@NotEmpty，NotNull和@NotBlank的区别

1.@NotNull：不能为null，但可以为empty
(""," ","   ")      

2.@NotEmpty：不能为null，而且长度必须大于0
(" ","  ")

3.@NotBlank：只能作用在String上，不能为null，而且调用trim()后，长度必须大于0
("test")    即：必须有实际字符

*
@NotNull: The CharSequence, Collection, Map or Array object is not null,
but can be empty.

@NotEmpty: The CharSequence, Collection, Map or Array object is not null
and size > 0.

@NotBlank: The string is not null and the trimmed length is greater than
zero.

4.examples:
1.String name = null;

@NotNull: false
@NotEmpty:false 
@NotBlank:false 

2.String name = "";

@NotNull:true
@NotEmpty: false
@NotBlank: false

3.String name = " ";

@NotNull: true
@NotEmpty: true
@NotBlank: false

4.String name = "Great answer!";

@NotNull: true
@NotEmpty:true
@NotBlank:true