Bean Validation specification定义：
约束注释必须定义一个有效负载元素，该元素指定与约束声明关联的有效负载。有效负载参数的类型为
Payload[]。Class<? extends Payload>[] payload() default {};默认值必须为空数组。
每个可附加的有效负载都扩展Payload。/** * Payload type that can be attached to a given * constraint declaration. * <p/> * Payloads are typically used to carry on metadata information * consumed by a validation client. * </p> * Use of payloads is not considered portable. */
我已经阅读了其示例，但是例如，我不理解如何在JSF中使用此元数据？您能解释现实世界中有效载荷的其他用例吗？有效负载携带的元数据是什么？
也许这个link会帮助你。
import javax.validation.*;
import javax.validation.constraints.NotNull;
import java.util.Set;
public class ConstraintPayloadExample2 {
private static final Validator validator;
static {
Configuration<?> config = Validation.byDefaultProvider().configure();
ValidatorFactory factory = config.buildValidatorFactory();
validator = factory.getValidator();
factory.close();
}
public interface AppErrorHandler<T> extends Payload {
void onError (ConstraintViolation<T> violation);
}
public static class ErrorEmailSender<T> implements AppErrorHandler<T> {
@Override
public void onError (ConstraintViolation<T> violation) {
System.out.println("Sending email to support team: " +
violation.getPropertyPath() + " " +
violation.getMessage());
}
}
public static class TestBean {
@NotNull(payload = {ErrorEmailSender.class})
private String str;
public String getStr () {
return str;
}
public void setStr (String str) {
this.str = str;
}
}
public static void main (String[] args) {
TestBean bean = new TestBean();
Set<ConstraintViolation<TestBean>> constraintViolations =
validator.validate(bean);
if (constraintViolations.size() > 0) {
constraintViolations.stream().forEach(
ConstraintPayloadExample2::processError);
} else {
//proceed using user object
System.out.println(bean);
}
}
private static void processError (ConstraintViolation<TestBean> violation) {
Set<Class<? extends Payload>> payload =
violation.getConstraintDescriptor().getPayload();
payload.forEach(p -> {
if (AppErrorHandler.class.isAssignableFrom(p)) {
try {
AppErrorHandler errorHandler = (AppErrorHandler) p.newInstance();
errorHandler.onError(violation);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
}