A domain service for Apache Isis that interpolates strings using OGNL expressions applied to graphs of domain objects.
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This module, intended for use within Apache Isis, provides a mechanism to interpolate string templates with either Isis system properties or values obtained from a domain object.

One use case for this service is in building URLs based on an object's state, parameterized by environment (prod/test/dev etc). These URLs could be anything; for example, to a reporting service:



  • ${property['reportServerBase']} is an Isis system property
  • ${this.property.id} is an expression that is evaluated in the context of a domain object (this), returning this.getProperty().getId()

Isis system properties are exposed as the properties map, while the target object is exposed as the this object.


The screenshots below show an example app's usage of the stringinterpolator module:

Install example fixtures

... returning an example entity:

The Open (contributed) action is:

public URL open(ToDoItem toDoItem) throws MalformedURLException {
    String urlStr = stringInterpolatorService.interpolate(
        toDoItem, "${properties['isis.website']}/${this.documentationPage}");
    return new URL(urlStr);

where WEB-INF/isis.properties contains:


and where (as the screenshot shows) ToDoItem entity has the structure:

public class ToDoItem ... {

    private String description;
    private String documentationPage;

    // getters and setters omitted 

Invoking the Open action computes the urlStr local variable, and then (because the action returns a URL), results in the browser opening the appropriate web page:

How to run the Demo App

The prerequisite software is:

  • Java JDK 8 (>= 1.9.0) or Java JDK 7 (<= 1.8.0) ** note that the compile source and target remains at JDK 7
  • maven 3 (3.2.x is recommended).

To build the demo app:

git clone https://github.com/isisaddons/isis-module-stringinterpolator.git
mvn clean install

To run the demo app:

mvn antrun:run -P self-host

Then log on using user: sven, password: pass

How to configure/use

You can either use this module "out-of-the-box", or you can fork this repo and extend to your own requirements.


To use "out-of-the-box":

  • update your classpath by adding this dependency in your dom project's pom.xml:
  • update your WEB-INF/isis.properties:

Check for later releases by searching Maven Central Repo.

"Out-of-the-box" (-SNAPSHOT)

If you want to use the current -SNAPSHOT, then the steps are the same as above, except:

  • when updating the classpath, specify the appropriate -SNAPSHOT version:
  • add the repository definition to pick up the most recent snapshot (we use the Cloudbees continuous integration service). We suggest defining the repository in a <profile>:

Forking the repo

If instead you want to extend this module's functionality, then we recommend that you fork this repo. The repo is structured as follows:

  • pom.xml // parent pom
  • dom // the module implementation, depends on Isis applib
  • fixture // fixtures, holding a sample domain objects and fixture scripts; depends on dom
  • integtests // integration tests for the module; depends on fixture
  • webapp // demo webapp (see above screenshots); depends on dom and fixture

Only the dom project is released to Maven Central Repo. The versions of the other modules are purposely left at 0.0.1-SNAPSHOT because they are not intended to be released.

API and Usage

The module consists of a single domain service, StringInterpolatorService.

The interpolation replaces each occurrence of ${...} with its interpolated value. The expression in within the braces is interpreted using OGNL.

Object graph interpolation

The main API exposed by this service provides object-graph interpolation:

public class StringInterpolatorService {

    // called by Isis (which passes in all Isis properties)
    public void init(final Map<String,String> properties) { ... }

    // public API
    public String interpolate(Object domainObject, String template) { ... }

Using this API makes domainObject available as this in the template.

For example, assuming an instance of the Customer class, that in turn has relationships to the Address class:

class Customer {
    private String firstName;
    private String lastName;
    private Address address;
    private Address billingAddress;
    // getters and setters omitted
class Address {
    private int houseNumber;
    private String town;
    private String postalCode;
    // getters and setters omitted

then the following are valid expressions:

  • ${this.firstName}
  • ${this.lastName != null? this.lastName : ''}
  • ${this.address.houseNumber}

Object graph interpolation (using the lower-level API)

The service also offers a lower-level API which allows multiple objects to be made accessible from the context:

public class StringInterpolatorService {

    public static class Root {
        public Root(final Object context) {
            this._this = context;
        public Object getThis() { return _this; }

    // public API
    public String interpolate(Root root, String template) { ... }

The Root class can be extended as necessary.

For example, create a custom subclass of the Root class:

final class CustomRoot extends StringInterpolatorService.Root {
    private Customer customer;
    public CustomRoot(Object context, Customer customer) {
        this.customer = customer;
    public Customer getCustomer() {
        return customer;

The example above exposes the customer property. This can then be used in the template, eg:

public void simple() throws Exception {
    String interpolated = service.interpolate(
        new CustomRoot(null, customer), "${customer.firstName}");
    assertThat(interpolated, is("Fred"));

Strict Mode (applies to both APIs)

By default, any expression that cannot be parsed or would generate an exception (eg null pointer exception) is instead returned unchanged in the interpolated string.

The service also provides a "strict" mode, which is useful for testing expressions:

StringInterpolatorService service = new StringInterpolatorService().withStrict(true);

If enabled, then an exception is thrown instead.

Related Modules/Services

Other modules can be found at the Isis Add-ons website.

Change Log

  • 1.13.0 - released against Isis 1.13.0
  • 1.12.0 - released against Isis 1.12.0
  • 1.11.0 - released against Isis 1.11.0
  • 1.10.0 - released against Isis 1.10.0
  • 1.9.0 - released against Isis 1.9.0
  • 1.8.0 - released against Isis 1.8.0
  • 1.7.0 - released against Isis 1.7.0
  • 1.6.0 - re-released as part of isisaddons, with classes under package org.isisaddons.module.stringinterpolator

Legal Stuff


Copyright 2014~2016 Dan Haywood

Licensed under the Apache License, Version 2.0 (the
"License"); you may not use this file except in compliance
with the License.  You may obtain a copy of the License at


Unless required by applicable law or agreed to in writing,
software distributed under the License is distributed on an
KIND, either express or implied.  See the License for the
specific language governing permissions and limitations
under the License.


In addition to Apache Isis, this module depends on:

  • ognl:ognl (ASL v2.0 License)

Maven deploy notes

Only the dom module is deployed, and is done so using Sonatype's OSS support (see user guide).

Release to Sonatype's Snapshot Repo

To deploy a snapshot, use:

pushd dom
mvn clean deploy

The artifacts should be available in Sonatype's Snapshot Repo.

Release an Interim Build

If you have commit access to this project (or a fork of your own) then you can create interim releases using the interim-release.sh script.

The idea is that this will - in a new branch - update the dom/pom.xml with a timestamped version (eg It then pushes the branch (and a tag) to the specified remote.

A CI server such as Jenkins can monitor the branches matching the wildcard origin/interim/* and create a build. These artifacts can then be published to a snapshot repository.

For example:

sh interim-release.sh 1.14.0 origin


  • 1.14.0 is the base release
  • origin is the name of the remote to which you have permissions to write to.

Release to Maven Central

The release.sh script automates the release process. It performs the following:

  • performs a sanity check (mvn clean install -o) that everything builds ok
  • bumps the pom.xml to a specified release version, and tag
  • performs a double check (mvn clean install -o) that everything still builds ok
  • releases the code using mvn clean deploy
  • bumps the pom.xml to a specified release version

For example:

sh release.sh 1.13.0 \
              1.14.0-SNAPSHOT \
              dan@haywood-associates.co.uk \
              "this is not really my passphrase"


  • $1 is the release version
  • $2 is the snapshot version
  • $3 is the email of the secret key (~/.gnupg/secring.gpg) to use for signing
  • $4 is the corresponding passphrase for that secret key.

Other ways of specifying the key and passphrase are available, see the pgp-maven-plugin's documentation).

If the script completes successfully, then push changes:

git push origin master
git push origin 1.13.0

If the script fails to complete, then identify the cause, perform a git reset --hard to start over and fix the issue before trying again. Note that in the dom's pom.xml the nexus-staging-maven-plugin has the autoReleaseAfterClose setting set to true (to automatically stage, close and the release the repo). You may want to set this to false if debugging an issue.

According to Sonatype's guide, it takes about 10 minutes to sync, but up to 2 hours to update search.