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What Is Bean Validation
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The name bean validation comes from how the feature leverages JavaBeans naming conventions so that the objects being validated are our old friends, POJOs Bean validation is a new feature in Java EE 6, specified as JSR-303, which generalizes the concept of validation so that it can be used beyond JSF In fact, the bean validation feature is so general that it can be used in standalone Java Swing applications, with no server involved at all However, because the process of including new features into the core JDK is so difficult and laborious, and because the main use-case for bean validation is server-side applications, it is delivered as a part of Java EE 6 In fact, the most popular expected usage of bean validation is within JSF applications, so the two expert groups, JSF and bean validation, worked very closely together during development to ensure sensible and intuitive interoperability between these two technologies The following three fundamental observations underlie both JSF validation and bean validation Good application design includes separation of concerns, including use of the Model-View-Controller paradigm The application needs a way to ensure that the model is valid according to arbitrary constraints defined by the application
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In the spirit of separation of concerns, the logic that defines and performs this validation is best kept separated, but closely related to, the model itself In other words, the validation can be seen as metadata1 for the model JSF and bean validation have different ways of specifying the validation logic that goes along with, but is separate from, the model
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Differences Between JSF Validation and Bean Validation
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There are two main differences between JSF validation and bean validation The first is that in bean validation, the primary way to declare that a validation should be applied to a POJO is to attach an annotation to a field or a JavaBeans getter method on the POJO The following example, taken from the validateBean sample application in the online code for this book, uses bean validation to validate the UserBean in the JSFReg application, instead of JSF validation
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package comjsfcompref; import import import import import javautilDate; javaxfacesapplicationFacesMessage; javaxfacescontextFacesContext; javaxfacesbeanManagedBean; javaxfacesbeanSessionScoped;
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@ManagedBean @SessionScoped public class UserBean { @NotEmpty(message="You must supply a first name") protected String firstName; @NotEmpty(message="You must supply a last name") protected String lastName; @NotEmpty(message="You must supply a birthday") protected Date dob; protected String sex; @NotEmpty(message="You must supply an email address") @Email protected String email; protected String serviceLevel = "medium"; public String getFirstName() { return firstName; } public void setFirstName(String firstName) { // additional code not shown It s the same as in chapter 2
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The @NotEmpty and @Email annotations are custom bean validation constraints Like JSF standard validators, a core set of constraints are built into bean validation, but, also like
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Metadata is a potentially confusing term that literally means data about data In this usage, it simply means that the validation logic, that is, the constraints to apply and how to apply them, are data that goes alongside the model data
8:
C o n v e r t i n g a n d Va l i d a t i n g D a t a
JSF validators, they often fall short of what you need to get real work done The steps required to implement a custom constraint will be covered later in this chapter, but for now it is sufficient to know that the preceding code says that the firstName, lastName, dob, and email fields are not empty, and that the email field must be a valid e-mail address Contrast this with JSF, where the association between the validation and the model is done in the JSF page This brings us to the second main difference between JSF validation and bean validation: where the validation happens In JSF validation, the model itself is not validated, but rather, the individual fields are validated before they are pushed into the model during the Update Model Values lifecycle phase Because bean validation was designed for use in any kind of application, it doesn t have a lifecycle to define when the validation happens Rather, bean validation requires the validation to be performed on the model itself, after it has been populated with input data Therefore, to use JSF and bean validation together, a technique was devised to resolve the differences between these two models Features were added to the core bean validation API that essentially answer the questions, If I were to push this value into the model, would it be valid and If the value is not valid, what validation message should I present to the user This section does not provide a complete description of bean validation While it is entirely possible to use every aspect of bean validation in an application that uses JSF, this section will only describe those aspects that are directly included in the JSF-to-bean validation integration feature set For complete information on bean validation, consult the specification, which may be downloaded from http://jcporg/en/jsr/summary id=303
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