Base 64 : Illegal base64 character 3 Exception

Question

I have a text file with a base64 encoded value, and I tried to decode that text file and save it into a PDF format. Below is my code

File inputfile = new File('/Users/Downloads/DownloadedPDF.txt')
File outputfile = new File('/Users/Downloads/test64.pdf')
byte[] data
try {
    FileInputStream fileInputStream = new FileInputStream(inputfile)
    data = new byte[(int) inputfile.length()]
    fileInputStream.read(data)
    fileInputStream.close()
}catch(Exception e) {
    e.getStackTrace()
}
//Decode the data
byte[] decoded = java.util.Base64.getDecoder().decode(data)
try {
    FileOutputStream fileOutputStream = new FileOutputStream(outputfile)
    //Write the decoded details to the output file [pdf format]
    fileOutputStream.write(decoded)
    fileOutputStream.flush()
    fileOutputStream.close()
}catch(Exception e) {
    e.getStackTrace()
}

While executing the code I received the below error.

java.lang.IllegalArgumentException: Illegal base64 character 3
    at java_util_Base64$Decoder$decode$0.call(Unknown Source)

i tried the below one using the URL decoder, but still received the same error.

byte[] decoded = Base64.getUrlDecoder().decode(data)

Is this Groovy or Kotlin? That doesn't look like valid Java code (no semicolons). — David Conrad
– David Conrad, Commented Mar 19, 2024 at 14:05
have you tried running the encoded data through some other base64 decoder to verify that it is actually valid? — jtahlborn
– jtahlborn, Commented Mar 19, 2024 at 14:05
If it's Groovy then it should be tagged groovy rather than java. — khelwood
– khelwood, Commented Mar 19, 2024 at 14:08

jtahlborn · Accepted Answer · 2024-03-19 14:10:32Z

2

Reading bytes from a stream does not guarantee that it will read all the bytes you request. try readNBytes() instead. (or you can use readAllBytes() as mentioned by @DavidConrad).

edited Mar 19, 2024 at 14:10

answered Mar 19, 2024 at 14:08

jtahlborn

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2 Comments

David Conrad Over a year ago

Or readAllBytes().

Mark Rotteveel Over a year ago

Or wrap the input stream so it decodes on the fly, instead of loading the entire base64 in memory before decoding. The OP can then use transferTo to write to the destination file, removing the need for materializing the entire file in memory as well. (Although I'd question a system where a PDF was saved in a base64 encoded text file to begin with.)

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