目录

• 目标
• 一、PathVariable 校验
• 二、方法参数校验
• 三、表单对象校验
• 四、RequestBody 校验
• 五、自定义校验规则
• 六、异常拦截器
• 参考文档

目标

1. 对于几种常见的入参方式，了解如何进行校验以及该如何处理错误消息；
2. 了解springboot 内置的参数异常类型，并能利用拦截器实现自定义处理；
3. 能实现简单的自定义校验规则

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
        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：

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。

码云同步代码

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

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