query.html

Geotools是一个开源的Java GIS工具包,可利用它来开发符合标准的地理信息系统。Geotools提供了OGC(Open Geospatial Consortium)规范的一个实现来作为他们的

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<A NAME="NO_NAMES"><!-- --></A><H3>
NO_NAMES</H3>
<PRE>
public static final <A HREF="http://java.sun.com/j2se/1.4/docs/api/java/lang/String.html" title="class or interface in java.lang">String</A>[] <B>NO_NAMES</B></PRE>
<DL>
<DD>Ask for no properties when used with setPropertyNames.

 <p>
 Note the query will still return a result - limited to FeatureIDs.
 </p>
<P>
<DL>
</DL>
</DL>
<HR>

<A NAME="ALL_NAMES"><!-- --></A><H3>
ALL_NAMES</H3>
<PRE>
public static final <A HREF="http://java.sun.com/j2se/1.4/docs/api/java/lang/String.html" title="class or interface in java.lang">String</A>[] <B>ALL_NAMES</B></PRE>
<DL>
<DD>Ask for all properties when used with setPropertyNames.
<P>
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</DL>
</DL>

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<B>Method Detail</B></FONT></TD>
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<A NAME="getPropertyNames()"><!-- --></A><H3>
getPropertyNames</H3>
<PRE>
public <A HREF="http://java.sun.com/j2se/1.4/docs/api/java/lang/String.html" title="class or interface in java.lang">String</A>[] <B>getPropertyNames</B>()</PRE>
<DL>
<DD>The properties array is used to specify the attributes that should be
 selected for the return feature collection.

 <ul>
 <li>
 ALL_NAMES: <code>null</code><br>
 If no properties are specified (getProperties returns ALL_NAMES or
 null) then the full schema should  be used (all attributes).
 </li>
 <li>
 NO_NAMES: <code>new String[0]</code><br>
 If getProperties returns an array of size 0, then the datasource should
 return features with no attributes, only their ids.
 </li>
 </ul>

 <p>
 The available properties can be determined with a getSchema call from
 the DataSource interface.  A datasource can use <A HREF="../../../org/geotools/data/Query.html#retrieveAllProperties()"><CODE>retrieveAllProperties()</CODE></A> as a shortcut to determine if all its
 available properties should be returned (same as checking to see if
 getProperties is ALL_NAMES, but clearer)
 </p>

 <p>
 If properties that are not part of the datasource's schema are requested
 then the datasource shall throw an exception.
 </p>

 <p>
 This replaces our funky setSchema method of retrieving select
 properties.  It makes it easier to understand how to get certain
 properties out of the datasource, instead of having users get the
 schema and then compose a new schema using the attributes that they
 want.  The old way had problems because one couldn't have multiple
 object reuse the same datasource object, since some other object could
 come along and change its schema, and would then return the wrong
 properties.
 </p>
<P>
<DD><DL>

<DT><B>Returns:</B><DD>the attributes to be used in the returned FeatureCollection.<DT><B>'TODO:'</B></DT>
  <DD>REVISIT: make a FidProperties object, instead of an array size 0.
       I think Query.FIDS fills this role to some degree.
       Query.FIDS.equals( filter ) would meet this need?</DD>
</DL>
</DD>
</DL>
<HR>

<A NAME="retrieveAllProperties()"><!-- --></A><H3>
retrieveAllProperties</H3>
<PRE>
public boolean <B>retrieveAllProperties</B>()</PRE>
<DL>
<DD>Convenience method to determine if the query should use the full schema
 (all properties) of the data source for the features returned.  This
 method is equivalent to if (query.getProperties() == null), but allows
 for more clarity on the part of datasource implementors, so they do not
 need to examine and use null values.  All Query implementations should
 return true for this function if getProperties returns null.
<P>
<DD><DL>

<DT><B>Returns:</B><DD>if all datasource attributes should be included in the schema of
         the returned FeatureCollection.</DL>
</DD>
</DL>
<HR>

<A NAME="getMaxFeatures()"><!-- --></A><H3>
getMaxFeatures</H3>
<PRE>
public int <B>getMaxFeatures</B>()</PRE>
<DL>
<DD>The optional maxFeatures can be used to limit the number of features
 that a query request retrieves.  If no maxFeatures is specified then
 all features should be returned.

 <p>
 This is the only method that is not directly out of the Query element in
 the WFS spec.  It is instead a part of a GetFeature request, which can
 hold one or more queries.  But each of those in turn will need a
 maxFeatures, so it is needed here.
 </p>
<P>
<DD><DL>

<DT><B>Returns:</B><DD>the max features the getFeature call should return.</DL>
</DD>
</DL>
<HR>

<A NAME="getFilter()"><!-- --></A><H3>
getFilter</H3>
<PRE>
public <A HREF="../../../org/geotools/filter/Filter.html" title="interface in org.geotools.filter">Filter</A> <B>getFilter</B>()</PRE>
<DL>
<DD>The Filter can be used to define constraints on a query.  If no Filter
 is present then the query is unconstrained and all feature instances
 should be retrieved.
<P>
<DD><DL>

<DT><B>Returns:</B><DD>The filter that defines constraints on the query.</DL>
</DD>
</DL>
<HR>

<A NAME="getTypeName()"><!-- --></A><H3>
getTypeName</H3>
<PRE>
public <A HREF="http://java.sun.com/j2se/1.4/docs/api/java/lang/String.html" title="class or interface in java.lang">String</A> <B>getTypeName</B>()</PRE>
<DL>
<DD>The typeName attribute is used to indicate the name of the feature type
 to be queried.  If no typename is specified, then the default typeName
 should be returned from the dataStore.  If the datasstore only supports
 one feature type then this part of the query may be ignored.
<P>
<DD><DL>

<DT><B>Returns:</B><DD>the name of the feature type to be returned with this query.</DL>
</DD>
</DL>
<HR>

<A NAME="getNamespace()"><!-- --></A><H3>
getNamespace</H3>
<PRE>
public <A HREF="http://java.sun.com/j2se/1.4/docs/api/java/net/URI.html" title="class or interface in java.net">URI</A> <B>getNamespace</B>()</PRE>
<DL>
<DD>The namespace attribute is used to indicate the namespace of the schema
 being represented.
<P>
<DD><DL>

<DT><B>Returns:</B><DD>the gml namespace of the feature type to be returned with this
         query</DL>
</DD>
</DL>
<HR>

<A NAME="getHandle()"><!-- --></A><H3>
getHandle</H3>
<PRE>
public <A HREF="http://java.sun.com/j2se/1.4/docs/api/java/lang/String.html" title="class or interface in java.lang">String</A> <B>getHandle</B>()</PRE>
<DL>
<DD>The handle attribute is included to allow a client to associate  a
 mnemonic name to the Query request. The purpose of the handle attribute
 is to provide an error handling mechanism for locating  a statement
 that might fail.
<P>
<DD><DL>

<DT><B>Returns:</B><DD>the mnemonic name of the query request.</DL>
</DD>
</DL>
<HR>

<A NAME="getVersion()"><!-- --></A><H3>
getVersion</H3>
<PRE>
public <A HREF="http://java.sun.com/j2se/1.4/docs/api/java/lang/String.html" title="class or interface in java.lang">String</A> <B>getVersion</B>()</PRE>
<DL>
<DD>From WFS Spec:  The version attribute is included in order to
 accommodate systems that  support feature versioning. A value of ALL
 indicates that all versions of a feature should be fetched. Otherwise
 an integer, n, can be specified  to return the n th version of a
 feature. The version numbers start at '1'  which is the oldest version.
 If a version value larger than the largest version is specified then
 the latest version is return. The default action shall be for the query
 to return the latest version. Systems that do not support versioning
 can ignore the parameter and return the only version  that they have.
<P>
<DD><DL>

<DT><B>Returns:</B><DD>the version of the feature to return, or null for latest.</DL>
</DD>
</DL>
<HR>

<A NAME="getCoordinateSystem()"><!-- --></A><H3>
getCoordinateSystem</H3>
<PRE>
public CoordinateReferenceSystem <B>getCoordinateSystem</B>()</PRE>
<DL>
<DD>Temporarily override the coordinate system.

 <p>
 This denotes a request to Temporarily to override the coordinate system
 contained in the FeatureSource being queried. The same coordinate
 values will be used, but the features created will appear in this
 Coordinate System.
 </p>

 <p>
 This change is not persistant at all, indeed it is only for the Features
 returned by this Query.  It may be used in conjunction with the
 reprojection Coordinate System, but this one will always be used first,
 the reprojection CS will perform its operation on this cs.
 </p>
<P>
<DD><DL>

<DT><B>Returns:</B><DD>The coordinate system to be returned for Features from this
         Query (override the set coordinate system).</DL>
</DD>
</DL>
<HR>

<A NAME="getCoordinateSystemReproject()"><!-- --></A><H3>
getCoordinateSystemReproject</H3>
<PRE>
public CoordinateReferenceSystem <B>getCoordinateSystemReproject</B>()</PRE>
<DL>
<DD>Request data reprojection.

 <p>
 Gets the coordinate System to reproject the data contained in the
 backend datastore to.
 </p>

 <p>
 If the DataStore can optimize the reprojection it should, if not then a
 decorator on the reader should perform the reprojection on the fly.
 </p>

 <p>
 If the datastore has the wrong CS then getOverrideCS() should be set to
 the CS to be used, this will perform the reprojection on that.
 </p>
<P>
<DD><DL>

<DT><B>Returns:</B><DD>The coordinate system that Features from the datasource should
         be reprojected to.</DL>
</DD>
</DL>
<HR>

<A NAME="getSortBy()"><!-- --></A><H3>
getSortBy</H3>
<PRE>
public SortBy[] <B>getSortBy</B>()</PRE>
<DL>
<DD>SortBy results according to indicated property and order.
 <p>
 SortBy is part of the Filter 1.1 specification, it is referenced
 by WFS1.1 and Catalog 2.0.x specifications and is used to organize
 results.
 </p>
 The SortBy's are ment to be applied in order:
 <ul>
 <li>SortBy( year, ascending )
 <li>SortBy( month, decsending )
 </ul>
 Would produce something like: <pre><code>
 [year=2002 month=4],[year=2002 month=3],[year=2002 month=2],
 [year=2002 month=1],[year=2003 month=12],[year=2002 month=4],
 </code></pre>
 </p>
 <p>

 SortBy should be considered at the same level of abstraction as Filter,
 and like Filter you may sort using properties not listed in
 getPropertyNames.
 </p>

 <p>
 At a technical level the interface SortBy2 is used to indicate the
 additional requirements of a GeoTools implementation. The pure
 WFS 1.1 specification itself is limited to SortBy.
 </p>
<P>
<DD><DL>

<DT><B>Returns:</B><DD>SortBy array or order of application</DL>
</DD>
</DL>
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