@NotNull和@NotEmpty和@NotBlank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

*参考链接：

http://stackoverflow.com/questions/17137307/in-hibernate-validator-4-1-what-is-the-difference-between-notnull-notempty