Java验证

摘要：校验器可以通过对象报告校验失败的信息接口定义示例如下，可以使用等工具测试用户名不能为空常用注解也可以自定义注解及其校验规则获取并初始化注解信息设置自定义校验规则人的姓名不能为空参考

Q: 为什么后端需要校验，只交给前端校验行不行
A: 前后端都需要校验
后端校验防止请求过来的非法数据，对后端进行破坏

http://commons.apache.org/ 这个地址apache提供了常用的工具类，包括校验框架

提供了大量的校验器，如时间、数值、正则表达式、邮箱、URL等待

以IntegerValidator为例

IntegerValidator integerValidator = new IntegerValidator();
        
Integer value = integerValidator.validate("10");
System.out.println(value);
        
value = integerValidator.validate("G");
System.out.println(value);

/**
     * 
Validate/convert an Integer using the default
     *    Locale.
     *
     * @param value The value validation is being performed on.
     * @return The parsed Integer if valid or null
     *  if invalid.
     */
    public Integer validate(String value) {
        return (Integer)parse(value, (String)null, (Locale)null);
    }

在校验传入的参数时，当能够解析成Integer类型就返回这个数字，如果不能就返回null

其它数值类型校验类似

Spring框架提供的用于校验对象的Validator接口，在校验过程中与Errors对象配合。校验器可以通过Errors对象报告校验失败的信息

org.springframework.validation.Validator接口定义

public interface Validator {

    /**
     * Can this {@link Validator} {@link #validate(Object, Errors) validate}
     * instances of the supplied {@code clazz}?
     * 
This method is typically implemented like so:
     * 
return Foo.class.isAssignableFrom(clazz);
     * (Where {@code Foo} is the class (or superclass) of the actual
     * object instance that is to be {@link #validate(Object, Errors) validated}.)
     * @param clazz the {@link Class} that this {@link Validator} is
     * being asked if it can {@link #validate(Object, Errors) validate}
     * @return {@code true} if this {@link Validator} can indeed
     * {@link #validate(Object, Errors) validate} instances of the
     * supplied {@code clazz}
     */
    boolean supports(Class clazz);

    /**
     * Validate the supplied {@code target} object, which must be
     * of a {@link Class} for which the {@link #supports(Class)} method
     * typically has (or would) return {@code true}.
     * 
The supplied {@link Errors errors} instance can be used to report
     * any resulting validation errors.
     * @param target the object that is to be validated (can be {@code null})
     * @param errors contextual state about the validation process (never {@code null})
     * @see ValidationUtils
     */
    void validate(Object target, Errors errors);

示例如下，可以使用POSTMAN等工具测试

package com.adagio.domain;

import javax.validation.constraints.Max;
import javax.validation.constraints.Min;
import javax.validation.constraints.NotNull;

public class Person {

    @NotNull
    private String name;
    
    @Min(0)
    @Max(150)
    private int age;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }
    
    
}

package com.adagio.validator;

import org.springframework.util.StringUtils;
import org.springframework.validation.Errors;
import org.springframework.validation.Validator;

import com.adagio.domain.Person;

public class PersonValidator implements Validator {

    @Override
    public boolean supports(Class clazz) {
        return Person.class.isAssignableFrom(clazz);
    }

    @Override
    public void validate(Object target, Errors errors) {
        Person person = Person.class.cast(target);
        
        String name = person.getName();
        if(!StringUtils.hasLength(name)){
            errors.reject("person.name.not.null", "用户名不能为空");
        }
    }

}

package com.adagio.controller;

import javax.validation.Valid;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;

import com.adagio.domain.Person;

@Controller 
public class PersonController {

    @PostMapping("/person/save")
    public Person save(@Valid @RequestBody Person person){
        
        return person;
    }
}

常用注解：@Valid、@NotNull、@Null、@Size、@Min、@Max

也可以自定义注解及其校验规则

package com.adagio.validator;

import static java.lang.annotation.ElementType.FIELD;
import static java.lang.annotation.ElementType.METHOD;
import static java.lang.annotation.RetentionPolicy.RUNTIME;

import java.lang.annotation.Documented;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;

import javax.validation.Constraint;
import javax.validation.Payload;

@Target({METHOD, FIELD})
@Retention(RUNTIME)
@Documented
@Constraint(validatedBy = {PersonNameConstraintValidator.class})
public @interface PersonName {

    String message() default "{person.name.not.null}";

    Class[] groups() default {};

    Class[] payload() default {};
}

package com.adagio.validator;

import javax.validation.ConstraintValidator;
import javax.validation.ConstraintValidatorContext;

public class PersonNameConstraintValidator implements ConstraintValidator{

    /**
     * 获取并初始化注解信息
     */
    @Override
    public void initialize(PersonName constraintAnnotation) {
        
    }

    /**
     * 设置自定义校验规则
     */
    @Override
    public boolean isValid(String value, ConstraintValidatorContext context) {
        return false;
    }

}

person.name.not.null=人的姓名不能为空

参考：https://segmentfault.com/l/15...