这在Python中是有效的:

def is_base64(string):
    if len(string) % 4 == 0 and re.test('^[A-Za-z0-9+\/=]+\Z', string):
        return(True)
    else:
        return(False)

PHP5试试这样做

//where $json is some data that can be base64 encoded
$json=some_data;

//this will check whether data is base64 encoded or not
if (base64_decode($json, true) == true)
{          
   echo "base64 encoded";          
}
else 
{
   echo "not base64 encoded"; 
}

在PHP7中使用这个

 //$string parameter can be base64 encoded or not

function is_base64_encoded($string){
 //this will check if $string is base64 encoded and return true, if it is.
 if (base64_decode($string, true) !== false){          
   return true;        
 }else{
   return false;
 }
}

你可以:

检查长度是否为4个字符的倍数 检查每个字符都在A-Z, A-Z, 0-9， +， /集合中，除了末尾的填充为0,1或2 '='字符

如果你期望它是base64，那么你可以使用平台上可用的任何库来尝试将它解码为字节数组，如果它不是有效的base64则抛出异常。当然，这取决于你的平台。

尝试使用前面提到的正则表达式:

String regex = "^([A-Za-z0-9+/]{4})*([A-Za-z0-9+/]{4}|[A-Za-z0-9+/]{3}=|[A-Za-z0-9+/]{2}==)$";
if("TXkgdGVzdCBzdHJpbmc/".matches(regex)){
    System.out.println("it's a Base64");
}

.．.我们还可以做一个简单的验证，比如，如果它有空格，它就不能是Base64:

String myString = "Hello World";
 if(myString.contains(" ")){
   System.out.println("Not B64");
 }else{
    System.out.println("Could be B64 encoded, since it has no spaces");
 }

检查字符串的长度是否为4的倍数。然后使用这个正则表达式来确保字符串中的所有字符都是base64字符。

\A[a-zA-Z\d\/+]+={，2}\z

如果您使用的库添加换行符作为遵守每行最多76个字符规则的一种方式，请将它们替换为空字符串。

Function Check_If_Base64(ByVal msgFile As String) As Boolean
Dim I As Long
Dim Buffer As String
Dim Car As String

Check_If_Base64 = True

Buffer = Leggi_File(msgFile)
Buffer = Replace(Buffer, vbCrLf, "")
For I = 1 To Len(Buffer)
    Car = Mid(Buffer, I, 1)
    If (Car < "A" Or Car > "Z") _
    And (Car < "a" Or Car > "z") _
    And (Car < "0" Or Car > "9") _
    And (Car <> "+" And Car <> "/" And Car <> "=") Then
        Check_If_Base64 = False
        Exit For
    End If
Next I
End Function
Function Leggi_File(PathAndFileName As String) As String
Dim FF As Integer
FF = FreeFile()
Open PathAndFileName For Binary As #FF
Leggi_File = Input(LOF(FF), #FF)
Close #FF
End Function