Scout/Tutorial/3.8/Jython Integration

Introduction

With Release 3.8 the Scout SDK offers support to integrate external JAR files into a Scout application with a few clicks. In this tutorial we use this capability to demonstrate how Jython may be integrated in your Scout application.

According to the Wiki "Jython is a Java implementation of Python" and Python itself claims "You can learn to use Python and see almost immediate gains in productivity and lower maintenance costs." In any case, we need an example library here and combining Java with a powerful scripting language can help to solve a significant variety of problems.

The result at the end of this tutorial will look similar to the screenshot below:

Building the Jythonlib.jar

For this example we need the jython.jar library extended with the set of the Python standard modules typically provided in the Lib folder. After downloading jython from the official download page and installing it to some arbitrary directory you should find therer the following to items:

• jython.jar
• Lib

Now, we are ready to build our jythonlib.jar according to the description provided in the jython Wiki (in case the description moves to some other location it is repeated below):

To build our jar, we first make a copy of jython.jar, then add the contents of the Lib/ directory (eg Lib/re.py) to it::

   $ cd $JYTHON_HOME
   $ cp jython.jar jythonlib.jar
   $ zip -r jythonlib.jar Lib

Create New Scout Project and add the Library bundle

Create a new Scout project as described in the Hello World tutorial with the follwing differences:

• Use org.eclipse.scout.jythontest as the project name.
• Don't (yet) add any form fields

Once the application model is shown in the Scout Explorer we can add the library bundle. To keep things as simple as possible this example we directly use the jython library in the client application. For this, select folder libraries below the orange client node in the Scout explorer. Then, right-click on context menu New Library Bundle ...

In the first dialog of the New Library Bundle wizard click on the Add button to select the jythonlib.jar file that we created above (in this step, one or several libraries may be assinged to a new bundle). That's it, we can now click on Finish. The curious reader can click on Next to see the second dialog of the wizard. For this tutorial all the filled in default values make sense and don't need to be changed, so please click Finish now.

Behind the scenes the Scout SDK wizard has created the plugin org.eclipse.scout.jython.jythonlib and added it as a required dependency on the client plugin org.eclipse.scout.jython.client with the result that from within the Java client code we can now access all elements in our jythonlib.jar as if it were part of the client bundle.

Add and Configure the Form Fields on the Desktop Form

• main box, new form field
  • type=group box, [next>]
  • class name=DesktopBox, [finish]

inside of desktop box

• new form field: type=string, [next>],
  • name=Line, double click on "New Translated Text ..." in dropdown field
  • add desired tranlsations, close translation dialog with [Ok]
  • close New String field with [Finish]
• new form field, type=String, Name="Python", add translations as above
• new form field, type=Sequence Box, Class Name=VariablesBox
• new form field, type=String, Name="Result", add translations as above

inside variables box

• new form field: type=String, Name="Input"
• new form field: type=String, Name="Output"
• new form field: type=Button, Name="Run"

configure main box

• properties: grid column count=1

configure python field

• grid h=5
• multiline text=selected
• advanced properties
  • tooltip text, insert the following ("to indicate how the User has to enter the Python script into this field")

tok = input.split() out = [] i = 0

for t in tok:

 i+=1
 out.append("[%i] %s" % (i,t))

output = '\n'.join(out)

• • background color=E1EAFF (or use color picker)
  • font=courier new

configure result field

• grid h =3
• multiline text=selected

Add Logic for Jython Interpreter and Interaction with Scout Form

1. In the Scout Explorer select the RunButton element of the DesktopForm
2. In the Scout Object Properties click on the green plus-icon next to the link Exec Click Action to add the corresponding method
3. Replace the proposed implementation with the code provided below

 @Override
 protected void execClickAction() throws ProcessingException {
   getResultField().clearErrorStatus();
   try {
     // make sure Lib is visible to access python modules
     PySystemState sys = Py.getSystemState();
     PyString pyLibPath = new PyString("__pyclasspath__/Lib");
     
     if (!sys.path.contains(pyLibPath)) {
       sys.path.append(pyLibPath);
     }
     
     // get interpreter, read input variable from input field
     PythonInterpreter pi = new PythonInterpreter();
     pi.set(getInputField().getValue(), new PyString(getLineField().getValue()));
     
     // run script, transfer output to result field
     pi.exec(getPythonField().getValue());
     getResultField().setValue(pi.get(getOutputField().getValue()).asString());
   }
   catch (Exception e) {
     getResultField().setValue(null);
     getResultField().setErrorStatus(e.toString());
   }
 }

Remarks:

• Updating the sys.path should conceptually go to a place where it's calles once per client startup.
• There might be more elegant ways to ensure Jython is able to access the Python modules provided in the Lib subfolder of the jythonlib.jar.

Play around

In the Scout SDK do the following

1. Select top level element org.eclipse.scout.jythontest in the Scout Explorer
2. Start the server by clicking on the corresponding icon in the server box of the section Product Launchers
3. Start a client by clicking on acorresponding icon in a client box (Swing, SWT, or RAP)
4. The client starts and the desktop form is shown

In the Application do the following

1. Enter some text into the Line field. For example hello world
2. Enter a python script into the Python field. Example script:

 import re
 
 tok = input_line.split()
 out = []
 i = 0
 
 for t in tok:
   i+=1
   if re.search(t, "hello", re.I):
     out.append("[%i] %s -- HELLO FOUND" % (i,t))
   else:
     out.append("[%i] %s" % (i,t))
 
 output_text = '\n'.join(out)

Add the Binding Names for Input and Output

1. In field Input specify the Python variable representing the text in the Line field. For the example above, use input_line
2. In field Output specify the Python variable holding the output of the Python script. For the example above, use output_text
3. Click on Run. The content of the output variable defined above is transferred to the form field Result