java MultipartEntityBuilder java.lang.LinkageError

Question

I have a Java application running under Apache Tomcat 8.0.21.0 on a RHEL 7.8 server. It takes input from a Browser and uploads a file to another Java application running on a remote server.

The partial code is:

// FileItem "fileToUpload" is passed by a HTML input type "file" in a JSP page
private void doPost (HttpServletRequest request, HttpServletResponse response) 
    throws IOException, ServletException
{
    try
    {
        if (ServletFileUpload.isMultipartContent (request))
        {
            FileItemFactory factory = new DiskFileItemFactory ();
            ServletFileUpload upload = new ServletFileUpload (factory);
            List<FileItem> fileItems = upload.parseRequest (request);

            // findFileItem () and generateFileDetails () are local functions
            FileItem fileItemToUpload = findFileItem (fileItems, "fileToUpload");
            String fileDetails = generateFileDetails (fileItemToUpload);

            MultipartEntityBuilder entityBuilder = MultipartEntityBuilder.create ();
            entityBuilder.setMode (HttpMultipartMode.BROWSER_COMPATIBLE);
            entityBuilder.addTextBody ("fileDetails", fileDetails);

            InputStream is = fileItemToUpload.getInputStream ();
            entityBuilder.addBinaryBody ("is", is);

            HttpEntity entity = entityBuilder.build ();  // Exception thrown here

            String url = "[remote server URL]";
            CloseableHttpClient httpClient = HttpClients.createDefault ();
            HttpPost httpPost = new HttpPost (url);
            httpPost.setEntity (entity);

            CloseableHttpResponse response = httpClient.execute (httpPost);
            .
            .
            .
            response.close ();
            httpClient.close ();
        }
        else
        {
            /* handle non-multipart POSTs */
        }
    }
    catch (Exception e)
    {
        .
        .
        .
    }
}

The rather verbose Exception:

java.lang.LinkageError: loader constraint violation: when resolving method "org.apache.http.entity.mime.MultipartEntityBuilder.build()Lorg/apache/http/HttpEntity;" the class loader (instance of org/apache/catalina/loader/WebappClassLoader) of the current class, uri_test_main/HttpHdlr, and the class loader (instance of java/net/URLClassLoader) for the method's defining class, org/apache/http/entity/mime/MultipartEntityBuilder, have different Class objects for the type er.build()Lorg/apache/http/HttpEntity; used in the signature

is thrown at the line: "HttpEntity entity = entityBuilder.build ();"

Note: the Exception is consistent across all browser products.

Is there a quick or obvious fix? I have several workarounds available, but would prefer not to use the deprecated class MultipartEntity.

Answer 1

This is an application developed under Eclipse IDE configured as a Maven project. The external JAR httpmime-4.5.6.jar needs to be added to the project's Java Build Path, and the dependency:

<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpmime</artifactId>
    <version>4.5.6</version>
</dependency>

needs to be added to the dependencies in pom.xml.