Servlets :: How To Implement A Callback Method For A Post Async Task
Mar 26, 2015
I am developing an app with a Java Servlet backend, and I am trying to get the Async call (AsyncTask - Android Developers) to get my response message Synced with the rest of the client and being able use this information wherever I want. Without a callback method, when from the caller class I use the commands:
ServletPostAsyncTask s = new ServletPostAsyncTask();
s.execute(new Pair<Context, String>(ListViewPrenota.this, "tours"));
Tours ttours = s.tours;
Tour tour = ttours.getTours().get(0);
I receive a NullPointerException pointing to the third line Tours ttours = s.tours;, since the s.execute() method doesn't wait for the rest of the lines to get executed.To solve this I thought about implementing a callback method with interfaces in Java, but I am not sure on how to do it. For example, what class does have to implement the interface, the ServletPostAsyncTask or the caller class?
I have a web app that accepts requests. Once a request is sent, I want to create a thread that will sleep for several days if no user action is taken on the request to remind the user to do something. The problem is, how do I ensure the timer will pick up at the same place if the server is restarted? Would serializing the thread do that? I'm guessing no because I think you're just creating a new instance at start up. Just checking If there's anything built into Java to do this.
We have a big application which is implemented in basic servlet. WE have Get and Post request in servlet. I want to provide them security if any malicious attack will happen on the form submit method. I want to make it secure. In detail, suppose if any user want to submit form/ any ajax request from my application and if he/she changes the method of submission from POST to GET then how I will recognize this?
I know that HTTPServletRequest object have GetMethod() but how I will detect that it is not changed by Tamper data/Fidler/Watir. One more way, I googled is by using GetQueryString() method but lot of the places I have query paramater in my POST request.
Now that I have set up my dev environment on a new machine with new eclipse, it does not work.
It displays Ï instead of π.
I've already tried adding URIEncoding="UTF-8" to server.xml which did not work since it only affect get not post. I figured out how to get the parameter with correct encoding on the new system:
I have an application and I would like it to send a file to a web page using POST method.
I've found the HttpClient from Apache, but I had no luck. All the tutorials and samples I can find on the net are for 3.x. I've tried adopting the samples with the HttpClient 4.1 docs, but I failed.
I have a target url of a page and source file path. I get the basic idea of what needs to happen, I am just finding it hard to implement it.
XML request message using HTTP POST is received by the Servlet interface. While we are reading and trying to parse the InputStreamObject, we are getting the following error message.
doPost java.io.CharConversionException: Characters larger than 4 bytes are not supported: byte 0x8e implies a length of more than 4 bytes
It looks like we are receiving some invalid Non-ASCII characters in the XML message.
The above error is thrown intermittently. Whenever we have this CharConversionException, the servlet gets corrupted and it impacts few good xml messages that follows after the error.
I need to know the following:
1. How to fix this exception and skip the bad message? 2. Is it possible to log the entire xml message in the catch block, whenever we have this exception?
NOTE: we tried different ways, not able to print the xml message, as the inputstream seems to be closed/null, when it reaches the catch block.
Tried the below code , but the servlet process/thread hungs and throws the below error:
Thread "WebContainer : 3" (00000028) has been active for 667781 milliseconds and may be hung. There is/are 1 thread(s) in total in the server that may be hung.
Below is the code snippet:
public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/xml"); request.setCharacterEncoding("ISO-8859-1"); OutputStream out = response.getOutputStream(); InputStream inputStream=null;
[Code] ....
Issue of either fixing/overcoming the actual exception and printing out the entire xml message(bad one) in ours log during the catch block.
how it is decided which class will implement a session listener interface? Which class will implement HttpSessionListener? Which one will implement HttpSessionActivationListener, HttpSessionBindingListener or HttpSessionAttributeListener?
I want to implement a 'Keep me signed in' option in the login page of an application. I have noticed this option is present in the form of a checkbox on the login page of many websites but i don't know how it can be coded . When selected, a user is no longer asked for his username and password on subsequent sessions but he is automatically given access.
I have configured form based JAAS in my app. Basically, in web.xml I have declared security constraints on certain jsp page, declared specific roles, login and error pages. So, my login form is:
so, i have a problem in implement method named viewAllFactor(User us,ResultSet rs)when i call this method using <T> like objet dont work because T obj is nulli ask if i can try something to have a good result.
I have 2 classes BaseDao<T> (DAO Pattern) and Class User extends from BaseDao
this is the code
package appweb.core; public abstract class BaseDao<T> { public ArrayList<T> viewall() { ResultSet rset = null; ArrayList<T> listAll = new ArrayList<T>(); String sql = "SELECT* FROM "+ this.tableName; System.out.println(sql); try {
if i call a class that implements an interface the method inside the interface will be triggered automatically by the compiler or happens only in the observer pattern? i keep simple to be surr the message came across, a typical example would be a listener on a button, or a collection that calls comparator)
I have a drop-down which contains the four sections simple buttons(filters). When click any of these buttons some settings are applied. I have successfully auotmated it using simple if else and switch but in that case i have to use 8 parameters(8 are the number of button)
public void editFilters(WebElement filter1, WebElement filter2, WebElement filter3, WebElement filter4,WebElement filter5,WebElement filter6,WebElement filter7,WebElement filter8 String edit, String expectedColour) { switch (edit) { case "selectFilter": if (filter1 != null) {
[Code] .....
But want to make it more effective by using hashes. I do not want to use 8 different parameters to perform action on the respective button.
So now what i want to implement.
Create a method in which i pass the parameter1 as hash and 2nd parameter as 0 or 1, 0 means unSelectFilter and 1 means select the filter.
With parameter 1, in code i want to pass the name or xpath or anything else for any number of filters , that those filters names should be stored into that hash and then by passing 0 or 1, i can select/unselect those filters.
if some of you worked with Unity Game engine (C#) the idea is that game has main loop and once per cycle it call for example Update() method in all objects which implement certain interface.
I would like to repeat such pattern in Java for another another program, not even game related, but I would still need a main loop and event driven behaviour with async call backsSo question is how to implement the fallowing scenario:
Imagine i have interface which implement some methods and one of them is Execute()
I have the main controller class which implement main loop, also multiple other classes which implement the same interface with method Execute(). How can i call this Execute() method on all objects which implement that interface each loop cycle?
Should i keep and track reference of each object which was implemented with this interface and go through inner "for" loop trough each reference and call manually Execute() method in each of them?what if each object implementing interface have to run Execute() method simultaneously? in parallel independent from each other?
Referring back to Unity engine and their Update() method - there is exactly the same situation:you can have multiple objects with script attached, thats script implement interface which has multiple methods and one of them is Update() and once per cycle all objects with that Update() method will be executed in parallel independently
I am trying to implement this method in another class but I'm not sure how to do so. My attempt is:
public getCalls(){ return getCalls(); }
When I run the program it sends the following exception:
Exception in thread "main" java.lang.StackOverflowError at FibonacciForget.getCalls(FibonacciForget.java:14) and it highlights the [return getCalls();] part.
What is the correct way to implement the getCalls() method?
abstract class A class B extends A class C extends B class D extends C implements SomeInterface
I'm trying to implement a method "doSomething" declared in SomeInterface in class D. While trying to call doSomething in main I get the error message ”The method doSomething is undefined for the type B”
This is my code i main:
B container = new D("1,2,3,4,5,6,7,8"); System.out.println(container.doSomething());
I need container to be an object of type B, because it goes later into a list of type B. According to what I've been told, the only file I need to edit to make this work is class D.
I am trying to make a ChessBoard class composed of an array of JLabels inside a JPanel with a grid layout. I am also trying to override the getPreferredSize method so that the board will change size when I resize the main window (in another class in which I will instancize this class as part of a larger GUI). I got this kind of layout working before, but now I am trying to get it to work with multiple classes. However, after copying in the part of the previous code corresponding to the panel's layout, I am encountering some errors that I don't know how to solve. Specifically, when I try to override the getPreferredSize method, the compiler tells me "method does not override or implement a method from a super type, " and that it can't find the method "getPreferredSize"
Here's my code:
public class ChessBoard extends JPanel//the panel that this class extends is the boardHousing { //mental chess board piece array Piece mentalBoard[][] = new Piece[8][8]; //actual GUI chessboard JLabel Array static JLabel chessBoard[][] = new JLabel[8][8];
[Code] ....
I would just think that I was overriding the method incorrectly, but the weird thing is that I got that specific section of code to work before -- the only thing different now is that there are multiple classes, so my ChessBoard class itself is extending JPanel.
I have been researching the Iterator and making a class implement iterable. I have seen this example shown below and was wondering how I could change this so that iterable() is not called upon in the main. I would like to be able to make a method that returns an instance of a class that implements the Iterator interface hopefully an inner class. This is because my program will not have a main and will be supplied with a main that includes a new Object with will use the iterator method.
import java.util.*; public class IteratorDemo { public static void main(String args[]) { // Create an array list ArrayList al = new ArrayList(); // add elements to the array list al.add("C");
[Code] ....
This is all I have been able to understand from what I want to do. This does not work and this is what I am trying to achieve
public class MyArrayList implements Iterable { public static final int DEFAULT_SIZE = 5; public static final int EXPANSION = 5; private int capacity; private int size; private Object[] items;
