User:Robertwenzel/LongOperations

Author
Robert Wenzel, Engineer, Potix Corporation

Date
January XX, 2015

Version
ZK 7.0.4

Introduction

Longoperations are useful - bla - leverage Java Threads - bla - here how to hide and reuse the technical details. support MVVM and MVC programming model

Long Operations de-mystified

A very Simple Example

This simple example shows a very simple use case of the LongOperation class. The operation creates a simple result which is added to the resultModel when it finishes. During the 3 seconds the default busy overlay is displayed, asking the user to wait.

public class SimpleLongOperationViewModel {
	private ListModelList<String> resultModel = new ListModelList<String>();

	@Command
	public void startLongOperation() {
		LongOperation longOperation = new LongOperation() {
			private List<String> result;

			@Override
			protected void execute() throws InterruptedException {
				Thread.sleep(3000); //simulate a long backend operation
				result = Arrays.asList("aaa", "bbb", "ccc");
			}

			protected void onFinish() {
				resultModel.addAll(result);
			};

			@Override
			protected void onCleanup() {
				Clients.clearBusy();
			}
		};

		Clients.showBusy("Result coming in 3 seconds, please wait!");
		longOperation.start();
	}

	public ListModelList<String> getResultModel() {
		return resultModel;
	}
}

• Line 10: Implement the execute callback to collecting the result asynchrously
• Line 15: Implement the onFinish callback to update the UI once the operation has finished successfully
• Line 26: Launch the operation

In the 'startLongOperation'-command handler the "busy"-overlay is shown. In onCancel it is cleared, however the long operation terminates (successful or not).

Here the straight forward zul code using this SimpleLongOperationViewModel and posting the startLongOperation-command

    <div apply="org.zkoss.bind.BindComposer" 
    	 viewModel="@id('vm') @init('zk.example.longoperations.example.SimpleLongOperationViewModel')">
        <button onClick="@command('startLongOperation')" label="start"/>
        <grid model="@load(vm.resultModel)" height="300px"/>
    </div>

Updating the UI during the Operation

To update the UI during a long operation the desktop needs to be activated for UI updates. For this the methods activate() and deactivate() can be used as in the example below. It is advisable to activate the UI as short as possible for the UI to remain responsive.

	private static final String IDLE = "idle";
	private String status = IDLE;

...

	@Command
	public void startLongOperation() {
		LongOperation longOperation = new LongOperation() {
			private List<String> result;

			@Override
			protected void execute() throws InterruptedException {
				step("Validating Parameters...", 10, 500);
				step("Fetching Data ...", 40, 1500);
				step("Filtering Data...", 60, 1750);
				step("Updating Model...", 90, 750);
				result = Arrays.asList("aaa", "bbb", "ccc");
			}

			private void step(String message, int progress, int duration) throws InterruptedException {
				activate();
				updateStatus(progress+ "% - " + message);
				deactivate();
				Thread.sleep(duration); //simulate processing time for the current step
			}

			@Override
			protected void onFinish() {
				resultModel.addAll(result);
				updateStatus(IDLE);
			}
		};
		longOperation.start();
	}

	private void updateStatus(String update) {
		status = update;
		BindUtils.postNotifyChange(null, null, UpdatingStatusLongOperationViewModel.this, "status");
	}

• Line 21: activate the Thread for UI updates
• Line 23: deactivate the Thread to send the updates back to the browser
• Line 38: notify the change to update the UI

    <div apply="org.zkoss.bind.BindComposer"
    	 viewModel="@id('vm') @init('zk.example.longoperations.example.UpdatingStatusLongOperationViewModel')">
    	<button onClick="@command('startLongOperation')" label="start" 
    	        disabled="@load(vm.status ne 'idle')" autodisable="self" />
    	<label value="@load(vm.status)" />
    	<grid model="@load(vm.resultModel)" height="300px" />
    </div>

• Line 3: The status label to update during the operation

Aborting a Long Operation

Refering to zk.example.longoperations.example.CancellableLongOperationViewModel you can cancel a long operation and give user feedback accordingly.

	private LongOperation currentOperation;

	@Command
	public void startLongOperation() {
		currentOperation = new LongOperation() {
...
			@Override
			protected void onCancel() {
				Clients.showNotification("Now you'll never know... be more patient next time");
			}

			@Override
			protected void onFinish() {
				Clients.showNotification(result);
			}
...
		}
	}

	@Command
	public void cancelOperation() {
		currentOperation.cancel();
	}

Resulting Demo

The video below demonstrates the results of the two advanced usages described above. For ease of demonstration here we use a PDF printer so the resulting screen is a PDF file, but you can definitely specify a real printer to print out the desired results on papers. ERROR: Link hasn't been found

Summary

With the printing utility explained in the article, you can print the desired sections in a ZK page with only little effort -- you can even include custom headers & footers or change the style easily for better readability. For your convenience we have wrapped this utility as a ready-to-use jar file. Refer to download section to download the jar file and put it in your project's WEB-INF/lib folder.

Download

• The source code for this article can be found in github.
• Download the packed jar file from github.

Comments

Copyright © Potix Corporation. This article is licensed under GNU Free Documentation License.