This guide will show you how to create a custom Java class, compile/package it into a JAR, include it in Mirth Connect, and invoke it in JavaScript. Your custom code can be invoked from any JavaScript context, including the global/channel scripts, filters/transformers, and JavaScript connectors.

• A working development environment, including the JDK (Java Development Kit). Generally you should use the same version of Java that your Mirth Connect server is using.
• You can look here to see how to set up Eclipse to checkout and develop Mirth Connect, but it's an optional step. For this example we'll just use a single .java file and a command-line terminal.

First create the class(es) you want to invoke from Mirth Connect. You may import internal Mirth Connect packages if you need to extend some class or implement some interface (see here for an example of extending AcceptMessage for a custom Web Service Listener), but you certainly don't need to. This example will just use a simple POJO called JarTest.java:

package com.example;
 
public class JarTest {
 
    public String returnSomething() {
        return "Hello, World!";
    }
}

Note that it must have the package name declared. You can implement your code in a single class or using many classes.

Now you need to convert your source code into compiled class files, which will be included in the JAR. In a command-line terminal, navigate to the top-level folder that contains your src and classes folders. Then do this:

javac -d classes -source 8 -target 8 src/com/example/*

If you need to include other libraries in the classpath, use the -cp option. Type javac -help for the full set of options. Official distributions of Mirth Connect currently target Java 8.

Now you should have JarTest.class in the classes/com/example folder, so the next step is to archive it into a JAR file. In the same top-level directory as before, do this:

jar -cf JarTest.jar -C classes com

The -c option means you're creating a new archive, and -f specifies the filename to output with. The -C option changes the working directory before adding files. Finally, the com at the end indicates what files/folders to include in the archive.

You can also compile source files and create a JAR in one step in Eclipse, with the export feature.

You will be able to use the custom class anywhere JavaScript is used. For example, you can create a new channel that uses a JavaScript Writer destination, and use the following code:

var obj = new Packages.com.example.JarTest();
logger.info(obj.returnSomething());

At first this channel won't yet work; we need to include the JAR that we just created.

• In version 3.2 or later you can define custom resources to point to any directory you want. So you can drop the JAR file into the custom-lib folder, or create a new folder anywhere on the server filesystem.
• Restarting Mirth Connect is not required. Instead, in the Administrator navigate to the Settings -> Resources tab.
• Create a new Directory resource if needed. If you're just using the custom-lib folder, and the default resource is pointing to custom-lib (it will by default), then you only need to hit Reload Resource and the JAR will automatically be picked up. Hit the refresh button if the JAR doesn't show up initially. You should now see it in the Loaded Libraries table at the bottom.
• Edit the channel you want to use the resource with, go to the Summary tab, and click the Set Libraries button. Make sure the resource is checked for the context you want to use it in. If you're using the default resource, it should already be checked by default.
• Redeploy the channel if you made any changes to it.

Now that you've included the JAR, send a message through the channel. You should see something like this in the server log:

[2015-05-12 10:45:54,666]  INFO  (js-connector:?): Hello, World!

If you get the error: [JavaPackage com.example.MyTest] is not a function, it is object, this typically means that the JAR file was not loaded properly.

• Check under Settings > Resources that the JAR file appears in the Loaded Libraries list for your directory resource (or the Default Resource). Click "Reload Resource" if necessary.
• Check the Library Resources tab under the Set Dependencies window in the channel configuration. Ensure that the resource that contains your JAR file is enabled for the appropriate channel context.
• Ensure that your JAR file was compiled using the same version of Java you are using to run Mirth Connect.