前面介绍了六种.NET组件，其中有一种组件是写文件的压缩和解压，现在介绍另一种文件的解压缩组件SharpZipLib。在这个组件介绍系列中，只为简单的介绍组件的背景和简单的应用，读者在阅读时可以结合官网的相关介绍和在本地实际操作。
相关的组件功能非常强大，在笔者的介绍中只是提及到简单的应用，需要了解更多的操作和特性，可以根据官网介绍，或者查看DLL文件的相关类和方法，以此来扩展相关的业务需要。
SharpZipLib是一个完全在C＃中为.NET平台编写的Zip，GZip，Tar和BZip2库。
一.SharpZipLib组件概述：
ziplib（SharpZipLib，以前的NZipLib）是一个完全在C＃为.NET平台编写的Zip，GZip，Tar和BZip2库。它实现为一个程序集（可安装在GAC中），因此可以轻松地集成到其他项目（任何.NET语言）中。 #ziplib的创建者这样说：“我已经将zip库移植到C＃，因为我需要gzip / zip压缩，我不想使用libzip.dll或类似的东西我想要的所有在纯C＃“。
SharpZipLib官网提供的下载操作：.NET 1.1，.NET 2.0（3.5，4.0），.NET CF 1.0，.NET CF 2.0的装配：下载237 KB，源代码和示例下载708 KB；源代码和示例下载708 KB；帮助文件下载1208 KB；
SharpZipLib是在GPL下发布，遵守开源协议。
二.SharpZipLib核心类和方法介绍：
以上简单的介绍了SharpZipLib组件的相关背景，现在具体看一下该组件的相关核心类和方法：
1.ZipOutputStream类PutNextEntry()：
public void PutNextEntry(ZipEntry entry) { bool hasCrc; if (entry == null) { throw new ArgumentNullException("entry"); } if (this.entries == null) { throw new InvalidOperationException("ZipOutputStream was finished"); } if (this.curEntry != null) { this.CloseEntry(); } if (this.entries.Count == 0x7fffffff) { throw new ZipException("Too many entries for Zip file"); } CompressionMethod compressionMethod = entry.CompressionMethod; int defaultCompressionLevel = this.defaultCompressionLevel; entry.Flags &= 0x800; this.patchEntryHeader = false; if (entry.Size == 0L) { entry.CompressedSize = entry.Size; entry.Crc = 0L; compressionMethod = CompressionMethod.Stored; hasCrc = true; } else { hasCrc = (entry.Size >= 0L) && entry.HasCrc; if (compressionMethod == CompressionMethod.Stored) { if (!hasCrc) { if (!base.CanPatchEntries) { compressionMethod = CompressionMethod.Deflated; defaultCompressionLevel = 0; } } else { entry.CompressedSize = entry.Size; hasCrc = entry.HasCrc; } } } if (!hasCrc) { if (!base.CanPatchEntries) { entry.Flags |= 8; } else { this.patchEntryHeader = true; } } if (base.Password != null) { entry.IsCrypted = true; if (entry.Crc < 0L) { entry.Flags |= 8; } } entry.Offset = this.offset; entry.CompressionMethod = compressionMethod; this.curMethod = compressionMethod; this.sizePatchPos = -1L; if ((this.useZip64_ == UseZip64.On) || ((entry.Size < 0L) && (this.useZip64_ == UseZip64.Dynamic))) { entry.ForceZip64(); } this.WriteLeInt(0x4034b50); this.WriteLeShort(entry.Version); this.WriteLeShort(entry.Flags); this.WriteLeShort((byte) entry.CompressionMethodForHeader); this.WriteLeInt((int) entry.DosTime); if (hasCrc) { this.WriteLeInt((int) entry.Crc); if (entry.LocalHeaderRequiresZip64) { this.WriteLeInt(-1); this.WriteLeInt(-1); } else { this.WriteLeInt(entry.IsCrypted ? (((int) entry.CompressedSize) + 12) : ((int) entry.CompressedSize)); this.WriteLeInt((int) entry.Size); } } else { if (this.patchEntryHeader) { this.crcPatchPos = base.baseOutputStream_.Position; } this.WriteLeInt(0); if (this.patchEntryHeader) { this.sizePatchPos = base.baseOutputStream_.Position; } if (entry.LocalHeaderRequiresZip64 || this.patchEntryHeader) { this.WriteLeInt(-1); this.WriteLeInt(-1); } else { this.WriteLeInt(0); this.WriteLeInt(0); } } byte[] buffer = ZipConstants.ConvertToArray(entry.Flags, entry.Name); if (buffer.Length > 0xffff) { throw new ZipException("Entry name too long."); } ZipExtraData extraData = new ZipExtraData(entry.ExtraData); if (entry.LocalHeaderRequiresZip64) { extraData.StartNewEntry(); if (hasCrc) { extraData.AddLeLong(entry.Size); extraData.AddLeLong(entry.CompressedSize); } else { extraData.AddLeLong(-1L); extraData.AddLeLong(-1L); } extraData.AddNewEntry(1); if (!extraData.Find(1)) { throw new ZipException("Internal error cant find extra data"); } if (this.patchEntryHeader) { this.sizePatchPos = extraData.CurrentReadIndex; } } else { extraData.Delete(1); } if (entry.AESKeySize > 0) { AddExtraDataAES(entry, extraData); } byte[] entryData = extraData.GetEntryData(); this.WriteLeShort(buffer.Length); this.WriteLeShort(entryData.Length); if (buffer.Length > 0) { base.baseOutputStream_.Write(buffer, 0, buffer.Length); } if (entry.LocalHeaderRequiresZip64 && this.patchEntryHeader) { this.sizePatchPos += base.baseOutputStream_.Position; } if (entryData.Length > 0) { base.baseOutputStream_.Write(entryData, 0, entryData.Length); } this.offset += (30 + buffer.Length) + entryData.Length; if (entry.AESKeySize > 0) { this.offset += entry.AESOverheadSize; } this.curEntry = entry; this.crc.Reset(); if (compressionMethod == CompressionMethod.Deflated) { base.deflater_.Reset(); base.deflater_.SetLevel(defaultCompressionLevel); } this.size = 0L; if (entry.IsCrypted) { if (entry.AESKeySize > 0) { this.WriteAESHeader(entry); } else if (entry.Crc < 0L) { this.WriteEncryptionHeader(entry.DosTime << 0x10); } else { this.WriteEncryptionHeader(entry.Crc); } } }
2.ZipOutputStream类Finish()：