Develop Reference

How to initiate a change event for a TreeModel in Java?

Suppose you got a JTree with a model that implements TreeModel, and all nodes implement TreeNode.
Suppose then that something happens in the background with the model (not through the GUI) like a CRUD-event, that update the model and should update the JTree.
Since the model is CRUD-affected from other views it does not seems like a good idea to use the DefaultTreeModel for this task, correct me if I'm wrong.
I guess you need to signal the change to the TreeModel in somehow, like fire some event in some way?
Btw I have not managed to implement the methods:
public void addTreeModelListener( TreeModelListener l )
public void removeTreeModelListener( TreeModelListener l )
I guess these methods need to be implemented for such a feature.

I like to use this kind of generic ListenerList:
public class ListenerList {
private final List<Object> list = new ArrayList<Object>();
public ListenerList() {
}
public void addListener(Object listener) {
list.add(listener);
}
public void removeListener(Object listener) {
list.remove(listener);
}
public <T> T getNotifier(Class<T> intf) {
ClassLoader cl = intf.getClassLoader();
return intf.cast(Proxy.newProxyInstance(cl, new Class[] {intf},
(Object proxy, Method method, Object[] args)
-> actualInvoke(method, args)));
}
private Object actualInvoke(Method method, Object args[]) {
Object result = null;
for (Object listener: list) {
try {
result = method.invoke(listener, args);
} catch (IllegalAccessException e) {
LOG.error("Error invoking listener method", e);
} catch (InvocationTargetException e) {
LOG.error("Error invoking listener method", e);
}
}
return result;
}
}
That I use in my model class:
public class MyTreeModel implements TreeModel {
private final ListenerList listeners = new ListenerList();
private final TreeModelListener notifier = listeners.getNotifier(TreeModelListener.class);
public void addTreeModelListener( TreeModelListener l ) {
listeners.addListener(l);
}
public void removeTreeModelListener( TreeModelListener l ) {
listeners.removeListener(l);
}
protected void fireTreeNodesChanged(TreeModelEvent e) {
notifier.treeNodesChanged(e);
}
protected void fireTreeNodesInserted(TreeModelEvent e) {
notifier.treeNodesInserted(e);
}
protected void fireTreeNodesRemoved(TreeModelEvent e) {
notifier.treeNodesRemoved(e);
}
protected void fireTreeStructureChanged(TreeModelEvent e)
notifier.treeStructureChanged(e);
}
...
}

Run method inside a method in java

I'm sending more than 1 request to a web service, below there is an example of that requests. Its important for my application to get the answer from the web service so if there is an exception application will try couple of times to get the answer.
Because of that getting something simple like
deviceList = serviceAdapter.getDevices(); is turn into below code.
boolean flag = true;
int counter = 1;
List<Device> deviceList = null;
while (flag) {
try {
deviceList = serviceAdapter.getDevices();
flag = false;
} catch (Exception e) {
try {
if (counter == 5) {
System.out.println("Timeout Occured!");
flag = false;
} else {
Thread.sleep(1000 * counter);
counter++;
}
} catch (InterruptedException e1) {
}
}
}
And in my application i have lots of requests which means there will be more ugly codes. Is there a way where i will call my request methods as parameter for another method something like this:
deviceList = wrapperMethod(serviceAdapter.getDevices());
Problem is there will be different type of requests, so they will return different type objects (list,array,string,int) and their paramaters will change. Is there a suitable solution in java for this problem?

You can pass a Supplier<T> to the wrapperMethod:
public static <T> T wrapperMethod (Supplier<T> supp) {
boolean flag = true;
int counter = 1;
T value = null;
while (flag) {
try {
value = supp.get();
flag = false;
} catch (Exception e) {
try {
if (counter == 5) {
System.out.println("Timeout Occured!");
flag = false;
} else {
Thread.sleep(1000 * counter);
counter++;
}
} catch (InterruptedException e1) {
}
}
}
}
And call it with:
List<Device> deviceList = wrapperMethod (() -> serviceAdapter.getDevices());
I'm afraid, though, that it will limit the methods you call within the lambda expression to throw only RuntimeExceptions.

You can use some command implementation to execute some specific codes :
Here is a simple example of a command
interface Command{
void run();
}
And a couple of implementations :
class SayHello implements Command{
#Override
public void run() {System.out.println("Hello World");}
}
class KillMe implements Command{
public void run() { throw new RuntimeException();};
}
All we have to do to execute those method is to receive an instance of Command and run the method :
public static void execCommand(Command cmd) {
cmd.run();
}
And to use this
public static void main(String[] args) {
execCommand(new SayHello());
execCommand(new KillMe());
}
Hello World
Exception in thread "main" java.lang.RuntimeException
It also accepts lambda expression :
execCommand(() -> System.out.println("Say goodbye"));
And method reference :
public class Test{
public static void testMe() {
System.out.println("I work");
}
}
execCommand(Test::testMe);
Note that I didn't specify that this could throw Exception so I am limited to unchecked exception like RuntimeException but of course void run() throws Exception could be a solution. That way you can do what ever you want.
Full example (with exceptions) :
public class Test {
public static void main(String[] args) {
try {
execCommand(new SayHello());
execCommand(() -> System.out.println("Say goodbye"));
execCommand(Test::testMe);
execCommand(new KillMe());
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
public static void testMe() throws IOException{
System.out.println("I work");
}
public static void execCommand(Command cmd) throws Exception {
cmd.run();
}
}
interface Command{
void run() throws Exception;
}
class SayHello implements Command{
#Override
public void run() {System.out.println("Hello World");}
}
class KillMe implements Command{
public void run() { throw new RuntimeException();};
}
Output:
Hello World
Say goodbye
I work
Exception in thread "main" java.lang.RuntimeException
at main.KillMe.run(Test.java:39)
at main.Test.execCommand(Test.java:25)
at main.Test.main(Test.java:17)

You can use #RetryOnFailure annotation from jcabi-aspects
Create a wrapper method then annotate it to enable auto retry upon Exception
As an example:
#RetryOnFailure(attempts = 5)
List<Device> retryWhenFailed(ServiceAdapter serviceAdapter) throws Exception {
return serviceAdapter.getDevices();
}

This solution uses Generics to be able to handle different Object with most of the same code and a Runnable to execute the fetching.
With this solution, you would need only to write the different adapters extending from ServiceAdapter<T extends Fetchable> to implement the logic to fetch the data for each different class (which would have to implement Fetchable).
Define an interface that abtracts the objects that can be fetched by the different services.
package so50488682;
public interface Fetchable {
}
The ojbect that are to be retrieved implement this interface so you can use the same code for different classes.
package so50488682;
public class Device implements Fetchable{
private String id;
public Device(String id) {
this.id = id;
}
public String toString() {
return "I am device " + id;
}
}
Define an abstract ServiceAdapter that the different service adapters will extend to implement the logic for each kind of object to be retrieved. We add throws Exception to the get() method so this method cand just delegate the exception handling to the FetcherService and decide if it should retry or fail.
package so50488682;
import java.util.List;
public abstract class ServiceAdapter<T extends Fetchable> {
public abstract List<T> get() throws Exception;
}
This is an example of an implementation done to get objects of class Device.
package so50488682;
import java.util.ArrayList;
import java.util.List;
public class DeviceServiceAdapter extends ServiceAdapter<Device>{
#Override
public List<Device> get() throws Exception{
List<Device> rtn = new ArrayList<>();
// fetch the data and put it into rtn, this is a mock
Device d = new Device("1");
rtn.add(d);
d = new Device("2");
rtn.add(d);
d = new Device("3");
rtn.add(d);
//
return rtn;
}
}
Finally this is a generic solution to run the different service adapters.
public class FetcherService<T extends Fetchable> implements Runnable{
List<T> result = new ArrayList<>();
ServiceAdapter<T> serviceAdapter;
#Override
public void run() {
boolean flag = true;
int counter = 1;
while (flag) {
try {
result = serviceAdapter.get();
flag = false;
} catch (Exception e) {
try {
if (counter == 5) {
System.out.println("Timeout Occured!");
flag = false;
} else {
Thread.sleep(1000 * counter);
counter++;
}
} catch (InterruptedException e1) {
throw new RuntimeException("Got Interrupted in sleep", e);
}
}
}
}
public List<T> getResult() {
return result;
}
public void setResult(List<T> result) {
this.result = result;
}
public void setAdapter(ServiceAdapter<T> adapter) {
this.serviceAdapter = adapter;
}
}
From the main or calling program it work like this:
package so50488682;
import java.util.List;
public class SO50488682 {
public static void main(String args[]) {
try {
DeviceServiceAdapter deviceServiceAdapter = new DeviceServiceAdapter();
FetcherService<Device> deviceFetcherService = new FetcherService<>();
deviceFetcherService.setAdapter(deviceServiceAdapter);
deviceFetcherService.run();
List<Device> devices = deviceFetcherService.getResult();
for(Device device : devices) {
System.out.println(device.toString());
}
}catch(Exception e) {
System.out.println("Exception after retrying a couple of times");
e.printStackTrace();
}
}
}

How to write a asynchronous file handler in Vertx

I am new to Vertx.
I am playing with the API and I am trying to write a FileSizeHandler. I don't know if it is the correct way to do it but I would like to have your opinions.
In my code I would like to use the handler like this :
public class MyVerticle extends AbstractVerticle {
#Override
public void start() throws Exception {
getFileSize("./my_file.txt", event -> {
if(event.succeeded()){
Long result = event.result();
System.out.println("FileSize is " + result);
} else {
System.out.println(event.cause().getLocalizedMessage());
}
});
}
private void getFileSize(String filepath, Handler<AsyncResult<Long>> resultHandler){
resultHandler.handle(new FileSizeHandler(filepath));
}
}
Here is my FileSizeHandler class :
public class FileSizeHandler implements AsyncResult<Long> {
private boolean isSuccess;
private Throwable cause;
private Long result;
public FileSizeHandler(String filePath){
cause = null;
isSuccess = false;
result = 0L;
try {
result = Files.size(Paths.get(filePath));
isSuccess = !isSuccess;
} catch (IOException e) {
cause = e;
}
}
#Override
public Long result() {
return result;
}
#Override
public Throwable cause() {
return cause;
}
#Override
public boolean succeeded() {
return isSuccess;
}
#Override
public boolean failed() {
return !isSuccess;
}
}
What bothers me in the handler, is that I have to do it in the constructor of the class. Is there a better way to do it?

First of all, you called your class FileHandler, but it's not. It's a result.
You declare handler in Vert.x like that:
public class MyHandler implements Handler<AsyncResult<Long>> {
#Override
public void handle(AsyncResult<Long> event) {
// Do some async code here
}
}
Now, for what you do, there's vertx.fileSystem():
public class MyVerticle extends AbstractVerticle {
#Override
public void start() throws Exception {
vertx.fileSystem().readFile("./my_file.txt", (f) -> {
if (f.succeeded()) {
System.out.println(f.result().length());
}
else {
f.cause().printStackTrace();
}
});
}
}

Overrided method in subclass is not called

I have an abstract superclass AsyncActor which extends the Actor class. This superclass contains two abstract methods, notifySuccess and notifyFailure. notifyFailure is overriden in AsyncActor, but notifySuccess isn't because it's implementation changes from subclass to subclass. I have two actors, CreateObjActor and DeleteObjActor. Each extends AsyncActor and overrides notifySuccess. The execute method located in AsyncTask calls notifySuccess, but nothing happens.
public class AsyncActor extends Action<String> {
private Future future;
private final Action action;
private final ExecutorService executor = Executors.newSingleThreadExecutor();
public AsyncActor(Action action) {
this.action = action;
}
public Action getAction() {
return action;
}
public Future getFuture() {
return future;
}
public void execute() {
if(action.execute()) {
executeAsynchronously();
}
}
public void executeAsynchronously() {
ServiceFw.log.debug("Writing directory to file...");
Callable<String> asyncTask = () -> {
try {
ServiceFw.entryManager.writeBack();
TimeUnit.SECONDS.sleep(3);
} catch (InterruptedException e) {
ServiceFw.log.debug("Exception thrown during asynchronous wait");
e.printStackTrace();
} catch (BusinessException e) {
notifyFailure();
}
return "write back operation";
};
future = executor.submit(asyncTask);
Runnable poll = () -> {
if(future!=null) {
notifySuccess();
} else {
error.setSeverity(ExtendedError.Severity.Warning);
notifyFailure(error);
}
};
poll.run();
}
#Override
public void notifySuccess() {
}
#Override
public void notifyFailure() {
ServiceFw.log.error("Error with asynchronous processing of write back" );
ServiceFw.entryManager.deleteActor(this);
}
}
public class CreateObjActor extends AsyncActor {
public CreateObjActor(Action action) {
super(action);
}
#Override
public void notifySuccess() {
try {
ServiceFw.log.debug("Finished asynchronous operation: " + getFuture().get());
Entry entry = getAction().getEntryModel();
if (getAction().isNotify()) {
Notification notification = new Notification(entry);
ServiceFw.notificationDispatcher.dispatchNotification(notification);
try {
ServiceFw.eventFramework.dispatchEvent("entry-added");
} catch (BusinessException e) {
ServiceFw.log.error("Event could not be dispatched for newly added entry: " + entry.toString());
}
}
}
} catch (InterruptedException | ExecutionException e) {
e.printStackTrace();
} finally {
ServiceFw.entryManager.deleteActor(this);
}
}
}
I've tried making AsyncActor not abstract and providing an empty implementation of notifySuccess, but this didn't work either. Is there a way I can call the method from the superclass? The execute method contains a lot of code (not shown here) that would result in a lot of duplicate code if it had to be placed in each subclass.

Try catch not being forced

I have this Exception:
public class ErrorException extends Exception
{
private static final long serialVersionUID = 1L;
private String errorMessage = "";
private int errorCode = 0;
private String errorLevel = "";
private Window errorSource = null;
public String getErrorMessage()
{
return errorMessage;
}
public int getErrorCode()
{
return errorCode;
}
public String getErrorLevel()
{
return errorLevel;
}
public Window getErrorSource()
{
return errorSource;
}
public ErrorException(String message, int code, int level, Window source)
{
super();
errorMessage = message;
errorCode = code;
switch (level)
{
case 0:
{
errorLevel = "benignError";
}
case 1:
{
errorLevel = "criticalError";
}
case 2:
{
errorLevel = "terminalError";
}
}
errorSource = source;
}
}
And I have this method:
public static Element check(final Document document) throws ErrorException
{
try
{
chapter.resetLatch();
final SecondaryLoop loop = Toolkit.getDefaultToolkit().getSystemEventQueue().createSecondaryLoop();
new Thread()
{
#Override
public void run()
{
SwingUtilities.invokeLater(new Runnable()
{
#Override
public void run()
{
answer.getPreviousElement().takeFocus();
question.removeAnswer(answer);
question.rewriteLetters();
Utils.update(chapter);
loop.exit();
}
});
}
}.start();
loop.enter();
chapter.getLatch().await();
}
catch (InterruptedException e)
{
throw new ErrorException("blankElementDialogError", 8, 1, Main.getGui().getMasterWindow());
}
return new Element();
}
And I use it in this constructor code:
public ConfirmCloseDialog(final Document document, final int postOperation)
{
final CustomJButton doSave = new CustomJButton(Main.getString("doSave"), false);
doSave.addActionListener(new ActionListener()
{
#Override
public void actionPerformed(ActionEvent arg0)
{
getConfirmCloseDialog().dispose();
new Thread()
{
#Override
public void run()
{
/*this method is the one above -->*/Element problem = BlankElementDialog.check(document);
if (problem == null)
{
new SaveChooser(document, postOperation);
}
else
{
new BlankElementDialog(problem);
}
}
}.start();
}
});
}
The code for the second part is not full, but there are no special constructs in the rest of the code (just some GUi objects being constructed and there is no try catch anywhere in the constructor).
However, Eclipse isn't forcing me to encapsulate the method call into try catch block, despite the fact that the method throws an Exception (ErorrException subclasses Exception).
And I know that Exception is checked exception, so it should force it, right?
Why?
What do I have to do so it would force it?

Even without any details Eclipse should notify, look at this:
Just restart the Eclipse should solve the issue.
public class TestClass {
public static void main(String[] args) {
method(2);//Notification here!
}
static void method(int a) throws myException {
}
}
class myException extends Exception {
}