B4X

Compressing StringBuilder Data Using CompressSb (Single Call and Chunked)

See more Compression Examples

This example demonstrates how to compress text stored in a StringBuilder using the CompressSb method in two ways:

1. Single-call compression, where the entire input is compressed in one operation.
2. Chunked compression, where the input is split into multiple parts and processed sequentially using the FirstChunk and LastChunk properties.

The example shows how compressed output is appended to a BinData object, and how the result can be verified by decompressing back to the original text. This is useful for both simple use cases and scenarios where data is processed incrementally (such as streaming or large inputs).

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Key Points

• CompressSb converts text to bytes using the Charset property (UTF-8 recommended).
• Compressed data is appended to a BinData object.
• When both FirstChunk and LastChunk are true, compression is done in a single call.
• For chunked processing:
  • First chunk → FirstChunk = true, LastChunk = false
  • Middle chunks → both false
  • Final chunk → LastChunk = true
• Chunked compression is useful when processing data incrementally.

B4X

Dim success As Boolean = False

'  This example assumes the Chilkat API has already been unlocked.
'  See Global Unlock Sample for sample code.

Dim compress As ChilkatCompression
compress.Initialize("compress")
compress.Algorithm = "zlib"

'  ================================================================
'  1) Single-call compression (entire data in one call)
'  ================================================================

Dim sb As ChilkatStringBuilder
sb.Initialize
sb.Append("The quick brown fox jumps over the lazy dog. ")
sb.Append("This is a simple example using CompressSb.")

Dim bdCompressed As ChilkatBinData
bdCompressed.Initialize

'  When both FirstChunk and LastChunk are true (the defaults),
'  the entire compression happens in a single call.
compress.FirstChunk = True
compress.LastChunk = True

success = compress.CompressSb(sb, bdCompressed)
If success = False Then
    Log(compress.LastErrorText)
    Return
End If


Dim compressedBase64 As String = bdCompressed.GetEncoded("base64")

Log("Single-call compressed (base64):")
Log(compressedBase64)

'  ================================================================
'  2) Chunked compression using FirstChunk / LastChunk
'  ================================================================

Dim bdChunkedOut As ChilkatBinData
bdChunkedOut.Initialize

'  First chunk
compress.FirstChunk = True
compress.LastChunk = False

Dim sbPart As ChilkatStringBuilder
sbPart.Initialize
sbPart.Append("The quick brown fox ")

success = compress.CompressSb(sbPart, bdChunkedOut)
If success = False Then
    Log(compress.LastErrorText)
    Return
End If


'  Middle chunk
compress.FirstChunk = False
compress.LastChunk = False

sbPart.Clear
sbPart.Append("jumps over the lazy dog. ")

success = compress.CompressSb(sbPart, bdChunkedOut)
If success = False Then
    Log(compress.LastErrorText)
    Return
End If


'  Final chunk
compress.FirstChunk = False
compress.LastChunk = True

sbPart.Clear
sbPart.Append("This is a chunked CompressSb example.")

success = compress.CompressSb(sbPart, bdChunkedOut)
If success = False Then
    Log(compress.LastErrorText)
    Return
End If


Dim chunkedBase64 As String = bdChunkedOut.GetEncoded("base64")

Log("Chunked compressed (base64):")
Log(chunkedBase64)

'  ================================================================
'  3) Decompress to verify correctness
'  ================================================================

Dim sbDecompressed As ChilkatStringBuilder
sbDecompressed.Initialize

'  Decompress in a single call (entire data already assembled)
compress.FirstChunk = True
compress.LastChunk = True

success = compress.DecompressSb(bdChunkedOut, sbDecompressed)
If success = False Then
    Log(compress.LastErrorText)
    Return
End If


Log("Decompressed text:")
Log(sbDecompressed.GetAsString)