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| 2 |
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| 3 | <head>
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| 4 | <meta http-equiv="Content-Language" content="en-us">
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| 5 | <title>XMLCatalog Type</title>
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| 6 | <link rel="stylesheet" type="text/css" href="../stylesheets/antmanual.css">
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| 7 | </head>
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| 8 |
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| 9 | <body>
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| 10 |
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| 11 | <h2><a name="XMLCatalog">XMLCatalog</a></h2>
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| 12 |
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| 13 | <p>An XMLCatalog is a catalog of public resources such as DTDs or
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| 14 | entities that are referenced in an XML document. Catalogs are
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| 15 | typically used to make web references to resources point to a locally
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| 16 | cached copy of the resource.</p>
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| 17 |
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| 18 | <p>This allows the XML Parser, XSLT Processor or other consumer of XML
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| 19 | documents
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| 20 | to efficiently allow a local substitution for a resource available on the
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| 21 | web.
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| 22 | </p>
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| 23 | <p><b>Note:</b> This task <em>uses, but does not depend on</em> external
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| 24 | libraries not included in the Ant distribution. See <a
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| 25 | href="../install.html#librarydependencies">Library Dependencies</a> for more
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| 26 | information.</p>
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| 27 | <p>This data type provides a catalog of resource locations based
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| 28 | on the <a
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| 29 | href="http://oasis-open.org/committees/entity/spec-2001-08-06.html">
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| 30 | OASIS "Open Catalog" standard</a>. The catalog entries are used
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| 31 | both for Entity resolution and URI resolution, in accordance with
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| 32 | the <code>org.xml.sax.EntityResolver</code> and <code>
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| 33 | javax.xml.transform.URIResolver</code> interfaces as defined
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| 34 | in the <a href="http://java.sun.com/xml/jaxp">Java API for XML
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| 35 | Processing (JAXP) Specification</a>.</p>
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| 36 | <p>For example, in a <code>web.xml</code> file, the DTD is referenced as:
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| 37 | <pre>
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| 38 | <!DOCTYPE web-app PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.2//EN"
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| 39 | "http://java.sun.com/j2ee/dtds/web-app_2_2.dtd">
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| 40 | </pre>
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| 41 | The XML processor, without XMLCatalog support, would need to retrieve the
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| 42 | DTD from
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| 43 | the URL specified whenever validation of the document was required.
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| 44 | </p>
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| 45 | <p>This can be very time consuming during the build process,
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| 46 | especially where network throughput is limited. Alternatively, you
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| 47 | can do the following:
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| 48 | <ol>
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| 49 | <li>Copy <code>web-app_2_2.dtd</code> onto your local disk somewhere (either in the
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| 50 | filesystem or even embedded inside a jar or zip file on the classpath).</li>
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| 51 | <li>Create an <code><xmlcatalog></code> with a <code><dtd></code>
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| 52 | element whose <code>location</code> attribute points to the file.</li>
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| 53 | <li>Success! The XML processor will now use the local copy instead of calling out
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| 54 | to the internet.</li>
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| 55 | </ol>
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| 56 | </p>
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| 57 | <p>XMLCatalogs can appear inside tasks
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| 58 | that support this feature or at the same level as <code>target</code>
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| 59 | - i.e., as children of <code>project</code> for reuse across different
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| 60 | tasks,
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| 61 | e.g. XML Validation and XSLT Transformation. The XML Validate task
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| 62 | uses XMLCatalogs for entity resolution. The XSLT Transformation
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| 63 | task uses XMLCatalogs for both entity and URI resolution.</p>
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| 64 | <p>XMLCatalogs are specified as either a reference to another
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| 65 | XMLCatalog, defined previously in a build file, or as a list of
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| 66 | <code>dtd</code> or <code>entity</code> locations. In addition,
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| 67 | external catalog files may be specified in a nested <code>catalogpath</code> ,
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| 68 | but they will be ignored unless the resolver library from
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| 69 | xml-commons is available in the system classpath. <b>Due to backwards
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| 70 | incompatible changes in the resolver code after the release of
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| 71 | resolver 1.0, Ant will not support resolver.jar in version 1.0 - we
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| 72 | expect a resolver release 1.1 to happen before Ant 1.6 gets
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| 73 | released.</b> A separate classpath for entity resolution may be
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| 74 | specified inline via nested <code>classpath</code> elements; otherwise
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| 75 | the system classpath is used for this as well.</p>
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| 76 | <p>XMLCatalogs can also be nested inside other XMLCatalogs. For
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| 77 | example, a "superset" XMLCatalog could be made by including several
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| 78 | nested XMLCatalogs that referred to other, previously defined
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| 79 | XMLCatalogs.</p>
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| 80 | <p>Resource locations can be specified either in-line or in
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| 81 | external catalog file(s), or both. In order to use an external
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| 82 | catalog file, the xml-commons resolver library ("resolver.jar")
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| 83 | must be in your path. External catalog files may be either <a
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| 84 | href="http://oasis-open.org/committees/entity/background/9401.html">
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| 85 | plain text format</a> or <a
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| 86 | href="http://www.oasis-open.org/committees/entity/spec-2001-08-06.html">
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| 87 | XML format</a>. If the xml-commons resolver library is not found in the
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| 88 | classpath, external catalog files, specified in <code>catalogpath</code>,
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| 89 | will be ignored and a warning
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| 90 | will be logged. In this case, however, processing of inline entries will
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| 91 | proceed normally.</p>
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| 92 | <p>Currently, only <code><dtd></code> and
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| 93 | <code><entity></code> elements may be specified inline; these
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| 94 | roughly correspond to OASIS catalog entry types <code>PUBLIC</code> and
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| 95 | <code>URI</code> respectively. By contrast, external catalog files
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| 96 | may use any of the entry types defined in the
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| 97 | <a href="http://oasis-open.org/committees/entity/spec-2001-08-06.html">
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| 98 | +OASIS specification</a>.</p>
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| 99 | <h3><a name="ResolverAlgorithm">Entity/DTD/URI Resolution Algorithm</a></h3>
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| 100 |
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| 101 | When an entity, DTD, or URI is looked up by the XML processor, the
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| 102 | XMLCatalog searches its list of entries to see if any match. That is,
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| 103 | it attempts to match the <code>publicId</code> attribute of each entry
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| 104 | with the PublicID or URI of the entity to be resolved. Assuming a
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| 105 | matching entry is found, XMLCatalog then executes the following steps:
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| 106 |
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| 107 | <h4>1. Filesystem lookup</h4>
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| 108 |
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| 109 | <p>The <code>location</code> is first looked up in the filesystem. If
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| 110 | the <code>location</code> is a relative path, the ant project basedir
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| 111 | attribute is used as the base directory. If the <code>location</code>
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| 112 | specifies an absolute path, it is used as is. Once we have an
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| 113 | absolute path in hand, we check to see if a valid and readable file
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| 114 | exists at that path. If so, we are done. If not, we proceed to the
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| 115 | next step.</p>
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| 116 |
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| 117 | <h4>2. Classpath lookup</h4>
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| 118 |
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| 119 | <p>The <code>location</code> is next looked up in the classpath.
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| 120 | Recall that jar files are merely fancy zip files. For classpath
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| 121 | lookup, the <code>location</code> is used as is (no base is
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| 122 | prepended). We use a Classloader to attempt to load the resource from
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| 123 | the classpath. For example, if hello.jar is in the classpath and it
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| 124 | contains <code>foo/bar/blat.dtd</code> it will resolve an entity whose
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| 125 | <code>location</code> is <code>foo/bar/blat.dtd</code>. Of course, it
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| 126 | will <em>not</em> resolve an entity whose <code>location</code> is
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| 127 | <code>blat.dtd</code>.
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| 128 |
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| 129 |
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| 130 | <h4>3a. Apache xml-commons resolver lookup</h4>
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| 131 |
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| 132 | <p>What happens next depends on whether the resolver library from
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| 133 | xml-commons is available on the classpath. If so, we defer all
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| 134 | further attempts at resolving to it. The resolver library supports
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| 135 | extremely sophisticated functionality like URL rewriting and so on,
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| 136 | which can be accessed by making the appropriate entries in external
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| 137 | catalog files (XMLCatalog does not yet provide inline support for all
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| 138 | of the entries defined in the <a
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| 139 | href="http://oasis-open.org/committees/entity/spec-2001-08-06.html">OASIS
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| 140 | standard</a>).</p>
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| 141 |
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| 142 | <h4>3. URL-space lookup</h4>
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| 143 |
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| 144 | <p>Finally, we attempt to make a URL out of the <code>location</code>.
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| 145 | At first this may seem like this would defeat the purpose of
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| 146 | XMLCatalogs -- why go back out to the internet? But in fact, this can
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| 147 | be used to (in a sense) implement HTTP redirects, substituting one URL
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| 148 | for another. The mapped-to URL might also be served by a local web
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| 149 | server. If the URL resolves to a valid and readable resource, we are
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| 150 | done. Otherwise, we give up. In this case, the XML processor will
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| 151 | perform its normal resolution algorithm. Depending on the processor
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| 152 | configuration, further resolution failures may or may not result in
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| 153 | fatal (i.e. build-ending) errors.</p>
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| 154 |
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| 155 | <h3>XMLCatalog attributes</h3>
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| 156 | <table border="1" cellpadding="2" cellspacing="0">
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| 157 | <tr>
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| 158 | <td valign="top"><b>Attribute</b></td>
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| 159 | <td valign="top"><b>Description</b></td>
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| 160 | <td align="center" valign="top"><b>Required</b></td>
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| 161 | </tr>
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| 162 | <tr>
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| 163 | <td valign="top">id</td>
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| 164 | <td valign="top">a unique name for an XMLCatalog, used for referencing
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| 165 | the
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| 166 | XMLCatalog's contents from another XMLCatalog</td>
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| 167 | <td valign="top" align="center">No</td>
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| 168 | </tr>
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| 169 | <tr>
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| 170 | <td valign="top">refid</td>
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| 171 | <td valign="top">the <code>id</code> of another XMLCatalog whose
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| 172 | contents
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| 173 | you would like to be used for this XMLCatalog</td>
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| 174 | <td valign="top" align="center">No</td>
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| 175 | </tr>
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| 176 | </table>
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| 177 |
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| 178 | <h3>XMLCatalog nested elements</h3>
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| 179 | <h4>dtd/entity</h4>
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| 180 | <p>The <code>dtd</code> and <code>entity</code> elements used to specify
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| 181 | XMLCatalogs are identical in their structure</p>
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| 182 | <table border="1" cellpadding="2" cellspacing="0">
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| 183 | <tr>
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| 184 | <td valign="top"><b>Attribute</b></td>
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| 185 | <td valign="top"><b>Description</b></td>
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| 186 | <td align="center" valign="top"><b>Required</b></td>
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| 187 | </tr>
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| 188 | <tr>
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| 189 | <td valign="top">publicId</td>
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| 190 | <td valign="top">The public identifier used when defining a dtd or
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| 191 | entity,
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| 192 | e.g. <code>"-//Sun Microsystems, Inc.//DTD Web Application
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| 193 | 2.2//EN"</code>
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| 194 | </td>
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| 195 | <td valign="top" align="center">Yes</td>
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| 196 | </tr>
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| 197 | <tr>
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| 198 | <td valign="top">location</td>
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| 199 | <td valign="top">The location of the local replacement to be used for
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| 200 | the public identifier specified. This may be specified as a file name,
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| 201 | resource name found on the classpath, or a URL. Relative paths will
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| 202 | be resolved according to the base, which by default is the Ant project
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| 203 | basedir.
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| 204 | </td>
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| 205 | <td valign="top" align="center">Yes</td>
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| 206 | </tr>
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| 207 | </table>
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| 208 | <h4>classpath</h4>
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| 209 | <p>The classpath to use for <a href="#ResolverAlgorithm">entity
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| 210 | resolution</a>. The nested <code><classpath></code> is a
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| 211 | <a href="../using.html#path">path</a>-like structure.</p>
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| 212 | <h4>catalogpath</h4>
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| 213 | <p>
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| 214 | The nested <code>catalogpath</code> element is a <a
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| 215 | href="../using.html#path">path</a>-like structure listing catalog files to
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| 216 | search. All files in this path are assumed to be OASIS catalog files, in
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| 217 | either
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| 218 | <a href="http://oasis-open.org/committees/entity/background/9401.html">
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| 219 | plain text format</a> or <a
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| 220 | href="http://www.oasis-open.org/committees/entity/spec-2001-08-06.html">
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| 221 | XML format</a>. Entries specifying nonexistent files will be ignored. If the
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| 222 | resolver library from xml-commons is not available in the classpath, all
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| 223 | <code>catalogpaths</code> will be ignored and a warning will be logged.
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| 224 | </p>
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| 225 | <h3>Examples</h3>
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| 226 | <p>Set up an XMLCatalog with a single dtd referenced locally in a user's
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| 227 | home
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| 228 | directory:</p>
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| 229 | <blockquote><pre>
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| 230 | <xmlcatalog>
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| 231 | <dtd
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| 232 | publicId="-//OASIS//DTD DocBook XML V4.1.2//EN"
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| 233 | location="/home/dion/downloads/docbook/docbookx.dtd"/>
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| 234 | </xmlcatalog>
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| 235 | </pre></blockquote>
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| 236 | <p>Set up an XMLCatalog with a multiple dtds to be found either in the
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| 237 | filesystem (relative to the Ant project basedir) or in the classpath:
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| 238 | </p>
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| 239 | <blockquote><pre>
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| 240 | <xmlcatalog id="commonDTDs">
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| 241 | <dtd
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| 242 | publicId="-//OASIS//DTD DocBook XML V4.1.2//EN"
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| 243 | location="docbook/docbookx.dtd"/>
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| 244 | <dtd
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| 245 | publicId="-//Sun Microsystems, Inc.//DTD Web Application 2.2//EN"
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| 246 | location="web-app_2_2.dtd"/>
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| 247 | </xmlcatalog>
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| 248 | </pre></blockquote>
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| 249 |
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| 250 | <p>Set up an XMLCatalog with a combination of DTDs and entities as
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| 251 | well as a nested XMLCatalog and external catalog files in both
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| 252 | formats:</p>
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| 253 |
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| 254 | <blockquote><pre>
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| 255 | <xmlcatalog id="allcatalogs">
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| 256 | <dtd
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| 257 | publicId="-//ArielPartners//DTD XML Article V1.0//EN"
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| 258 | location="com/arielpartners/knowledgebase/dtd/article.dtd"/>
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| 259 | <entity
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| 260 | publicId="LargeLogo"
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| 261 | location="com/arielpartners/images/ariel-logo-large.gif"/>
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| 262 | <xmlcatalog refid="commonDTDs"/>
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| 263 | <catalogpath>
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| 264 | <pathelement location="/etc/sgml/catalog"/>
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| 265 | <fileset
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| 266 | dir="/anetwork/drive"
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| 267 | includes="**/catalog"/>
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| 268 | <fileset
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| 269 | dir="/my/catalogs"
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| 270 | includes="**/catalog.xml"/>
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| 271 | </catalogpath>
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| 272 | </xmlcatalog>
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| 273 | </xmlcatalog>
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| 274 | </pre></blockquote>
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| 275 | <p>To reference the above XMLCatalog in an <code>xslt</code> task:<p>
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| 276 | <blockquote><pre>
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| 277 | <xslt basedir="${source.doc}"
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| 278 | destdir="${dest.xdocs}"
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| 279 | extension=".xml"
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| 280 | style="${source.xsl.converter.docbook}"
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| 281 | includes="**/*.xml"
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| 282 | force="true">
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| 283 | <xmlcatalog refid="allcatalogs"/>
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| 284 | </xslt>
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| 285 | </pre></blockquote>
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| 286 |
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| 287 | <hr>
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| 288 | <p align="center">Copyright © 2002,2004 The Apache Software Foundation. All
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| 289 | rights
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| 290 | Reserved.</p>
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| 291 |
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| 292 | </body>
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| 293 | </html>
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