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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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原文地址：http://www.cnblogs.com/chenying99/p/3789695.html
