Java Frameworks Miscs

Validation
Bean Validation and JSR 303
https://dzone.com/articles/bean-validation-and-jsr-303

http://stackoverflow.com/questions/28702809/how-to-manually-trigger-spring-validation

   <bean id="validator" class="org.springframework.validation.beanvalidation.LocalValidatorFactoryBean" />

    @Autowired
    private Validator validator;

http://docs.spring.io/spring/docs/current/spring-framework-reference/html/validation.html#validation-beanvalidation

http://www.codejava.net/frameworks/spring/spring-mvc-form-validation-example-with-bean-validation-api
We will need the validation-api-1.1.0.Final.jar and hibernate-validator-5.0.1.Final.jar files in order to use the Bean Validation API in our Spring MVC application.
    public String doLogin(@Valid User user, BindingResult result) {

@Pattern(regexp="[0-9]*")
@Size(min=5, max=5)
@Constraint(validatedBy = FrenchZipcodeValidator.class)

http://stackoverflow.com/questions/17344473/does-the-following-validation-mean-that-the-field-cannot-be-null

You can read "null elements are considered valid."
Therefore you need to specify @NotNull on the top of your field.
You have two alternatives:

@NotNull 
@Size(min = 2, max = 50)
private Integer age;

Or like Riccardo F. suggested:

@NotNull @Min(13) @Max(110)
private Integer age;

http://docs.jboss.org/hibernate/validator/5.1/reference/en-US/pdf/hibernate_validator_reference.pdf

https://raymondhlee.wordpress.com/2014/07/26/including-field-value-in-validation-message-using-spring-validation-framework-for-jsr-303/

@Size(min = 10, message =”phone number entered [${validatedValue}] is invalid. It must have at least {min} digits”)

@Size(min = 10, message = “{Size.order.customerName.custom} ${validatedValue}”)

http://blog.codeleak.pl/2014/06/better-error-messages-with-bean.html

@Size(min = 5, message = "\"${validatedValue}\" is too short.") @Size(min = 5, message = "\"${validatedValue}\" is ${validatedValue.length() < 2 ? 'way' : ''} too short.") @Future(message = "The value \"${formatter.format('%1$tY-%1$tm-%1$td', validatedValue)}\" is not in future!")
http://beanvalidation.org/1.0/spec/#validationapi-message

http://hibernate.org/validator/documentation/getting-started/
hibernate-validator need javax.el-api,