一、PathVariable 校验
在定义 Restful 风格的接口时，通常会采用 PathVariable 指定关键业务参数，如下：
@GetMapping("/path/{group:[a-zA-Z0-9_]+}/{userid}")
@ResponseBody
public String path(@PathVariable("group") String group, @PathVariable("userid") Integer userid) {
return group + ":" + userid; }{group:[a-zA-Z0-9_]+} 这样的表达式指定了 group 必须是以大小写字母、数字或下划线组成的字符串。
我们试着访问一个错误的路径：
GET /path/testIllegal.get/10000此时会得到 404的响应，因此对于PathVariable 仅由正则表达式可达到校验的目的
二、方法参数校验
类似前面的例子，大多数情况下，我们都会直接将HTTP请求参数映射到方法参数上。
@GetMapping("/param")
@ResponseBody
public String param(@RequestParam("group")@Email String group,
@RequestParam("userid") Integer userid) {
return group + ":" + userid; }上面的代码中，@RequestParam 声明了映射，此外我们还为 group 定义了一个规则(复合Email格式)
这段代码是否能直接使用呢？答案是否定的，为了启用方法参数的校验能力，还需要完成以下步骤：
- 声明 MethodValidationPostProcessor
@Bean
public MethodValidationPostProcessor methodValidationPostProcessor() { return new MethodValidationPostProcessor(); }- Controller指定@Validated注解
@Controller
@RequestMapping("/validate")
@Validated
public class ValidateController {如此之后，方法上的@Email规则才能生效。
校验异常
如果此时我们尝试通过非法参数进行访问时，比如提供非Email格式的 group
会得到以下错误：
GET /validate/param?group=simple&userid=10000
====>
{
"timestamp": 1530955093583,
"status": 500, "error": "Internal Server Error", "exception": "javax.validation.ConstraintViolationException", "message": "No message available", "path": "/validate/param" }而如果参数类型错误，比如提供非整数的 userid，会得到：
GET /validate/param?group=simple&userid=1f
====>
{
"timestamp": 1530954430720,
"status": 400, "error": "Bad Request", "exception": "org.springframework.web.method.annotation.MethodArgumentTypeMismatchException", "message": "Failed to convert value of type 'java.lang.String' to required type 'java.lang.Integer'; nested exception is java.lang.NumberFormatException: For input string: \"1f\"", "path": "/validate/param" }当存在参数缺失时，由于定义的@RequestParam注解中，属性 required=true，也将会导致失败：
GET /validate/param?userid=10000
====>
{
"timestamp": 1530954345877,
"status": 400, "error": "Bad Request", "exception": "org.springframework.web.bind.MissingServletRequestParameterException", "message": "Required String parameter 'group' is not present", "path": "/validate/param" }三、表单对象校验
页面的表单通常比较复杂，此时可以将请求参数封装到表单对象中，
并指定一系列对应的规则，参考JSR-303
public static class FormRequest { @NotEmpty @Email private String email; @Pattern(regexp = "[a-zA-Z0-9_]{6,30}") private String name; @Min(5) @Max(199) private int age;上面定义的属性中：
- email必须非空、符合Email格式规则；
- name必须为大小写字母、数字及下划线组成，长度在6-30个；
- age必须在5-199范围内
Controller方法中的定义：
@PostMapping("/form")
@ResponseBody
public FormRequest form(@Validated FormRequest form) { return form; }@Validated指定了参数对象需要执行一系列校验。
校验异常
此时我们尝试构造一些违反规则的输入，会得到以下的结果：
{
"timestamp": 1530955713166,
"status": 400,
"error": "Bad Request", "exception": "org.springframework.validation.BindException", "errors": [ { "codes": [ "Email.formRequest.email", "Email.email", "Email.java.lang.String", "Email" ], "arguments": [ { "codes": [ "formRequest.email", "email" ], "arguments": null, "defaultMessage": "email", "code": "email" }, [], { "arguments": null, "codes": [ ".*" ], "defaultMessage": ".*" } ], "defaultMessage": "不是一个合法的电子邮件地址", "objectName": "formRequest", "field": "email", "rejectedValue": "tecom", "bindingFailure": false, "code": "Email" }, { "codes": [ "Pattern.formRequest.name", "Pattern.name", "Pattern.java.lang.String", "Pattern" ], "arguments": [ { "codes": [ "formRequest.name", "name" ], "arguments": null, "defaultMessage": "name", "code": "name" }, [], { "arguments": null, "codes": [ "[a-zA-Z0-9_]{6,30}" ], "defaultMessage": "[a-zA-Z0-9_]{6,30}" } ], "defaultMessage": "需要匹配正则表达式\"[a-zA-Z0-9_]{6,30}\"", "objectName": "formRequest", "field": "name", "rejectedValue": "fefe", "bindingFailure": false, "code": "Pattern" }, { "codes": [ "Min.formRequest.age", "Min.age", "Min.int", "Min" ], "arguments": [ { "codes": [ "formRequest.age", "age" ], "arguments": null, "defaultMessage": "age", "code": "age" }, 5 ], "defaultMessage": "最小不能小于5", "objectName": "formRequest", "field": "age", "rejectedValue": 2, "bindingFailure": false, "code": "Min" } ], "message": "Validation failed for object='formRequest'. Error count: 3", "path": "/validate/form" } 如果是参数类型不匹配，会得到：
{
"timestamp": 1530955359265,
"status": 400,
"error": "Bad Request", "exception": "org.springframework.validation.BindException", "errors": [ { "codes": [ "typeMismatch.formRequest.age", "typeMismatch.age", "typeMismatch.int", "typeMismatch" ], "arguments": [ { "codes": [ "formRequest.age", "age" ], "arguments": null, "defaultMessage": "age", "code": "age" } ], "defaultMessage": "Failed to convert property value of type 'java.lang.String' to required type 'int' for property 'age'; nested exception is java.lang.NumberFormatException: For input string: \"\"", "objectName": "formRequest", "field": "age", "rejectedValue": "", "bindingFailure": true, "code": "typeMismatch" } ], "message": "Validation failed for object='formRequest'. Error count: 1", "path": "/validate/form" }Form表单参数上，使用@Valid注解可达到同样目的，而关于两者的区别则是：
@Valid 基于JSR303，即 Bean Validation 1.0，由Hibernate Validator实现；
@Validated 基于JSR349，是Bean Validation 1.1，由Spring框架扩展实现；
后者做了一些增强扩展，如支持分组校验，有兴趣可参考这里。
四、RequestBody 校验
对于直接Json消息体输入，同样可以定义校验规则：
@PostMapping("/json")
@ResponseBody
public JsonRequest json(@Validated @RequestBody JsonRequest request) { return request; } ... public static class JsonRequest { @NotEmpty @Email private String email; @Pattern(regexp = "[a-zA-Z0-9_]{6,30}") private String name; @Min(5) @Max(199) private int age;校验异常
构造一个违反规则的Json请求体进行输入，会得到：
{
"timestamp": 1530956161314,
"status": 400,
"error": "Bad Request", "exception": "org.springframework.web.bind.MethodArgumentNotValidException", "errors": [ { "codes": [ "Min.jsonRequest.age", "Min.age", "Min.int", "Min" ], "arguments": [ { "codes": [ "jsonRequest.age", "age" ], "arguments": null, "defaultMessage": "age", "code": "age" }, 5 ], "defaultMessage": "最小不能小于5", "objectName": "jsonRequest", "field": "age", "rejectedValue": 1, "bindingFailure": false, "code": "Min" } ], "message": "Validation failed for object='jsonRequest'. Error count: 1", "path": "/validate/json" } 此时与FormBinding的情况不同，我们得到了一个MethodArgumentNotValidException异常。
而如果发生参数类型不匹配，比如输入age=1f，会产生以下结果：
{
"timestamp": 1530956206264,
"status": 400,
"error": "Bad Request", "exception": "org.springframework.http.converter.HttpMessageNotReadableException", "message": "Could not read document: Can not deserialize value of type int from String \"ff\": not a valid Integer value\n at [Source: java.io.PushbackInputStream@68dc9800; line: 2, column: 8] (through reference chain: org.zales.dmo.boot.controllers.ValidateController$JsonRequest[\"age\"]); nested exception is com.fasterxml.jackson.databind.exc.InvalidFormatException: Can not deserialize value of type int from String \"ff\": not a valid Integer value\n at [Source: java.io.PushbackInputStream@68dc9800; line: 2, column: 8] (through reference chain: org.zales.dmo.boot.controllers.ValidateController$JsonRequest[\"age\"])", "path": "/validate/json" }这表明在JSON转换过程中已经失败！
五、自定义校验规则
框架内预置的校验规则可以满足大多数场景使用，
但某些特殊情况下，你需要制作自己的校验规则，这需要用到ContraintValidator接口。
我们以一个密码校验的场景作为示例，比如一个注册表单上，
我们需要检查 密码输入 与 密码确认 是一致的。
**首先定义 PasswordEquals 注解
@Documented
@Constraint(validatedBy = { PasswordEqualsValidator.class })
@Target({ ElementType.METHOD, ElementType.FIELD, ElementType.TYPE }) @Retention(RetentionPolicy.RUNTIME) public @interface PasswordEquals { String message() default "Password is not the same"; Class<?>[] groups() default {}; Class<? extends Payload>[] payload() default {}; }在表单上声明@PasswordEquals 注解
@PasswordEquals
public class RegisterForm { @NotEmpty @Length(min=5,max=30) private String username; @NotEmpty private String password; @NotEmpty private String passwordConfirm;针对@PasswordEquals实现校验逻辑
public class PasswordEqualsValidator implements ConstraintValidator<PasswordEquals, RegisterForm> { @Override public void initialize(PasswordEquals anno) { } @Override public boolean isValid(RegisterForm form, ConstraintValidatorContext context) { String passwordConfirm = form.getPasswordConfirm(); String password = form.getPassword(); boolean match = passwordConfirm != null ? passwordConfirm.equals(password) : false; if (match) { return true; } String messageTemplate = context.getDefaultConstraintMessageTemplate(); // disable default violation rule [ 禁用默认违规规则] context.disableDefaultConstraintViolation(); // assign error on password Confirm field context.buildConstraintViolationWithTemplate(messageTemplate).addPropertyNode("passwordConfirm") .addConstraintViolation(); return false; } } 如此，我们已经完成了自定义的校验工作。
六、异常拦截器
SpringBoot 框架中可通过 @ControllerAdvice 实现Controller方法的拦截操作。
可以利用拦截能力实现一些公共的功能，比如权限检查、页面数据填充，以及全局的异常处理等等。
在前面的篇幅中，我们提及了各种校验失败所产生的异常，整理如下表：
| 异常类型 | 描述 |
|---|---|
| ConstraintViolationException | 违反约束，javax扩展定义 |
| BindException | 绑定失败，如表单对象参数违反约束 |
| MethodArgumentNotValidException | 参数无效，如JSON请求参数违反约束 |
| MissingServletRequestParameterException | 参数缺失 |
| TypeMismatchException | 参数类型不匹配 |
如果希望对这些异常实现统一的捕获，并返回自定义的消息，
可以参考以下的代码片段：
@ControllerAdvice
public static class CustomExceptionHandler extends ResponseEntityExceptionHandler { @ExceptionHandler(value = { ConstraintViolationException.class }) public ResponseEntity<String> handle(ConstraintViolationException e) { Set<ConstraintViolation<?>> violations = e.getConstraintViolations(); StringBuilder strBuilder = new StringBuilder(); for (ConstraintViolation<?> violation : violations) { strBuilder.append(violation.getInvalidValue() + " " + violation.getMessage() + "\n"); } String result = strBuilder.toString(); return new ResponseEntity<String>("ConstraintViolation:" + result, HttpStatus.BAD_REQUEST); } @Override protected ResponseEntity<Object> handleBindException(BindException ex, HttpHeaders headers, HttpStatus status, WebRequest request) { return new ResponseEntity<Object>("BindException:" + buildMessages(ex.getBindingResult()), HttpStatus.BAD_REQUEST); } @Override protected ResponseEntity<Object> handleMethodArgumentNotValid(MethodArgumentNotValidException ex, HttpHeaders headers, HttpStatus status, WebRequest request) { return new ResponseEntity<Object>("MethodArgumentNotValid:" + buildMessages(ex.getBindingResult()), HttpStatus.BAD_REQUEST); } @Override public ResponseEntity<Object> handleMissingServletRequestParameter(MissingServletRequestParameterException ex, HttpHeaders headers, HttpStatus status, WebRequest request) { return new ResponseEntity<Object>("ParamMissing:" + ex.getMessage(), HttpStatus.BAD_REQUEST); } @Override protected ResponseEntity<Object> handleTypeMismatch(TypeMismatchException ex, HttpHeaders headers, HttpStatus status, WebRequest request) { return new ResponseEntity<Object>("TypeMissMatch:" + ex.getMessage(), HttpStatus.BAD_REQUEST); } private String buildMessages(BindingResult result) { StringBuilder resultBuilder = new StringBuilder(); List<ObjectError> errors = result.getAllErrors(); if (errors != null && errors.size() > 0) { for (ObjectError error : errors) { if (error instanceof FieldError) { FieldError fieldError = (FieldError) error; String fieldName = fieldError.getField(); String fieldErrMsg = fieldError.getDefaultMessage(); resultBuilder.append(fieldName).append(" ").append(fieldErrMsg).append(";"); } } } return resultBuilder.toString(); } }默认情况下，对于非法的参数输入，框架会产生 HTTP_BAD_REQUEST(status=400) 错误码，
并输出友好的提示消息，这对于一般情况来说已经足够。
更多的输入校验及提示功能应该通过客户端去完成(服务端仅做同步检查)，
客户端校验的用户体验更好，而这也符合富客户端(rich client)的发展趋势。
参考文档
springmvc-validation样例
使用validation api进行操作
hibernate-validation官方文档
Bean-Validation规范