问题
Here I am getting below error while connect using HttpPost,
Caused by: java.lang.LinkageError: loader constraint violation: loader
(instance of org/jboss/osgi/framework/internal/HostBundleClassLoader)
previously initiated loading for a different type with name
"org/apache/http/client/methods/HttpPost"
And I am using OSGI bundle so I have added all required dependent files.
So can anyone help me to resolve it?
回答1:
The Java language is based on a single namespace. That is, the language is built around the concept that a class name is used only once. Classloaders were designed to load code over the internet but accidentally allowed the same class name to be used by 2 class loaders.
In OSGi, each bundle has a class loader that directly loads the classes from its own bundle but uses the class loader of other bundles for any imported classes.
In such a mesh of class loaders, you get the situation that you can load a class C from a Bundle that references a class X and a class Y loaded from other class loaders. Since they have different names that is ok. However, X could refer to class Z and Y could refer to Z, and they could come from different loaders. The original class C from Bundle A, therefore, can see Z from two different class loaders. And is a Linkage Error.
This mesh of classloaders works very well when all bundles are correct, you should never get this kind of errors when you do not hack your bundles. These errors are inevitably caused by complex setups that do not follow the OSGi rules and maintain the Bundle's manifest by hand.
In this case, the class name that can be seen multiple times is org.apache.http.client.methods.HttpPost. So you have a setup where there are multiple bundles exporting this class, which is the first place to look. Since you could start the bundle, the metadata is wrong. OSGi has special metadata that makes this error detected before you start the bundle, the so-called uses constraints.
On Apache Felix, you get an extensive analysis of the problem. If you could run your code on Apache Felix, that would be the easiest route. Looking at your error, you seem to be running on JBoss. They always have played a bit loose with the OSGi rules to make it easier to run enterprise software. Software that rarely does the work to provide OSGi metadata and is well known for its class loader hacks. (A lot of people are only after the Java Module System starting to understand what OSGi was doing and needed.)
来源：https://stackoverflow.com/questions/62956624/java-lang-linkageerror-loader-constraint-violation-loader