Velocity various judgements are null or "null" or "" Summary

In web development, there is often a need to determine whether a variable is empty (null) or an empty string (""), which affects the presentation logic of the page, and there is a corresponding method in velocity that can be judged. Of course, you can also convert the Java backend to a valid value before judging. The following is my own summary in the development, I hope to help you.
(1) determine null
#if ($name  =  null)
 something code
#end
(2) to determine null or FALSE
#if (! $name) The
 something Code
#end
(3) determines null or an empty string
#if ("$!name" = "")
 something code
#end

A, color type (lottery_type) the corresponding JSON file a) Case: if the color type (lottery_type) corresponds to the JSON file exists/does not exist,

I. Methods of judgement and results:

#if ($lottery _type_10)
    has lottery results
#end
#if (! $lottery _type_10)
    without lottery results
#end

second, the color period a) Condition: Color period (phase) the corresponding attribute exists/does not exist

I. Methods of judgement and results:

#if ($lottery _type_50.phase)
    color period (phase) the corresponding property exists
#end
#if (! $lottery _type_50.phase)
    color period (phase) The corresponding property does not exist
#end

b) Condition: Color period (phase) the corresponding property exists, but value is null

I. Methods of judgement and results:

#if ($lottery _type_50.phase)
    value is not
a null #end
#if (! $lottery _type_50.phase)
    value is null
#end

c) Condition: Color period (phase) the corresponding property exists, but value is "null"

I. Methods of judgement and results
1. If the object is passed '. ' Way to get properties

#if ($lottery _type_50.phase)
    value is not a "null"
#end
#if (! $lottery _type_50.phase)
    value is "null"

2. If you get the property directly

#if (${phase} = = "null")
    value is a "null"
#end
#if (${phase}!= "null")
    value is not "null"
#end

D) Condition: the color period (phase) corresponds to the attribute exists, but value is ""
I. Methods of judgement and results:

#if ($lottery _type_50.phase = = "")
    value is ""
#end
#if ($lottery _type_50.phase!= "")
    value is not ""
#end

e) Examples:

#if ($lottery _type_50.phase)
#if ($lottery _type_50.phase!= "") 333 #end #if
($lottery _type _50.phase = = "")
    444
#end
#if ($lottery _type_50.phase!= "null")
    555
#end
#if ($lottery _ Type_50.phase = = "null")
    666
#end
#end
#if (! $lottery _type_50.phase)
    222
#end

If the color period (phase) property does not exist, result: 222 If the color period (phase) attribute exists, but the value is null or "null", the result: 222 If the color period (phase) attribute exists, but the value is "", Result: 111 444 555 If the color period (phase) attribute exists , the value is "2011036", and the result: 111 333 555 third, lottery date a) Situation: if the Lottery date (Draw_time) attribute does not exist, or the lottery date (Draw_time) attribute exists, but the value is null or "null",

I. Methods of judgement and results:

#if ($lottery _type_50.draw_time)
    property does not exist or the value is null or "null"
#end
#if (! $lottery _type_50.draw_time)
    property exists and the value BU is null and not "null"
#end

(b) Situation: If the Lottery date (Draw_time) attribute exists, the value is ""

I. Methods of judgement and results:

#if ($lottery _type_50.draw_time = = "")
    property value is ""
#end
#if ($lottery _type_50.draw_time!= "")
    property value is not ""
#end

c) Examples:

#if ($lottery _type_50.draw_time)
#end
#if (! $lottery _type_50.draw_time)
    222
#end
# if ($lottery _type_50.draw_time = "")
    333
#end
#if ($lottery _type_50.draw_time!= "")
    444
# End
#if ($lottery _type_50.draw_time = = "null")
    555
#end
#if ($lottery _type_50.draw_time!= "null") ")
    666
#end

If the lottery date attribute (draw_time) does not exist, the result: 222 444 666 If the Lottery date property (Draw_time) exists, but the value is null or "null," The result: 222 444 666 If the Lottery date attribute (draw_time) exists, but the value is "", Result: 111 333 666 If the Lottery date attribute (Draw_time exists, and the value is "2011-03-31 22:30:00", results: 111 444 666 four, the prize pool rollover a) Situation: the prize pool (pool_amount) does not exist, or the prize pool (Pool_amount) exists, the value is null or "null"

I. Methods of judgement and results

The #if ($lottery _type_50.pool_amount)
    prize Pool (Pool_amount) exists and the prize pool (Pool_amount) value is not NULL or "null"
#end
#if (!$ The Lottery_type_50.pool_amount)
    prize Pool (pool_amount) does not exist, or the prize pool (Pool_amount) exists, the value is null or "null"
#end

(b) Situation: The prize pool (pool_amount) value is ""

I. Methods of judgement and results

#if ($lottery _type_50.pool_amount = = "")
    Prize Pool (pool_amount) value is ""
#end
#if ($lottery _type_50.pool_amount!= "") the
    value of the pool (Pool_amount) is not ""
#end

Five, test machine number

A) Condition: FC3D_SJH does not exist, or FC3D_SJH exists, the value is null or "null"
I. Method of judgement and Description:

The #if ($lottery _type_52.fc3d_sjh)
    FC3D_SJH exists and the value is not NULL or "null"
#end
#if (! $lottery _TYPE_52.FC3D_SJH
    FC3D_SJH does not exist, or FC3D_SJH exists, the value is null or "null"
#end

(b) Situation: FC3D_SJH exists, value is ""

I. Method of judgement and Description:

#if ($lottery _TYPE_52.FC3D_SJH = = "")
    FC3D_SJH value is "
" #end
#if (! $lottery _type_52.fc3d_sjh!= "")
    Fc3d_ The SJH value is not ""
#end

c) Situation: "FC3D_SJH": {} need to enter {} for judgment d) Examples:

#if ($lottery _TYPE_52.FC3D_SJH) # # First-level attribute FC3D_SJH exists and the value is not null and is not a "null" #if ($lottery _type_52.fc3d _SJH!= "") # # First-level property FC3D_SJH value is not "" #if ($lottery _type_52.fc3d_sjh.fc3d_sjh) # # Two properties fc3d_sjh exist, and
                                        Value is not NULL or "null" #if ($lottery _type_52.fc3d_sjh.fc3d_sjh!= "") # Two-level property FC3D_SJH value is not ' " #if ($lottery _type_52.fc3d_sjh.fc3d_sjh.machine | | $lottery _type_52.fc3d_sjh.fc3d_sjh.b all | |
                                               $lottery _type_52.fc3d_sjh.fc3d_sjh.sjh) # # # As long as machine or ball or SJH exist, and the value is not NULL or ' null '
                                                   #if ($lottery _type_52.fc3d_sjh.fc3d_sjh.machine) # # machine exists and the value is not NULL or ' null '
                                                       #if ($lottery _type_52.fc3d_sjh.fc3d_sjh.machine!= "") # #machine exists, the value is not ""
                         $lottery _type_52.fc3d_sjh.fc3d_sjh.machine                           #else # #machine exists with a value of ' 0 #end #else # # Machine does not exist or exists but the value is null
                                                or "null" 0 #end Machine #if ($lottery _type_52.fc3d_sjh.
                                                       Fc3d_sjh.ball) #if ($lottery _type_52.fc3d_sjh.fc3d_sjh.ball!= "")
                                                    $lottery _type_52.fc3d_sjh.fc3d_sjh.ball
                                                    #else 0
                                                    #end #else
                   0                             #end Ball #if ($lottery _type_52.fc3d_sjh.fc3d_sjh.sjh) #fo  Reach ($sjh $lottery _type_52.fc3d_sjh.fc3d_sjh.sjh) #if ($SJH!=
                                                        "Null" && $sjh!= "") $SJH
                                               #end #end
                                                #end #else # # machine or ball or SJH does not exist, or exists but the value is null or null   
                                    No results #end
                           #else # # Two property value is "" No results #end   #else # # Two property fc3d_sjh does not exist, or the value is null or "NULL" has no results #end
                     #else # # First-level property value is "" No results #end #else # # First-level property FC3D_SJH does not exist or the value is null or "NULL" has no results #end

Vi. Lottery Results a) Situation: Lottery results attribute (result) exists/does not exist

I. Methods of judgement and results:

#if ($lottery _type_50.result)
    Lottery Results Property (result) exists
#end
#if (! $lottery _type_50.result)
    Lottery Results Property (Result ) does not exist
#end

situation: Lottery results attribute (result) exists, but the value is null

I. Methods of judgement and results:

#if ($lottery _type_50.result)
    Lottery Results attribute (result) exists, the value is not null
#end
#if (! $lottery _type_50.result)
    The lottery results attribute (result) exists, but the value is null
#end

c) Condition: Lottery Results attribute (result) exists, but the value is "null"

I. Methods of judgement and results:
1. If the object gets the object through '. '

#if ($lottery _type_50.result)
    Lottery Results attribute (result) exists, the value is not null
#end
#if (! $lottery _type_50.result)
    The lottery results attribute (result) exists, but the value is null
#end

2. If you get the object directly

#if (Result = = "null")
    Lottery Results Property (outcome) exists with a value of "null"
#end
#if (result!= "null")
    lottery Results attribute (outcome) exists, but the value is " Null "
#end

d) Condition: Lottery Results attribute (result) exists, but the value is ""

I. Methods of judgement and results:

#if ($lottery _type_50.result = = "")
    Lottery Results Property (result) value is ""
#end
#if ($lottery _type_50.result!= "")
    The lottery Results property (result) value is not ""
#end

e) Condition: Lottery Results attribute (result) exists, but the value is an empty array []

I. Methods of judgement and results:

#if ($lottery _type_50.result.size () = = 0)
    lottery Results (Result) value is not []
#end
#if ($lottery _type_50.result.size ( != 0)
    lottery Results (Result) value is []
#end

f) Case: "Result": [,]; "Effect": ["," "];

I. "Result": [,]; ' Result ': [null,null]; "Result": ["null", "null"];
1. Method of judgment and result

#if ($result = = "null")
    element is "null"
#end
#if ($result!= "null") element is
    not "null"
#end
    Result: element is "null"

II. "Result": ["", ""]
1. Method of judgment and result

#if ($result = = ")
    element is" "
#end
#if ($result!=" ")
    element is not" "
#end

Result: Element is "" g)

Situation: "Result": [,]; ' Result ': [{"Key": "Red"},{"key": "Blue"}]; "Result": [{"Key": "Red", "Data": null},{"key": "Blue", " Data ": null}"; "Result": [{"Key": "Red", "data": "Null"},{"key": "Blue", "data": "NULL"}];
"Result": [{"Key": "Red", "Data": ""},{"key": "Blue", "Data": "}];
"Result": [{"Key": "Red", "Data": []},{"Key": "Blue", "Data": []}]; data must be judged

I. "Result": [{"Key": "Red"},{"key": "Blue"}]; "Result": [{"Key": "Red", "Data": null},{"key": "Blue", "data": null}]; " Result ": [{" Key ":" Red "," data ":" Null "},{" key ":" Blue "," data ":" NULL "}];
1. Method of judgment and result:

#if ($result. Data)
    Data property exists
#end
#if (! $result. Data) The Data property
    does not exist, or the data property exists, the value is null or "null"
# End

II. "Result": [{"Key": "Red", "Data": ""},{"key": "Blue", "Data": ""}];
1. Method of judgment and result:

#if ($result. Data = "") The
    value of the Data property is ""
#end
#if ($result. Data!= "") the value of the
    data property is not ""
#end

III. "Result": [{"Key": "Red", "Data": []},{"Key": "Blue", "Data": []}]
1. Method of judgment and result:

#if ($result. data.size () > 0) The
    data array has
#end
#if ($result. data.size () = = 0)
    No data array
End

h)

Condition: "Result": [{"Key": "Red", "data": [,,,,,]},{"key": "Blue", "Data": []}]; "Result": [{"Key": "Red", "Data": ["," "," "," "", "", "" " , "", ""]},{"key": "Blue", "Data": ["]}];
IV. "Result": [{"Key": "Red", "data": [,,,,,]},{"key": "Blue", "Data": []}]
1. Method of judgment and result:

The #if ($data!= "null")
    333
#end
#if ($data = = "null")
    444
#end

Results: 444

V. "Result": [{"Key": "Red", "Data": ["," "," "," "," "," "", "" "", "" "" "" "]},{" "," "" "" ""
1. Method of judgment and result:

#if ($data = = "") is "
    "
#end
#if ($data!= "") is not ""
#end

i) Examples:

#if ($lottery _type_50.result) # # has a defined result property and the result property value is not null and is not a ' null ' #if ($lottery _type_50.result!= "") # if ($lottery _type_50.result.size () > 0) # # for result:[], size = 0, and result:[,,],size>0 #set ($exist = "0") #  # declare variable $exist to record whether there is a lottery result, the initial value is "0" #foreach ($result in $lottery _type_50.result) #if ($result!=
                            "Null" && $result!= "") #if ($result. Key) #if ($result. Key = = ' Red ')
                                    #if ($result. Data) #if ($result. Data!= "")
                                            #if ($result. data.size () > 0) #foreach ($data in $result. Data) #if ($data!= "null" && $data!= "") # # If there is a data property and the value of the data property is not NULL, not ' Nu ll ", and not data:[" "," "," "" "in this case, non-data:[,,,] This case #set ($exist =" 1 ") # # variable $e
            Xist Assignment "1"                                #end #end #end
                        #end #end #end #if ($result. Key = = ' Blue ') #foreach ($data in $result. Data) #
                                if ($data!= "null" && $data!= "") #set ($exist = "1")
            #end #end #end #end #end #end # # $exist: 0 represents no lottery results, 1 delegates have lottery results #if ($exist = = "0") No lottery results #else #foreach ($result in $lottery _type_ 50.result) #if ($result!= "null" && $result!= "") #if ($result. Key) #if ($resul
                            T.key = = ' Red ') #if ($result. Data) #if ($result. Data!= "") #if ($result. Data. Size () > 0) #foreach ($data in $result. Data) #if ($d 
                                    ATA!= "null" && $data!= "") <div class= "RedBall" > $data </div>
                        #end #end #end
                    #end #end #end #if ($result. Key = = ' Blue ') #if ($result. Data) #if ($result. Data!= "") #if ($result. Data.size (  ) > 0) #foreach ($data in $result. Data) #if ($data!=
                                    "Null" && $data!= "") <div class= "RedBall" > $data </div>
                        #end #end #end
           #end         #end #end #end #end #end #end # #else: [] No lottery results