotation instance for a given constraint declaration
*/
@Override
public void initialize(Mobile constraintAnnotation) {
this.required = constraintAnnotation.required();
}
/**
* 判断参数是否合法
*
* @param value object to validate
* @param context context in which the constraint is evaluated
*/
@Override
public boolean isValid(CharSequence value, ConstraintValidatorContext context) {
if (this.required) {
// 验证
return isMobile(value);
}
if (StringUtils.hasText(value)) {
// 验证
return isMobile(value);
}
return true;
}
private boolean isMobile(final CharSequence str) {
Matcher m = pattern.matcher(str);
return m.matches();
}
}
| 自定义异常与统一拦截异常
抛出的异常不够具体，只是简单地把错误信息放到了 Exception 中
抛出异常后，Controller 不能具体地根据异常做出反馈
虽然做了参数自动校验，但是异常返回结构和正常返回结构不一致
//自定义异常
public class ForbiddenException extends RuntimeException {
public ForbiddenException(String message) {
super(message);
}
}
//自定义异常
public class BusinessException extends RuntimeException {
public BusinessException(String message) {
super(message);
}
}
//统一拦截异常
@RestControllerAdvice(basePackages = "com.example.demo")
public class ExceptionAdvice {
/**
* 捕获 {@code BusinessException} 异常
*/
@ExceptionHandler({BusinessException.class})
public Result<?> handleBusinessException(BusinessException ex) {
return Result.failed(ex.getMessage());
}
/**
* 捕获 {@code ForbiddenException} 异常
*/
@ExceptionHandler({ForbiddenException.class})
public Result<?> handleForbiddenException(ForbiddenException ex) {
return Result.failed(ResultEnum.FORBIDDEN);
}
/**
* {@code @RequestBody} 参数校验不通过时抛出的异常处理
*/
@ExceptionHandler({MethodArgumentNotValidException.class})
public Result<?> handleMethodArgumentNotValidException(MethodArgumentNotValidException ex) {
BindingResult bindingResult = ex.getBindingResult();
StringBuilder sb = new StringBuilder("校验失败:");
for (FieldError fieldError : bindingResult.getFieldErrors()) {
sb.append(fieldError.getField()).append("：").append(fieldError.getDefaultMessage()).append(", ");
}
String msg = sb.toString();
if (StringUtils.hasText(msg)) {
return Result.failed(ResultEnum.VALIDATE_FAILED.getCode(), msg);
}
return Result.failed(ResultEnum.VALIDATE_FAILED);
}
/**
* {@code @PathVariable} 和 {@code @RequestParam} 参数校验不通过时抛出的异常处理
*/
@ExceptionHandler({ConstraintViolationException.class})
public Result<?> handleConstraintViolationException(ConstraintViolationException ex) {
if (StringUtils.hasText(ex.getMessage())) {
return Result.failed(ResultEnum.VALIDATE_FAILED.getCode(), ex.getMessage());
}
return Result.failed(ResultEnum.VALIDATE_FAILED);
}
/**
* 顶级异常捕获并统一处理，当其他异常无法处理时候选择使用
*/
@ExceptionHandler({Exception.class})
public Result<?> handle(Exception ex) {
return Result.failed(ex.getMessage());
}
}
（完）
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