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

RESTful Java Web Service For Solr

You have your Solr server set-up, now what?  You want people to be able to perform queries and have some control over what can be input, well you need a Java Web Service!  This is a short guide on how to create your Java Web Service which may not be tailored to your particular needs but you can tweak it as you please.

Set-Up

To set up the Java Web Service you will need:

• Netbeans 7 with GlassFish
• Solr Set-up and Running

Steps Involved

Project Set-Up

• Start Netbeans and Go to File→New Project→Java Web→Web Applications and then hit Next.
• Give your project a name and then hit Next
• Ensure that Glassfish is the selected server and hit Finish

HelloResource.java

• Right click the Default Package and create a new Java Class and call it HelloResource.java
• Enter the following code:
  
  

  import java.net.URL;
  import javax.ws.rs.GET;
  import javax.ws.rs.Path;
  import javax.ws.rs.Produces;
  import javax.ws.rs.QueryParam;
  import java.io.BufferedReader;
  import java.io.InputStreamReader;
  import java.net.URLConnection;
   
  /**
   *
   * @author alamil
   */
   
  //Looks for hello in the pathname
  @Path("hello")
  public class HelloResource {
   
      /**
       *
       * @param arg
       * @param rows
       * @return
       */
      @GET
      @Path("/query")     //Looks for /query in the pathname
      @Produces("text/xml")       //Returns xml
      public String hello(@QueryParam("q") String arg, @QueryParam("rows") String rows, @QueryParam("filter") String filter){
   
          //Variables
          String xmldoc = "";
          String inputLine;
   
          //If the user has not selected a number of rows to display then 50 is set to defualt
          if (rows == null) 
              rows = "50";
   
          //If the user has not selected fields to filter on then it uses the default
          if (filter == null)
              filter = "id,title";
   
          try{
   
              //Trys to connect to the Solr Server with the query
              URL solr = new URL("http://localhost:8080/solr/select?q=url:(" + arg.replaceAll(" ","%20") 
                      + ")^25%20text:(" + arg.replaceAll(" ","%20") + ")&fl=" + filter + "&rows=" + rows);
   
              URLConnection yc = solr.openConnection();
   
              //Reads the returned xml file from the server
              BufferedReader in = new BufferedReader(new InputStreamReader(yc.getInputStream()));
   
              while ((inputLine = in.readLine()) != null){ 
                      xmldoc = xmldoc + inputLine;
              }
   
              //Close the file
              in.close();
   
              //Return the xml document (Replacing the %20's with spaces)
              return xmldoc.replaceAll("%20", " ");
          }catch (Exception e){
                  return "Exception";
          }
      }
  }

RESTConfig.java

• Right click the Default Package and create a new Java Class and call it RESTConfig.java
• Enter the following code:
  
  

  import javax.ws.rs.core.Application;
  import javax.ws.rs.ApplicationPath;
  /**
   *
   * @author alamil
   */
  @ApplicationPath("SearchInt")
  public class RESTConfig extends Application {
   
  }

Testing

• Go to Run→Run Project and your server should start
• A browser window will open to the index.html page that is there which you can tweak and edit to your own liking
• Start your solr server
• In your browser, Navigate to:
  localhost:8080/HelloRest/SearchInt/hello/query?q=[query term]&filter=[filter term]&rows=[rows]

• The input parameters set up are:
  1. q=… : representing the keywords in the query
  2. rows=… : representing the number of rows you wish to have returned
  3. filter=… :representing which fields are displayed to the user

Your server and Solr server may be running from the same port which can cause problems

C# Web Service To Query Solr (REST)

Preparation

You should have a Solr Server set-up on port 8080, configured to use Tika's extracting reuqest handler as well as having the highlighting functionality: 
http://amac4.blogspot.co.uk/2013/08/setting-up-highlighting-for-solr-4.html
http://amac4.blogspot.co.uk/2013/07/setting-up-tika-extracting-request.html
http://amac4.blogspot.co.uk/2013/07/setting-up-solr-with-apache-tomcat-be.html

Now that you have your Solr server up and running, now what? How do you query? How to you make use of the server? Well, you need to create a web service that will query Solr when the method is called from an ASP page. If you want your search service to be used on the web then you should most certainly consider creating a web service to provide you with a clean solution to the problem.

I am a novice when it comes to C# and this was my first involvement with the language, but due to the similarities it holds with Java, it wasn't difficult to understand the basics and get the web service up and running. It will return an xml file based on the input parameters and has the capability of highlighting too

You will require:

• Microsoft Visual Studio with .NET framework of 3.5 or higher

Running The Web Service

• Open Microsoft Visual Studio

• Go to File→New Project and ensure that .NET Framework 3.5 is selected from the pull-down menu. Then select ASP.NET Web Service Application using Visual C#. Give your Web Service a relevant name and hit OK

• Input the source code:
  

  
  

  using System;
  using System.Collections.Generic;
  using System.Linq;
  using System.Web;
  using System.Web.Services;
  using System.Net;
  using System.Xml;
  using System.Web.UI;
   
  namespace Query
  {
      /// <summary>
      /// Queries the Solr Server based on input parameters and returns the XML response
      /// </summary>
      [WebService(Namespace = "http://tempuri.org/")]
      [WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
      [System.ComponentModel.ToolboxItem(false)]
      // To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment the following line. 
      // [System.Web.Script.Services.ScriptService]
      public class Service1 : System.Web.Services.WebService
      {
   
          [WebMethod(Description = "Query Solr server and return XML response")]
          public XmlDocument QuerySolr(string keyword, string notKeyword, string exact, string rows, string filter,
              string fuzzy, string highlight)
          {
   
   
              /*  Default values should the user not enter anything */
              if (rows.Equals(""))
                  rows = "50";
   
              if (keyword.Equals("") && notKeyword.Equals("") && exact.Equals(""))
                  keyword = "*";
   
              if (filter.Equals(""))
                  filter = "id,title";
   
              if (!exact.Equals(""))
                  exact = " \"" + exact + "\"";
   
              if(!highlight.Equals(""))
                  highlight = "&hl=true&hl.fl=content";
   
              /* Should the user require that a certain word or words are not present */
              if (!notKeyword.Equals(""))
              {
   
                  /* Split each word */
                  string[] nwords = notKeyword.Split(null);
                  notKeyword = "";
   
                  /* Loops and adds the hyphen to each word */
                  for (int i = 0; i < nwords.Length; i++)
                  {
                      notKeyword = notKeyword + "-" + nwords[i] + " ";
                  }
                  notKeyword = notKeyword.Substring(0, notKeyword.Length - 1);
   
              }
   
              /* Should the user enable a fuzzy search a tilda must be added on to the end of each word */
              if (fuzzy.Equals("true") && !keyword.Equals(""))
              {
   
                  /* Splits the words by whitespace */
                  string[] words = keyword.Split(null);
                  keyword = "";
   
                  /* Loops and adds the tilda to each word */
                  for (int i = 0; i < words.Length; i++)
                  {
                      keyword = keyword + words[i] + "~ ";
                  }
                  keyword = keyword.Substring(0, keyword.Length - 1);
   
              }    
   
              /* Will throw an error should it have problems connecting to the Solr server */
              try
              {
   
                  /* Connecting to the Solr server and querying it with the search criteria that the user has provided*/
                  WebClient client = new WebClient();
                  string text = client.DownloadString(
                      "http://localhost:8080/solr/select?q=url:("+ keyword + " " + notKeyword + exact + ")^20%20text:("+ keyword
                      + " " + notKeyword + exact + ")&fl=" + filter + "&rows=" + rows + highlight);
   
                  /* The response is returned as a string so it must turn it into an XML document */
                  XmlDocument xml = new XmlDocument();
                  xml.LoadXml(text.Replace("%20", " ").Replace("\\", "/"));   //Changes to windows style filepath
   
                  return xml;
   
              }
              catch (Exception)
              {
                  /* Should an exception occur it returns an XML document with details of the problem */
                  XmlDocument xmle = new XmlDocument();
                  xmle.LoadXml("<Problem>Solr server cannot be reached</Problem>");
   
                  return xmle;
              }
          }
   
      }
  }

• To test the Web Service hit the Green Triangle in the Top Menu

• A Browser Window should open and display the Web Services that are currently being offered, click on the Query Solr Web Service

• You should be able to enter the search criteria beneath and hit invoke to test your results