.net 下如何将文档文件(Word, Pdf等) 中的文本提取出来
经常有人问我怎么将类似word，pdf这样的文档转换为文本然后索引，.net 这方面的解决方案不是很多，为了方便大家，我花了一天时间自己做了一个。
Java 版本的 lucence 提供了一个 tika 的工具用于将 word, excel, pdf 等文档转换为文本，然后进行索引。但这个工具没有 .net 版本，要在 .net 下用，需要用 IKVM.net，很麻烦。而且这个工具实际上底层是调用 POI 和 PDFParse 来转换的。从网上搜索到的信息看,POI 对 office 2007 以上版本的文档处理有问题，不知道最新版本是否解决了，我没有试过。 PDFParse 这个东西，我用过 .net 版本，对中文不支持，不知道 Java 版本是否支持。
其实 .net 下完全不需要用这些开源解决方案来解决，因为微软提供了一个官方的解决方案，这个解决方案叫 IFilter，这个过滤器是为 SQL SERVER 的全文索引设计的，但第三方软件可以调用API来完成文档的提取工作。
为了方便大家，我把 IFilter 转换的功能封装到了一个开源的组件中去，大家可以到下面地址去下载源码：HBTextParse .
调用很简单：
这个是提取文件中的文本到字符串的代码
if (openFileDialog.ShowDialog() == DialogResult.OK) { //要转换的文件 textBoxFilePath.Text = openFileDialog.FileName; //实例化 TextParse ，传入要转换的文件路径 TextParse textParse = new TextParse(textBoxFilePath.Text); //提取文件中的文本，并输出 richTextBoxView.Text = textParse.ConvertToString(); }
这个是将文件转换为文本文件的代码：
if (saveFileDialog.ShowDialog() == DialogResult.OK) { try { //实例化 TextParse，传入要转换的文件的路径 TextParse textParse = new TextParse(textBoxFilePath.Text); //将文件转换到 saveFileDialog.FileName 指定的文本文件中 textParse.ConvertToFile(saveFileDialog.FileName); } catch (Exception ex) { MessageBox.Show(ex.Message, "Error", MessageBoxButtons.OK, MessageBoxIcon.Error); } }
要注意的问题是提取 Pdf 文档，如果机器是 64为操作系统，必须要安装 Adobe PDF iFilter 9 for 64-bit platforms. 否则会报异常。这个问题我搞了将近一天才搞定。
支持的文档类型：
目前这个组件可以支持所有 Microsoft office 提供的文档类型，包括 *.rtf, *.doc, *.docx, *.xls, *.xlsx, *.ppt, *.pptx 等等
除了微软Office的文档外，还可以转换
- html 文档:可以把html文档中的文本提取出来（不包含标签）
- Pdf 文档:我测试过，对中文支持没有问题
- Txt 文档
这个代码的核心部分是一个叫 FilterCode 的类。这个类是从 http://ifilter.codeplex.com/ 这个地方下载的，我对这个类做了改进，加入了转换到文件的方法。我把这个类的代码贴出来，如果对如何调用IFilter的windows API感兴趣，可以参考这段代码
IFilter 的相关API函数如下：通常这些API函数就可以通过IFilter接口提取文本。
[DllImport("query.dll", SetLastError = true, CharSet = CharSet.Unicode)] static extern int LoadIFilter(string pwcsPath, [MarshalAs(UnmanagedType.IUnknown)] object pUnkOuter, ref IFilter ppIUnk);
[ComImport, Guid("89BCB740-6119-101A-BCB7-00DD010655AF")] [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)] public interface IFilter { /// <summary> /// The IFilter::Init method initializes a filtering session. /// </summary> [PreserveSig] IFilterReturnCodes Init( //[in] Flag settings from the IFILTER_INIT enumeration for // controlling text standardization, property output, embedding // scope, and IFilter access patterns. IFILTER_INIT grfFlags, // [in] The size of the attributes array. When nonzero, cAttributes // takes // precedence over attributes specified in grfFlags. If no // attribute flags // are specified and cAttributes is zero, the default is given by // the // PSGUID_STORAGE storage property set, which contains the date and // time // of the last write to the file, size, and so on; and by the // PID_STG_CONTENTS // 'contents' property, which maps to the main contents of the // file. // For more information about properties and property sets, see // Property Sets. int cAttributes, //[in] Array of pointers to FULLPROPSPEC structures for the // requested properties. // When cAttributes is nonzero, only the properties in aAttributes // are returned. IntPtr aAttributes, // [out] Information about additional properties available to the // caller; from the IFILTER_FLAGS enumeration. out IFILTER_FLAGS pdwFlags); /// <summary> /// The IFilter::GetChunk method positions the filter at the beginning /// of the next chunk, /// or at the first chunk if this is the first call to the GetChunk /// method, and returns a description of the current chunk. /// </summary> [PreserveSig] IFilterReturnCodes GetChunk(out STAT_CHUNK pStat); /// <summary> /// The IFilter::GetText method retrieves text (text-type properties) /// from the current chunk, /// which must have a CHUNKSTATE enumeration value of CHUNK_TEXT. /// </summary> [PreserveSig] IFilterReturnCodes GetText( // [in/out] On entry, the size of awcBuffer array in wide/Unicode // characters. On exit, the number of Unicode characters written to // awcBuffer. // Note that this value is not the number of bytes in the buffer. ref int pcwcBuffer, // Text retrieved from the current chunk. Do not terminate the // buffer with a character. [Out(), MarshalAs(UnmanagedType.LPWStr)] StringBuilder awcBuffer); /// <summary> /// The IFilter::GetValue method retrieves a value (public /// value-type property) from a chunk, /// which must have a CHUNKSTATE enumeration value of CHUNK_VALUE. /// </summary> [PreserveSig] IFilterReturnCodes GetValue( // Allocate the PROPVARIANT structure with CoTaskMemAlloc. Some // PROPVARIANT // structures contain pointers, which can be freed by calling the // PropVariantClear function. // It is up to the caller of the GetValue method to call the // PropVariantClear method. // ref IntPtr ppPropValue // [MarshalAs(UnmanagedType.Struct)] ref IntPtr PropVal); /// <summary> /// The IFilter::BindRegion method retrieves an interface representing /// the specified portion of the object. /// Currently reserved for future use. /// </summary> [PreserveSig] IFilterReturnCodes BindRegion(ref FILTERREGION origPos, ref Guid riid, ref object ppunk); }
从文档中提取文本的代码如下：
/// <summary> /// Utilizes IFilter interface in Windows to parse the contents of files. /// </summary> /// <param name="path">Path - Location of file to parse</param> /// <param name="buffer">Buffer - Return text artifacts</param> /// <returns>Raw set of strings from the document in plain text format.</returns> public void GetTextFromDocument(string path, ref StringBuilder buffer) { IFilter filter = null; int hresult; IFilterReturnCodes rtn; // Initialize the return buffer to 64K. buffer = new StringBuilder(64 * 1024); // Try to load the filter for the path given. hresult = LoadIFilter(path, new IntPtr(0), ref filter); if (hresult == 0) { IFILTER_FLAGS uflags; // Init the filter provider. rtn = filter.Init( IFILTER_INIT.IFILTER_INIT_CANON_PARAGRAPHS | IFILTER_INIT.IFILTER_INIT_CANON_HYPHENS | IFILTER_INIT.IFILTER_INIT_CANON_SPACES | IFILTER_INIT.IFILTER_INIT_APPLY_INDEX_ATTRIBUTES | IFILTER_INIT.IFILTER_INIT_INDEXING_ONLY, 0, new IntPtr(0), out uflags); if (rtn == IFilterReturnCodes.S_OK) { STAT_CHUNK statChunk; // Outer loop will read chunks from the document at a time. For those // chunks that have text, the contents will be pulled and put into the // return buffer. bool bMoreChunks = true; while (bMoreChunks) { rtn = filter.GetChunk(out statChunk); if (rtn == IFilterReturnCodes.S_OK) { // Ignore all non-text chunks. if (statChunk.flags != CHUNKSTATE.CHUNK_TEXT) continue; // Check for white space items and add the appropriate breaks. switch (statChunk.breakType) { case CHUNK_BREAKTYPE.CHUNK_NO_BREAK: break; case CHUNK_BREAKTYPE.CHUNK_EOW: buffer.Append(' '); break; case CHUNK_BREAKTYPE.CHUNK_EOC: case CHUNK_BREAKTYPE.CHUNK_EOP: case CHUNK_BREAKTYPE.CHUNK_EOS: buffer.AppendLine(); break; } // At this point we have a text chunk. The following code will pull out // all of it and add it to the buffer. bool bMoreText = true; while (bMoreText) { // Create a temporary string buffer we can use for the parsing algorithm. int cBuffer = DefaultBufferSize; StringBuilder sbBuffer = new StringBuilder(DefaultBufferSize); // Read the next piece of data up to the size of our local buffer. rtn = filter.GetText(ref cBuffer, sbBuffer); if (rtn == IFilterReturnCodes.S_OK || rtn == IFilterReturnCodes.FILTER_S_LAST_TEXT) { // If any data was returned, scrub it and then add it to the buffer. CleanUpCharacters(cBuffer, sbBuffer); buffer.Append(sbBuffer.ToString()); // If we got back some text but there is no more, terminate the loop. if (rtn == IFilterReturnCodes.FILTER_S_LAST_TEXT) { bMoreText = false; break; } } // Once all data is exhausted, we are done so terminate. else if (rtn == IFilterReturnCodes.FILTER_E_NO_MORE_TEXT) { bMoreText = false; break; } // Check for any fatal errors. It is a bug if you land here. else if (rtn == IFilterReturnCodes.FILTER_E_NO_TEXT) { System.Diagnostics.Debug.Assert(false, "Should not get here"); throw new InvalidOperationException(); } } } // Once all chunks have been read, we are done with the file. else if (rtn == IFilterReturnCodes.FILTER_E_END_OF_CHUNKS) { bMoreChunks = false; break; } else if (rtn == IFilterReturnCodes.FILTER_E_EMBEDDING_UNAVAILABLE || rtn == IFilterReturnCodes.FILTER_E_LINK_UNAVAILABLE) { continue; } else { throw new COMException("IFilter COM error: " + rtn.ToString()); } } } } else { // If you get here there is no filter for the file type you asked for. Throw an // exception for the caller. throw new InvalidOperationException("Failed to find IFilter for file " + path); } }