How to deal with LinkageErrors in Java?

May be this will help someone because it works out pretty good for me. The issue can be solve by integrating your own dependencies. Follow this simple steps

First check the error which should be like this :

• Method execution failed:
• java.lang.LinkageError: loader constraint violation:
• when resolving method "org.slf4j.impl.StaticLoggerBinder.getLoggerFactory()Lorg/slf4j/ILoggerFactory;"
• the class loader (instance of org/openmrs/module/ModuleClassLoader) of the current class, org/slf4j/LoggerFactory,
• and the class loader (instance of org/apache/catalina/loader/WebappClassLoader) for resolved class, org/slf4j/impl/StaticLoggerBinder,
• have different Class objects for the type taticLoggerBinder.getLoggerFactory()Lorg/slf4j/ILoggerFactory; used in the signature

---

2. See the two highlighted class. Google search for them like "StaticLoggerBinder.class jar download" & "LoggeraFactory.class jar download". This will show you first or in some case second link (Site is http://www.java2s.com ) which is one of the jar version you have included in your project. You can smartly identify it yourself, but we are addicted of google ;)

3. After that you will know the jar file name, in my case it is like slf4j-log4j12-1.5.6.jar & slf4j-api-1.5.8

4. Now the latest version of this file is available here http://mvnrepository.com/ (actually all version till date, this is the site from where maven get your dependencies).
5. Now add both file as a dependencies with the latest version (or keep both file version same, either chosen version is old). Following is the dependency you have to include in pom.xml

---

<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-api</artifactId>
    <version>1.7.7</version>
</dependency>
<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-log4j12</artifactId>
    <version>1.7.7</version>
</dependency>

---

Can you specify a class loader? If not, try specifying the context class loader like so:

Thread thread = Thread.currentThread();
ClassLoader contextClassLoader = thread.getContextClassLoader();
try {
    thread.setContextClassLoader(yourClassLoader);
    callDom4j();
} finally {
    thread.setContextClassLoader(contextClassLoader);
}

I'm not familiar with the Java Plugin Framework, but I write code for Eclipse, and I run into similar issues from time to time. I don't guarantee it'll fix it, but it's probably worth a shot.

Sounds like a classloader hierarchy problem. I can't tell what type of environment your application is deployed in, but sometimes this problem can occur in a web environment - where the application server creates a hierarchy of classloaders, resembling something like:

javahome/lib - as root
appserver/lib - as child of root
webapp/WEB-INF/lib - as child of child of root
etc

Usually classloaders delegate loading to their parent classloader (this is known as "parent-first"), and if that classloader cannot find the class, then the child classloader attempts to. For example, if a class deployed as a JAR in webapp/WEB-INF/lib tries to load a class, first it asks the classloader corresponding to appserver/lib to load the class (which in turn asks the classloader corresponding to javahome/lib to load the class), and if this lookup fails, then WEB-INF/lib is searched for a match to this class.

In a web environment, you can run into problems with this hierarchy. For example, one mistake/problem I've run into before was when a class in WEB-INF/lib depended on a class deployed in appserver/lib, which in turn depended on a class deployed in WEB-INF/lib. This caused failures because while classloaders are able to delegate to the parent classloader, they cannot delegate back down the tree. So, the WEB-INF/lib classloader would ask appserver/lib classloader for a class, appserver/lib classloader would load that class and try to load the dependent class, and fail since it could not find that class in appserver/lib or javahome/lib.

So, while you may not be deploying your app in a web/app server environment, my too-long explanation might apply to you if your environment has a hierarchy of classloaders set up. Does it? Is JPF doing some sort of classloader magic to be able to implement it's plugin features?

LinkageError is what you'll get in a classic case where you have a class C loaded by more than one classloader and those classes are being used together in the same code (compared, cast, etc). It doesn't matter if it is the same Class name or even if it's loaded from the identical jar - a Class from one classloader is always treated as a different Class if loaded from another classloader.

The message (which has improved a lot over the years) says:

Exception in thread "AWT-EventQueue-0" java.lang.LinkageError: 
loader constraint violation in interface itable initialization: 
when resolving method "org.apache.batik.dom.svg.SVGOMDocument.createAttribute(Ljava/lang/String;)Lorg/w3c/dom/Attr;" 
the class loader (instance of org/java/plugin/standard/StandardPluginClassLoader) 
of the current class, org/apache/batik/dom/svg/SVGOMDocument, 
and the class loader (instance of ) for interface org/w3c/dom/Document 
have different Class objects for the type org/w3c/dom/Attr used in the signature

So, here the problem is in resolving the SVGOMDocument.createAttribute() method, which uses org.w3c.dom.Attr (part of the standard DOM library). But, the version of Attr loaded with Batik was loaded from a different classloader than the instance of Attr you're passing to the method.

You'll see that Batik's version seems to be loaded from the Java plugin. And yours is being loaded from " ", which is most likely one of the built-in JVM loaders (boot classpath, ESOM, or classpath).

The three prominent classloader models are:

• delegation (the default in the JDK - ask parent, then me)
• post-delegation (common in plugins, servlets, and places where you want isolation - ask me, then parent)
• sibling (common in dependency models like OSGi, Eclipse, etc)

I don't know what delegation strategy the JPF classloader uses, but the key is that you want one version of the dom library to be loaded and everyone to source that class from the same location. That may mean removing it from the classpath and loading as a plugin, or preventing Batik from loading it, or something else.