Overview

LabKey Server supports transformation scripts for assay data at upload time. This feature is primarily targeted for Perl or R scripts; however, the framework is general enough that any application that can be externally invoked can be run as well, including a Java program.

Java appeals to programmers who desire a stronger-typed language than most script-based languages. Most important, using a Java-based validator allows a developer to leverage the remote client API and take advantage of the classes available for assays, queries, and security.

This page outlines the steps required to configure and create a Java-based transform script. The ProgrammaticQCTest script, available in the BVT test, provides an example of a script that uses the remote client API.

Configure the Script Engine

In order to use a Java-based validation script, you will need to configure an external script engine to bind a file with the .jar extension to an engine implementation.

To do this:

  • Go to the Admin Console for your site.
  • Select the [views and scripting configuration] option.
  • Create a new external script engine.
  • Set up the script engine by filling in its required fields:
    • File extension: jar
    • Program path: (the absolute path to java.exe)
    • Program command: -jar "${scriptFile}" "${runInfo}"
      • scriptFile - The full path to the (processed and rewritten) transform script. This is usually in a temporary location the server manages.
      • runInfo - The full path to the run properties file the server creates. For further info on this file, see the "Run Properties File" section of the Transformation Scripts documentation.
      • srcDirectory - The original directory of the transform script (usually specified in the assay definition).

The program command configured above will invoke the java.exe application against a .jar file passing in the run properties file location as an argument to the java program. The run properties file contains information about the assay properties including the uploaded data and the location of the error file used to convey errors back to the server. Specific details about this file are contained in the data exchange specification for Programmatic QC.

Implement a Java Validator

The implementation of your java validator class must contain an entry point matching the following function signature:

public static void main(String[] args)

The location of the run properties file will be passed from the script engine configuration (described above) into your program as the first element of the args array.

The following code provides an example of a simple class that implements the entry point and handles any arguments passed in:

public class AssayValidator
{
private String _email;
private String _password;
private File _errorFile;
private Map<String, String> _runProperties;
private List<String> _errors = new ArrayList<String>();

private static final String HOST_NAME = "http://localhost:8080/labkey";
private static final String HOST = "localhost:8080";

public static void main(String[] args)
{
if (args.length != 1)
throw new IllegalArgumentException("Input data file not passed in");

File runProperties = new File(args[0]);
if (runProperties.exists())
{
AssayValidator qc = new AssayValidator();

qc.runQC(runProperties);
}
else
throw new IllegalArgumentException("Input data file does not exist");
}

Create a Jar File

Next, compile and jar your class files, including any dependencies your program may have. This will save you from having to add a classpath parameter in your engine command. Make sure that a ‘Main-Class’ attribute is added to your jar file manifest. This attribute points to the class that implements your program entry point.

Set Up Authentication for Remote APIs

Most of the remote APIs require login information in order to establish a connection to the server. Credentials can be hard-coded into your validation script or passed in on the command line. Alternatively, a .netrc file can be used to hold the credentials necesasry to login to the server. For further information, see: Create a .netrc or _netrc file.

The following sample code can be used to extract credentials from a .netrc file:

private void setCredentials(String host) throws IOException
{
NetrcFileParser parser = new NetrcFileParser();
NetrcFileParser.NetrcEntry entry = parser.getEntry(host);

if (null != entry)
{
_email = entry.getLogin();
_password = entry.getPassword();
}
}

Associate the Validator with an Assay Instance

Finally, the QC validator must be attached to an assay. To do this, you will need to editing the assay design and specify the absolute location of the .jar file you have created. The engine created earlier will bind the .jar extension to the java.exe command you have configured.

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