关于FieldInfos类和FieldInfo类。
FieldInfo类与一个Document中的一个Field相对应，而FieldInfos类又是多个FieldInfo的容器，对每个Document的所有Field对应的FieldInfo进行管理。
FieldInfos类和FieldInfo类之间的关系，恰似SegmentInfos类(可以参考文章 Lucene-2.2.0 源代码阅读学习(18))和SegmentInfo类(可以参考文章 Lucene-2.2.0 源代码阅读学习(19))之间的关系。
FieldInfo类的实现比较简单，该类的定义如下所示：
package org.apache.lucene.index;
final class FieldInfo {String name; // 一个Field的名称boolean isIndexed; // 该Field是否被索引int number; // 该Field的编号
// 是否存储该Field的词条向量boolean storeTermVector;boolean storeOffsetWithTermVector;boolean storePositionWithTermVector;
boolean omitNorms; // 是否忽略与被索引的该Field相关的norm文件信息 boolean storePayloads; // 是否该Field存储与词条位置相关的Payload
// 构造一个FieldInfo对象
FieldInfo(String na, boolean tk, int nu, boolean storeTermVector, boolean storePositionWithTermVector, boolean storeOffsetWithTermVector, boolean omitNorms, boolean storePayloads) { name = na; isIndexed = tk; number = nu; this.storeTermVector = storeTermVector; this.storeOffsetWithTermVector = storeOffsetWithTermVector; this.storePositionWithTermVector = storePositionWithTermVector; this.omitNorms = omitNorms; this.storePayloads = storePayloads;}}
上面就是2.2.0版本中FieldInfo类的全部定义。
下面是FieldInfos了的定义了，该类主要是通过FieldInfo来管理一个Document中的全部Field，源代码如下所示：
package org.apache.lucene.index;
import org.apache.lucene.document.Document;import org.apache.lucene.document.Fieldable;import org.apache.lucene.store.Directory;import org.apache.lucene.store.IndexInput;import org.apache.lucene.store.IndexOutput;
import java.io.IOException;import java.util.*;
// FieldInfo描述的是Document中的Field的信息，而FieldInfos类是用来管理一个个的FieldInfo的。final class FieldInfos {
// 下面一组byte成员，使用十六进制数初始化，用来管理FieldInfo的属性 static final byte IS_INDEXED = 0x1; // 是否索引static final byte STORE_TERMVECTOR = 0x2; // 是否存储词条向量static final byte STORE_POSITIONS_WITH_TERMVECTOR = 0x4; // 是否存储与词条向量相关的位置static final byte STORE_OFFSET_WITH_TERMVECTOR = 0x8; // 是否存储与词条向量相关的offsetstatic final byte OMIT_NORMS = 0x10; // 是否存储被忽略的normsstatic final byte STORE_PAYLOADS = 0x20; // 是否存储Payload private ArrayList byNumber = new ArrayList(); // byNumber是通过编号，用来存放FieldInfo的列表private HashMap byName = new HashMap(); // byNname是通过名称，用来存放FieldInfo的列表
FieldInfos() { } // 没有参数的FieldInfos的构造函数
// 通过索引目录d和一个索引输入流name构造一个FieldInfos对象FieldInfos(Directory d, String name) throws IOException { IndexInput input = d.openInput(name); try { read(input); // input输入流已打开，从索引目录中读取 } finally { input.close(); }}
// 为一个Document添加Field的信息(这种添加和直接向Document中添加Field不一样，这次添加的不是一些固有信息，是一些更详细的补充信息)public void add(Document doc) { List fields = doc.getFields(); // 先获取到该Document中已经添加进去的所有Field Iterator fieldIterator = fields.iterator(); while (fieldIterator.hasNext()) { Fieldable field = (Fieldable) fieldIterator.next(); add(field.name(), field.isIndexed(), field.isTermVectorStored(), field.isStorePositionWithTermVector(), field.isStoreOffsetWithTermVector(), field.getOmitNorms()); // 传参，调用核心的add方法执行添加 }}/** * 添加被索引的Field，需要指定是否具有词条向量 */public void addIndexed(Collection names, boolean storeTermVectors, boolean storePositionWithTermVector,boolean storeOffsetWithTermVector) { Iterator i = names.iterator(); while (i.hasNext()) { add((String)i.next(), true, storeTermVectors, storePositionWithTermVector, storeOffsetWithTermVector); }}
/** * 当Field没有存储词条向量，添加Field * * @param names The names of the fields * @param isIndexed Whether the fields are indexed or not * * @see #add(String, boolean) */public void add(Collection names, boolean isIndexed) { Iterator i = names.iterator(); while (i.hasNext()) { add((String)i.next(), isIndexed); }}
/** * Calls 5 parameter add with false for all TermVector parameters. * * @param name The name of the Fieldable * @param isIndexed true if the field is indexed * @see #add(String, boolean, boolean, boolean, boolean) */public void add(String name, boolean isIndexed) { add(name, isIndexed, false, false, false, false);}
/** * Calls 5 parameter add with false for term vector positions and offsets. * * @param name The name of the field * @param isIndexed true if the field is indexed * @param storeTermVector true if the term vector should be stored */public void add(String name, boolean isIndexed, boolean storeTermVector){ add(name, isIndexed, storeTermVector, false, false, false);}/** If the field is not yet known, adds it. If it is known, checks to make * sure that the isIndexed flag is the same as was given previously for this * field. If not - marks it as being indexed. Same goes for the TermVector * parameters. * * @param name The name of the field * @param isIndexed true if the field is indexed * @param storeTermVector true if the term vector should be stored * @param storePositionWithTermVector true if the term vector with positions should be stored * @param storeOffsetWithTermVector true if the term vector with offsets should be stored */public void add(String name, boolean isIndexed, boolean storeTermVector, boolean storePositionWithTermVector, boolean storeOffsetWithTermVector) {
add(name, isIndexed, storeTermVector, storePositionWithTermVector, storeOffsetWithTermVector, false);}
/** If the field is not yet known, adds it. If it is known, checks to make * sure that the isIndexed flag is the same as was given previously for this * field. If not - marks it as being indexed. Same goes for the TermVector * parameters. * * @param name The name of the field * @param isIndexed true if the field is indexed * @param storeTermVector true if the term vector should be stored * @param storePositionWithTermVector true if the term vector with positions should be stored * @param storeOffsetWithTermVector true if the term vector with offsets should be stored * @param omitNorms true if the norms for the indexed field should be omitted */public void add(String name, boolean isIndexed, boolean storeTermVector, boolean storePositionWithTermVector, boolean storeOffsetWithTermVector, boolean omitNorms) { add(name, isIndexed, storeTermVector, storePositionWithTermVector, storeOffsetWithTermVector, omitNorms, false);}/** 如果该Field没有被添加过，则添加它。如果已经添加过，核查后确保它的是否被索引标志位与已经存在的一致，如果是“不索引”标志，则修改标志位为true. *该add添加方法才是最核心的实现方法。 * @param name The name of the field * @param isIndexed true if the field is indexed * @param storeTermVector true if the term vector should be stored * @param storePositionWithTermVector true if the term vector with positions should be stored * @param storeOffsetWithTermVector true if the term vector with offsets should be stored * @param omitNorms true if the norms for the indexed field should be omitted * @param storePayloads true if payloads should be stored for this field */public FieldInfo add(String name, boolean isIndexed, boolean storeTermVector, boolean storePositionWithTermVector, boolean storeOffsetWithTermVector, boolean omitNorms, boolean storePayloads) { FieldInfo fi = fieldInfo(name); // 根据指定的name构造一个FieldInfo对象 if (fi == null) { // 如果构造的FieldInfo为null，则调用addInternal()方法，重新构造一个 return addInternal(name, isIndexed, storeTermVector, storePositionWithTermVector, storeOffsetWithTermVector, omitNorms, storePayloads); } else { // 如果构造的FieldInfo不为null(即已经存在一个相同name的FieldInfo) if (fi.isIndexed != isIndexed) { // 如果存在的FieldInfo被索引 fi.isIndexed = true; // 一旦被索引了，总是索引 } if (fi.storeTermVector != storeTermVector) { fi.storeTermVector = true; // 一旦存储词条向量，总是存储 } if (fi.storePositionWithTermVector != storePositionWithTermVector) { fi.storePositionWithTermVector = true; // once vector, always vector } if (fi.storeOffsetWithTermVector != storeOffsetWithTermVector) { fi.storeOffsetWithTermVector = true; // once vector, always vector } if (fi.omitNorms != omitNorms) { fi.omitNorms = false; // 一旦存储norms，则总是存储norms } if (fi.storePayloads != storePayloads) { fi.storePayloads = true; }
} return fi; // 返回一个FieldInfo对象}
private FieldInfo addInternal(String name, boolean isIndexed, boolean storeTermVector, boolean storePositionWithTermVector, boolean storeOffsetWithTermVector, boolean omitNorms, boolean storePayloads) { FieldInfo fi = new FieldInfo(name, isIndexed, byNumber.size(), storeTermVector, storePositionWithTermVector, storeOffsetWithTermVector, omitNorms, storePayloads); byNumber.add(fi); // byNumber是一个List，将构造的FieldInfo加入到列表中 byName.put(name, fi); // byName是一个HashMap，其中的键值对<name,fi>表示一个名字为键，一个FieldInfo对象的引用作为值 return fi;}
public int fieldNumber(String fieldName) { // 根据指定的Field的名称，获取该Field的编号 try { FieldInfo fi = fieldInfo(fieldName); if (fi != null) return fi.number; } catch (IndexOutOfBoundsException ioobe) { return -1; } return -1;}
public FieldInfo fieldInfo(String fieldName) { // 根据指定的Field的名称，从byName列表中取出该Field return (FieldInfo) byName.get(fieldName);}
// 根据指定的编号，获取Field的名称namepublic String fieldName(int fieldNumber) { try { return fieldInfo(fieldNumber).name; } catch (NullPointerException npe) { return ""; }}
// 根据指定的Field的编号，获取一个FieldInfo对象public FieldInfo fieldInfo(int fieldNumber) { try { return (FieldInfo) byNumber.get(fieldNumber); // 从byNymber列表中取出索引为指定fieldNumber的FieldInfo对象 } catch (IndexOutOfBoundsException ioobe) { return null; }}
public int size() { // 计算byName这个HashMap的大小 return byNumber.size();}
public boolean hasVectors() { // 返回byName这个HashMap中FieldInfo指定对应的Field不存储词条向量的标志值，即false boolean hasVectors = false; for (int i = 0; i < size(); i++) { if (fieldInfo(i).storeTermVector) { hasVectors = true; break; } } return hasVectors;}
public void write(Directory d, String name) throws IOException { // 将FieldInfo的信息输出到索引目录中，name是索引目录中存在的索引段文件名segments.fnm(可以参考文章 Lucene-2.2.0 源代码阅读学习(21) 中，DocumentWriter的addDocument()方法) IndexOutput output = d.createOutput(name); try { write(output); // 调用下面的write方法，对FieldInfo的信息进行格式化(输出)写入索引目录 } finally { output.close(); }}
public void write(IndexOutput output) throws IOException { // 对FieldInfo的信息进行格式化(输出)写入索引目录 output.writeVInt(size()); for (int i = 0; i < size(); i++) { FieldInfo fi = fieldInfo(i); byte bits = 0x0; if (fi.isIndexed) bits |= IS_INDEXED; if (fi.storeTermVector) bits |= STORE_TERMVECTOR; if (fi.storePositionWithTermVector) bits |= STORE_POSITIONS_WITH_TERMVECTOR; if (fi.storeOffsetWithTermVector) bits |= STORE_OFFSET_WITH_TERMVECTOR; if (fi.omitNorms) bits |= OMIT_NORMS; if (fi.storePayloads) bits |= STORE_PAYLOADS; output.writeString(fi.name); output.writeByte(bits); }}
private void read(IndexInput input) throws IOException { // 通过打开一个输入流，读取FieldInfo的信息 int size = input.readVInt();//read in the size for (int i = 0; i < size; i++) { String name = input.readString().intern(); 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; addInternal(name, isIndexed, storeTermVector, storePositionsWithTermVector, storeOffsetWithTermVector, omitNorms, storePayloads); // 调用addInternal()在内存中构造一个FieldInfo对象，对它进行管理 } }
}
对FieldInfo类和FieldInfos类进行总结：
1、FieldInfo作为一个实体，保存了Field的一些主要的信息；
2、因为对Field的操作比较频繁，而每次管理都在内存中加载FieldInfo这个轻量级但信息很重要的对象，能够大大提高建立索引的速度；
3、FieldInfos包含的信息比较丰富，通过一个FieldInfo对象，调出Document中的Field到内存中，对每个Field进行详细的管理。
4、FieldInfos支持独立从索引目录中读取Document中的信息(主要根据Document参数，管理其中的Field)，然后再写回到索引目录。
综合总结：
FieldInfos是对Document中的Field进行管理的，它主要是在内存中进行管理，然后写入到索引目录中。具体地，它所拥有的信息都被写入了一个与索引段文件相关的segments.fnm文件中(可以参考文章 Lucene-2.2.0 源代码阅读学习(21) ，在DocumentWriter类的addDocument()方法中可以看到)
DocumnetWriter类的实现，是在FieldInfos类的基础上。FieldInfos类对Document的所有的Field的静态信息进行管理，而DocumentWriter类表现出了更强大的管理Document的功能，主要是对Field进行了一些高级的操作，比如使用Analyzer分析器进行分词、对切分出来的词条进行排序(文档倒排)等等。
下一步，就要仔细研究DocumnetWriter类了。
