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  • Does collections type conversion util methods already exist in any API?

    - by Delta
    interface TypeConverter<T, E> { T convert(E e); } class CollectionUtil() { public static <E> List<T> convertToList(List<E> fromList, TypeConverter<T, E> conv) { { if(fromList== null) return null; List<T> newList = new ArrayList<T>(fromList.size()) for(E e : fromList) { newList.add(conv.convert(e)); } return newList; } } Above code explains converting from List of String to List of Integer by implementing TypeConverter interface for String, Integer. Are there already any collections conversion utility methods exists in any API like list to set and so on?

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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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  • Download dynamic file with GWT

    - by Maksim
    I have a GWT page where user enter data (start date, end date, etc.), then this data goes to the server via RPC call. On the server I want to generate Excel report with POI and let user save that file on their local machine. This is my test code to stream file back to the client but for some reason I think it does not know how to stream file to the client when I'm using RPC: public class ReportsServiceImpl extends RemoteServiceServlet implements ReportsService { public String myMethod(String s) { File f = new File("/excelTestFile.xls"); String filename = f.getName(); int length = 0; try { HttpServletResponse resp = getThreadLocalResponse(); ServletOutputStream op = resp.getOutputStream(); ServletContext context = getServletConfig().getServletContext(); resp.setContentType("application/octet-stream"); resp.setContentLength((int) f.length()); resp.setHeader("Content-Disposition", "attachment; filename*=\"utf-8''" + filename + ""); byte[] bbuf = new byte[1024]; DataInputStream in = new DataInputStream(new FileInputStream(f)); while ((in != null) && ((length = in.read(bbuf)) != -1)) { op.write(bbuf, 0, length); } in.close(); op.flush(); op.close(); } catch (Exception ex) { ex.printStackTrace(); } return "Server says: " + filename; } } I've red somewhere on internet that you can't do file stream with RPC and I have to use Servlet for that. Is there any example of how to use Servlet and how to call that servlet from ReportsServiceImpl. Do I really need to make a servlet or it is possible to stream it back with my RPC?

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  • Hibernate session method to update object

    - by EugeneP
    I need this roadmap of a Hibernate managed object instance. First, I create an instance with initial properties and persist this object in a db. Then session associated with this object is closed. But still, I serialize my object and on the next step deserialize it, invoke some setters, and again, I need to update what changed in a database. What methods of Hibernate session should I use? persist() or save() on the first step and saveOrUpdate() on the second? In fact I see that saveOrUpdate() can be used on each step. What would you recommend?

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  • Two entities with @ManyToOne should join the same table

    - by Ivan Yatskevich
    I have the following entities Student @Entity public class Student implements Serializable { @Id @GeneratedValue(strategy = GenerationType.AUTO) private Long id; //getter and setter for id } Teacher @Entity public class Teacher implements Serializable { @Id @GeneratedValue(strategy = GenerationType.AUTO) private Long id; //getter and setter for id } Task @Entity public class Task implements Serializable { @Id @GeneratedValue(strategy = GenerationType.AUTO) private Long id; @ManyToOne(optional = false) @JoinTable(name = "student_task", inverseJoinColumns = { @JoinColumn(name = "student_id") }) private Student author; @ManyToOne(optional = false) @JoinTable(name = "student_task", inverseJoinColumns = { @JoinColumn(name = "teacher_id") }) private Teacher curator; //getters and setters } Consider that author and curator are already stored in DB and both are in the attached state. I'm trying to persist my Task: Task task = new Task(); task.setAuthor(author); task.setCurator(curator); entityManager.persist(task); Hibernate executes the following SQL: insert into student_task (teacher_id, id) values (?, ?) which, of course, leads to null value in column "student_id" violates not-null constraint Can anyone explain this issue and possible ways to resolve it?

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  • 1 error with an array "missing return statement"

    - by danielit0w
    import javax.swing.JOptionPane; public class Mate { double suma (double x1,double x2) {return x1+x2;} double suma (double x1,double x2,double x3) {return x1+x2+x3;} double suma (int num [ ]) {int i=num.length; int j=0; int s=0; for(j=0;j < i;j++) {return (double)(s);}}} // here appears the error "missing return statement" class AplicacionMate {public static void main (String arg []) {int n[ ]={5,4,3,2,1}; double r=0.0; Mate m=new Mate ( ); r=m.suma(5,4); JOptionPane.showMessageDialog(null,"La suma 1="+r); r=m.suma(5,5,4); JOptionPane.showMessageDialog(null,"La suma 2="+r); r=m.suma(n); JOptionPane.showMessageDialog(null,"La suma del arreglo="+r); System.exit(0);}}

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  • In this example, would Customer or AccountInfo properly be the entity group parent?

    - by Badhu Seral
    In this example, the Google App Engine documentation makes the Customer the entity group parent of the AccountInfo entity. Wouldn't AccountInfo encapsulate Customer rather than the other way around? Normally I would think of an AccountInfo class as including all of the information about the Customer. import javax.jdo.annotations.IdGeneratorStrategy; import javax.jdo.annotations.PersistenceCapable; import javax.jdo.annotations.Persistent; import javax.jdo.annotations.PrimaryKey; import com.google.appengine.api.datastore.Key; import com.google.appengine.api.datastore.KeyFactory; @PersistenceCapable public class AccountInfo { @PrimaryKey @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY) private Key key; public void setKey(Key key) { this.key = key; } } // ... KeyFactory.Builder keyBuilder = new KeyFactory.Builder(Customer.class.getSimpleName(), "custid985135"); keyBuilder.addChild(AccountInfo.class.getSimpleName(), "acctidX142516"); Key key = keyBuilder.getKey(); AccountInfo acct = new AccountInfo(); acct.setKey(key); pm.makePersistent(acct);

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  • getSystemResourceAsStream() returns null

    - by Hitesh Solanki
    Hiii... I want to get the content of properties file into InputStream class object using getSystemResourceAsStream(). I have built the sample code. It works well using main() method,but when i deploy the project and run on the server, properties file path cannot obtained ... so inputstream object store null value. Sample code is here.. public class ReadPropertyFromFile { public static Logger logger = Logger.getLogger(ReadPropertyFromFile.class); public static String readProperty(String fileName, String propertyName) { String value = null; try { //fileName = "api.properties"; //propertyName = "api_loginid"; System.out.println("11111111...In the read proprty file....."); // ClassLoader loader = ClassLoader.getSystemClassLoader(); InputStream inStream = ClassLoader.getSystemResourceAsStream(fileName); System.out.println("In the read proprty file....."); System.out.println("File Name :" + fileName); System.out.println("instream = "+inStream); Properties prop = new Properties(); try { prop.load(inStream); value = prop.getProperty(propertyName); } catch (Exception e) { logger.warn("Error occured while reading property " + propertyName + " = ", e); return null; } } catch (Exception e) { System.out.println("Exception = " + e); } return value; } public static void main(String args[]) { System.out.println("prop value = " + ReadPropertyFromFile.readProperty("api.properties", "api_loginid")); } }

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  • Tomcat Postgres Connection

    - by user191207
    Hi, I'm using a singleton class for a PostgresSQL connection inside a servelet. The problem is that once it is open it works for a while (I guess until some timeout), and then it starts throwing a I/O exception. Any idea what is happening to the singleton class inside Tomcat VM? Thanks

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  • How can I load a property lazily in JDO (on Google App Engine)?

    - by luciano
    I have this code in one of my @PersistenceCapable classes: @Persistent private Blob data; The Blob can be quite big, so I'd like to load it lazily since most of the times I don't need it. How can I annotate that property to avoid immediate loading? I could create another class that contains the Blob alone and then use a lazy one-to-one, but I'd like to solve this with annotations.

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  • GWT: stange import collision error in visualisation api

    - by parag_
    hi, I'm attempting to add two charts to a gwt page using the visualization api, but for some strange and inexplicable reason, eclipse claims that the following two imports are colliding - which makes no sense to me. In the methods where i am calling them, I have even tried using the fully qualified names, but that doesnt seem to help either. Any idea what may be going on ? import com.google.gwt.visualization.client.visualizations.Table.Options; import com.google.gwt.visualization.client.visualizations.LineChart.Options;

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  • Refreshing a JPA result list which is bound with a jTable

    - by exhuma
    First off, I hage to write this on my mobile. But I'll try to format it properly. In Netbeans I created a jTable and bound it's values to a JPA result set. This works great. The qery contains a param which i set in the pre-create box of the "query result" component. So just before netbeans creates the query result i write this: myQuery.setParameter("year", "1997"); This works fine. Now, I have an event handler which is supposed to change the param and display the new values in the table. So I do this: myQuery.setParameter("year", "2005"); myResultList.clear(); myResultList.addAll(myQuery.getResultList()); jTable1.updateUI(); This works, but it feels wrong to me. Note: the result set is bound to the table. So I was hoping there was something like this: myQuery.setParameter("year", "2005"); myResultList.refresh(); Is there something like this?

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  • Embedding XSL Stylesheet into XML

    - by user700996
    I have the following XML: <?xml version="1.0" encoding="ISO-8859-1"?> <?xml-stylesheet type="text/xsl" href="http://www.fakedomain.com/sally.xsl"?> And the following content in sally.xsl: <?xml version="1.0" encoding="ISO-8859-1"?> <xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"> <xsl:template match="/"> <html> <body> <xsl:for-each select="documentcollection/document"> <p> <xsl:for-each select="rss/channel/item"> <xsl:value-of select="title"/><br /> <xsl:value-of select="description"/><br /> <xsl:value-of select="link"/><br /> </xsl:for-each> </p> </xsl:for-each> </body> </html> </xsl:template> </xsl:stylesheet> However, the browser displays the XML as though the XSL line is not present. Do you know why the browser is ignoring the XSL stylesheet? Is the style sheet wrong? Thanks

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  • Androids ExpandableListView - where to put the button listener for buttons that are children

    - by CommonKnowledge
    I have been playing around a lot with the ExpandableListView and I cannot figure out where to add the button listeners for the button that will be the children in the view. I did manage to get a button listener working that uses getChildView() below, but it seems to be the same listener for all the buttons. The best case scenario is that I would be able to implement the button listeners in the class that instantiates the ExpandableListAdapter class, and not have to put the listeners in the actual ExpandableListAdapter class. At this point I don't even know if that is possible I have been experimenting with this tutorial/code: HERE getChildView() @Override public View getChildView(int set_new, int child_position, boolean view, View view1, ViewGroup view_group1) { ChildHolder childHolder; if (view1 == null) { view1 = LayoutInflater.from(info_context).inflate(R.layout.list_group_item_lv, null); childHolder = new ChildHolder(); childHolder.section_btn = (Button)view1.findViewById(R.id.item_title); view1.setTag(childHolder); childHolder.section_btn.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { Toast.makeText(info_context, "button pushed", Toast.LENGTH_SHORT).show(); } }); }else { childHolder = (ChildHolder) view1.getTag(); } childHolder.section_btn.setText(children_collection.get(set_new).GroupItemCollection.get(child_position).section); Typeface tf = Typeface.createFromAsset(info_context.getAssets(), "fonts/AGENCYR.TTF"); childHolder.section_btn.setTypeface(tf); return view1; } Any help would be much appreciated. Thank you and I will be standing by.

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  • Concurrent Programming:Should I write a sequential program first, then add thread safety?

    - by evthim
    I'm working on a project where we have to create a number of threads(actual number will be inputted in by testers (TA's)). I'm having trouble not only with the programming but also with the design, I can't wrap my head around all of the threads that will be invoked and where I might cause errors. The project is due soon so I don't want to waste time on this if it'll actually set me back, but I was wondering if I should write the program like only one thread will be running and everything should be sequential and then later go back and try to add the thread safety parts of the code? Would that take twice the original amount of time? Project Description: Note:I'm going to be as vague as possible so I don't violate any honor codes, sorry :( your program should accept n number of objectA threads, m number of objectB threads, and r number of objectC objectB threads interact with code in objectA. objectA threads interact with code in objectB and objectC objectB and objectC don't directly interact, but do so indirectly through objectA -ex: objectB needs something from objectA. objectA gets the result for that something by calling objectC my confusion stems mostly from the fact that all of this interactions will be done by m+n threads and there are various restrictions throughout the descriptions, like objectB can request something from objectA, and objectA has to wait for objectC to finish that something before returning it to objectB. Also each objectA thread can only work on one instruction from objectB at a time, etc. etc. I just want to know if I write the code so that there is only 1 objectA, 1 objectB and 1 object C, can I go back and easily modify it so that those 1's can be changed to m, n and r? Sorry again, if my description is a little bit confusing.

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  • Defining tokens at runtime

    - by Peter Crenshaw
    I want to write a parser for EDIFACT messages with JavaCC. My problem is that I cannot define all terminal symbols before parsing a message because at the begining of each message there is a so called "Advice Segment" ("UNA" Segment) which defines things like element seperator symbol, escape symbol, segment terminator symbol and decimal notation (e.g. '.' or ','). So I think/guess the production rules need some kind of variables which must be set at runtime during parsing. Can this be done with JavaCC and if so how? Or is there another way I am missing?

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  • Scanner cuts off my String after about 2400 characters

    - by Ventrue
    I've got some very basic code like while (scan.hasNextLine()) { String temp = scan.nextLine(); System.out.println(temp); } where scan is a Scanner over a file. However, on one particular line, which is about 6k chars long, temp cuts out after something like 2470 characters. There's nothing special about when it cuts out; it's in the middle of the word "Australia." If I delete characters from the line, the place where it cuts out changes; e.g. if I delete characters 0-100 in the file then Scanner will get what was previously 100-2570. I've used Scanner for larger strings before. Any idea what could be going wrong?

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  • Calculated group-by fields in MongoDB

    - by Navin Viswanath
    For this example from the MongoDB documentation, how do I write the query using MongoTemplate? db.sales.aggregate( [ { $group : { _id : { month: { $month: "$date" }, day: { $dayOfMonth: "$date" }, year: { $year: "$date" } }, totalPrice: { $sum: { $multiply: [ "$price", "$quantity" ] } }, averageQuantity: { $avg: "$quantity" }, count: { $sum: 1 } } } ] ) Or in general, how do I group by a calculated field?

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  • How can I use BeanUtils copyProperties to copy from boolean to Boolean?

    - by carrier
    BeanUtils copyProperties, out of the box, doesn't seem to handle copying from Boolean object properties to boolean primitive properties. I figured I could create and register a converter to handle this, but that just didn't seem to work. So, how can I use BeanUtils to copy the properties from class Source to class Destination where: public class Destination { private boolean property; public boolean isProperty() { return property; } public void setProperty(boolean property) { this.property = property; } } public class Source{ private Boolean property; public Boolean getProperty() { return property; } public void setProperty(Boolean property) { this.property = property; } }

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  • tomcat isolate webapps

    - by cometta
    multiple webapp running on same tomcat using same jvm. sometime, one webapp that have memory leak will cause entire jvm to crash and affect other webapps. any recommendation how to isolated that without need to use multiple jvm and tomcat

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