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  • Threadsafe way of exposing keySet()

    - by Jake
    This must be a fairly common occurrence where I have a map and wish to thread-safely expose its key set: public MyClass { Map<String,String> map = // ... public final Set<String> keys() { // returns key set } } Now, if my "map" is not thread-safe, this is not safe: public final Set<String> keys() { return map.keySet(); } And neither is: public final Set<String> keys() { return Collections.unmodifiableSet(map.keySet()); } So I need to create a copy, such as: public final Set<String> keys() { return new HashSet(map.keySet()); } However, this doesn't seem safe either because that constructor traverses the elements of the parameter and add()s them. So while this copying is going on, a ConcurrentModificationException can happen. So then: public final Set<String> keys() { synchronized(map) { return new HashSet(map.keySet()); } } seems like the solution. Does this look right?

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  • Using JSF, JPA and DAO. Without Spring?

    - by ich-bin-drin
    Hi, till now i still worked with JSF and JPA without DAOs. Now i'd like to use DAOs. But how can i initialize the EntityManager in the DAO-Classes? public class AdresseHome { @PersistenceContext private EntityManager entityManager; public void persist(Adresse transientInstance) { log.debug("persisting Adresse instance"); try { entityManager.persist(transientInstance); log.debug("persist successful"); } catch (RuntimeException re) { log.error("persist failed", re); throw re; } } } Have I to use Spring or is there a solution that works without Spring? Thanks.

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  • unable to set fields of a collection-property elements after changing their order (elements becoming

    - by Jaroslav Záruba
    Hello I want to change order of objects in a collection, and then to access+modify fields of those items. Unfortunately the items somehow become 'deleted'. This is what I do... if(someCondition) { MainEvent mainEvent = pm.getObjectById(MainEvent.class, mainEventKey); /* * events in the original order * MainEvent.subEvents field is not in default fetch group, * therefore I also tried to add the named group into the * persistenceManeger fetch plan, no difference * (mainEvent is not instance of the Event sub/class BTW) */ List<Event> subEvents = mainEvent.getSubEvents(); // re-arrange the events according to keysOrdered { Map<Key, Event> eventMap = new HashMap<Key, Event>(); for(Event event : subEvents) eventMap.put(event.getKey(), event); List<Event> eventsOrdered = new LinkedList<Event>(); for(Key eventKey : keysOrdered) eventsOrdered.add(eventMap.put(eventKey, eventMap.get(eventKey))); // } // put the re-arranged items back into the collection property { subEvents.clear(); subEvents.addAll(eventsOrdered); // } pm.makePersistent(mainEvent); eventsOrdered = subEvents; } else eventsOrdered = getEventsUsingAlternateApproach(); /* * so by now the mainEvent variable does not exist; * could it be this lead the persistence manager to mark * my events as abandoned/obsolete/invalid/deleted...? */ for(Event event : eventsOrdered) event.setDate(new Date()); // -> "Cannot write fields to a deleted object" What am I doing wrong please?

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  • Why are static imports of static methods with same names legal?

    - by user1055638
    Lets say we have these packages and classes: package p1; public class A1 { public static void a() {} } package p2; public class A1 { public static void a() {} } package p3; import static p1.A1.a; import static p2.A1.a; public class A1 { public static void test() { } } I am wondering, why the static import of methods is legal (won't result in compile time error) in package p3? We won't be able to use them further in the test() method as such usage will result in the compile time error. Why it is not the same as with a normal import of classes. Lets say we would like to import classes A1 from packages p1 and p2 into p3: package p3; import p1.A1; import p2.A1; such import is illegal and will result in the compile time error.

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  • How do you create your own drag-n-drop GUI designer ?

    - by panzerschreck
    Hello I was looking at creating a UI for developing web forms, similar to the Netbeans Visual JSF form designer.It will be targeted to use GWT/GXT components.I am looking at a look very similar to VS/Netbeans. Any thoughts on where/how to start ? Initially, I would prefer to have it as a standalone application, later develop it as eclipse plugin. I have already evaluated the extjs designer and the eclipse plugin from instantiations, but i would prefer to have it developed on my own, as it looks challenging, Also, I have few custom components that have been developed. Thanks

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  • Many returned records cause stackoverflow with Hibernate

    - by mimi law
    If there are many return records from DB. It will get stackoverflow problem. User is a class, which has a one to many relationship (to 3 other classes). When I print out the SQL, i found that the system runs the same query many time to get the data from DB. Does anyone know what the problem is? result.addAll(getCurrentSession().createCriteria(User.class) .add(Restrictions.ilike("name", "tom", MatchMode.ANYWHERE)) .setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY) .list());

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  • Weird output of Throwable getMessage()

    - by Ravi Gupta
    Hi I have below pseudo code with throws an exception like this throw new MyException("Bad thing happened","com.stuff.errorCode"); where MyException extends Exception class. So the problem is when I try to get the message from MyException class by calling myEx.getMessage() it returns ???en_US.Bad thing happened??? instead of my original message i.e. Bad thing happened I have checked that MyException class doesn't overrides Throwable class's getMessage() behavior. Below is the how the call passes from MyException.getMessage() to Throwable.getMessage() public MyException(String msg, String sErrorCode){ super(msg); this.sErrorCode = sErrorCode; this.iSeverity = 0; } which then calls public Exception(String message) { super(message); } and finally public Throwable(String message) { fillInStackTrace(); detailMessage = message; } when I do a getMessage on myexception it calls Throwable's getMessage as below public String getMessage() { return detailMessage; } So ideally it should return the original message as I set when throwing the exception. What's the ???en_US thing ?

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  • Problem with extending JPanel

    - by Halo
    I have an abstract entity: public abstract class Entity extends JPanel implements FocusListener And I have a TextEntity: public class TextEntity extends Entity Inside TextEntity's constructor I want to put a JTextArea that will cover the panel: textArea = new JTextArea(); textArea.setSize(getWidth(),getHeight()); add(textArea); But getWidth() and getHeight() returns 0. Is it a problem with the inheritance or the constructor?

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  • Strange IP addresses in tomcat

    - by mdev
    Some where I have this in some generic class. public static String getRequestIp (HttpServletRequest request){ String ipaddr = request.getHeader("X-FORWARDED-FOR"); if (ipaddr == null)ipaddr = request.getRemoteAddr(); return ipaddr; } For every request i call that method and in a certain moment i insert a record in a mysql database. In most cases it works normally and i can see a record for every request with a valid ip address in the right field. But sometimes where the IP should be there is something like this. "unknown, 93.186.30.120" or "10.0.1.169, 186.38.84.3" Apache is at the front listening at port 80 and used as proxy to Tomcat that listens at port 8081. My router config would not allow to pass any conection that come by any port other than 80. Any Help? Thanks in advance.

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  • Is System.nanoTime() consistent across threads?

    - by obvio171
    I want to count the time elapsed between two events in nanoseconds. To do that, I can use System.nanoTime() as mentioned here. The problem is that the two events are happening in different threads. Since nanoTime() doesn't return an absolute timestamp but instead can only be used to calculate time differences, I'd like to know if the values I get on the two different threads are consistent with the physical time elapsed between the two events.

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  • Why my object sees variables which were not given to it in the constructor?

    - by Roman
    I have the following code. Which is "correct" and which I do not understand: private static void updateGUI(final int i, final JLabel label) { SwingUtilities.invokeLater( new Runnable() { public void run() { label.setText("You have " + i + " seconds."); } } ); } I create a new instance of the Runnable class and then in the run method of this instance I use variables label and i. It works, but I do not understand why it work. Why the considered object sees values of these variables. According to my understanding the code should look like that (and its wrong): private static void updateGUI(final int i, final JLabel label) { SwingUtilities.invokeLater(new Runnable(i,label) { public Runnable(int i, JLabel label) { this.i = i; this.label = label; } public void run() { label.setText("You have " + i + " seconds."); } }); } So, I would give the i and label variables to the constructor so the object can access them... By the way, in the updateGUI I use final before the i and label. I think I used final because compiler wanted that. But I do not understand why.

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  • [hibernate - jpa] @OneToOne annotoation problem (i think...)

    - by blow
    Hi all, im new in hibernate and JPA and i have some problems with annotations. My target is to create this table in db (PERSON_TABLE with personal-details) ID ADDRESS NAME SURNAME MUNICIPALITY_ID First of all, i have a MUNICIPALITY table in db containing all municipality of my country. I mapped this table in this ENTITY: @Entity public class Municipality implements Serializable { @Id @GeneratedValue(strategy=GenerationType.IDENTITY) private Long id; private String country; private String province; private String name; @Column(name="cod_catasto") private String codCatastale; private String cap; public Municipality() { } ... Then i make an EMBEDDABLE class Address containing fields that realize a simple address... @Embeddable public class Address implements Serializable { @OneToOne(cascade=CascadeType.ALL) @JoinColumn(name="id_municipality") private Municipality municipality; @Column(length=45) private String address; public Address() { } ... Finally i embedded this class into Person ENTITY @Entity public class Person implements Serializable { @Id @GeneratedValue(strategy=GenerationType.IDENTITY) private Long id; private String name; private String surname; @Embedded private Address address; public Person() { } ... All works good when i have to save a new Person record, in fact hibernate creates a PERSON_TABLE as i want, but if i try to retrieve a Person record i have an exception. HQL is simply "from Person" The excpetion is (Entities is the package containing all classes above-mentioned): org.hibernate.AnnotationException: @OneToOne or @ManyToOne on Entities.Person.address.municipality references an unknown entity: Entities.Municipality Is the @OneToOne annotation the problem? Thanks.

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  • Do Hibernate table classes need to be Serializable?

    - by Scott Leis
    I have inherited a Websphere Portal project that uses Hibernate 3.0 to connect to a SQL Server database. There are about 130 Hibernate table classes in this project. They all implement Serializable. None of them declare a serialVersionUID field, so the Eclipse IDE shows a warning for all of these classes. Is there any actual need for these classes to implement Serializable? If so, is there any tool to add a generated serialVersionUID field to a large number of classes at once (just to make the warnings go away) ?

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  • Setting jvmargs in log4j.properties file

    - by Thomas
    Hey This is a bit of a weird request but I am trying to set some jvmargs in the log4j.properties file. At present I use ant to for example set some args.... jvmarg value="-Dmail.smtp.socketFactory.port=465" ... but it would be great to group a few of these logging relevant arguments into the .properties file. Does anyone know how to do this? Thanks in advance!

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  • Create a triangle out of stars using only recursion

    - by Ramblingwood
    I need to to write a method that is called like printTriangle(5);. We need to create an iterative method and a recursive method (without ANY iteration). The output needs to look like this: * ** *** **** ***** This code works with the iterative but I can't adapt it to be recursive. public void printTriangle (int count) { int line = 1; while(line <= count) { for(int x = 1; x <= line; x++) { System.out.print("*"); } System.out.print("\n"); line++; } } I should not that you cannot use any class level variables or any external methods. Thanks.

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  • Does anyone know why my maps only show grid

    - by NickTFried
    I've doubled checked my API key is right and that is right I doubled checked that it was correct. Here is my source and XML could anyone check to see what is wrong. Also I make sure I have internet. <?xml version="1.0" encoding="utf-8"?> <uses-permission android:name="android.permissions.INTERNET"/> <uses-permission android:name="android.permissions.ACCESS_FINE_LOCATION"/> <application android:icon="@drawable/icon" android:label="@string/app_name"> <uses-library android:name="com.google.android.maps" /> <activity android:name=".CadetCommand" android:label="@string/app_name"> <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> <activity android:name="RedLight"></activity> <activity android:name="PTCalculator"></activity> <activity android:name="LandNav"></activity> </application> <uses-sdk android:minSdkVersion="4"/> package edu.elon.cs.mobile; import com.google.android.maps.MapActivity; import com.google.android.maps.MapView; import android.os.Bundle; public class LandNav extends MapActivity{ public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.landnav); } @Override protected boolean isRouteDisplayed() { return false; } }

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  • Spring import runs hibernate persistence twice

    - by Jaanus
    I have 2 spring configurations : spring-servlet.xml spring-security.xml needed to add this line to security: <beans:import resource="spring-servlet.xml"/> Now hibernate is ran twice, this is log screenshot : my web.xml: <servlet> <servlet-name>spring</servlet-name> <servlet-class> org.springframework.web.servlet.DispatcherServlet </servlet-class> <load-on-startup>1</load-on-startup> </servlet> <servlet-mapping> <servlet-name>spring</servlet-name> <url-pattern>/</url-pattern> </servlet-mapping> <listener> <listener-class> org.springframework.web.context.ContextLoaderListener </listener-class> </listener> <context-param> <param-name>contextConfigLocation</param-name> <param-value> /WEB-INF/spring-security.xml </param-value> </context-param>

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