在java项目中，我们经常需要对java对象的格式进行验证，比如接口传进来的User对象的name不能为空，我们传出去的数据的数据要符合规范，传出去前先手动验证， 如果用代码一个一个判断，那可太low了，幸好Spring项目中含有相应的工具。
手动验证
怎么判断一个对象是否符合注解说明的格式？上代码
场景：一个学生有个书包，学生和书包的名字都不能为空
@Data
public class Student {
@NotBlank(message = "学生名字不能为空")
private String name;
@NotNull
@Min(0)
private Integer age;
@Valid
@NotNull
private Bag bag;
}
@Data
public class Bag {
private Integer weight;
@NotBlank(message = "书包名字不能为空")
private String name;
}
private static Validator validator = Validation.buildDefaultValidatorFactory()
.getValidator();
public static void main(String[] args) {
Bag bag = new Bag();
bag.setName("");
bag.setWeight(343);
Student student = new Student();
student.setAge(343);
student.setName("fdsfs");
student.setBag(bag);
Set<ConstraintViolation> set = validator.validate(student, Default.class);
if (set != null && set.size() > 0) {
for (ConstraintViolation cv : set) {
System.out.println("====");
System.out.println(cv);
}
}
}
当需要对嵌套的对象也进行验证的时候，需要在被嵌套的属性上加上 @Valid注解 ，默认如果嵌套的属性为null，那就不验证它了，如果你想验证它不为null,加@NotNull注解。
spring 框架中使用的 Validator
spring 框架中也有同样的代码，主要有两块：
1，添加到注入的Component里面，spring 初始化容器对象的时候会进行验证，
org/springframework/validation/beanvalidation/BeanValidationPostProcessor.java
@Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
if (this.afterInitialization) {
doValidate(bean);
}
return bean;
}
/**
* Perform validation of the given bean.
* @param bean the bean instance to validate
* @see javax.validation.Validator#validate
*/
protected void doValidate(Object bean) {
Assert.state(this.validator != null, "No Validator set");
Set<ConstraintViolation<Object>> result = this.validator.validate(bean);
if (!result.isEmpty()) {
StringBuilder sb = new StringBuilder("Bean state is invalid: ");
for (Iterator<ConstraintViolation<Object>> it = result.iterator(); it.hasNext();) {
ConstraintViolation<Object> violation = it.next();
sb.append(violation.getPropertyPath()).append(" - ").append(violation.getMessage());
if (it.hasNext()) {
sb.append("; ");
}
}
throw new BeanInitializationException(sb.toString());
}
}
这个BeanPostProcessor就是在每个bean被创建的时候，属性设置完成后，拦截一下，验证一下这个bean的属性符不符合注解的要求，不符合就扔异常
2，controller,service方法参数里面，对参数验证
org/springframework/validation/beanvalidation/MethodValidationInterceptor.java
@Override
@SuppressWarnings("unchecked")
public Object invoke(MethodInvocation invocation) throws Throwable {
Class<?>[] groups = determineValidationGroups(invocation);
// Standard Bean Validation 1.1 API
ExecutableValidator execVal = this.validator.forExecutables();
Method methodToValidate = invocation.getMethod();
Set<ConstraintViolation<Object>> result;
try {
result = execVal.validateParameters(
invocation.getThis(), methodToValidate, invocation.getArguments(), groups);
}
catch (IllegalArgumentException ex) {
// Probably a generic type mismatch between interface and impl as reported in SPR-12237 / HV-1011
// Let's try to find the bridged method on the implementation class...
methodToValidate = BridgeMethodResolver.findBridgedMethod(
ClassUtils.getMostSpecificMethod(invocation.getMethod(), invocation.getThis().getClass()));
result = execVal.validateParameters(
invocation.getThis(), methodToValidate, invocation.getArguments(), groups);
}
if (!result.isEmpty()) {
throw new ConstraintViolationException(result);
}
Object returnValue = invocation.proceed();
result = execVal.validateReturnValue(invocation.getThis(), methodToValidate, returnValue, groups);
if (!result.isEmpty()) {
throw new ConstraintViolationException(result);
}
return returnValue;
}
这个拦截的是被 @Validated注解的类上的方法，对方法的入参进行一个拦截，
当然第二个其实我不是看的懂，以后更新。
