//在DirectoryReader中有一下函數。

public boolean isCurrent() throws CorruptIndexException, IOException {?
? return SegmentInfos.readCurrentVersion(directory) == segmentInfos.getVersion();?
}

IndexWriter writer = new IndexWriter(FSDirectory.open(INDEX_DIR), new StandardAnalyzer(Version.LUCENE_CURRENT), true, IndexWriter.MaxFieldLength.LIMITED);?
writer.setUseCompoundFile(false);?
indexDocs(writer, docDir);//docDir中只有兩篇文檔

//文檔一為：Students should be allowed to go out with their friends, but not allowed to drink beer.

//文檔二為：My friend Jerry went to school to see his students but found them drunk which is not allowed.

writer.commit();//提交兩篇文檔，形成_0段。

writer.deleteDocuments(new Term("contents", "school"));//刪除文檔二?
writer.commit();//提交刪除，形成_0_1.del?
indexDocs(writer, docDir);//再次索引兩篇文檔，Lucene不能判別文檔與文檔的不同，因而算兩篇新的文檔。?
writer.commit();//提交兩篇文檔，形成_1段?
writer.deleteDocuments(new Term("contents", "school"));//刪除第二次添加的文檔二?
writer.close();//提交刪除，形成_1_1.del

IndexWriter.applyDeletes()

-> DocumentsWriter.applyDeletes(SegmentInfos)

???? -> reader.deleteDocument(doc);

IndexWriter.commit()

-> IndexWriter.applyDeletes()

??? -> IndexWriter$ReaderPool.release(SegmentReader)

???????? -> SegmentReader(IndexReader).commit()

???????????? -> SegmentReader.doCommit(Map)

????????????????? -> SegmentInfo.advanceDelGen()

?????????????????????? -> if (delGen == NO) {?
????????????????????????????? delGen = YES;?
?????????????????????????? } else {?
????????????????????????????? delGen++;?
?????????????????????????? }

IndexWriter writer = new IndexWriter(FSDirectory.open(INDEX_DIR), new StandardAnalyzer(Version.LUCENE_CURRENT), true, IndexWriter.MaxFieldLength.LIMITED);?
writer.setUseCompoundFile(false);

indexDocs(writer, docDir);//索引兩篇文檔，一篇包含"school"，另一篇包含"beer"?
writer.commit();//提交兩篇文檔到索引文件，形成段(Segment) "_0"?
writer.deleteDocuments(new Term("contents", "school"));//刪除包含"school"的文檔，其實是刪除了兩篇文檔中的一篇。?
writer.commit();//提交刪除到索引文件，形成"_0_1.del"?
writer.deleteDocuments(new Term("contents", "beer"));//刪除包含"beer"的文檔，其實是刪除了兩篇文檔中的另一篇。?
writer.commit();//提交刪除到索引文件，形成"_0_2.del"?
indexDocs(writer, docDir);//索引兩篇文檔，和上次的文檔相同，但是Lucene無法區分，認為是另外兩篇文檔。?
writer.commit();//提交兩篇文檔到索引文件，形成段"_1"?
writer.deleteDocuments(new Term("contents", "beer"));//刪除包含"beer"的文檔，其中段"_0"已經無可刪除，段"_1"被刪除一篇。?
writer.close();//提交刪除到索引文件，形成"_1_1.del"

形成的索引文件如下：

????? IndexWriter writer = new IndexWriter(FSDirectory.open(INDEX_DIR), new StandardAnalyzer(Version.LUCENE_CURRENT), true, IndexWriter.MaxFieldLength.LIMITED);?
????? writer.setUseCompoundFile(false);

????
????? indexDocs(writer, docDir);?
????? writer.flush();

//flush生成segment "_0"，并且flush函數中，flushDocStores設為false，也即下個段將同本段共享域和詞向量信息，這時DocumentsWriter中的docStoreSegment= "_0"。

????? indexDocs(writer, docDir);?
????? writer.commit();

//commit生成segment "_1"，由于上次flushDocStores設為false，于是段"_1"的域以及詞向量信息是保存在"_0"中的，在這個時刻，段"_1"并不生成自己的"_1.fdx"和"_1.fdt"。然而在commit函數中，flushDocStores設為true，也即下個段將單獨使用新的段來存儲域和詞向量信息。然而這時，DocumentsWriter中的docStoreSegment= "_1"，也即當段"_2"存儲其域和詞向量信息的時候，是存在"_1.fdx"和"_1.fdt"中的，而段"_1"的域和詞向量信息卻是存在"_0.fdt"和"_0.fdx"中的，這一點非常令人困惑。 如圖writer.commit的時候，_1.fdt和_1.fdx并沒有形成。

????? indexDocs(writer, docDir);?
????? writer.flush();

//段"_2"形成，由于上次flushDocStores設為true，其域和詞向量信息是新創建一個段保存的，卻是保存在_1.fdt和_1.fdx中的，這時候才產生了此二文件。

????? indexDocs(writer, docDir);?
????? writer.flush();

//段"_3"形成，由于上次flushDocStores設為false，其域和詞向量信息是共享一個段保存的，也是是保存在_1.fdt和_1.fdx中的

????? indexDocs(writer, docDir);?
????? writer.commit();

//段"_4"形成，由于上次flushDocStores設為false，其域和詞向量信息是共享一個段保存的，也是是保存在_1.fdt和_1.fdx中的。然而函數commit中flushDocStores設為true，也意味著下一個段將新創建一個段保存域和詞向量信息，此時DocumentsWriter中docStoreSegment= "_4"，也表明了雖然段"_4"的域和詞向量信息保存在了段"_1"中，將來的域和詞向量信息卻要保存在段"_4"中。此時"_4.fdx"和"_4.fdt"尚未產生。???

????? indexDocs(writer, docDir);?
????? writer.flush();

//段"_5"形成，由于上次flushDocStores設為true，其域和詞向量信息是新創建一個段保存的，卻是保存在_4.fdt和_4.fdx中的，這時候才產生了此二文件。

????? indexDocs(writer, docDir);?
????? writer.commit();?
????? writer.close();

//段"_6"形成，由于上次flushDocStores設為false，其域和詞向量信息是共享一個段保存的，也是是保存在_4.fdt和_4.fdx中的

讀取此文件格式參考SegmentInfos.read(Directory directory, String segmentFileName):

• int format = input.readInt();
• version = input.readLong(); // read version
• counter = input.readInt(); // read counter
• for (int i = input.readInt(); i > 0; i--) // read segmentInfos
  • add(new SegmentInfo(directory, format, input));
    • name = input.readString();
    • docCount = input.readInt();
    • delGen = input.readLong();
    • docStoreOffset = input.readInt();
    • docStoreSegment = input.readString();
    • docStoreIsCompoundFile = (1 == input.readByte());
    • hasSingleNormFile = (1 == input.readByte());
    • int numNormGen = input.readInt();
    • normGen = new long[numNormGen];
    • for(int j=0;j
    • normGen[j] = input.readLong();
  • isCompoundFile = input.readByte();
  • delCount = input.readInt();
  • hasProx = input.readByte() == 1;
  • diagnostics = input.readStringStringMap();

• userData = input.readStringStringMap();
• final long checksumNow = input.getChecksum();
• final long checksumThen = input.readLong();

public static final String ID_PAYLOAD_FIELD = "_ID";

public static final String ID_PAYLOAD_TERM = "_ID";

public static final Term ID_TERM = new Term(ID_PAYLOAD_TERM, ID_PAYLOAD_FIELD);

//聲明一個特殊的TokenStream，它只生成一個詞(Term)，就是那個特殊的詞，在特殊的域里面。

static class SinglePayloadTokenStream extends TokenStream {?
??? private Token token;?
??? private boolean returnToken = false;

??? SinglePayloadTokenStream(String idPayloadTerm) {?
??????? char[] term = idPayloadTerm.toCharArray();?
??????? token = new Token(term, 0, term.length, 0, term.length);?
??? }

??? void setPayloadValue(byte[] value) {?
??????? token.setPayload(new Payload(value));?
??????? returnToken = true;?
??? }

??? public Token next() throws IOException {?
??????? if (returnToken) {?
??????????? returnToken = false;?
??????????? return token;?
??????? } else {?
??????????? return null;?
??????? }?
??? }?
}

//對于每一篇文檔，都讓它包含這個特殊的詞，在特殊的域里面

SinglePayloadTokenStream singlePayloadTokenStream = new SinglePayloadTokenStream(ID_PAYLOAD_TERM);?
singlePayloadTokenStream.setPayloadValue(long2bytes(id));?
doc.add(new Field(ID_PAYLOAD_FIELD, singlePayloadTokenStream));

long id = 0;?
TermPositions tp = reader.termPositions(ID_PAYLOAD_TERM);?
boolean ret = tp.skipTo(docID);?
tp.nextPosition();?
int payloadlength = tp.getPayloadLength();?
byte[] payloadBuffer = new byte[payloadlength];?
tp.getPayload(payloadBuffer, 0);?
id = bytes2long(payloadBuffer);?
tp.close();

FieldInfos.read(IndexInput, String)

• int firstInt = input.readVInt();
• size = input.readVInt();
• for (int i = 0; i < size; i++)
  • String name = input.readString();
  • byte bits = input.readByte();
  • boolean isIndexed = (bits & IS_INDEXED) != 0;
  • boolean storeTermVector = (bits & STORE_TERMVECTOR) != 0;
  • boolean storePositionsWithTermVector = (bits & STORE_POSITIONS_WITH_TERMVECTOR) != 0;
  • boolean storeOffsetWithTermVector = (bits & STORE_OFFSET_WITH_TERMVECTOR) != 0;
  • boolean omitNorms = (bits & OMIT_NORMS) != 0;
  • boolean storePayloads = (bits & STORE_PAYLOADS) != 0;
  • boolean omitTermFreqAndPositions = (bits & OMIT_TERM_FREQ_AND_POSITIONS) != 0;

Document FieldsReader.doc(int n, FieldSelector fieldSelector)

• long position = indexStream.readLong();//indexStream points to ".fdx"
• fieldsStream.seek(position);//fieldsStream points to "fdt"
• int numFields = fieldsStream.readVInt();
• for (int i = 0; i < numFields; i++)
  • int fieldNumber = fieldsStream.readVInt();
  • byte bits = fieldsStream.readByte();
  • boolean compressed = (bits & FieldsWriter.FIELD_IS_COMPRESSED) != 0;
  • boolean tokenize = (bits & FieldsWriter.FIELD_IS_TOKENIZED) != 0;
  • boolean binary = (bits & FieldsWriter.FIELD_IS_BINARY) != 0;
  • if (binary)
    • int toRead = fieldsStream.readVInt();
    • final byte[] b = new byte[toRead];
    • fieldsStream.readBytes(b, 0, b.length);
    • if (compressed)
      • int toRead = fieldsStream.readVInt();
      • final byte[] b = new byte[toRead];
      • fieldsStream.readBytes(b, 0, b.length);
      • uncompress(b),
  • else
    • fieldsStream.readString()

TermVectorsReader.get(int docNum, String field, TermVectorMapper)

• int fieldNumber = fieldInfos.fieldNumber(field);//通過field名字得到field號
• seekTvx(docNum);//在tvx文件中按docNum文檔號找到相應文檔的項
• long tvdPosition = tvx.readLong();//找到tvd文件中相應文檔的偏移量
• tvd.seek(tvdPosition);//在tvd文件中按偏移量找到相應文檔的項
• int fieldCount = tvd.readVInt();//此文檔包含的域的個數。
• for (int i = 0; i < fieldCount; i++) //按域號查找域
  • number = tvd.readVInt();
  • if (number == fieldNumber)
    • found = i;
• position = tvx.readLong();//在tvx中讀出此文檔的第一個域在tvf中的偏移量
• for (int i = 1; i <= found; i++)
  • position += tvd.readVLong();//加上所要找的域在tvf中的偏移量
• tvf.seek(position);
• int numTerms = tvf.readVInt();
• byte bits = tvf.readByte();
• storePositions = (bits & STORE_POSITIONS_WITH_TERMVECTOR) != 0;
• storeOffsets = (bits & STORE_OFFSET_WITH_TERMVECTOR) != 0;
• for (int i = 0; i < numTerms; i++)
  • start = tvf.readVInt();
  • deltaLength = tvf.readVInt();
  • totalLength = start + deltaLength;
  • tvf.readBytes(byteBuffer, start, deltaLength);
  • term = new String(byteBuffer, 0, totalLength, "UTF-8");
  • if (storePositions)
    • positions = new int[freq];
    • int prevPosition = 0;
    • for (int j = 0; j < freq; j++)
      • positions[j] = prevPosition + tvf.readVInt();
      • prevPosition = positions[j];
  • if (storeOffsets)
    • offsets = new TermVectorOffsetInfo[freq];
    • int prevOffset = 0;
    • for (int j = 0; j < freq; j++)
    • int startOffset = prevOffset + tvf.readVInt();
    • int endOffset = startOffset + tvf.readVInt();
    • offsets[j] = new TermVectorOffsetInfo(startOffset, endOffset);
    • prevOffset = endOffset;