尝试加载HttpUriRequest时Websphere上的java.lang.LinkageError

Question

我的项目使用的是CUPS4J，它依赖于http-client、http-core和slf4j。

为了解决依赖关系，我们使用Maven，我将依赖关系定义如下：

<dependency>
    <groupId>cups4j</groupId>
    <artifactId>cups4j</artifactId>
    <version>0.6.4</version>
</dependency>

<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpclient</artifactId>
    <version>4.0.3</version>
</dependency>

<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpcore</artifactId>
    <version>4.1</version>
</dependency>

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

cups4j依赖项在我们的ArtiFactory服务器上(我在网上找不到它)。

如果我创建了一个样例main方法来打印一些文档并将其作为java应用程序启动，那么一切工作起来都很棒。

当我将我的类发布到Websphere服务器并从网页调用该方法时，它会生成一个java.lang.LinkageError。

这是堆栈跟踪的相关部分：

Caused by: java.lang.LinkageError: loader constraint violation: loader "org/eclipse/osgi/internal/baseadaptor/DefaultClassLoader@208c132" previously initiated loading for a different type with name "org/apache/http/client/methods/HttpUriRequest" defined by loader "com/ibm/ws/classloader/CompoundClassLoader@1e0f797"
    at java.lang.ClassLoader.defineClassImpl(Native Method)
    at java.lang.ClassLoader.defineClass(ClassLoader.java:260)
    at org.eclipse.osgi.internal.baseadaptor.DefaultClassLoader.defineClass(DefaultClassLoader.java:188)
    at org.eclipse.osgi.baseadaptor.loader.ClasspathManager.defineClass(ClasspathManager.java:580)
    at org.eclipse.osgi.baseadaptor.loader.ClasspathManager.findClassImpl(ClasspathManager.java:550)
    at org.eclipse.osgi.baseadaptor.loader.ClasspathManager.findLocalClassImpl(ClasspathManager.java:481)
    at org.eclipse.osgi.baseadaptor.loader.ClasspathManager.findLocalClass_LockClassName(ClasspathManager.java:460)
    at org.eclipse.osgi.baseadaptor.loader.ClasspathManager.findLocalClass(ClasspathManager.java:447)
    at org.eclipse.osgi.internal.baseadaptor.DefaultClassLoader.findLocalClass(DefaultClassLoader.java:216)
    at org.eclipse.osgi.internal.loader.BundleLoader.findLocalClass(BundleLoader.java:393)
    at org.eclipse.osgi.internal.loader.BundleLoader.findClassInternal(BundleLoader.java:469)
    at org.eclipse.osgi.internal.loader.BundleLoader.findClass(BundleLoader.java:422)
    at org.eclipse.osgi.internal.loader.BundleLoader.findClass(BundleLoader.java:410)
    at org.eclipse.osgi.internal.baseadaptor.DefaultClassLoader.loadClass(DefaultClassLoader.java:107)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:612)
    at org.apache.http.impl.client.AbstractHttpClient.determineTarget(AbstractHttpClient.java:584)
    at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:708)
    at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:700)
    at org.cups4j.operations.IppOperation.sendRequest(IppOperation.java:207)
    at org.cups4j.operations.IppOperation.request(IppOperation.java:76)
    at org.cups4j.CupsPrinter.print(CupsPrinter.java:113)
    at it.dropcomp.tasks.print.PrinterService.printPDF(PrinterService.java:160)

这是打印PDF的方法(在it.dropcomp.tasks.print.PrinterService中)：

public void printPDF() throws RemoteServiceException {
    /* 
     * generatedPDF is defined as File, and it's properly initialized 
     * before calling this method.
     */
    if(generatedPDF == null) {
        throw new RemoteServiceException("You must generate a file first!");
    }
    try {
        CupsPrinter selectedPrinter = new CupsPrinter(
            new URL(Constants.PRINTER_FULL_URL), 
            Constants.PRINTER_NAME, true
        );
        InputStream is = new FileInputStream(generatedPDF);
        PrintJob pj = new PrintJob.Builder(is).build();
        selectedPrinter.print(pj); //this is line 160
    } catch (Exception e) {
        LOG.error("Exception", e);
        throw new RemoteServiceException(e);
    }
}

HttpUriRequest似乎已经存在，并与Apache中的httpclient库提供的依赖项发生冲突，但是如果我尝试从pom.xml中删除该依赖项，我会得到该类的NoClassDefFoundException。

如果重要的话，我的集成开发环境是Eclipse的露娜。

如何解决此异常？

Answer 1

WebSphere还使用了httpclient库，这可能与您提供的库冲突。尝试通过Environment > Shared Libraries在管理控制台中创建独立的共享库。将http-*、slf4j和cups4j jars放在那里，并将该共享库与您的应用程序相关联。