User Defined Java Expression

If you have a Java expression like :

Then you can simply enter the right side of the expression in the dialog:

The values are exposed to the expressions as the Java objects they are :

All fields of this transform support metadata injection. You can use this transform with ETL Metadata Injection to pass metadata to your pipeline at runtime.

Add 2 integers, A and B

Concatenate 2 Strings : firstname and name and put a space in between

or if you really care about performance, this might be faster:

Use native Java and API functions

Business rules (If / Then / Else)

This can be more complicated

even with OR and AND and other operators and functions

Using Constants

If you use a constant, you may need to define the right type in some expressions otherwise it could throw an error. Eg if you use "0" that is "int" but Apache Hop "Integer" is "java.lang.Long", so you’ll get an exception:

Incompatible expression types "int" and "java.lang.Long"

To solve this, use:

The above expression checks if "test" is null and replaces it with a zero Long. Otherwise, it return "test" unchanged.

Cut a string from end and test for null and minimal length

Imagine you have input strings "location" like

and you want to separate the state and city. You could use the following expressions:

For state (get the last 2 characters):

For city (get the beginning without the last 2 characters and trim):

Functionality of a LIKE operator (contains string)

The following example returns 1 when abc is within the source string, otherwise 2. It returns also 2 when the source string is null. If you prefer the return values to be of value type Integer, use "new Long(1)" and "new Long(2)".