Android Code Snippet [B4X] IsValidJSON (Conclusion)

jahswant said:

B4X:

Private Sub IsValidJson(jsonString As String) As Boolean
    Dim stack As List ' Stack to keep track of opened brackets/braces
    stack.Initialize
    Dim inString As Boolean ' Flag to indicate if currently inside a string
    Dim escapeNextChar As Boolean ' Flag to indicate if the next character is escaped
    Dim i As Int

    For i = 0 To jsonString.Length - 1
        Dim c As Char = jsonString.CharAt(i)

        If escapeNextChar Then ' If the previous character was an escape character '\'
            escapeNextChar = False ' Reset the flag as the next character is escaped.
            Continue ' Move to the next character without further processing.
        End If

        If c = "\" Then ' Check for escape character '\'
            escapeNextChar = True ' Set the flag to indicate that the next character is escaped.
        Else If c = """" Then ' Check for double quote to indicate start/end of a string.
            inString = Not(inString) ' Toggle the flag for inside/outside of a string.
        End If

        If Not(inString) Then ' Process characters only outside of a string.
            If c = "{" Or c = "[" Then ' Opening brace or bracket found.
                stack.Add(c) ' Add it to the stack.
            Else If c = "}" Or c = "]" Then ' Closing brace or bracket found.
                If stack.Size = 0 Or stack.Get(stack.Size - 1) <> GetMatchingOpeningChar(c) Then
                    Return False ' Unmatched closing brace/bracket, invalid JSON.
                Else
                    stack.RemoveAt(stack.Size - 1) ' Remove the matched opening brace/bracket.
                End If
            End If
        End If
    Next

    Return stack.Size = 0 ' If the stack is empty, it means all opening braces/brackets are matched.
End Sub

Private Sub GetMatchingOpeningChar(c As Char) As Char
    Select Case c
        Case "}": Return "{"
        Case "]": Return "["
        Case Else: Return Chr(0) ' Return a null character for unmatched closing character.
    End Select
End Sub

I use this routine because sometimes the JSON library will cause an exception on invalid json.

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aeric said:

I recall this thread

How to know if string is parseable as JSON "list" or "Map"

Hi, I would like to be able to determine if a JSON string will be parseable as a LIST or as a MAP before processing it. Am I missing something, or is the only way to know is to test the first character? "[" = LIST "{" = MAP Dim json As JSONParser json.Initialize(StdOut) If...

www.b4x.com

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aeric said:

JSON:

[2,a]

Is this a valid JSON?

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aeric said:

JSON:

[2,a]

Is this a valid JSON?

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Public Sub Test2
    Dim s As String = "[2,a]"
    Dim mRoot As List = s.As(JSON).ToList
    For Each colroot As Object In mRoot
        Log(colroot.As(String))
        Log(GetType(colroot))
    Next
End Sub

emexes said:

Invalid json, or valid json?

If invalid json, then perhaps use Try ... Catch to reduce program complexity and size and probably run time, not to mention programming time spent effectively rewriting a json parser. Unless you're going for space shuttle reliability by writing multiple versions of the program and putting their output to a vote. ?

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