XSLT Error For Solr - HTTP Status 500 - {msg=getTransformer fails in getContentType...

It is common to apply an XSLT stylesheet to an xml file to give it a cleaner look and Solr is no different coming with 4 pre-written xslt files for you to choose from.  

The error message XSLT Error For Solr - HTTP Status 500 - {msg=getTransformer fails in getContentType... is a common one and in most cases is easily fixed.  There are a few reasons that the error message appears:

1. You have not specified a stylesheet to use
          e.g http://localhost:8080/solr/select?q=*&wt=xslt
   Make sure you have specified a stylesheet and that the stylesheet you specified actually exists
          e.g http://localhost:8080/solr/select?q=*&wt=xslt&tr=example.xsl
   
2. A common mistake is to think that a stylesheet has a .xslt file extension - THEY DONT! The file extension is .xsl so be sure when you save your file and when you specify it in your query that you use .xsl
   
3. There are errors in you XSL file - Be careful if you are working in an environment that does not do syntax checking (notepad) - It is easy to forget to close a tag or make a spelling mistake.

Stack Trace:

 {msg=getTransformer fails in getContentType,trace=java.lang.RuntimeException: getTransformer fails in getContentType at org.apache.solr.response.XSLTResponseWriter.getContentType(XSLTResponseWriter.java:74) at org.apache.solr.servlet.SolrDispatchFilter.writeResponse(SolrDispatchFilter.java:623) at org.apache.solr.servlet.SolrDispatchFilter.doFilter(SolrDispatchFilter.java:372) at org.apache.solr.servlet.SolrDispatchFilter.doFilter(SolrDispatchFilter.java:155) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99) at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408) at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1008) at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589) at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.run(AprEndpoint.java:1852) at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source) at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at java.lang.Thread.run(Unknown Source) Caused by: java.io.IOException: 'tr' request parameter is required to use the XSLTResponseWriter at org.apache.solr.response.XSLTResponseWriter.getTransformer(XSLTResponseWriter.java:1