日常开发中经常会遇到需要参数校验的情况，比如某个字段不能为空、长度不能超过5等都属于参数校验的范围。对于简单的参数校验通过写几个if-else判断语句就搞定，但是对于复杂的多个参数校验的情况，就不是那么简单了，通常是各种循环嵌套+一堆if-else语句。一个字，丑！

所以，这就需要引进本文的主人公——Hibernate Validator（下文简称hb）。顾名思义，这是出自ORM框架Hibernate之手，那么，这个玩意可以帮助我们什么呢？

Express validation rules in a standardized way using annotation-based constraints and benefit from transparent integration with a wide variety of frameworks.

使用基于注解的约束，以标准化的方式表达验证规则，并可以与大多数框架无缝集成。

既然是基于注解进行阐述校验，那么有哪些注解呢？

参数注解

hv的参数校验有多个级别：

1. bean
2. method

bean也就是JavaBean（一个标准的）校验又有三种：

• field constraints（字段）

• property constraints（属性）

• class constraints（类）

参数注解可以附加到字段、getter方法，类或者接口上面。对于一些特定的需求，用户可以很容易的开发定制化的约束。

hv提供了JSR规范中所有内置constraint的实现，除此之外还有一些附加的constraint。

快速入门

引入pom依赖：

        <dependency>
            <groupId>javax.validation</groupId>
            <artifactId>validation-api</artifactId>
        </dependency>

        <dependency>
            <groupId>org.glassfish</groupId>
            <artifactId>javax.el</artifactId>
            <version>3.0.1-b08</version>
        </dependency>

        <dependency>
                <groupId>org.hibernate</groupId>
                <artifactId>hibernate-validator</artifactId>
                <version>5.3.4.Final</version>
        </dependency>

JavaBean:

public class CarBO {

    @NotNull
    private String manufacturer;

    @NotNull
    @Size(min = 2, max = 5)
    private String licensePlate;

    @Min(5)
    private int seatCount;

    public CarBO(String manufacturer, String licencePlate, int seatCount) {
        this.manufacturer = manufacturer;
        this.licensePlate = licencePlate;
        this.seatCount = seatCount;
    }

    //setter、getter
}

编写测试类：

public class CarTest {
    private static Validator validator;

    @BeforeClass
    public static void setUp() {
        ValidatorFactory factory = Validation.buildDefaultValidatorFactory();
        validator = factory.getValidator();
    }

    @Test
    public void manufacturerIsNull() {
        CarBO car = new CarBO( null, "DD-AB-123", 4 );

        Set<ConstraintViolation<CarBO>> constraintViolations =
                validator.validate( car );

        assertEquals( 1, constraintViolations.size() );
        assertEquals(
                "may not be null",
                constraintViolations.iterator().next().getMessage()
        );
    }

    @Test
    public void licensePlateTooShort() {
        CarBO car = new CarBO( "Morris", "D", 4 );

        Set<ConstraintViolation<CarBO>> constraintViolations =
                validator.validate( car );

        assertEquals( 1, constraintViolations.size() );
        assertEquals(
                "size must be between 2 and 14",
                constraintViolations.iterator().next().getMessage()
        );
    }

    @Test
    public void seatCountTooLow() {
        CarBO car = new CarBO( "Morris", "DD-AB-123", 1 );

        Set<ConstraintViolation<CarBO>> constraintViolations =
                validator.validate( car );

        assertEquals( 1, constraintViolations.size() );
        assertEquals(
                "must be greater than or equal to 2",
                constraintViolations.iterator().next().getMessage()
        );
    }

    @Test
    public void carIsValid() {
        CarBO car = new CarBO( "Morris", "DD-AB-123", 2 );

        Set<ConstraintViolation<CarBO>> constraintViolations =
                validator.validate( car );

        assertEquals( 0, constraintViolations.size() );
    }

}

在实际场景中，对于非法的参数需要抛出异常，比如哪个参数因为什么校验不通过。具体哪个字段可以通过ConstraintViolation的getPropertyPath方法获取，校验的提示信息可以通过ConstraintViolation的getMessage方法获取。

实例如下：

private void validate(CarBO car) {
        Set<ConstraintViolation<CarBO>> constraintViolations = validator.validate( car );
        if (!constraintViolations.isEmpty()) {
            throw new RuntimeException("参数非法！！" + getValidateMsg(constraintViolations));
        }
    }

    private String getValidateMsg(Set<ConstraintViolation<CarBO>> constraintViolations) {
        StringBuilder msg = new StringBuilder();
        for (ConstraintViolation<CarBO> violation : constraintViolations) {
            msg.append(violation.getPropertyPath())
                    .append(violation.getMessage())
                    .append(",");
        }
        return msg.substring(0, msg.lastIndexOf(","));
    }