hop-user-manual/modules/ROOT/pages/plugins/transforms/janino.adoc

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= User Defined Java Expression

== Description

This transform allows you to enter User Defined Java Expressions as a basis for the calculation of new values.

If you have a Java expression like :
[source,java]
----
C=A+B
----

Then you can simply enter the right side of the expression in the dialog:
[source,java]
----
A+B
----

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

[width="90%", options="header"]
|===
|Data type|Java Class
|BigNumber|BigDecimal
|Binary|byte[]
|Date|java.util.Date
|Integer|java.lang.Long
|Number|java.lang.Double
|String|java.lang.String 
|===

== Options

[width="90%", options="header"]
|===
|Option|Description
|New Field|The new field in the data stream. If you want to overwrite an existing field, you need to define the field here and in the "Replace value" option.
|Java Expression|The Java Expression, see examples below.
|Value Type|Type
|Length|Length
|Precision|Precision
|Replace value|Select this identical to the "New field" name when you want to replace
|===

== Metadata Injection Support

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.

== Examples

**Add 2 integers, A and B**

[source,java]
----
A+B
----

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

[source,java]
----
firstname+" "+name
----

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

[source,java]
----
new StringBuffer(firstname).append(" ").append(name).toString()
----

**Use native Java and API functions**

[source,java]
----
System.getProperty("os.name")
----

**Business rules (If / Then / Else)**

[source,java]
----
a<c?true:false
----

This can be more complicated

[source,java]
----
a<c?(a==1?1:2):3
----

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:

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

To solve this, use:

[source,java]
----
test == null ? new Long(0) : test
----

In this case, it checks if test is null and replaces with zero. If it is not null, it will return test.

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

Imagine you have input strings with

    Orlando FL
    New York NY

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

For state (get the last 2 characters):

[source,java]
----
location != null && location.length()>2 ? location.substring(location.length()-2, location.length()) : null
----

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

[source,java]
----
location != null && location.length()>2 ? location.substring(0, location.length()-2).trim() : location
----

**Functionality of a LIKE operator (contains string)  and replacing values**

The following example returns 1 when abc is within the source string, otherwise 2. It returns also 2 when the source string is null. The return values could be of value type Integer.

[source,java]
----
samplestr !=null && samplestr.indexOf("abc")>-1 ? 1 : 2
----