Java Se Bean Validation Example

21.1 Using Bean Validation Constraints

The Bean Validation model is supported by constraints in the form of annotations placed on a field, method, or class of a JavaBeans component, such as a managed bean.

Constraints can be built in or user defined. User-defined constraints are called custom constraints. Several built-in constraints are available in the javax.validation.constraints package. Table 21-1 lists all the built-in constraints. See Creating Custom Constraints for information on creating custom constraints.

Table 21-1 Built-In Bean Validation Constraints

Constraint	Description	Example
@AssertFalse	The value of the field or property must be false.	@AssertFalse boolean isUnsupported;
@AssertTrue	The value of the field or property must be true.	@AssertTrue boolean isActive;
@DecimalMax	The value of the field or property must be a decimal value lower than or equal to the number in the value element.	@DecimalMax("30.00") BigDecimal discount;
@DecimalMin	The value of the field or property must be a decimal value greater than or equal to the number in the value element.	@DecimalMin("5.00") BigDecimal discount;
@Digits	The value of the field or property must be a number within a specified range. The integer element specifies the maximum integral digits for the number, and the fraction element specifies the maximum fractional digits for the number.	@Digits(integer=6, fraction=2) BigDecimal price;
@Future	The value of the field or property must be a date in the future.	@Future Date eventDate;
@Max	The value of the field or property must be an integer value lower than or equal to the number in the value element.	@Max(10) int quantity;
@Min	The value of the field or property must be an integer value greater than or equal to the number in the value element.	@Min(5) int quantity;
@NotNull	The value of the field or property must not be null.	@NotNull String username;
@Null	The value of the field or property must be null.	@Null String unusedString;
@Past	The value of the field or property must be a date in the past.	@Past Date birthday;
@Pattern	The value of the field or property must match the regular expression defined in the regexp element.	@Pattern(regexp="\\(\\d{3}\\)\\d{3}-\\d{4}") String phoneNumber;
@Size	The size of the field or property is evaluated and must match the specified boundaries. If the field or property is a String, the size of the string is evaluated. If the field or property is a Collection, the size of the Collection is evaluated. If the field or property is a Map, the size of the Map is evaluated. If the field or property is an array, the size of the array is evaluated. Use one of the optional max or min elements to specify the boundaries.	@Size(min=2, max=240) String briefMessage;

In the following example, a constraint is placed on a field using the built-in @NotNull constraint:

public class Name {     @NotNull      private String firstname;      @NotNull      private String lastname;     ... }            

You can also place more than one constraint on a single JavaBeans component object. For example, you can place an additional constraint for size of field on the firstname and the lastname fields:

public class Name {     @NotNull     @Size(min=1, max=16)     private String firstname;      @NotNull      @Size(min=1, max=16)     private String lastname;     ... }            

The following example shows a method with a user-defined constraint that checks for a predefined email address pattern, such as a corporate email account:

@ValidEmail  public String getEmailAddress() {     return emailAddress; }            

For a built-in constraint, a default implementation is available. A user-defined or custom constraint needs a validation implementation. In the preceding example, the @ValidEmail custom constraint needs an implementation class.

Any validation failures are gracefully handled and can be displayed by the h:messages tag.

Any managed bean that contains Bean Validation annotations automatically gets validation constraints placed on the fields on a JavaServer Faces application's web pages.

For more information on using validation constraints, see the following:

• Chapter 22, "Bean Validation: Advanced Topics"

• Validating Resource Data with Bean Validation

• Validating Persistent Fields and Properties

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Source: https://docs.oracle.com/javaee/7/tutorial/bean-validation001.htm

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