Adding Constraint Validation Annotations to Your Beans

Although you can create your own constraint annotations any time you like, the Bean Validation API comes with several built-in annotations that satisfy the most common validation requirements.
These are all very simple constraints, but in many cases they are all you need to use. All these
constraints are in the package javax.validation.constraints.

@Null : You can apply this to any type, and it ensures that the annotated target is null.

@NotNull : You can also apply this to any type. It ensures that the target is not null.

@AssertTrue and @AssertFalse : These ensure that their annotated targets are true and false, respectively. As such, the field, parameter, or method (return value) that they annotate must be of the type boolean or Boolean. A null Boolean is considered valid for either constraint, so combine these with @NotNull if you do not accept null values.

@DecimalMax : This defines an upper limit for a numeric type, specified with the value attribute. It may annotate fields, parameters, and methods (return values) of type BigDecimal, BigInteger, CharSequence (String), byte, Byte, short, Short, int, Integer, long, and Long. The primitives double, Double, float, and Float are not supported due to precision concerns. CharSequences are converted to a decimal before validation, and null values are considered valid. The optional inclusive attribute specifies whether the test should be inclusive (less than or equal to) or exclusive (less than), and defaults to inclusive (true).

@DecimalMin : This is the counterpart to @DecimalMax. It applies to all the same types with the same rules. It also contains an inclusive attribute.

@Digits : You can use this to ensure that the annotated target is a parseable number (if it’s a CharSequence) and then tests the limits of that number’s parts (whether it’s a CharSequence, BigDecimal, BigInteger, byte, Byte, short, Short, int, Int, long, or Long). The mandatory integer attribute specifies the maximum number of integral digits (before the decimal point) allowed, whereas the required fraction attribute specifies the maximum number of fractional digits (after the decimal point) allowed. As always, null values are considered valid.

@Future : Ensures that the Date or Calendar field, parameter, or method (return value) is at some point in the future, however near or distant. As of Bean Validation 1.1, there is no support for Java 8 Date and Time API types. null values are considered valid.

@Past : Ensures that Date and Calendar targets are at some point in the past.

@Max and @Min : These are similar to @DecimalMax and @DecimalMin, but they do not support CharSequence targets, and they do not host an inclusive attribute; they are always inclusive. Targets that are null are considered valid.

@Pattern : This defines a regular expression regexp that the target CharSequence (String) must match, and it considers null values to be valid. It hosts an optional flags attribute that supports an array of any of Pattern.Flag enum values. Supported flags are:
     CANON_EQ : Enables canonical equivalence
     CASE_INSENSITIVE : Enables case-insensitive matching
     COMMENTS : Enables white space and comments in the pattern
     DOTALL : Turns dotall mode on
     MULTILINE : Turns multiline mode on
     UNICODE_CASE : Enables Unicode case folding
     UNIX_LINES : Turns Unix lines mode on

@Size : This defines inclusive max and min limits for the length of a CharSequence (String), the number of values in a Collection, the number of entries in a Map, or the number of elements in an array of any type.