bundles/org.eclipse.platform.doc.isv/guide/resInt_content.htm - platform/eclipse.platform.common - Git at Google

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 File encoding and content types
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 <H2>
 File encoding and content types</H2>
 <P >
 The platform runtime plug-in defines infrastructure for defining and discovering <b>content types</b> for data
 streams.  (See <a href="runtime_content.htm">Content types</a> for an overview of the content framework.)
 An important part of the content type system is the ability to specify different encodings (character sets)
 for different kinds of content.  The resources API further allows default character sets to be established for
 projects, folders, and files.  These default character sets are consulted if the content of the file itself
 does not define a particular encoding inside its data stream.
 </P>
 <h3>
 Setting a character set
 </h3>
 <p>
 We've seen in <a href="runtime_content.htm">Content types</a> that default file encodings can be established
 for content types.  More fine-grained control is provided by the resources API.
 </p>
 <p>
 <b><a href="../reference/api/org/eclipse/core/resources/IContainer.html">IContainer</a></b>
 defines protocol for setting the default character set for a particular project or folder.  This gives
 plug-ins (and ultimately the user) more freedom in determining an appropriate character set for a set of files when
 the default character sets from the content type may not be appropriate.</p>
 <p>
 <b><a href="../reference/api/org/eclipse/core/resources/IFile.html">IFile</a></b> defines API for setting
 the default character set for a particular file.  If no encoding is specified inside the file contents,
 then this character set will be used.  The file's default character set takes precedence over any default
 character set specified in the file's folder, project, or content type.
 </p>
 <p>
 Both of these features are available to the end-user in the properties page for a resource.
 </p>
 <h3>Querying the character set</h3>

 <p><b><a href="../reference/api/org/eclipse/core/resources/IFile.html">IFile</a></b> also defines API for
 querying the character set of a file.  A boolean flag specifies whether only the character set explicitly
 defined for the file should be returned, or whether an implied character set should be returned.  For example:
 </p>
 <pre>	String charset = myFile.getCharset(false);
 </pre>
 <p>returns null if no character set was set explicitly on myFile.  However,
 </p>
 <pre>	String charset = myFile.getCharset(true);
 </pre>
 <p>will first check for a character set that was set explicitly on the file.  If none is found, then the content of the file
 will be checked for a description of the character set.  If none is found, then the file's containing folders and projects
 will be checked for a default character set.  If none is found, the default character set defined for the content type
 itself will be checked.  And finally, the platform default character set will be returned if there is no other designation
 of a default character set.  The convenience method <b>getCharset()</b> is the same as using <b>getCharset(true)</b>.
 </p>
 <h3>Content types for files in the workspace</h3>
 <p>For files in the workspace, <a href="../reference/api/org/eclipse/core/resources/IFile.html"><strong>IFile</strong></a> provides API for obtaining
   the file content description:</p>
 <pre>IFile file = ...;
 IContentDescription description = file.getDescription();</pre>
 <p>This API should be used even when clients are only interested in determining
   the content type - the content type can be easily obtained from the content
   description. It is possible to detect the content type or describe files in
   the workspace by obtaining the contents and name and using the API described
   in <a href="runtime_content_using.htm">Using content types</a>, but that is not recommended. Content type determination
   using <strong>IFile.getContentDescription()</strong> takes into account <a href="resAdv_natures.htm">project
   natures</a> and project-specific settings. If you go directly to the content
   type manager, you are ignoring that. But more importantly, because reading the
   contents of files from disk is very expensive. The Resources plug-in maintains
   a cache of content descriptions for files in the workspace. This reduces the
   cost of content description to an acceptable level.</p>
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	<HEAD>

	<meta name="copyright" content="Copyright (c) IBM Corporation and others 2000, 2005. This page is made available under license. For full details see the LEGAL in the documentation book that contains this page." >

	<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=ISO-8859-1">
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	File encoding and content types
	</TITLE>

	<link rel="stylesheet" type="text/css" HREF="../book.css">
	</HEAD>
	<BODY BGCOLOR="#ffffff">
	<H2>
	File encoding and content types</H2>
	<P >
	The platform runtime plug-in defines infrastructure for defining and discovering <b>content types</b> for data
	streams. (See <a href="runtime_content.htm">Content types</a> for an overview of the content framework.)
	An important part of the content type system is the ability to specify different encodings (character sets)
	for different kinds of content. The resources API further allows default character sets to be established for
	projects, folders, and files. These default character sets are consulted if the content of the file itself
	does not define a particular encoding inside its data stream.
	</P>
	<h3>
	Setting a character set
	</h3>
	<p>
	We've seen in <a href="runtime_content.htm">Content types</a> that default file encodings can be established
	for content types. More fine-grained control is provided by the resources API.
	</p>
	<p>
	<b><a href="../reference/api/org/eclipse/core/resources/IContainer.html">IContainer</a></b>
	defines protocol for setting the default character set for a particular project or folder. This gives
	plug-ins (and ultimately the user) more freedom in determining an appropriate character set for a set of files when
	the default character sets from the content type may not be appropriate.</p>
	<p>
	<b><a href="../reference/api/org/eclipse/core/resources/IFile.html">IFile</a></b> defines API for setting
	the default character set for a particular file. If no encoding is specified inside the file contents,
	then this character set will be used. The file's default character set takes precedence over any default
	character set specified in the file's folder, project, or content type.
	</p>
	<p>
	Both of these features are available to the end-user in the properties page for a resource.
	</p>
	<h3>Querying the character set</h3>

	<p><b><a href="../reference/api/org/eclipse/core/resources/IFile.html">IFile</a></b> also defines API for
	querying the character set of a file. A boolean flag specifies whether only the character set explicitly
	defined for the file should be returned, or whether an implied character set should be returned. For example:
	</p>
	<pre> String charset = myFile.getCharset(false);
	</pre>
	<p>returns null if no character set was set explicitly on myFile. However,
	</p>
	<pre> String charset = myFile.getCharset(true);
	</pre>
	<p>will first check for a character set that was set explicitly on the file. If none is found, then the content of the file
	will be checked for a description of the character set. If none is found, then the file's containing folders and projects
	will be checked for a default character set. If none is found, the default character set defined for the content type
	itself will be checked. And finally, the platform default character set will be returned if there is no other designation
	of a default character set. The convenience method <b>getCharset()</b> is the same as using <b>getCharset(true)</b>.
	</p>
	<h3>Content types for files in the workspace</h3>
	<p>For files in the workspace, <a href="../reference/api/org/eclipse/core/resources/IFile.html"><strong>IFile</strong></a> provides API for obtaining
	the file content description:</p>
	<pre>IFile file = ...;
	IContentDescription description = file.getDescription();</pre>
	<p>This API should be used even when clients are only interested in determining
	the content type - the content type can be easily obtained from the content
	description. It is possible to detect the content type or describe files in
	the workspace by obtaining the contents and name and using the API described
	in <a href="runtime_content_using.htm">Using content types</a>, but that is not recommended. Content type determination
	using <strong>IFile.getContentDescription()</strong> takes into account <a href="resAdv_natures.htm">project
	natures</a> and project-specific settings. If you go directly to the content
	type manager, you are ignoring that. But more importantly, because reading the
	contents of files from disk is very expensive. The Resources plug-in maintains
	a cache of content descriptions for files in the workspace. This reduces the
	cost of content description to an acceptable level.</p>
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