连接器里面采用的什么样的数据结构，我们先从Document迭代器开始入手，具体的Document迭代器类都实现了DocumentList接口，该接口定义了两个方法
public interface DocumentList {
public Document nextDocument() throws RepositoryException;
public String checkpoint() throws RepositoryException;
}
前者用于获取Document对象，后者获取断点状态
上文中分析的DiffingConnectorDocumentList类即实现了DocumentList接口，从List<CheckpointAndChange> guaranteedChanges集合的迭代器中迭代获取CheckpointAndChange对象然后包装为Document类型对象
Document也是一接口类型
public interface Document {
public Property findProperty(String name) throws RepositoryException;
public Set<String> getPropertyNames() throws RepositoryException;
}
从Document接口定义的方法可以看出，Document接口类似于Map容器结构，如果进一步考察String类型的key对应的value类型Property，可以发现Document接口很类似于HashMap结构
public interface Property {
public Value nextValue() throws RepositoryException;
}
下面继续考察Document接口的具体实现类，以JsonDocument类说明：
/**
*省略了其他部分成员属性及方法
* A simple {@link Document} implementation created from a {@link JSONObject}.
*/
public class JsonDocument implements Document { private final Map<String, List<Value>> properties; /**
* Constructor used by {@link DBHandle} when deserializing a
* {@code DocumentHandle} from the recovery file.
*/
public JsonDocument(JSONObject jsonObject) {
this(buildJsonProperties(jsonObject), jsonObject);
} /**
* Constructor used by the {@link DocumentBuilder} for creating a
* {@link JsonDocument} object used by {@link RepositoryHandler}
* for building a collection over JsonDocument.
*/
public JsonDocument(Map<String, List<Value>> properties,
JSONObject jsonObject) {
this.properties = properties;
this.jsonObject = jsonObject;
objectId = getSingleValueString(SpiConstants.PROPNAME_DOCID);
if (Strings.isNullOrEmpty(objectId)) {
throw new IllegalArgumentException(
"Unable to parse for docID from the properties:" + properties);
}
} @Override
public Set<String> getPropertyNames() {
return properties.keySet();
} @Override
public Property findProperty(String name) throws RepositoryException {
List<Value> property = properties.get(name);
if (name.equals(SpiConstants.PROPNAME_CONTENT) && filterMimeType()) {
property = null;
}
return (property == null) ? null : new SimpleProperty(property);
} }
JsonDocument类还有什么好说的呢，内部实际是对Map<String, List<Value>> properties的封装
属性类型SimpleProperty实现了Property接口
/**
* Simple implementation of the {@link Property} interface.
* Implementors may use this directly or for reference.
*
* @since 1.0
*/
public class SimpleProperty implements Property { final Iterator<Value> iterator; /**
* Constructs a property with a single value.
*
* @param value the property's {@link Value}
* @since 2.4
*/
public SimpleProperty(Value value) {
this(Collections.singletonList(value));
} /**
* Constructs a property with multiple values.
*
* @param values a {@code List} of the property's {@link Value Values}
*/
public SimpleProperty(List<Value> values) {
this.iterator = values.iterator();
} @Override
public Value nextValue() {
return (iterator.hasNext()) ? iterator.next() : null;
}
}
成员属性final Iterator<Value> iterator保存值的迭代器，功能与HashMap的entry链表类似
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