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POTomcat class loading order when serving modules without publishing
 

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  1. POTomcat class loading order when serving modules without publishing
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    <p>I am using tomcat with eclipse.</p> <p>According to tomcat's documentation:<br /><br /> <strong>from the perspective of a web application, class or resource loading looks in the following repositories, in this order:</strong><br/></p> <ul> <li>Bootstrap classes of your JVM System class loader classes (described above)</li> <li>/WEB-INF/classes of your web application </li> <li>/WEB-INF/lib/*.jar of your web application </li> <li>Common class loader classes (described above)</li> </ul> <p>So when loading a classes, tomcat will look up <strong>WEB-INF/classes</strong> before <strong>WEB-INF/lib</strong>. And we can overwrite some class in jar files in WEB-INF/lib, tomcat will pick up the overwritten one.</p> <p>But now if I changed the tomcat server options by checking "Serve modules with out publishing" , then overwritten classes will not be loaded any more.</p> <p>Is there any solution to make that works again, but I still want tomcat to serve modules without publishing.</p> <hr> <p>Edits:<br /> I have found something may be useful, in this folder <strong>f:\eclipse_projects\.metadata.plugins\org.eclipse.wst.server.core\tmp0\conf</strong> there is a server.xml it contains such content:</p> <pre><code>&lt;Resources className="org.eclipse.jst.server.tomcat.loader.WtpDirContext" extraResourcePaths="" virtualClasspath="F:\eclipse_projects\ALS7C3\bin"/&gt; &lt;Loader className="org.eclipse.jst.server.tomcat.loader.WtpWebappLoader" useSystemClassLoaderAsParent="false" virtualClasspath="F:\eclipse_projects\ALS7C3\bin"/&gt; </code></pre> <p>It seems that when running tomcat with option "Serve modules without publishing" checked, eclipse will use it's own loader.This loader is contained in a jar file which will be copied to <strong>f:\eclipse_projects\.metadata.plugins\org.eclipse.wst.server.core\tmp0\lib** when you start tomcat in eclipse. Here is part of source code of **org.eclipse.jst.server.tomcat.loader.WtpDirContext</strong>:</p> <pre><code>public Object lookup(String name) throws NamingException { if (name.startsWith("/WEB-INF/") &amp;&amp; name.endsWith(".tld")) { String tldName = name.substring(name.lastIndexOf("/") + 1); if (virtualMappings != null &amp;&amp; virtualMappings.containsKey(tldName)) { return new FileResource(virtualMappings.get(tldName)); } } else if (tagfileMappings != null &amp;&amp; name.startsWith("/META-INF/tags") &amp;&amp; (name.endsWith(".tag") || name.endsWith(".tagx"))) { // already loaded tag file return new FileResource(tagfileMappings.get(name)); } Object retSuper; NamingException superEx; try { retSuper = super.lookup(name); return retSuper; } catch (NamingException ex) { retSuper = null; superEx = ex; } if (mappedResourcePaths != null) { // Perform lookup using the extra resource paths for (Map.Entry&lt;String, List&lt;String&gt;&gt; mapping : mappedResourcePaths.entrySet()) { String path = mapping.getKey(); List&lt;String&gt; dirList = mapping.getValue(); if (name.equals(path)) { for (String resourcesDir : dirList) { File f = new File(resourcesDir); if (f.exists() &amp;&amp; f.canRead()) { if (f.isFile()) { return new FileResource(f); } else { // TODO Handle directory } } } } path += "/"; if (name.startsWith(path)) { String res = name.substring(path.length()); for (String resourcesDir : dirList) { File f = new File (resourcesDir + "/" + res); if (f.exists() &amp;&amp; f.canRead()) { if (f.isFile()) { return new FileResource(f); } else { // TODO Handle directory } } } } } } throw superEx; } </code></pre> <p>it seems that if it will first handle jsp tag library then call <strong>super.lookup</strong>, if can't find in <strong>super.lookup</strong>, it will try to load resource in virtualClasspath, "F:\eclipse_projects\ALS7C3\bin" in my example, it's where eclipse output class files when serving modules without publishing.</p> <p>So, I guess, I can get what I want if I can overwrite the <strong>lookup</strong> method of <strong>org.eclipse.jst.server.tomcat.loader.WtpDirContext</strong>, however this jar file is contained in <strong>org.eclipse.jst.server.tomcat.core.jar</strong>, both of them are signed.</p> <p>I don't know how to overwrite such a jar file.</p> <p>Any one can help ?</p>
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    1. COWhy do you want to override your classes? Programs shouldn't depend on the behaviour of classloading. Implementations differ.
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      1. USKeerthivasan
    2. CO@Keerthi For convenience at development time, we have some jar files that have no source code or documentation. For example, I want to change the log format to get rid of useless information when developing, but the log format is hard coded in some class in those jars.
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      1. USCaiNiaoCoder
    3. COYou can control the logging levels based on the package.As per my knowledge,Class loader will not load a class with the same name and package structure again. i.e. override. The order in which the classes are loaded are important.Please let me know if i wrong
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