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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"><html><head><title>Java Image I/O API Guide: 4 - Writing Image I/O Plug-ins</title></head><body bgcolor="#ffffff"> <table summary="layout" width="100%"><tr><td><!-- Bug in Communicator w/font: NavBar text disappears for Times 14pt pref. --><!-- font size="-1" --> <a href="imageio_guideTOC.fm.html" tppabs="http://java.sun.com/j2se/1.4.2/docs/guide/imageio/spec/imageio_guideTOC.fm.html">CONTENTS</a> | <a href="apps.fm8.html" tppabs="http://java.sun.com/j2se/1.4.2/docs/guide/imageio/spec/apps.fm8.html">PREV</a> | <a href="extending.fm2.html" tppabs="http://java.sun.com/j2se/1.4.2/docs/guide/imageio/spec/extending.fm2.html">NEXT</a> <!-- | <a href="copyright.fm.html">INDEX</a> --><!-- /font --></td><td align=right><i>Java<sup><font size="-1">TM</font></sup></font> Image I/O API Guide</i></td></tr></table><br> <p><hr size="8" width="35%" align="left" noshade><br><U><B><FONT FACE="ARIAL,HELVETICA,TIMES ROMAN">CHAPTER</FONT>4</B></U><a name="5529"><!-- --></a><h1>Writing Image I/O Plug-ins</h1><h2><a name="996730"><i>4.1 </i> The Plug-in Concept</a></h2><blockquote><a name="996892"><!-- --></a>The Image I/O API is designed as a pluggable framework into which any developer may add their own "plug-ins." A plug-in is defined as a set of Java language classes which may be loaded into the API at run-time and which add functionality to the API. In the context of the Java Image I/O API, a plug-in may provide the ability to read image data from a new file format, to write image data in a new format, to "transcode" non-image metadata between two formats, or to read or write streaming data from or to a new data source or sink. A plug-in may also provide support for the same format as another plug-in, perhaps providing better performance, more features, or a different view of the data stored by the format.<p><a name="996897"><!-- --></a>In order for plug-ins to be added to a running Java<sup><font size="-1">TM</font></sup> Virtual Machine*, theymust be compiled into Java bytecode files (class files). These class files will contain the code for subclasses of various classes defined by the API. For example, a plug-in that provides the capability to read images will include a new subclass of the abstract <code>javax.imageio.ImageReader</code> class defined by the API. The usual reversed Internet domain name convention may be used to guarantee uniqueness of class names.<p><a name="996910"><!-- --></a>Because loading and instantiating an entire plug-in may be expensive, an additional class is used as a "stand-in" to provide information about the plug-in. This class may be used, for example, to determine what formats are handled by the plug-in prior to actually instantiating the plug-in.<p><a name="996918"><!-- --></a>The "stand-in" object is lightweight enough that it can be loaded and a single instance instantiated every time the API is used within a given invocation of the Java virtual machine. This pattern, in which a small class is used to provide information about an available service, is referred to as a "service provider interface."<p></blockquote><br>* As used on this web site, the terms "Java Virtual Machine" or "JVM" meana virtual machine for the Java platform.<br><hr><!-- Bug in Communicator w/font: NavBar text disappears for Times 14pt pref. --><!-- font size="-1" --> <a href="imageio_guideTOC.fm.html" tppabs="http://java.sun.com/j2se/1.4.2/docs/guide/imageio/spec/imageio_guideTOC.fm.html">CONTENTS</a> | <a href="apps.fm8.html" tppabs="http://java.sun.com/j2se/1.4.2/docs/guide/imageio/spec/apps.fm8.html">PREV</a> | <a href="extending.fm2.html" tppabs="http://java.sun.com/j2se/1.4.2/docs/guide/imageio/spec/extending.fm2.html">NEXT</a> <!-- | <a href="copyright.fm.html">INDEX</a> --><!-- /font --><hr><font size="-1"><i><A HREF="copyright.fm.html" tppabs="http://java.sun.com/j2se/1.4.2/docs/guide/imageio/spec/copyright.fm.html">Copyright</a> © 2001 Sun Microsystems, Inc. All Rights Reserved.</i></font></body><script language="JavaScript" src="s_code_remote.js" tppabs="http://java.sun.com/js/omi/jsc/s_code_remote.js"></script></html>⌨️ 快捷键说明
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