Extend Your Application with Custom Java

Last update: Edit

1 Introduction

Most application logic can be developed using microflows. Microflows are very powerful and contain a lot of the features that you need in every application. To prevent you from getting stuck due to a missing feature, Mendix microflows are extendable. So, whenever you feel something is missing, you can add it yourself with the use of Java actions.

This how-to will teach you how to do the following:

  • Extend your application with custom Java code

2 Prerequisites

Before starting this how-to, make sure you have completed the following prerequisite:

  • Have Eclipse installed (download it here)
  • Have an app ready using the Asset Management template.

3 Adding a Java Action in Studio Pro

  1. Right-click the AssetManager module and select Add other > Java action.
  2. Enter ReverseAssetName for the Name of the new Java action and click OK.
  3. In the Java Action wizard, click Add to add a parameter and do the following:

    1. Enter inputAssets for the Name of the new parameter.
    2. Select Object for the Type.
    3. Click Select for Entity and select AssetManager.Asset as the object type.
    4. Click OK.

  4. Back on the Java Action wizard, change the Return type of the Java action to String and click OK to save the Java action.

  5. Select App > Deploy for Eclipse from the top Studio Pro toolbar.

4 Editing the Java Action in Eclipse

To edit the Java action in Eclipse, follow these steps:

  1. Open Eclipse, right-click in the Package Explorer window, and select Import.

  2. In the Import window, select Existing Projects into Workspace and click Next.

  3. Set the app directory as the root directory for this app and click Finish.

  4. Double-click ReverseAssetName.java in the Package Explorer of Eclipse.

    In the Java code, there is a placeholder marked with //BEGIN USER CODE and //END USER CODE comment statements. This is where you can add your own Java code. Studio Pro will never overwrite the code between those two statements.

        public java.lang.String executeAction() throws Exception
            this.inputAssets = __inputAssets == null ? null : assetmanager.proxies.Asset.initialize(getContext(), __inputAssets);
            // BEGIN USER CODE
            throw new com.mendix.systemideinterfaces.MendixRuntimeException("Java action was not implemented");
            // END USER CODE

    Studio Pro generates a variable for inputAssets. You can use that variable to get the name of the asset and reverse it.

  5. Replace the existing line:

        throw new com.mendix.systemideinterfaces.MendixRuntimeException("Java action was not implemented");

    between //BEGIN USER CODE and //END USER CODE, with the code:

    String assetsAssetName = this.inputAssets.getAssetName(this.getContext());
    return new StringBuilder(assetsAssetName).reverse().toString();
  6. Select File > Save to save the Java action in Eclipse.

5 Calling the Java Action from a Microflow

  1. Back in Studio Pro, locate the Home page via App Explorer.

  2. Under {AssetName}, right-click and select Add widget.

  3. In the Select widget dialog box that appears, select Button widgets > Call microflow button.

  4. In the Select Microflow dialog box, click New to create a new microflow.

  5. Enter ReverseName for the Name of the new microflow and click OK.

  6. Right-click the Reverse name button you just created and select Go to on click microflow to open the new microflow.

  7. Drag the ReverseAssetName Java action from the App Explorer onto the line between the green start event and red end event. This generates a Java action activity.

  8. Double-click the generated activity to open the Call Java Action properties editor, and then click Edit for the first input to open the argument editor.

  9. Press and hold the Ctrl key and then press the spacebar to open the code completion editor.

  10. Select $Asset (AssetManager.Asset).

  11. Click OK to save the expression.

  12. In the Call Java Action properties editor, change the output Variable to ReversedName.

  13. Click OK to save the properties. The microflow should now look like this:

  14. From the Toolbox (select View > Toolbox to open it, if necessary), drag a Show message activity into the microflow.

  15. Double-click the activity to open the Show Message properties editor and enter Reversed name: {1} for Template.

  16. In the Parameters section, click New to open the expression editor.

  17. Select $ReversedName (String), which is the output variable of the Java action.

  18. Click OK to save the parameter. The Show Message properties should now look like this:

  19. Click OK to save the show message activity. The microflow should now look like this:

6 Deploying & Seeing the Results

  1. Click the play button (Run Locally) to deploy the application locally and click View App to open the application in your browser.

  2. Select Add asset from the top right.

  3. In the new window input Asset to Reverse in the Name field.

  4. Select Save.

  5. Select the new asset from the app’s Dashboard.

  6. On the Home page, click Reverse name for the newly created asset:

  7. The reversed name of the asset appears in a dialog box.

7 Troubleshooting

If you get an UnsupportedClassVersionError when running your app, follow these steps:

  1. Clean your app’s deployment folder by selecting App > Clean Deployment Directory.

  2. Add the same JDK version to Eclipse as that which you are using in Studio Pro (this is the recommended version correlation). For details on JDK requirements, see the Mendix Studio Pro section of System Requirements.

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