Use SpEL with Application Accelerator

This topic tells you about some common Spring Expression Language (SpEL) use cases in Application Accelerator.

For more information, see Spring Expression Language documentation.

Variables

You can reference all the values added as options in the accelerator section from the YAML file as variables in the engine section of accelerator.axl. You can access the value using the syntax #OPTION-NAME.

Example accelerator.yaml:

options:
  - name: foo
    dataType: string
    inputType: text
...

Example accelerator.axl:

engine {
  Include({"some/file.txt"})
  ReplaceText(substitutions: {{text: 'bar', with: #foo}})
}

This sample replaces every occurrence of the text bar in the file some/file.txt with the contents of the foo option.

Implicit variables

Some variables are made available to the model by the engine, including:

• artifactId is a built-in value derived from the projectName passed in from the UI with spaces replaced by “_”. If that value is empty, it is set to app.
• files is a helper object that currently exposes the contentsOf(<path>) method. For more information, see ReplaceText.
• camel2Kebab and other variations of the form xxx2Yyyy is a series of helper functions for dealing with changing case of words. For more information, see ReplaceText.

Conditionals

You can use Boolean options for conditionals in your transformations.

Example accelerator.yaml:

options:
  - name: numbers
    inputType: select
    choices:
    - text: First Option
      value: first
    - text: Seconf Option
      value: second
    defaultValue: first

Example accelerator.axl:

engine {
  if (#numbers == 'first') {
    Include({"some/file.txt"})
    ReplaceText({{text: "bar", with: #foo}})
  }
}

This replaces the text only if the selected option is the first one.

Rewrite path concatenation

String templates are available in Application Accelerator using backticks. These are useful, for example, when using RewritePath.

Example accelerator.yaml:

options:
  - name: renameTo
    dataType: string
    inputType: text
...

Example accelerator.axl:

engine {
  Include({"some/file.txt"})
  RewritePath(rewriteTo: `somewhere/#{#renameTo}.txt`)
}

Regular expressions

Regular expressions allow you to use patterns as a matcher for strings. Here is an example of what you can do with them.

Example accelerator.yaml:

options:
  - name: foo
    dataType: string
    inputType: text
    defaultValue: abcZ123
...

Example accelerator.axl:

engine {
  if (#foo.matches('[a-z]+Z\d+')) {
    Include({"some/file.txt"})
    ReplaceText({{text: "bar", with: #foo}})
  }
}

This example uses RegEx to match a string of letters that ends with a capital Z and any number of digits. If this condition is fulfilled, the text is replaced in the file, file.txt.

Dealing with string arrays

Options with a dataType of [string] come out as an array of strings.

To use them and, for example, format the result as a bulleted list, you can use the Java static String.join() method.

Example accelerator.yaml:

accelerator:
  options:
    - name: meals
      dataType: [string]
      inputType: checkbox
      choices:
        - value: fish
        - value: chips
        - value: BLT
...

Example accelerator.axl:

engine {
  ReplaceText({{text: recipe, with: ' * ' + T(java.lang.String).join('\n * ', #meals)  }})
}