Load a snapshot and add a pillar

This page comes from Java-TourOptimizer-Examples, last changed in commit 4cfefdb.

This example loads a saved optimization state from myopti.json.bz2 and adds one pillar node (a fixed appointment) to it before the next run. It shows how a planned state can take a new appointment with a strict time window without rebuilding the model: the pillar Koeln-Pillar goes into the loaded solution through addReassignNodes. The page is for developers who add fixed appointments to a plan that is already optimized. The snapshot comes from SaveOptimizationToJsonExample, which Load and save optimization snapshots describes; run it first.

What the example shows

  • Load: the importer reads the nodes, the resources, the properties and the solution of the snapshot into the optimization. The next run starts from the loaded solution.
  • Reassign: addReassignNodes(...) hands the pillar to the loaded optimization, so the next run plans it together with the elements from the snapshot. Unlike addElement, it puts the pillar into the loaded solution.
  • Pillar: a pillar is a fixed appointment: its time window must be met.

Scenario

The dates, times and coordinates are sample values.

  • The snapshot: SaveOptimizationToJsonExample writes the two resources Jack and John, who start in Aachen, and eight TimeWindowGeoNode objects for March 6 and 7, 2020 (Europe/Berlin), together with the solution of its run.
  • The added pillar: one PillarTimeWindowGeoNode:
    • id: Koeln-Pillar
    • position: 50.9333, 6.95 (the coordinates the other examples use for Koeln)
    • opening hours: March 7, 2020, 08:00 to 17:00 (Europe/Berlin)
    • visit duration: 20 minutes

The code does not attach the pillar to a resource (there is no attachResource(...) call, unlike in PillarExample).

The next run sets two properties: JOptExitCondition.JOptGenerationCount to 2000 and JOpt.Algorithm.PreOptimization.SA.NumIterations to 100000. Both are below their defaults, which keeps the run short; the defaults are in the property reference.

How the code works

The source is LoadOptimizationFromJsonAndReassignPillar.java. example() does the following:

ExampleLicenseHelper.setLicense(this);
if (!loadFromJson(this)) {
  return;
}
addReassignPillar(this);
// The snapshot brings its own properties, and addElement(Properties) replaces them. The
// properties of the new run are therefore added after the load.
addProperties(this);
attachToObservables(this);
startAndPresentResult(this);
  1. Sets the license: your license file if you put one where ExampleLicenseHelper looks for it, the public evaluation license otherwise.
  2. Loads the snapshot. If that fails, example() returns without a run.
  3. Adds the pillar through reassignment.
  4. Sets the properties of the next run, after the load (see the comment in the code).
  5. Subscribes to the progress, warning, status and error events with the recommended event API, before the run starts.
  6. Starts the run, waits up to 5 minutes for the result and prints it.

Loading the snapshot

The file name is a constant of the class:

private static final String JSON_FILE = "myopti.json.bz2";

loadFromJson reads it:

IOptimizationImporter importer = new OptimizationJSONImporter();
try (InputStream in = new FileInputStream(JSON_FILE)) {
  boolean loaded = importer.update(in, opti);
  if (!loaded) {
    System.out.println("JSON import failed: " + JSON_FILE);
  }
  return loaded;
} catch (FileNotFoundException e) {
  System.out.println(JSON_FILE + " not found. Run SaveOptimizationToJsonExample first.");
  return false;
}

update returns false if it cannot read the snapshot; the example then prints JSON import failed: myopti.json.bz2. The try-with-resources block closes the file in every case.

Adding the pillar

IPillarNode koelnPillar =
    new PillarTimeWindowGeoNode("Koeln-Pillar", 50.9333, 6.95, openingHours, visitDuration);

// Unlike addElement, addReassignNodes puts the pillar into the loaded solution.
opti.addReassignNodes(List.of(koelnPillar));

Output and what to look for

The status lines show that the run starts from the loaded solution and reassigns the pillar. These two lines appear in two test runs:

StatusEvent(OPTIMIZATION_USING_PROVIDED_SOLUTION, Using a provided solution as starting point for the optimization.)
StatusEvent(ADDITIONAL_ELEMENT, Adding additional elements to be reassigned to optimization. Reassigning Nodes: Koeln-Pillar)

The run starts with the simulated annealing step; no construction algorithm starts, because the loaded solution is the starting point.

In the result, the line of Koeln-Pillar is marked Pillar. It lies on a route of March 7, inside its time window, directly after the nodes Koeln and Koeln1, which have the same coordinates (Driving: 0.0 [min], 0.0 [km]). Which resource takes the pillar and the cost of the result can change between runs.

If myopti.json.bz2 is missing, loadFromJson prints myopti.json.bz2 not found. Run SaveOptimizationToJsonExample first. and the example starts no run.

Run it

The example reads myopti.json.bz2 from the working directory. Run SaveOptimizationToJsonExample first, in the same working directory; it writes that file at the end of its run.

  1. Run the main(String[] args) method of SaveOptimizationToJsonExample.
  2. Run the main(String[] args) method of LoadOptimizationFromJsonAndReassignPillar in the same working directory.

You need a JDK in the version that the examples pom sets. You need no license file: without one, both examples use the public evaluation license (see the license guide).

Related

Added: 2026-10-15 (JOpt core 7.5.3-rc5-j17) | Last updated: 2026-10-20

Load and save optimization snapshots

This page comes from Java-TourOptimizer-Examples, last changed in commit 4734793.

Pillar nodes with hard time windows

This page comes from Java-TourOptimizer-Examples, last changed in commit 38a6a99.