40 lines
1.7 KiB
HTML
40 lines
1.7 KiB
HTML
<H2>Class Evolution</H2>
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<P>This is a demonstration of the class evolution mechanism
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implemented with Javassist. This mechanism enables a Java program to
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reload an existing class file. Although the reloaded class file is
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not applied to exiting objects (the old class file is used for those
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objects), it is effective in newly created objects.
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<P>Since the reloading is transparently executed, no programming
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convention is needed. However, there are some limitations on possible
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changes of the class definition. For example, the new class definition
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must have the same set of methods as the old one. These limitations are
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necessary for keeping the type system consistent.
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<H3><a href="java.html">Run WebPage.show()</a></H3>
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<P>The web server creates a new <code>WebPage</code> object and
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calls <code>show()</code> on that object. This method works as
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if it is a CGI script or a servlet and you will see the html file
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produced by this method on your browser.
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<H3><a href="update.html">Change WebPage.class</a></H3>
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<P>The web server overwrites class file <code>WebPage.class</code>
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on the local disk. Then it signals that <code>WebPage.class</code>
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must be reloaded into the JVM. If you run <code>WebPage.show()</code>
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again, you will see a different page on your browser.
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<H3>Source files</H3>
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<P>Web server: <A HREF="DemoServer.java"><code>DemoServer.java</code></A>
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<P>WebPage: <A HREF="WebPage.java"><code>WebPage.java</code></A> and
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another <A HREF="sample/evolve/WebPage.java"><code>WebPage.java</code></A>
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<P>Class loader: <A HREF="DemoLoader.java"><code>DemoLoader.java</code></A>,
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<A HREF="Evolution.java"><code>Evolution.java</code></A>, and
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<A HREF="VersionManager.java"><code>VersionManager.java</code></A>.
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