經常有人問我怎么將類似word，pdf這樣的文檔轉換為文本然后索引，.net 這方面的解決方案不是很多，為了方便大家，我花了一天時間自己做了一個。

Java 版本的 lucence 提供了一個 tika 的工具用于將 word, excel, pdf 等文檔轉換為文本，然后進行索引。但這個工具沒有 .net 版本，要在 .net 下用，需要用 IKVM.net，很麻煩。而且這個工具實際上底層是調用 POI 和 PDFParse 來轉換的。從網上搜索到的信息看,POI 對 office 2007 以上版本的文檔處理有問題，不知道最新版本是否解決了，我沒有試過。 PDFParse 這個東西，我用過 .net 版本，對中文不支持，不知道 Java 版本是否支持。

其實 .net 下完全不需要用這些開源解決方案來解決，因為微軟提供了一個官方的解決方案，這個解決方案叫 IFilter，這個過濾器是為 SQL SERVER 的全文索引設計的，但第三方軟件可以調用API來完成文檔的提取工作。

為了方便大家，我把 IFilter 轉換的功能封裝到了一個開源的組件中去，大家可以到下面地址去下載源碼：HBTextParse .

調用很簡單：

這個是提取文件中的文本到字符串的代碼

if (openFileDialog.ShowDialog() == DialogResult.OK)
{ //要轉換的文件 textBoxFilePath.Text = openFileDialog.FileName; //實例化 TextParse ，傳入要轉換的文件路徑 TextParse textParse = new TextParse(textBoxFilePath.Text); //提取文件中的文本，并輸出 richTextBoxView.Text = textParse.ConvertToString();
}

這個是將文件轉換為文本文件的代碼：

if (saveFileDialog.ShowDialog() == DialogResult.OK)
{ try { //實例化 TextParse，傳入要轉換的文件的路徑 TextParse textParse = new TextParse(textBoxFilePath.Text); //將文件轉換到 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);
    }
}

要注意的問題是提取 Pdf 文檔，如果機器是 64為操作系統，必須要安裝 Adobe PDF iFilter 9 for 64-bit platforms. 否則會報異常。這個問題我搞了將近一天才搞定。

支持的文檔類型：

目前這個組件可以支持所有 Microsoft office 提供的文檔類型，包括 *.rtf, *.doc, *.docx, *.xls, *.xlsx, *.ppt, *.pptx 等等

除了微軟Office的文檔外，還可以轉換

• html 文檔:可以把html文檔中的文本提取出來（不包含標簽）
• Pdf 文檔:我測試過，對中文支持沒有問題
• Txt 文檔

這個代碼的核心部分是一個叫 FilterCode 的類。這個類是從 http://ifilter.codeplex.com/ 這個地方下載的，我對這個類做了改進，加入了轉換到文件的方法。我把這個類的代碼貼出來，如果對如何調用IFilter的windows API感興趣，可以參考這段代碼

IFilter 的相關API函數如下：通常這些API函數就可以通過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);
        }

從文檔中提取文本的代碼如下：

        /// <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);
            }
        }