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POJava ServiceLoader with multiple Classloaders
 

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    <p>What are the best practices for using <a href="http://download.oracle.com/javase/6/docs/api/java/util/ServiceLoader.html" rel="nofollow noreferrer">ServiceLoader</a> in an Environment with multiple ClassLoaders? The documentation recommends to create and save a single service instance at initialization:</p> <pre><code>private static ServiceLoader&lt;CodecSet&gt; codecSetLoader = ServiceLoader.load(CodecSet.class); </code></pre> <p>This would initialize the ServiceLoader using the current context classloader. Now suppose this snippet is contained in a class loaded using a shared classloader in a web container and multiple web applications want to define their own service implementations. These would not get picked up in the above code, it might even be possible that the loader gets initialized using the first webapps context classloader and provide the wrong implementation to other users.</p> <p>Always creating a new ServiceLoader seems wasteful performance wise since it has to enumerate and parse service files each time. <strong>Edit:</strong> This can even be a big performance problem as shown in <a href="https://stackoverflow.com/questions/6340802/java-xpath-apache-jaxp-implementation-performance/6341739#6341739">this answer regarding java's XPath implementation</a>.</p> <p>How do other libraries handle this? Do they cache the implementations per classloader, do they reparse their configuration everytime or do they simply ignore this problem and only work for one classloader?</p>
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    1. USJörn Horstmann
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    1. COhi Horstmann Look this you.http://stackoverflow.com/questions/1959991/when-to-use-serviceloader-over-something-like-osgi
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      1. USClark Bao
    2. COTake a look at Apache Camel - it handles this problem elegantly, both in JEE apps and OSGi (note there's a specific module for jboss classloading in the Camel extras package hosted on googlecode)
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    3. CO@earcam: can you point me to some more details on how Apache Camel solves this problem?
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