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• Way to store a large dictionary with low memory footprint + fast lookups (on Android)

  - by BobbyJim

  I'm developing an android word game app that needs a large (~250,000 word dictionary) available. I need: reasonably fast look ups e.g. constant time preferable, need to do maybe 200 lookups a second on occasion to solve a word puzzle and maybe 20 lookups within 0.2 second more often to check words the user just spelled. EDIT: Lookups are typically asking "Is in the dictionary?". I'd like to support up to two wildcards in the word as well, but this is easy enough by just generating all possible letters the wildcards could have been and checking the generated words (i.e. 26 * 26 lookups for a word with two wildcards). as it's a mobile app, using as little memory as possible and requiring only a small initial download for the dictionary data is top priority. My first naive attempts used Java's HashMap class, which caused an out of memory exception. I've looked into using the SQL lite databases available on android, but this seems like overkill. What's a good way to do what I need?

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• java: libraries for immutable functional-style data structures

  - by Jason S

  This is very similar to another question (Functional Data Structures in Java) but the answers there are not particularly useful. I need to use immutable versions of the standard Java collections (e.g. HashMap / TreeMap / ArrayList / LinkedList / HashSet / TreeSet). By "immutable" I mean immutable in the functional sense (e.g. purely functional data structures), where updating operations on the data structure do not change the original data, but instead return a new instance of the same kind of data structure. Also typically new and old instances of the data structure will share immutable data to be efficient in time and space. From what I can tell my options include: Functional Java Scala Clojure but I'm not sure whether any of these are particularly appealing to me. I have a few requirements/desirements: the collections in question should be usable directly in Java (with the appropriate libraries in the classpath). FJ would work for me; I'm not sure if I can use Scala's or Clojure's data structures in Java w/o having to use the compilers/interpreters from those languages and w/o having to write Scala or Clojure code. Core operations on lists/maps/sets should be possible w/o having to create function objects with confusing syntaxes (FJ looks slightly iffy) They should be efficient in time and space. I'm looking for a library which ideally has done some performance testing. FJ's TreeMap is based on a red-black tree, not sure how that rates. Documentation / tutorials should be good enough so someone can get started quickly using the data structures. FJ fails on that front. Any suggestions?

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• java: retrieving the "canonical value" from a Set<T> where T has a custom equals()

  - by Jason S

  I have a class Foo which overrides equals() and hashCode() properly. I would like to also would like to use a HashSet<Foo> to keep track of "canonical values" e.g. I have a class that I would like to write like this, so that if I have two separate objects that are equivalent I can coalesce them into references to the same object: class Canonicalizer<T> { final private Set<T> values = new HashSet<T>(); public T findCanonicalValue(T value) { T canonical = this.values.get(value); if (canonical == null) { // not in the set, so put it there for the future this.values.add(value); return value; } else { return canonical; } } } except that Set doesn't have a "get" method that would return the actual value stored in the set, just the "contains" method that returns true or false. (I guess that it assumes that if you have an object that is equal to a separate object in the set, you don't need to retrieve the one in the set) Is there a convenient way to do this? The only other thing I can think of is to use a map and a list: class Canonicalizer<T> { // warning: neglects concurrency issues final private Map<T, Integer> valueIndex = new HashMap<T, Integer>(); final private List<T> values = new ArrayList<T>(); public T findCanonicalValue(T value) { Integer i = this.valueIndex.get(value); if (i == null) { // not in the set, so put it there for the future i = this.values.size(); this.values.add(value); this.valueIndex.put(value, i); return value; } else { // in the set return this.values.get(i); } } }

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• What design pattern to use for one big method calling many private methods

  - by Jeune

  I have a class that has a big method that calls on a lot of private methods. I think I want to extract those private methods into their own classes for one because they contain business logic and I think they should be public so they can be unit tested. Here's a sample of the code: public void handleRow(Object arg0) { if (continueRunning){ hashData=(HashMap<String, Object>)arg0; Long stdReportId = null; Date effDate=null; if (stdReportIds!=null){ stdReportId = stdReportIds[index]; } if (effDates!=null){ effDate = effDates[index]; } initAndPutPriceBrackets(hashData, stdReportId, effDate); putBrand(hashData,stdReportId,formHandlerFor==0?true:useLiveForFirst); putMultiLangDescriptions(hashData,stdReportId); index++; if (stdReportIds!=null && stdReportIds[0].equals(stdReportIds[1])){ continueRunning=false; } if (formHandlerFor==REPORTS){ putBeginDate(hashData,effDate,custId); } //handle logic that is related to pricemaps. lstOfData.add(hashData); } } What design pattern should I apply to this problem?

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• Why do Scala maps have poor performance relative to Java?

  - by Mike Hanafey

  I am working on a Scala app that consumes large amounts of CPU time, so performance matters. The prototype of the system was written in Python, and performance was unacceptable. The application does a lot with inserting and manipulating data in maps. Rex Kerr's Thyme was used to look at the performance of updating and retrieving data from maps. Basically "n" random Ints were stored in maps, and retrieved from the maps, with the time relative to java.util.HashMap used as a reference. The full results for a range of "n" are here. Sample (n=100,000) performance relative to java, smaller is worse: Update Read Mutable 16.06% 76.51% Immutable 31.30% 20.68% I do not understand why the scala immutable map beats the scala mutable map in update performance. Using the sizeHint on the mutable map does not help (it appears to be ignored in the tested implementation, 2.10.3). Even more surprisingly the immutable read performance is worse than the mutable read performance, more significantly so with larger maps. The update performance of the scala mutable map is surprisingly bad, relative to both scala immutable and plain Java. What is the explanation?

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• android - how to cache an image from a remote site

  - by Lynnooi

  Hi, Can anyone please provide me some example on how to save an image i fetch from websites into a cache. I had try to include the following function into my code and call it once i run the activity. public void getRemoteImage(String imageUrl) { imageUrl = "http://marga.mobile9.com/download/thumb/295/sexylady7_xo6npovn.jpg"; URL aURL = null; URLConnection conn = null; Bitmap bmp = null; CacheResult cache_result = CacheManager.getCacheFile(imageUrl, new HashMap()); if (cache_result == null) { try { aURL = new URL(imageUrl); conn = aURL.openConnection(); conn.connect(); InputStream is = conn.getInputStream(); cache_result = new CacheManager.CacheResult(); CacheManager.saveCacheFile(imageUrl, cache_result); } catch (Exception e) { //return null; } } bmp = BitmapFactory.decodeStream(cache_result.getInputStream());*/ Toast.makeText(context,"Please work.. namo namo namo", Toast.LENGTH_SHORT).show(); //return bmp; } However, I got a nullPointerException. Can someone please help me with it as i'm quite new in android.

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• How to compare two arrays of integers order-insensitively

  - by stdnoit

  I want Java code that can compare in this way (for example): <1 2 3 4> = <3 1 2 4> <1 2 3 4> != <3 4 1 1> I can't use hashmap table or anything; just pure code without library. I know there are two ways. sort them and compare the array index by index use two for loops and compare the outer index with the inner index. I have been trying with this but still not working: for(int i = 0; i < n; i++) { for(int j = 0; j < n; j++) { if(a[i] != a[j] && j == n) return false; } } return true; anything wrong with the code ? thanks

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• Best (Java) book for understanding 'under the bonnet' for programming?

  - by Ben

  What would you say is the best book to buy to understand exactly how programming works under the hood in order to increase performance? I've coded in assembly at university, I studied computer architecture and I obviously did high level programming, but what I really dont understand is things like: -what is happening when I perform a cast -whats the difference in performance if I declare something global as opposed to local? -How does the memory layout for an ArrayList compare with a Vector or LinkedList? -Whats the overhead with pointers? -Are locks more efficient than using synchronized? -Would creating my own array using int[] be faster than using ArrayList -Advantages/disadvantages of declaring a variable volatile I have got a copy of Java Performance Tuning but it doesnt go down very low and it contains rather obvious things like suggesting a hashmap instead of using an ArrayList as you can map the keys to memory addresses etc. I want something a bit more Computer Sciencey, linking the programming language to what happens with the assembler/hardware. The reason im asking is that I have an interview coming up for a job in High Frequency Trading and everything has to be as efficient as possible, yet I cant remember every single possible efficiency saving so i'd just like to learn the fundamentals. Thanks in advance

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• Python to Java translation

  - by obelix1337

  Hello, i get quite short code of algorithm in python, but i need to translate it to Java. I didnt find any program to do that, so i will really appreciate to help translating it. I learned python a very little to know the idea how algorithm work. The biggest problem is because in python all is object and some things are made really very confuzing like sum(self.flow[(source, vertex)] for vertex, capacity in self.get_edges(source)) and "self.adj" is like hashmap with multiple values which i have no idea how to put all together. Is any better collection for this code in java? code is: [CODE] class FlowNetwork(object): def __init__(self): self.adj, self.flow, = {},{} def add_vertex(self, vertex): self.adj[vertex] = [] def get_edges(self, v): return self.adj[v] def add_edge(self, u,v,w=0): self.adj[u].append((v,w)) self.adj[v].append((u,0)) self.flow[(u,v)] = self.flow[(v,u)] = 0 def find_path(self, source, sink, path): if source == sink: return path for vertex, capacity in self.get_edges(source): residual = capacity - self.flow[(source,vertex)] edge = (source,vertex,residual) if residual > 0 and not edge in path: result = self.find_path(vertex, sink, path + [edge]) if result != None: return result def max_flow(self, source, sink): path = self.find_path(source, sink, []) while path != None: flow = min(r for u,v,r in path) for u,v,_ in path: self.flow[(u,v)] += flow self.flow[(v,u)] -= flow path = self.find_path(source, sink, []) return sum(self.flow[(source, vertex)] for vertex, capacity in self.get_edges(source)) g = FlowNetwork() map(g.add_vertex, ['s','o','p','q','r','t']) g.add_edge('s','o',3) g.add_edge('s','p',3) g.add_edge('o','p',2) g.add_edge('o','q',3) g.add_edge('p','r',2) g.add_edge('r','t',3) g.add_edge('q','r',4) g.add_edge('q','t',2) print g.max_flow('s','t') [/CODE] result of this example is "5". algorithm find max flow in graph(linked list or whatever) from source vertex "s" to destination "t". Many thanx for any idea

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• Hadoop File Read

  - by user3684584

  Hadoop Distributed Cache Wordcount example in hadoop 2.2.0. Copied file into hdfs filesystem to be used inside setup of mapper class. protected void setup(Context context) throws IOException,InterruptedException { Path[] uris = DistributedCache.getLocalCacheFiles(context.getConfiguration()); cacheData=new HashMap(); for(Path urifile: uris) { try { BufferedReader readBuffer1 = new BufferedReader(new FileReader(urifile.toString())); String line; while ((line=readBuffer1.readLine())!=null) { System.out.println("**************"+line); cacheData.put(line,line); } readBuffer1.close(); } catch (Exception e) { System.out.println(e.toString()); } } } Inside Driver Main class Configuration conf = new Configuration(); String[] otherArgs = new GenericOptionsParser(conf,args).getRemainingArgs(); if (otherArgs.length != 3) { System.err.println("Usage: wordcount <in> <out>"); System.exit(2); } Job job = new Job(conf, "word_count"); job.setJarByClass(WordCount.class); job.setMapperClass(Map.class); job.setReducerClass(Reduce.class); job.setOutputKeyClass(Text.class); job.setOutputValueClass(IntWritable.class); FileInputFormat.addInputPath(job, new Path(otherArgs[0])); Path outputpath=new Path(otherArgs[1]); outputpath.getFileSystem(conf).delete(outputpath,true); FileOutputFormat.setOutputPath(job,outputpath); System.out.println("CachePath****************"+otherArgs[2]); DistributedCache.addCacheFile(new URI(otherArgs[2]),job.getConfiguration()); System.exit(job.waitForCompletion(true) ? 0 : 1); But getting exception java.io.FileNotFoundException: file:/home/user12/tmp/mapred/local/1408960542382/cache (No such file or directory) So Cache functionality not working properly. Any Idea ?

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• Android ProgressDialog inside another dialog

  - by La bla bla

  I'm working on a game using AndEngine, and I need to show the users the list of his Facebook friends. I've created my custom Adatper and after the loading finishes everything works great. I have a problem with the loading it self. The ListView is inside a custom dialog, since I don't really know how to create one using AndEngine, So inside this dialog, I'm running an AsyncTask to fetch the friends' info, in that AsyncTask I'm have a ProgressDialog. The problem is, the ProgressDialog shows up behind the dialog that contains the to-be list (which while loading, is just the title). I can see the ProgressDialog "peeking" behind that dialog.. Any Ideas? Here's some code: FriendsDialog.java private ProgressDialog dialog; //Constructor of the AsyncTask public FriendsLoader(Context context) { dialog = new ProgressDialog(context); dialog.setMessage("Please wait..\nLoading Friends List."); } @Override protected void onPreExecute() { dialog.requestWindowFeature(Window.FEATURE_NO_TITLE); LayoutInflater inflater = (LayoutInflater)context.getSystemService(Context.LAYOUT_INFLATER_SERVICE); dialog.setView(inflater.inflate(R.layout.loading, null)); dialog.setMessage("Please wait..\nLoading friends."); dialog.show(); } @Override protected void onPostExecute(ArrayList<HashMap<String, Object>> data) { if (dialog.isShowing()) { dialog.dismiss(); } MyAdapter myAdapter = new MyAdapter(context, data); listView = (ListView) findViewById(R.id.list); listView.setAdapter(myAdapter); listView.setOnItemClickListener(new AdapterView.OnItemClickListener() { @Override public void onItemClick(AdapterView<?> myAdapter, View myView, int myItemInt, long mylng) { String id = (String) listView.getItemAtPosition(myItemInt); listener.onUserSelected(id); dismiss(); } }); }

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• Java / Spring MVC 3 validation of an email address

  - by Tim

  I have a Java backend with Spring MVC and I am using validation in this way on my domain object for an email address: import javax.validation.constraints.NotNull; import javax.validation.constraints.Pattern; import javax.validation.constraints.Size; ... @NotNull @Size(min = 1, max = 100) @Pattern(regexp="^([a-zA-Z0-9\\-\\.\\_]+)'+'(\\@)([a-zA-Z0-9\\-\\.]+)'+'(\\.)([a-zA-Z]{2,4})$") private String email; But all I get with these lines of code Set<ConstraintViolation<Person>> failures = validator.validate(personObject); ... Map<String, String> failureMessages = new HashMap<String, String>(); for (ConstraintViolation<Person> failure : failures) { failureMessages.put(failure.getPropertyPath().toString(), failure.getMessage()); System.out.println(failure.getPropertyPath().toString()+" - "+failure.getMessage()) } I get this on the console: email - must match "^([a-zA-Z0-9\\-\\.\\_]+)'+'(\\@)([a-zA-Z0-9\\-\\.]+)'+'(\\.)([a-zA-Z]{2,4})$" but I have as email address [email protected], so the regexp does not match. So I have two prolems: What's wrong here? And how can I define a error message on my own, because display this to the user, that is not a good thing :-) Thank you in advance for your help and Best Regards.

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• Java order jlist by status

  - by Takami

  i have a small problem, i don't know how to sort my jlist by status which is retrieved from database. i want sort by "online" and "offline", i mean online computers go first and then offline computers, i have this code now, it just makes the icon+text for the jlist Can you tell me how can i filter/sortby status? public void acx_pc(String query) { try { Statement st = con.createStatement(); ResultSet rs = st.executeQuery(query); String comb; Map<Object, Icon> icons = new HashMap<>(); ArrayList<String> pc_list = new ArrayList<>(); int i = 0; while (rs.next()) { //Getting info from DB String pc_name = rs.getString("nombre_pc"); String pc_ip = rs.getString("IP"); String status = rs.getString("estado"); //Setting text for the jList comb = pc_name + " - " + pc_ip; //Comparing Status switch (status) { case "online": //This is just for rendering an image+text to Jlist icons.put(comb, new ImageIcon(getClass().getResource("/Imagenes/com_on_30x30.png"))); break; case "offline": //This is just for rendering an image to Jlist icons.put(comb, new ImageIcon(getClass().getResource("/Imagenes/com_off_30x30.png"))); break; } //Adding info to ArrayList pc_list.add(i, comb); i++; } con.close(); // Setting the list/text on Jlist Home.computer_jlist.setListData(pc_list.toArray()); // create a cell renderer to add the appropriate icon Home.computer_jlist.setCellRenderer(new pc_cell_render(icons)); } catch (Exception e) { System.out.println("Error aqui: " + e); } } I want to do something like (should automatically order) http://imageshack.us/a/img27/9018/2mx1.png and not: http://imageshack.us/a/img407/346/e9r.png

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• Update table instantly or “Bulk” Update in database later? And is it advisable?

  - by Mestika

  Hi, I have a question regarding a semi-constant update in a database. In short it is regarding a checkout function on a web page, which each time the checkout function is evoked it do five steps. I want to try to optimize this function and have my eye on a step where I update a table each time the checkout is performed. I take the information retrieved from the shopping cart and then update the table in question. I do have some indexes on the table, the gain from those are greater than leaving them so this is a cost I’m willing to take. Now, my question is. Could it in some way regarding to performance be better to not update the table instantly but collect every checkout items and save them in some way (maybe in a file) and then at a specific time (or several times) at day take this file and then update the table with the new information. Then I started thinking about if there was a possibility to use some sort of Bulk Update to take a file, hashmap, array (or?) and then update it. And I’m using IBM DB2 version 9.7 Mestika

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• What is my error in a map in java?

  - by amveg

  Hello everyone I am trying to solve this problem: http://www.cstutoringcenter.com/problems/problems.php?id=4, but I cant figure out why my code doesnt solve this, I mean in the "for" how can I can multiply the letters? what is my error?, It just tell always 7, but I want to multiple all the letters, I hope you can help me enter code here public class ejercicio3 { public static void main(String args[]) { Map<Character, Integer> telefono = new HashMap<Character, Integer>(); telefono.put('A', 2); telefono.put('B', 2); telefono.put('C', 2); telefono.put('D', 3); telefono.put('E', 3); telefono.put('F', 3); telefono.put('G', 4); telefono.put('H', 4); telefono.put('I', 4); telefono.put('J', 5); telefono.put('K', 5); telefono.put('L', 5); telefono.put('M', 6); telefono.put('N', 6); telefono.put('O', 6); telefono.put('P', 7); telefono.put('R', 7); telefono.put('S', 7); telefono.put('T', 8); telefono.put('U', 8); telefono.put('V', 8); telefono.put('W', 9); telefono.put('X', 9); telefono.put('Y', 9); String mensaje = "Practice"; int producto = 1; for (char c : mensaje.toCharArray()) { if (telefono.containsKey(c)) { producto = telefono.get(c) * producto; System.out.println(producto); } } } }

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• java class that simulates a simple database table

  - by ericso

  I have a collection of heterogenous data that I pull from a database table mtable. Then, for every unique value uv in column A, I compute a function of (SELECT * FROM mtable WHERE A=uv). Then I do the same for column B, and column C. There are rather a lot of unique values, so I don't want to hit the db repeatedly - I would rather have a class that replicates some of the functionality (most importantly some version of SELECT WHERE). Additionally, I would like to abstract the column names away from the class definition, if that makes any sense - the constructor should take a list of names as a parameter, and also, I suppose, a list of types (right now this is just a String[], which seems hacky). I'm getting the initial data from a RowSet. I've more or less done this by using a hashmap that maps Strings to lists/arrays of Objects, but I keep getting bogged down in comparisons and types, and am thinking that my current implementation really isn't as clean and clear as it could be. I'm pretty new to java, also, and am not sure if I'm not going down a completely incorrect path. Does anyone have any suggestions?

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• How to get java singleton object manager to return any type of object?

  - by Robert

  I'm writing an interactive fiction game in java from scratch. I'm currently storing all of my game object references in a hashmap in a singleton called ObjectManager. ObjectManager has a function called get which takes an integer ID and returns the appropriate reference. The problem is that it returns a BaseObject when I need to return subclasses of BaseObject with more functionality. So, what I've done so far is I've added a getEntity function which returns BaseEntity (which is a subclass of BaseObject). However, when I need the function to return to an object that is a subclass of BaseEntity that has added, required functionality, I will need to make another function. I know there is a better way, but I don't know what it is. I know very little of design patterns, and I'm not sure which one to use here. I tried passing 'class' as a parameter, but that didn't get me anywhere. public BaseObject get(int ID){ return (BaseObject)refMap.get(ID); } public BaseEntity getEntity(int ID){ return (BaseEntity)refMap.get(ID); } Thanks, java ninjas!

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• Printing the results in the original order

  - by Sam

  String[] numbers = new String[] {"3", "4", "s", "a", "c", "h", "i", "n", "t", "e", "n", "d", "u", "l", "k"}; Map<String, Integer> map = new HashMap<String, Integer>(); for (int i = 0; i < numbers.length; i++) { String key = numbers[i]; if (map.containsKey(key)) { int occurrence = map.get(key); occurrence++; map.put(key, occurrence); } else { map.put(key, 1); }// end of if else }// end of for loop Iterator<String> iterator = map.keySet().iterator(); while (iterator.hasNext()) { String key = iterator.next(); int occurrence = map.get(key); System.out.println(key + " occur " + occurrence + " time(s)."); } This program tries to count the number of occurrences of a string. When I execute it I am getting the answer, but the output is not in the original order, it is shuffled. How can I output the strings in the original order?

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• Log4j Logging to the Wrong Directory

  - by John

  I have a relatively complex log4j.xml configuration file with many appenders. Some machines the application runs on need a separate log directory, which is actually a mapped network drive. To get around this, we embed a system property as part of the filename in order to specify the directory. Here is an example: The "${user.dir}" part is set as a system property on each system, and is normally set to the root directory of the application. On some systems, this location is not the root of the application. The problem is that there is always one appender where this is not set, and the file appears not to write to the mapped drive. The rest of the appenders do write to the correct location per the system property. As a unit test, I set up our QA lab to hard-code the values for the appender above, and it worked: however, a different appender will then append to the wrong file. The mis-logged file is always the same for a given configuration: it is not a random file each time. My best educated guess is that there is a HashMap somewhere containing these appenders, and for some reason, the first one retrieved from the map does not have the property set. Our application does have custom system properties loading: the main() method loads a properties file and calls into System.setProperties(). My first instinct was to check the static initialization order, and to ensure the controller class with the main method does not call into log4j (directly or indirectly) before setting the properties just in case this was interfering with log4j's own initialization. Even removing all vestiges of log4j from the initialization logic, this error condition still occurs.

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• Designing status management for a file processing module

  - by bot

  The background One of the functionality of a product that I am currently working on is to process a set of compressed files ( containing XML files ) that will be made available at a fixed location periodically (local or remote location - doesn't really matter for now) and dump the contents of each XML file in a database. I have taken care of the design for a generic parsing module that should be able to accommodate the parsing of any file type as I have explained in my question linked below. There is no need to take a look at the following link to answer my question but it would definitely provide a better context to the problem Generic file parser design in Java using the Strategy pattern The Goal I want to be able to keep a track of the status of each XML file and the status of each compressed file containing the XML files. I can probably have different statuses defined for the XML files such as NEW, PROCESSING, LOADING, COMPLETE or FAILED. I can derive the status of a compressed file based on the status of the XML files within the compressed file. e.g status of the compressed file is COMPLETE if no XML file inside the compressed file is in a FAILED state or status of the compressed file is FAILED if the status of at-least one XML file inside the compressed file is FAILED. A possible solution The Model I need to maintain the status of each XML file and the compressed file. I will have to define some POJOs for holding the information about an XML file as shown below. Note that there is no need to store the status of a compressed file as the status of a compressed file can be derived from the status of its XML files. public class FileInformation { private String compressedFileName; private String xmlFileName; private long lastModifiedDate; private int status; public FileInformation(final String compressedFileName, final String xmlFileName, final long lastModified, final int status) { this.compressedFileName = compressedFileName; this.xmlFileName = xmlFileName; this.lastModifiedDate = lastModified; this.status = status; } } I can then have a class called StatusManager that aggregates a Map of FileInformation instances and provides me the status of a given file at any given time in the lifetime of the appliciation as shown below : public class StatusManager { private Map<String,FileInformation> processingMap = new HashMap<String,FileInformation>(); public void add(FileInformation fileInformation) { fileInformation.setStatus(0); // 0 will indicates that the file is in NEW state. 1 will indicate that the file is in process and so on.. processingMap.put(fileInformation.getXmlFileName(),fileInformation); } public void update(String filename,int status) { FileInformation fileInformation = processingMap.get(filename); fileInformation.setStatus(status); } } That takes care of the model for the sake of explanation. So whats my question? Edited after comments from Loki and answer from Eric : - I would like to know if there are any existing design patterns that I can refer to while coming up with a design. I would also like to know how I should go about designing the status management classes. I am more interested in understanding how I can model the status management classes. I am not interested in how other components are going to be updated about a change in status at the moment as suggested by Eric.

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• I am trying to figure out the best way to understand how to cache domain objects

  - by Brett Ryan

  I've always done this wrong, I'm sure a lot of others have too, hold a reference via a map and write through to DB etc.. I need to do this right, and I just don't know how to go about it. I know how I want my objects to be cached but not sure on how to achieve it. What complicates things is that I need to do this for a legacy system where the DB can change without notice to my application. So in the context of a web application, let's say I have a WidgetService which has several methods: Widget getWidget(); Collection<Widget> getAllWidgets(); Collection<Widget> getWidgetsByCategory(String categoryCode); Collection<Widget> getWidgetsByContainer(Integer parentContainer); Collection<Widget> getWidgetsByStatus(String status); Given this, I could decide to cache by method signature, i.e. getWidgetsByCategory("AA") would have a single cache entry, or I could cache widgets individually, which would be difficult I believe; OR, a call to any method would then first cache ALL widgets with a call to getAllWidgets() but getAllWidgets() would produce caches that match all the keys for the other method invocations. For example, take the following untested theoretical code. Collection<Widget> getAllWidgets() { Entity entity = cache.get("ALL_WIDGETS"); Collection<Widget> res; if (entity == null) { res = loadCache(); } else { res = (Collection<Widget>) entity.getValue(); } return res } Collection<Widget> loadCache() { // Get widgets from underlying DB Collection<Widget> res = db.getAllWidgets(); cache.put("ALL_WIDGETS", res); Map<String, List<Widget>> byCat = new HashMap<>(); for (Widget w : res) { // cache by different types of method calls, i.e. by category if (!byCat.containsKey(widget.getCategory()) { byCat.put(widget.getCategory(), new ArrayList<Widget>); } byCat.get(widget.getCatgory(), widget); } cacheCategories(byCat); return res; } Collection<Widget> getWidgetsByCategory(String categoryCode) { CategoryCacheKey key = new CategoryCacheKey(categoryCode); Entity ent = cache.get(key); if (entity == null) { loadCache(); } ent = cache.get(key); return ent == null ? Collections.emptyList() : (Collection<Widget>)ent.getValue(); } NOTE: I have not worked with a cache manager, the above code illustrates cache as some object that may hold caches by key/value pairs, though it's not modelled on any specific implementation. Using this I have the benefit of being able to cache all objects in the different ways they will be called with only single objects on the heap, whereas if I were to cache the method call invocation via say Spring It would (I believe) cache multiple copies of the objects. I really wish to try and understand the best ways to cache domain objects before I go down the wrong path and make it harder for myself later. I have read the documentation on the Ehcache website and found various articles of interest, but nothing to give a good solid technique. Since I'm working with an ERP system, some DB calls are very complicated, not that the DB is slow, but the business representation of the domain objects makes it very clumsy, coupled with the fact that there are actually 11 different DB's where information can be contained that this application is consolidating in a single view, this makes caching quite important.

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• How-to call server side Java from JavaScript

  - by frank.nimphius

  Normal 0 false false false EN-US X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} The af:serverListener tag in Oracle ADF Faces allows JavaScript to call into server side Java. The example shown below uses an af:clientListener tag to invoke client side JavaScript in response to a key stroke in an Input Text field. The script then call a defined af:serverListener by its name defined in the type attribute. The server listener can be defined anywhere on the page, though from a code readability perspective it sounds like a good idea to put it close to from where it is invoked. <af:inputText id="it1" label="...">   <af:clientListener method="handleKeyUp" type="keyUp"/>   <af:serverListener type="MyCustomServerEvent"                      method="#{mybean.handleServerEvent}"/> </af:inputText> The JavaScript function below reads the event source from the event object that gets passed into the called JavaScript function. The call to the server side Java method, which is defined on a managed bean, is issued by a JavaScript call to AdfCustomEvent. The arguments passed to the custom event are the event source, the name of the server listener, a message payload formatted as an array of key:value pairs, and true/false indicating whether or not to make the call immediate in the request lifecycle. <af:resource type="javascript">     function handleKeyUp (evt) {    var inputTextComponen = event.getSource();       AdfCustomEvent.queue(inputTextComponent,                         "MyCustomServerEvent ",                         {fvalue:component.getSubmittedValue()},                         false);    event.cancel();}   </af:resource> The server side managed bean method uses a single argument signature with the argument type being ClientEvent. The client event provides information about the event source object - as provided in the call to AdfCustomEvent, as well as the payload keys and values. The payload is accessible from a call to getParameters, which returns a HashMap to get the values by its key identifiers.  public void handleServerEvent(ClientEvent ce){    String message = (String) ce.getParameters().get("fvalue");   ...  } Normal 0 false false false EN-US X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} Find the tag library at: http://download.oracle.com/docs/cd/E15523_01/apirefs.1111/e12419/tagdoc/af_serverListener.html

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• Profiling NetBeans 7.0 Beta 2 and Reporting Problems

  - by christopher.jones

  With NetBeans 7.0 recently going into Beta 2 phase, now is the time to test it out properly and report issues. The development team has been squashing bugs, including memory issues with the PHP bundle.There are some great new PHP related features in NetBeans 7.0, so you know you want to try it out.If you identify something wrong with NetBeans, please report it following the guidelines http://wiki.netbeans.org/IssueReportingGuidelinesDepending on the issues, data to attach to the report is mentioned on: http://wiki.netbeans.org/FaqLogMessagesFile and http://wiki.netbeans.org/FaqProfileMeNowIf you have a memory issue then a memory dump would also be useful. Run the jmap tool for this. There is some background information on http://wiki.netbeans.org/FaqMemoryDump. Here's how I used it.First I set my environment to match the JDK used by NetBeans. In my case I am using a nightly build so the JDK is in the configuration file under $HOME/netbeans-dev-201102210501:$ egrep netbeans_jdkhome $HOME/netbeans-dev-201102210501/etc/netbeans.conf netbeans_jdkhome="/home/cjones/src/jdk1.6.0_24" $ export JAVA_HOME=/home/cjones/src/jdk1.6.0_24 $ export PATH=$JAVA_HOME/bin:$PATH Next, I found the correct process number to examine:$ ps -ef | egrep 'netbeans|jdk'cjones   23230     1  0 16:07 ?        00:00:00 /bin/bash /home/cjones/netbeans-cjones   23438 23230  2 16:07 ?        00:00:09 /home/cjones/src/jdk1.6.0_24/binFinally I used the parent JDK process as the jmap argument:$ jmap -histo:live 23438 num     #instances         #bytes  class name----------------------------------------------   1:         12075        9028656  [I   2:         49535        6581920  <constMethodKlass>   3:         49535        3964128  <methodKlass>   4:         80256        3840776  <symbolKlass>   5:         36093        3635336  [C   6:          5095        3341312  <constantPoolKlass>   7:          5095        2486016  <instanceKlassKlass>   8:          4325        1961432  <constantPoolCacheKlass>   9:         18729        1763976  [B  10:         59952        1438848  java.util.HashMap$Entry  . . .This histogram memory report will help identify the kind of memory issues you are seeing. It may not be as complete as an often tens of megabyte jmap -dump:live,file=/tmp/nbheap.log 23438 heap dump, but is much more easily attached to a bug report.If you want to keep up to date with NetBeans, nightly builds are at: http://bits.netbeans.org/download/trunk/nightly/latest/zip/

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• Getting Started with Amazon Web Services in NetBeans IDE

  - by Geertjan

  When you need to connect to Amazon Web Services, NetBeans IDE gives you a nice start. You can drag and drop the "itemSearch" service into a Java source file and then various Amazon files are generated for you. From there, you need to do a little bit of work because the request to Amazon needs to be signed before it can be used. Here are some references and places that got me started: http://associates-amazon.s3.amazonaws.com/signed-requests/helper/index.html http://docs.aws.amazon.com/AWSSimpleQueueService/latest/SQSGettingStartedGuide/AWSCredentials.html https://affiliate-program.amazon.com/gp/flex/advertising/api/sign-in.html You definitely need to sign up to the Amazon Associates program and also register/create an Access Key ID, which will also get you a Secret Key, as well. Here's a simple Main class that I created that hooks into the generated RestConnection/RestResponse code created by NetBeans IDE: public static void main(String[] args) {    try {        String searchIndex = "Books";        String keywords = "Romeo and Juliet";        RestResponse result = AmazonAssociatesService.itemSearch(searchIndex, keywords);        String dataAsString = result.getDataAsString();        int start = dataAsString.indexOf("<Author>")+8;        int end = dataAsString.indexOf("</Author>");        System.out.println(dataAsString.substring(start,end));    } catch (Exception ex) {        ex.printStackTrace();    }} Then I deleted the generated properties file and the authenticator and changed the generated AmazonAssociatesService.java file to the following: public class AmazonAssociatesService {    private static void sleep(long millis) {        try {            Thread.sleep(millis);        } catch (Throwable th) {        }    }    public static RestResponse itemSearch(String searchIndex, String keywords) throws IOException {        SignedRequestsHelper helper;        RestConnection conn = null;        Map queryMap = new HashMap();        queryMap.put("Service", "AWSECommerceService");        queryMap.put("AssociateTag", "myAssociateTag");        queryMap.put("AWSAccessKeyId", "myAccessKeyId");        queryMap.put("Operation", "ItemSearch");        queryMap.put("SearchIndex", searchIndex);        queryMap.put("Keywords", keywords);        try {            helper = SignedRequestsHelper.getInstance(                    "ecs.amazonaws.com",                    "myAccessKeyId",                    "mySecretKey");            String sign = helper.sign(queryMap);            conn = new RestConnection(sign);        } catch (IllegalArgumentException | UnsupportedEncodingException | NoSuchAlgorithmException | InvalidKeyException ex) {        }        sleep(1000);        return conn.get(null);    }} Finally, I copied this class into my application, which you can see is referred to above: http://code.google.com/p/amazon-product-advertising-api-sample/source/browse/src/com/amazon/advertising/api/sample/SignedRequestsHelper.java Here's the completed app, mostly generated via the drag/drop shown at the start, but slightly edited as shown above: That's all, now everything works as you'd expect.

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• OIM 11g - Multi Valued attribute reconciliation of a child form

  - by user604275

  This topic gives a brief description on how we can do reconciliation of a child form attribute which is also multi valued from a flat file . The format of the flat file is (an example): ManagementDomain1|Entitlement1|DIRECTORY SERVER,EMAIL ManagementDomain2|Entitlement2|EMAIL PROVIDER INSTANCE - UMS,EMAIL VERIFICATION In OIM there will be a parent form for fields Management domain and Entitlement.Reconciliation will assign Servers ( which are multi valued) to corresponding Management  Domain and Entitlement .In the flat file , multi valued fields are seperated by comma(,). In the design console, Create a form with 'Server Name' as a field and make it a child form . Open the corresponding Resource Object and add this field for reconcilitaion.While adding , choose 'Multivalued' check box. (please find attached screen shot on how to add it , Child Table.docx) Open process definiton and add child form fields for recociliation. Please click on the 'Create Reconcilitaion Profile' buttton on the resource object tab. The API methods used for child form reconciliation are : 1.           reconEventKey =   reconOpsIntf.createReconciliationEvent(resObjName, reconData,                                                            false); ·                                    ‘False’  here tells that we are creating the recon for a child table . 2.               2.       reconOpsIntf.providingAllMultiAttributeData(reconEventKey, RECON_FIELD_IN_RO, true);                RECON_FIELD_IN_RO is the field that we added in the Resource Object while adding for reconciliation, please refer the screen shot) 3.    reconOpsIntf.addDirectBulkMultiAttributeData(reconEventKey,RECON_FIELD_IN_RO, bulkChildDataMapList);                 bulkChildDataMapList  is coded as below :                 List<Map> bulkChildDataMapList = new ArrayList<Map>();                   for (int i = 0; i < stokens.length; i++) {                            Map<String, String> attributeMap = new HashMap<String, String>();                           String serverName = stokens[i].toUpperCase();                           attributeMap.put("Server Name", stokens[i]);                           bulkChildDataMapList.add(attributeMap);                         } 4                  4.       reconOpsIntf.finishReconciliationEvent(reconEventKey); 5.       reconOpsIntf.processReconciliationEvent(reconEventKey); Now, we have to register the plug-in, import metadata into MDS and then create a scheduled job to execute which will run the reconciliation.

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