# User Defined Java Class You can use the User Defined Java Class step to provide a custom Java class that drives the behavior of the step. This step is not intended for full-scale Java plugin development. Instead, it lets you define Java methods and logic directly in the transformation. The step uses the [Janino](https://janino-compiler.github.io/janino/apidocs/) libraries to compile Java code at runtime. ### How the step compiles your code Janino (and this step) does not require a full Java class declaration. You provide the class body (for example, imports, constructors, and methods). Your main code lives in the **Processor** tab, which defines the `processRow()` method. The following imports are available in the Processor code by default: * `org.pentaho.di.trans.steps.userdefinedjavaclass.*` * `org.pentaho.di.trans.step.*` * `org.pentaho.di.core.row.*` * `org.pentaho.di.core.*` * `org.pentaho.di.core.exception.*` If you add additional class code tabs, those default Processor imports do not automatically apply. If you need other imports, add them at the top of your Processor code, for example: ```java import java.util.*; ``` Janino supports a subset of the Java 1.8.x specification. For details, see the [Janino homepage](http://janino-compiler.github.io/janino/). ### General ![User Defined Java Class step](https://773338310-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FYwnJ6Fexn4LZwKRHghPK%2Fuploads%2Fgit-blob-95a4d4af64a6f20a86cb41eb5deb58850177893b%2FPDITransStep_UserDefinedJavaClass_PropertiesDialogBox.png?alt=media) * **Step name**: Specify the unique name of the step on the canvas. You can customize the name or leave it as the default. Use the **Class code** panel and option tabs to define your class. Select **Test class** to validate the class. ### Class code panel ![Class code panel](https://773338310-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FYwnJ6Fexn4LZwKRHghPK%2Fuploads%2Fgit-blob-4a69340617a11cd8d8dfd5216dc808b737e06ee2%2FPDITransStep_UserDefinedJavaClass_ClassCode.png?alt=media) Add your Java code in the **Processor** tab. You can add additional tabs by right-clicking and selecting **Add new**. ### Processor (processRow) The Processor defines the `processRow()` method. The transformation calls this method repeatedly until it returns `false`. {% hint style="info" %} Call `getRow()` before the first `get(Fields.In, FIELD_NAME)` call. This helps avoid unexpected field-order issues (for example, with Mapping Input Specification). {% endhint %} Example Processor code (concatenate first name and last name): ```java String firstnameField; String lastnameField; String nameField; public boolean processRow(StepMetaInterface smi, StepDataInterface sdi) throws KettleException { // Let's look up parameters only once for performance reason. // if (first) { firstnameField = getParameter("FIRSTNAME_FIELD"); lastnameField = getParameter("LASTNAME_FIELD"); nameField = getParameter("NAME_FIELD"); first=false; } // First, get a row from the default input hop // Object[] r = getRow(); // If the row object is null, we are done processing. // if (r == null) { setOutputDone(); return false; } // Ensure output row is large enough for new fields. // Object[] outputRow = createOutputRow(r, data.outputRowMeta.size()); String firstname = get(Fields.In, firstnameField).getString(r); String lastname = get(Fields.In, lastnameField).getString(r); // Set the value in the output field // String name = firstname+" "+lastname; get(Fields.Out, nameField).setValue(outputRow, name); // Send the row to the next step // putRow(data.outputRowMeta, outputRow); return true; } ``` ### Error handling To route errors to an error hop: 1. Right-click the step on the canvas. 2. Select **Error handling**. 3. Configure the target step and field names. Example (from `User Defined Java Class – Lambda Examples.ktr`): ```java try { Object numList = strsList.stream() .map( new ToInteger() ) .sorted( new ReverseCase() ) .collect( Collectors.toList() ); get( Fields.Out, "reverseOrder" ).setValue( row, numList.toString() ); } catch (NumberFormatException ex) { // Number List contains a value that cannot be converteds to an Integer. rowInError = true; errMsg = ex.getMessage(); errCnt = errCnt + 1; } if ( !rowInError ) { putRow( data.outputRowMeta, row ); } else { // Output errors to the error hop. Right click on step and choose "Error Handling..." putError(data.outputRowMeta, row, errCnt, errMsg, "Not allowed", "DEC_0"); } ``` ### Logging If you want PDI to log actions from your code, add logging logic. Example: ```java putRow( data.outputMeta, r ); if ( checkFeedback( getLinesOutput() ) ) { if ( log.isBasic() ) { logBasic( "Have I got rows for you! " + getLinesOutput() ); } } ``` ### Classes and code fragments panel ![Classes and code fragments panel](https://773338310-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FYwnJ6Fexn4LZwKRHghPK%2Fuploads%2Fgit-blob-8a2313297fe99308bb38417840987d5a22d82121%2FPDITransStep_UserDefinedJavaClass_ClassesAndCodeFragments.png?alt=media) Use the **Classes and Code Fragments** panel to navigate your class code and related snippets. * **Classes**: Shows which classes have corresponding code tabs. * **Code snippets**: Shows internal PDI reference snippets. * **Input fields** / **Info fields** / **Output fields**: Shows fields referenced or defined by your code. Example: get input row metadata: ```java RowMetaInterface inputRowMeta = getInputRowMeta(); ``` For more details about PDI row data, see [PDI Rows Of Data](https://wiki.pentaho.com/display/EAI/PDI+Rows+Of+Data). ### Fields tab ![Fields tab](https://773338310-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FYwnJ6Fexn4LZwKRHghPK%2Fuploads%2Fgit-blob-ab044990455f170197cb34c56627d5e70b766090%2FPDITransStep_UserDefinedJavaClass_FieldsTab.png?alt=media) Use the **Fields** table to define output fields passed to downstream steps. Fields you define appear under **Output fields** in the **Classes and Code Fragments** panel. ### Parameters tab ![Parameters tab](https://773338310-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FYwnJ6Fexn4LZwKRHghPK%2Fuploads%2Fgit-blob-a8a7a4e34e2f7d0b6d3c738158b50702dc6a1d4b%2FPDITransStep_UserDefinedJavaClass_ParametersTab.png?alt=media) Use the **Parameters** table to avoid hard-coded strings (for example, field names). Example: ``` getParameter("YEAR") ``` #### Class member variables and getVariable If you call `getVariable()` in the `init()` method, variables resolve as expected. If you call it in a class member initializer, it does not resolve by design. Example: ```java private final String par = getVariable("somePar"); // DOES NOT resolve correctly private String par2 = null; public boolean processRow(StepMetaInterface smi, StepDataInterface sdi) throws KettleException { logBasic("Parameter value="+par+"[MEMBER INIT]"); logBasic("Parameter value="+par2+"[INIT FUNCTION]"); setOutputDone(); return false; } public boolean init(StepMetaInterface stepMetaInterface, StepDataInterface stepDataInterface) { par2 = getVariable("somePar"); // WORKS FINE return parent.initImpl(stepMetaInterface, stepDataInterface); } ``` ### Info steps tab ![Info steps tab](https://773338310-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FYwnJ6Fexn4LZwKRHghPK%2Fuploads%2Fgit-blob-1903cfacbea153ee808e54387d9eace50ea8c1e4%2FPDITransStep_UserDefinedJavaClass_InfoStepsTab.png?alt=media) Because `getRow()` returns the first row from any input stream (input or info), configure **Info steps** when input and info row metadata differ. Read info rows before calling `getRow()`. Example: ```java if (first){ first = false; /* TODO: Your code here. (Using info fields) FieldHelper infoField = get(Fields.Info, "info_field_name"); RowSet infoStream = findInfoRowSet("info_stream_tag"); Object[] infoRow = null; int infoRowCount = 0; // Read all rows from info step before calling getRow() method. while((infoRow = getRowFrom(infoStream)) != null){ // do something with info data infoRowCount++; } */ } Object[] r = getRow(); if (r == null) { setOutputDone(); return false; } ``` ### Target steps tab ![Target steps tab](https://773338310-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FYwnJ6Fexn4LZwKRHghPK%2Fuploads%2Fgit-blob-4aeebc797b2d02460700fbf115fa0a1224785f9a%2FPDITransStep_UserDefinedJavaClass_TargetStepsTab.png?alt=media) Use the **Target steps** table to route step output to specific steps in your transformation. ### Examples The `data-integration/samples/transformations` directory contains these examples: * `User Defined Java Class - Calculate the date of Easter.ktr` * `User Defined Java Class - Concatenate firstname and lastname.ktr` * `User Defined Java Class - Query the database catalog.ktr` * `User Defined Java Class - Real-time search on Twitter.ktr` * `User Defined Java Class - LambdaExamples.ktr` We recommend starting with `User Defined Java Class - Calculate the date of Easter.ktr`. ### Metadata injection support All fields of this step support metadata injection. 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