Avoid data problems caused by null in velocity

Take a look at the following code:

2. # Foreach ($ ID in [1 .. 50])
4. # Set ($User = $ user. Get ($ id ))
6. $ ID: $ {user. name}
8. # End

12. In the above Code, assume that only one user with the ID of 1 exists, but it will show that 50 IDs are the users with the ID of 1 and their names, because in velocity, if the result returned by a value assignment statement is null, the value of the assigned object is not changed, that is, the $ user variable remains the previous valid value.

    The solution provided in the official document is to change the above Code:

14. # foreach ($ ID in [1 .. 50])
    • # Set ($ User = false)
    • # Set ($ User = $ user. Get ($ id)
    • $ id :$ {user. name}
    • # End

    other methods (recommended):

    the problem was finally met by me. The fundamental solution should be:

    solution: Modify velocity. properties

    original configuration: Directive. set. null. allowed = false

    modified configuration: Directive. set. null. allowed = true

    after the modification is complete, use # If ($ diary) to determine whether the object is empty ~~~

    see: http://www.itsmile.net/blog/article_show/20/273559/Velocity-Set-Null-value-method-Foreach