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  • How do I calculate a good hash code for a list of strings?

    - by Ian Ringrose
    Background: I have a short list of strings. The number of strings is not always the same, but are nearly always of the order of a “handful” In our database will store these strings in a 2nd normalised table These strings are never changed once they are written to the database. We wish to be able to match on these strings quickly in a query without the performance hit of doing lots of joins. So I am thinking of storing a hash code of all these strings in the main table and including it in our index, so the joins are only processed by the database when the hash code matches. So how do I get a good hashcode? I could: Xor the hash codes of all the string together Xor with multiply the result after each string (say by 31) Cat all the string together then get the hashcode Some other way So what do people think? (If you care we are using .NET and SqlServer)

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  • Gson serialization depending on field value

    - by Serj Lotutovici
    I have a POJO that is similar to: public class MyGsonPojo { @Expose @SerializedName("value1") private String valueOne; @Expose @SerializedName("value2") private boolean valueTwo; @Expose @SerializedName("value3") private int valueThree; // Getters and other stuff here } The issue is that this object has to be serialized into a json body for a call to the server. Some fields are optional for the request and if I even send it with default and null values, the API responds differently (Unfortunately changing the api is not an option). So basically I need to exclude fields from serialization if any of them is set to a default value. For example if the field valueOne is null the resulting json should be: { "value2" : true, "value3" : 2 } Any idea how to make this a painless effort? I wouldn't want to build the json body manually. Any help would be great. Thank you in advice.

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  • Consistent HashCode() and Equals() results, but inconsistent TreeMap.containsKey() result

    - by smessing
    I have the following object Node: private class Node implements Comparable<Node>(){ private String guid(); ... public boolean equals(Node o){ return (this == o); } public int hashCode(){ return guid.hashCode(); } ... } And I use it in the following TreeMap: TreeMap<Node, TreeSet<Edge>> nodes = new TreeMap<Node, TreeSet<Edge>>(); Now, the tree map is used in a class called Graph to store nodes currently in the graph, along with a set of their edges (from the class Edge). My problem is when I try to execute: public containsNode(n){ for (Node x : nodes.keySet()) { System.out.println("HASH CODE: "); System.out.print(x.hashCode() == n.hashCode()); System.out.println("EQUALS: "); System.out.print(x.equals(n)); System.out.println("CONTAINS: "); System.out.print(nodes.containsKey(n)); System.out.println("N: " + n); System.out.println("X: " + x); } } I sometimes get the following: HASHCODE: true EQUALS: true CONTAINS: false N: foo X: foo Anyone have an idea as to what I'm doing wrong? I'm still new to all this, so I apologize in advance if I'm overlooking something simple (I know hashCode() doesn't really matter for TreeMap, but I figured I'd include it).

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  • Simple explaination of Arraylists

    - by Jeremy
    I'm new to programming and I'm looking for a simple answer to build my foundation of understanding Arrays. I've used google and searched this site. After a bit of trial and error I get how to make and reference Arrays like thing[3] gets you the fourth thing in the thing array(since 0 is the first). which lets me do something like thing[3].getStupidNumber() to get the StupidNumber of the 4th thing in the thing array. Then I get to ArrayLists which seem to have much more utility but I cant make logical sense of them like Arrays. When i search I cant find this or word this correctly and thus far everything else I've learned clicked easily. so say I make an ArrayList thing with 5 things in it. how do i get to the .getStupidNumber() method inside the fourth thing, if possible? I think if I learn this I can learn the rest on my own. Thanks!

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  • Correct handling of return data

    - by Serhiy
    Hello, I have a question related to correct handling of returns of the DAO library I'm writing for one project. This library probably is going to be used by another people and I want to do it correctly. So I would like to know, how I should deal with return statements of the functions of my DAO. Example 1 I have function to getCustomer which should return String. In case query doesn't return any result should I return null, empty string or throw some kind of Exception? Example 2 I have function getCutomerList which return ArrayList. In case query doesn't return any result should I return null, empty ArrayList or throw some Exception? Example 3 Some sql exception was detected, what should I do: throw exception or do try..catch of the block where it can occur? What is the "good" practice or "best" practice to apply in my case? Thanks on advance, Serhiy.

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  • How to point to other table's ID with hibernate?

    - by Wilhelm
    The problem: let's say I have two tables Client, and Product, in which Client has its primary key and a column called products (that points to pk's in Product table)... ok, if I need products to point only one row, it's nice, but if I need it to point for... 1000 rows in Product table, the products column would have to be larger enought... but I can't predict this situation. So, how could I design my table and how would I use hibernate with it, to achieve that "pointing" in a optmized and maybe "easy" way. NOTE: I excluded some columns of the "design" presented here, just to keep the simplicity.

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  • Spring 3: task namespace: How to find out time of next execution?

    - by Bernd Haug
    I have a bean that has a method executed on a schedule using <task:scheduled> in the context configuration. Is there a way for me to find the time of the next scheduled run during execution of that method? The same method is also executed manually, and the mechanism for receiving scheduler information may not break executions from outside the scheduler...

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  • Strange behavior while returning csv file from spring controller

    - by Fanooos
    I working in a spring application which have an action method that returns a CSV file. This action works fine but in some cases it throws a predefined exception (MyAppException). I have another method that is annotated @ExceptionHandler(MyAppException.class) In the exception handler method I return another csv file but with different contents. The code that returns the csv file is almost the same in the two methods. List<String[]> list= new ArrayList<String[]>(); list.add(new String[]{ integrationRequestErrorLog.getErrorMessage(), Long.toString(integrationRequestErrorLog.getId()), Integer.toString(integrationRequestErrorLog.getErrorCode()) }); CSVWriter writer = new CSVWriter(response.getWriter(), ','); writer.writeAll(list); writer.close(); the difference between the two method is the list of contents. In the first method the file is returned normally while in the exception handler method I have a strange behavior. The exception handler method works fine with Opera browser while it gives me a 404 with FireFox. Opera browser give me 404 also but it download the file while firefox does not? Really I do not understand what is the difference here.

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  • Call HashMap from jsp EL ?

    - by Parhs
    Here is my Entity Class public enum UnitType { HOSPITAL, HEALTHCENTER } public static LinkedHashMap<UnitType, String> unitType = new LinkedHashMap<UnitType, String>() { { put(UnitType.HEALTHCENTER, "???t?? ??e?a?"); put(UnitType.HOSPITAL, "??s???µe??"); } }; @Id @GeneratedValue(strategy = GenerationType.IDENTITY) private Long id; private String name; private String address; @Column(columnDefinition = "TEXT") private String info; @Enumerated(EnumType.STRING) private UnitType type; At my jsp <c:forEach var="unit" items="${requestScope.units}"> <tr> <td>${unit.id}</td> <td>${unit.name}</td> <td>${unit.address}</td> <td>??!?</td> <td><a href="#">?e??ss?te?a</a></td> </tr> </c:forEach> How can i place the text value of the enum at ??!? .. Any idea? Tried some ways but nothing worked..

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  • how to log digester with apache commons?

    - by Bruce
    Hi all I'm having trouble getting digester to log anything. I'd be hugely grateful for any light anyone can shed. In my code I'm doing this: Digester digester = new Digester(); .. some digester set up stuff // What on earth should go in here???? digester.setLogger(LogFactory.getLog("org.apache.commons.logging.Log")); I have a commons-logging.properties file in my classpath as follows: org.apache.commons.logging.Log=org.apache.commons.logging.impl.SimpleLog org.apache.commons.logging.simplelog.log.org.apache.commons.digester.Digester=debug org.apache.commons.logging.simplelog.log.org.apache.commons.digester.Digester.sax=info I just get no debug info at all.. Thanks for your help!

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  • how to avoid if conditions,

    - by kumar kasimala
    Hi all, can anyone suggest best way to avoid most if conditions? I have below code, I want avoid most of cases if conditions, how to do it ? any solution is great help; if (adjustment.adjustmentAccount.isIncrease) { if (adjustment.increaseVATLine) { if (adjustment.vatItem.isSalesType) { entry2.setDebit(adjustment.total); entry2.setCredit(0d); } else { entry2.setCredit(adjustment.total); entry2.setDebit(0d); } } else { if (adjustment.vatItem.isSalesType) { entry2.setCredit(adjustment.total); entry2.setDebit(0d); } else { entry2.setDebit(adjustment.total); entry2.setCredit(0d); } } } else { if (adjustment.increaseVATLine) { if (adjustment.vatItem.isSalesType) { entry2.setCredit(adjustment.total); entry2.setDebit(0d); } else { entry2.setDebit(adjustment.total); entry2.setCredit(0d); } } else { if (adjustment.vatItem.isSalesType) { entry2.setDebit(adjustment.total); entry2.setCredit(0d); } else { entry2.setCredit(adjustment.total); entry2.setDebit(0d); } }

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  • How to declare a warning on field with AspectJ

    - by Ralph
    I want to declare a warning on all fields Annotated with @org.jboss.weld.context.ejb.Ejb in AspectJ. But I do not find a way how to select that field. I guess the aspect should be something like that: public aspect WrongEjbAnnotationWarningAspect { declare warning : within(com.queomedia..*) && ??? (@org.jboss.weld.context.ejb.Ejb) : "WrongEjbAnnotationErrorAspect: use javax.ejb.EJB instead of weld Ejb!"; } Or is it impossible to declare warnings on fields at all?

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  • How to set attribs in GWT?

    - by Jonas Byström
    I'm not getting any effect out of DOM.setElementAttribute, am I doing something wrong? class MyListBox extends com.google.gwt.user.client.ui.ListBox { .... protected void setHoverAutoWidth() { addDomHandler(new MouseOverHandler() { public void onMouseOver(MouseOverEvent event) { DOM.setElementAttribute(getElement(), "width", "auto"); } }, MouseOverEvent.getType()); addDomHandler(new BlurHandler(){ public void onBlur(BlurEvent event) { DOM.setElementAttribute(getElement(), "width", "100px"); } }, BlurEvent.getType()); } } (I know there are less hacky ways to change the width than to set the style attribute directly, but I don't care about css right now.) Edit: Oops, just realized that width does not change the style width, just adds a width attribute to the tag (which explains why nothing happens). Any suggestions on how to modify the style are still welcome!

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  • Eclipse: Should I create a workspace for each project ?

    - by Zombies
    I am simply wondering whether it is best to put all of my Eclipse projects into one workspace, or do a 1 workspace per 1 project. I am just a solo developer, for hobby more or less, but the apps I create do actually have production versions that are running on rather frequent cron jobs, so its almost like an amateur production environment. The only problems I have noticed so far is for exporting JARs, I have the potential to include source files from other projects which seems like it could get messy (maybe?).

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  • JSP request parameter is returning null on a jsp include win Weblogic.

    - by doug
    Hello, I am having trouble with the jsp:include tag. I have code like the following: <jsp:include page="./Address.jsp"> <jsp:param value="30" name="tabIndex"/> <jsp:param value="true" name="showBox"/> <jsp:param value="none" name="display"/> </jsp:include> The page is included fine, but when I try to access the parameters on the Address.jsp page, they are null. I have tried accessing them the following ways (with jstl): <c:out value="${param.tabIndex}" /> <c:out value="${param['tabIndex']} /> <%= request.getParameter("tabIndex") %> <c:out value="${pageScope.param.tabIndex} /> ${param.tabIndex} etc... Here is the kicker, The above works fine in tomcat 5.5. However, when I deploy the application in Weblogic 10, it does not. Also, the code works fine in other areas of my application (on weblogic) just not a particular page. Any Ideas? Thanks!

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  • Hibernate: getting a record but it's being updated in the database?

    - by jack
    For some reason Hibernate seems to be keeping my session open and updating the object without me explicitely invoking a save/update/saveorupdate. I guess the session is staying open and it's beeing marked as dirty. However this is not the desired behaviour, so what's the cleanest way to fix this? The issue seems to occur because I store a phone number without formatting in the database but the getter of the object returns a formatted telephone number. My flow: go to a jsp = controller = service = dao DAO getter function if(userId != 0) { return (User)dbFactory.get(User.class, userId); } return null; The service just passes it to the controller and the controller puts te User object in the request scope. I display it on my JSP page using EL.

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  • Servlet mapping for ajax call parameters

    - by Woho87
    Hi guys! <servlet-mapping> <servlet-name>Test</servlet-name> <url-pattern>/GetContacts*</url-pattern> </servlet-mapping> I got a simple problem where I can't find any solution on the internet. I have a ajax calls that have the url http://localhost:80/Push/GetContacts?id=23..... The above servlet mapping is not correct for the AJAX call. it issues a http 404 not found call. What is the right syntax to enable my ajax call?

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  • Google Data Api returning an invalid access token

    - by kingdavies
    I'm trying to pull a list of contacts from a google account. But Google returns a 401. The url used for requesting an authorization code: String codeUrl = 'https://accounts.google.com/o/oauth2/auth' + '?' + 'client_id=' + EncodingUtil.urlEncode(CLIENT_ID, 'UTF-8') + '&redirect_uri=' + EncodingUtil.urlEncode(MY_URL, 'UTF-8') + '&scope=' + EncodingUtil.urlEncode('https://www.google.com/m8/feeds/', 'UTF-8') + '&access_type=' + 'offline' + '&response_type=' + EncodingUtil.urlEncode('code', 'UTF-8') + '&approval_prompt=' + EncodingUtil.urlEncode('force', 'UTF-8'); Exchanging the returned authorization code for an access token (and refresh token): String params = 'code=' + EncodingUtil.urlEncode(authCode, 'UTF-8') + '&client_id=' + EncodingUtil.urlEncode(CLIENT_ID, 'UTF-8') + '&client_secret=' + EncodingUtil.urlEncode(CLIENT_SECRET, 'UTF-8') + '&redirect_uri=' + EncodingUtil.urlEncode(MY_URL, 'UTF-8') + '&grant_type=' + EncodingUtil.urlEncode('authorization_code', 'UTF-8'); Http con = new Http(); Httprequest req = new Httprequest(); req.setEndpoint('https://accounts.google.com/o/oauth2/token'); req.setHeader('Content-Type', 'application/x-www-form-urlencoded'); req.setBody(params); req.setMethod('POST'); Httpresponse reply = con.send(req); Which returns a JSON array with what looks like a valid access token: { "access_token" : "{access_token}", "token_type" : "Bearer", "expires_in" : 3600, "refresh_token" : "{refresh_token}" } However when I try and use the access token (either in code or curl) Google returns a 401: curl -H "Authorization: Bearer {access_token}" https://www.google.com/m8/feeds/contacts/default/full/ Incidentally the same curl command but with an access token acquired via https://code.google.com/oauthplayground/ works. Which leads me to believe there is something wrong with the exchanging authorization code for access token request as the returned access token does not work. I should add this is all within the expires_in time frame so its not that the access_token has expired

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  • Is it okay to pass injected EntityManagers to EJB bean's helper classes and use it?

    - by Zwei steinen
    We have some JavaEE5 stateless EJB bean that passes the injected EntityManager to its helpers. Is this safe? It has worked well until now, but I found out some Oracle document that states its implementation of EntityManager is thread-safe. Now I wonder whether the reason we did not have issues until now, was only because the implementation we were using happened to be thread-safe (we use Oracle). @Stateless class SomeBean { @PersistenceContext private EntityManager em; private SomeHelper helper; @PostConstruct public void init(){ helper = new SomeHelper(em); } @Override public void business(){ helper.doSomethingWithEm(); } } Actually it makes sense.. If EntityManager is thread-unsafe, a container would have to do inercept business() this.em = newEntityManager(); business(); which will not propagate to its helper classes. If so, what is the best practice in this kind of a situation? Passing EntityManagerFactory instead of EntityManager?

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  • can a .class file be added to the urlpath of a URLClassLoader

    - by java_geek
    I have a custom class loader which extends from a URLClassLoader. I added a .class file to the urlpath using addURL(); but when i do a class.forname() using this loader i get a ClassNotFoundException. However, if i create a jar and add the jar to the urlpath, i do not get any exception. What can be added to the urlpath of a URLClassLoader usign addURL()

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  • Getting N random numbers that the sum is M

    - by marionmaiden
    Hello I want to get N random numbers that the sum of them is a value. For example, let's suppose I want 5 random numbers that their sum is 1 Then, a valid possibility is: 0.2 0.2 0.2 0.2 0.2 Other possibility is: 0.8 0.1 0.03 0.03 0.04 And so on. I need this for the creation of the matrix of belongings of the Fuzzy C-means.

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  • Does add() on LinkedBlockingQueue notify waiting threads?

    - by obvio171
    I have a consumer thread taking elements from a LinkedBlockingQueue, and I make it sleep manually when it's empty. I use peek() to see if the queue empty because I have to do stuff because sending the thread to sleep, and I do that with queue.wait(). So, when I'm in another thread and add()an element to the queue, does that automatically notify the thread that was wait()ing on the queue?

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