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  • Java Constructor Style (Check parameters aren't null)

    - by Peter
    What are the best practices if you have a class which accepts some parameters but none of them are allowed to be null? The following is obvious but the exception is a little unspecific: public class SomeClass { public SomeClass(Object one, Object two) { if (one == null || two == null) { throw new IllegalArgumentException("Parameters can't be null"); } //... } } Here the exceptions let you know which parameter is null, but the constructor is now pretty ugly: public class SomeClass { public SomeClass(Object one, Object two) { if (one == null) { throw new IllegalArgumentException("one can't be null"); } if (two == null) { throw new IllegalArgumentException("two can't be null"); } //... } Here the constructor is neater, but now the constructor code isn't really in the constructor: public class SomeClass { public SomeClass(Object one, Object two) { setOne(one); setTwo(two); } public void setOne(Object one) { if (one == null) { throw new IllegalArgumentException("one can't be null"); } //... } public void setTwo(Object two) { if (two == null) { throw new IllegalArgumentException("two can't be null"); } //... } } Which of these styles is best? Or is there an alternative which is more widely accepted? Cheers, Pete

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  • Unique number generation with Java Server Faces

    - by Buddhika Ariyaratne
    I am developing an application for a medical channelling centre where multiple users reserve bookings for doctors with JSF and JPA. A sequence number is unique to the Doctor, Date and Session. I tried to get a unique sequence number from counting the previous bookings and add one, but if two requests comes at the same time, two bookings get the same number causing trouble to functionality. How can I get unique number in this case? Can I use an application wide bean to generate it? (I thought it is not practicle to get the unique number from the database sequence number as there are several doctors, sessions and daily they have to have different booking number.)

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  • Joining remote paths in Java

    - by Mickael Marrache
    I'm using the FTP library provided by Apache (commons-net). I want to check if a file exists on the FTP server so I use the listFiles method of FTPClient: ftpClient.listFiles(remoteFileDir + "\\" + fileName); The current directory is the FTP server root directory. So, the value of remoteFileDir is a path relative to this root directory. My question concerns the merge between the remote directory path and the file name. What is the right way to do it? For a local file, I would do: File file = new File(remoteFileDir,fileName); but here it doesn't work since when I call file.getAbsolutePath(), I get an absolute path for the file in the local current directory which is not what I want. Also, I guess the merging has been done according to my local environment. PS: I looked at How are paths determined on a remote machines? but it doesn't help me. Thanks

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  • Java - how to tell class of an object?

    - by lkm
    Given a method that accepts as a parameter a certain supertype. Is there any way, within that method, to determine the actual class of the object that was passed to it? I.e. if a subtype of the allowable parameter was actually passed, is there a way to find out which type it is? If this isn't possible can someone explain why not (from a language design perspective)? Thanks Update: just to make sure I was clear void doSomething(MyType myType) { //determine if myType is MyType OR one of its subclasses } Since the method signature specifies the parameter as being MyType, then how can one tell if the object is actually a subtype of MyType (and which one).

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  • Using java class HttpsURLConnection

    - by KB22
    Hi all, I have a small piece of code which basically impements a HTTP-Client, i.e. it POSTS request and works with re RESPONSE. As long as HTTP is concenerned everthing work well. For some reason I now have to support HTTPS too. So here is briefly what I do in order to get a connection opened: URL url = new URL(serverAddress); HttpsURLConnection httpsConn = (HttpsURLConnection) url.openConnection(); This fails, stating: sun.net.www.protocol.https.HttpsURLConnectionImpl cannot be cast to com.sun.net.ssl.HttpsURLConnection I guess this is kinda trivial, but I just don't get what I'm doing wrong in this one... Googled it, and the code just looks right - not? any ideas are appreciated! thanks, K

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  • Confusion in RegExp Reluctant quantifier? Java

    - by Dusk
    Hi, Could anyone please tell me the reason of getting an output as: ab for the following RegExp code using Relcutant quantifier? Pattern p = Pattern.compile("abc*?"); Matcher m = p.matcher("abcfoo"); while(m.find()) System.out.println(m.group()); // ab and getting empty indices for the following code? Pattern p = Pattern.compile(".*?"); Matcher m = p.matcher("abcfoo"); while(m.find()) System.out.println(m.group());

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  • HQL make query searching by date (Java+NetBeans)

    - by Zloy Smiertniy
    Hi all I have the following issue. I have a table of reserves in my MySQL DB, the date columns is defined DATETIME. I need to make a query using hibernate to find all reserves in one day no matter the hour, just that its the same year month and date, and I'm doing this public List<Reserve> bringAllResByDate(Date date){ em = emf.createEntityManager(); Query q = em.createQuery("SELECT r FROM Reserve r WHERE r.date=:date "); q.setParameter("date", date); ... I really dont know how to make it compare, and bring me just those from the specified date, any help??

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  • How to extract byte-array from one xml and store it in another in Java

    - by grobartn
    So I am using DocumentBuilderFactory and DocumentBuilder to parse an xml. So it is DOM parser. But what I am trying to do is extract byte-array data (its an image encoded in base64) Store it in one object and later in code write it out to another xml encoded in base64. What is the best way to store this in btw. Store it as string? or as ByteArray? How can I extract byte array data in best way and write it out. I am not experienced with this so wanted to get opinion from the group. UPDATE: I am given XML I do not have control of incoming XML that comes in binary64 encoded < byte-array > ... base64 encoded image ... < /byte-array > Using parser I have I need to store this node and question is should that be byte or string and then writing it out to another node in new xml. again in base64 encoding. thanks

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  • Ask StackOverFlow : Canny a LightWeight Authorization library in Java

    - by eltados
    In the course of my work i need to develop an authorization engine ( i'm already authenticated and i check access of a user to an action ) in order to store all the authorization logic inside a same place and be able to reuse it and i have created the mini library. http://github.com/eltados/canny (updated) what do you think about it? What are the limits of my approch ? Do you understand the benefit or it? Is there any lightweight Authorization engine library i could have a look at? I had a look at spring security and it does not really answer my requirement. The main idea is that i want to be able to reuse the same code to controll access in the controllers and the views.

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  • Gracefully avoiding NullPointerException in Java

    - by Yuval A
    Consider this line: if (object.getAttribute("someAttr").equals("true")) { // .... Obviously this line is a potential bug, the attribute might be null and we will get a NullPointerException. So we need to refactor it to one of two choices: First option: if ("true".equals(object.getAttribute("someAttr"))) { // .... Second option: String attr = object.getAttribute("someAttr"); if (attr != null) { if (attr.equals("true")) { // .... The first option is awkward to read but more concise, while the second one is clear in intent, but verbose. Which option do you prefer in terms of readability?

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  • Shift operator in Java bizarre program output

    - by Umesh Kacha
    I came across the following program and it behaving in unexpected manner. public class ShiftProgram { public static void main(String[] args) { int i = 0; while(-1 << i != 0) i++; System.out.println(i); } } If we think about this program output, when it reaches 32 while loop condition should return false and terminate and it should print 32. If you ran this program, it does not print anything but goes into an infinite loop. Any idea whats going on? Thank you in advance.

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  • Java Application/Thread Server

    - by Manrico Corazzi
    I am looking for something very close to an application server with these features: it should handle a series of threads/daemons, allowing the user to start-stop-reload each one without affecting the others it should keep libraries separated between different threads/daemons it should allow to share some libraries Currently we have some legacy code reinventing the wheel... and not a perflectly round-shaped one at that! I thought to use Tomcat, but I don't need a web server, except maybe for the simple backoffice user interface (/manager/html). Any suggestion? Is there a non-web application server, or is there a better alternative to Tomcat (more lightweight, for example, or easier to configure)? Thanks in advance.

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  • help with reflections and annotations in java

    - by Yonatan
    Hello Internet ! I'm having trouble with doubling up on my code for no reason other than my own lack of ability to do it more efficiently... `for (Method curr: all){ if (curr.isAnnotationPresent(anno)){ if (anno == Pre.class){ for (String str : curr.getAnnotation(Pre.class).value()){ if (str.equals(method.getName()) && curr.getReturnType() == boolean.class && curr.getParameterTypes().length == 0){ toRun.add(curr); } } } if (anno == Post.class) { for (String str : curr.getAnnotation(Post.class).value()){ if (str.equals(method.getName()) && curr.getReturnType() == boolean.class && curr.getParameterTypes().length == 0){ toRun.add(curr); } } } } }` anno is a parameter - Class, and Pre and Post are my annotations, both have a value() which is an array of strings. Of course, this is all due to the fact that i let Eclipse auto fill code that i don't understand yet.

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  • quick java question

    - by j-unit-122
    private static char[] quicksort (char[] array , int left , int right) { if (left < right) { int p = partition(array , left, right); quicksort(array, left, p - 1 ); quicksort(array, p + 1 , right); } for (char i : array) System.out.print(i + ” ”); System.out.println(); return array; } private static int partition(char[] a, int left, int right) { char p = a[left]; int l = left + 1, r = right; while (l < r) { while (l < right && a[l] < p) l++; while (r > left && a[r] >= p) r--; if (l < r) { char temp = a[l]; a[l] = a[r]; a[r] = temp; } } a[left] = a[r]; a[r] = p; return r; } } hi guys just a quick question regarding the above coding, i know that the above coding returns the following B I G C O M P U T E R B C E G I M P U T O R B C E G I M P U T O R B C E G I M P U T O R B C E G I M P U T O R B C E G I M O P T U R B C E G I M O P R T U B C E G I M O P R T U B C E G I M O P R T U B C E G I M O P R T U B C E G I M O P R T U B C E G I M O P R T U B C E G I M O P R T U when the sequence BIGCOMPUTER is used but my question is can someone explain to me what is happening in the code and how? i know abit about the quick-sort algorithm but it doesnt seem to be the same in the above example.

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  • Java BoxLayout alignment issue

    - by ManInMoon
    Can anyone help me. Why is the Label "Current" NOT left aligned in Panel/Frame? public static void main(String[] args) { JFrame TFrame = new JFrame("Test DisplayLayout"); TFrame.setResizable(true); TFrame.setSize(new Dimension(900, 840)); TFrame.setLocationRelativeTo(null); TFrame.setTitle("DisplayLayout"); TFrame.setVisible(true); JPanel P = DisplayLayout2(); P.setVisible(true); P.setOpaque(true); P.setLayout(new BoxLayout(P, BoxLayout.Y_AXIS)); TFrame.add(P); TFrame.revalidate(); TFrame.repaint(); } public static JPanel DisplayLayout2() { JPanel Panel=new JPanel(); Panel.setVisible(true); Panel.setOpaque(true); Panel.setLayout(new BoxLayout(Panel, BoxLayout.Y_AXIS)); Panel.setAlignmentX(Component.LEFT_ALIGNMENT); JLabel lab = new JLabel("Current"); lab.setHorizontalAlignment(SwingConstants.LEFT); lab.setForeground(Color.WHITE); lab.setBackground(Color.PINK); lab.setOpaque(true); Panel.add(lab,Component.LEFT_ALIGNMENT); JPanel posPanel = new JPanel(); JScrollPane scrollPane = new JScrollPane(posPanel,JScrollPane.VERTICAL_SCROLLBAR_ALWAYS,JScrollPane.HORIZONTAL_SCROLLBAR_NEVER); scrollPane.setPreferredSize(new Dimension(290, 200)); scrollPane.setOpaque(true); posPanel.setBackground(Color.YELLOW); posPanel.setPreferredSize(new Dimension(290, 200)); posPanel.setLayout(new BoxLayout(posPanel, BoxLayout.Y_AXIS)); posPanel.setAlignmentX(Component.LEFT_ALIGNMENT); Panel.add(scrollPane); return Panel; }

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  • Adding to arrays and printing arrays in Java

    - by nfoggia
    I need help figuring out how to get the user to input a number of integers no more than 10, and then add them to an array and print them out from the array. The code I have below, when run, asks the user for the integers and then runs forever and doesn't work. What am I doing wrong? public static void main(String[] args) { Scanner input = new Scanner(System.in); // create a new scanner System.out.print("Enter integers between 1 and 100\n "); int[] nextNumber = new int[10]; int i = 0; int number = input.nextInt(); while (i < nextNumber.length){ i++; nextNumber[i] = number; number = input.nextInt(); } int a = 0; while (a < nextNumber.length){ a++; System.out.println(nextNumber[a]); }

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  • Enumeration classes in Java

    - by Crystal
    I have one class that declares an enumeration type as: public enum HOME_LOAN_TERMS {FIFTEEN_YEAR, THIRTY_YEAR}; Is this type usable in another class? I'm basically trying to complete a homework assignment where we have two types of loans, and one loanManager class. When I try to use the HOME_LOAN_TERMS.THIRTY_YEAR in my loanManager class that does not extend or implement the loan class, I get an error saying it 'cannot find symbol HOME_LOAN_TERMS.' So I did not know if my loanManager class needed to implement the two different loan classes. Thanks.

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  • Java days of week calculation

    - by Shahid
    I have an Enum for Days of week (with Everyday, weekend and weekdays) as follows where each entry has an int value. public enum DaysOfWeek { Everyday(127), Weekend(65), Weekdays(62), Monday(2), Tuesday(4), Wednesday(8), Thursday(16), Friday(32), Saturday(64), Sunday(1); private int bitValue; private DaysOfWeek(int n){ this.bitValue = n; } public int getBitValue(){ return this.bitValue; } } Given a TOTAL of any combination of the entries, what would be the simplest way to calculate all individual values and make an arraylist from it. For example given the number 56 (i.e. Wed+Thur+Fri), how to calculate the list of individual values.

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  • java : how to handle the design when template methods throw exception when overrided method not throw

    - by jiafu
    when coding. try to solve the puzzle: how to design the class/methods when InputStreamDigestComputor throw IOException? It seems we can't use this degisn structure due to the template method throw exception but overrided method not throw it. but if change the overrided method to throw it, will cause other subclass both throw it. So can any good suggestion for this case? abstract class DigestComputor{ String compute(DigestAlgorithm algorithm){ MessageDigest instance; try { instance = MessageDigest.getInstance(algorithm.toString()); updateMessageDigest(instance); return hex(instance.digest()); } catch (NoSuchAlgorithmException e) { LOG.error(e.getMessage(), e); throw new UnsupportedOperationException(e.getMessage(), e); } } abstract void updateMessageDigest(MessageDigest instance); } class ByteBufferDigestComputor extends DigestComputor{ private final ByteBuffer byteBuffer; public ByteBufferDigestComputor(ByteBuffer byteBuffer) { super(); this.byteBuffer = byteBuffer; } @Override void updateMessageDigest(MessageDigest instance) { instance.update(byteBuffer); } } class InputStreamDigestComputor extends DigestComputor{ // this place has error. due to exception. if I change the overrided method to throw it. evey caller will handle the exception. but @Override void updateMessageDigest(MessageDigest instance) { throw new IOException(); } }

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  • Modifying annotation attribute value at runtime in java

    - by Lici
    Hi folks: some methods in our model pojos have been annotated like this: @Column(name="cli_clipping_id", updatable=false, columnDefinition = "varchar(" + ModelUtils.ID_LENGTH + ") COLLATE utf8_bin") columnDefinition attribute is database vendor dependant, so when trying to drop schema in HSQLDB using Hibernate it fails: [ERROR] 16 jun 12:58:42.480 PM main [org.hibernate.tool.hbm2ddl.SchemaExport] Unexpected token: COLLATE in statement [create table cms.edi_editorial_obj (edi_uuid varchar(23) COLLATE ] To fix this, i'm thinking on this solution (but don't want to spend time if it isn't possible) , at runtime, for each method column annotated: Get @Column annotation Create a copy of the column annotation, setting columnDefinition null using javaassist. set column method annotation to the copy column annotation object overriding the old one (i don't know it this is possible) Is it possible to "hack" these methods this way? Any help would be much appreciated ...

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  • Getting the 'external' IP address in Java

    - by Caylem
    Hi I'm not too sure how to go about getting the external IP address of the machine as a computer outside of a network would see it. My following IPAddress class only gets the local IP address of the machine. Any help would be appreciated. Thanks. public class IPAddress { private InetAddress thisIp; private String thisIpAddress; private void setIpAdd(){ try{ InetAddress thisIp = InetAddress.getLocalHost(); thisIpAddress = thisIp.getHostAddress().toString(); } catch(Exception e){} } protected String getIpAddress(){ setIpAdd(); return thisIpAddress; } }

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  • java servlet: generate zip file from BLOBs

    - by Zack
    I'm trying to zip a large number of pdf files (stored as BLOBs in the DB) and then return the zip as an attachment to the user. What's the best way to do this without running into memory issues? Another note: I actually need to merge some PDFs prior to adding them to the ZipOutputStream. Therefore, a couple PDFs will need to be stored in memory at a time. I assume it would be best to then store them as temporary files on the server before zipping them all?

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