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  • Create java sandbox based on security policies

    - by argos
    I need to create environment to run potentially untrusted code. Program allowed to connect to preconfigured address:port and nothing else (even read the system time). I have compiled the class whitelist. I'd searched similar questions, but found only template that based on SecurityManager which AFAIK is deprecated. Can anybody give me a simple sample how to run code in sandbox based on security policies and AccessController?

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  • The best way to assign an immutable instance to a Collection in Java

    - by Ali
    Today I was reading through some Hibernate code and I encounter something interesting. There is a class called CollectionHelper that defines the following constant varibale: public final class CollectionHelper { public static final List EMPTY_LIST = Collections.unmodifiableList( new ArrayList(0 ) ; public static final Collection EMPTY_COLLECTION = Collections.unmodifiableCollection(new ArrayList(0) ); public static final Map EMPTY_MAP = Collections.unmodifiableMap( new HashMap(0) ); They have used these constants to initialize collections with immutable instances. Why they didn't simply use the Collections.EMPTY_LIST for initializing lists? Is there a benefit in using the following method?

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  • Java NullPointerException when traversing a non-null recordset

    - by Tim
    Hello again - I am running a query on Sybase ASE that produces a ResultSet that I then traverse and write the contents out to a file. Sometimes, this will throw a NullPointerException, stating that the ResultSet is null. However, it will do this after printing out one or two records. Other times, with the same exact input, I will receive no errors. I have been unable to consistently produce this error. The error message is pointing to a line: output.print(rs.getString(1)); It appears to happen when the query takes a little longer to run, for some reason. The recordset returns thus far have been very small (4 to 7 records). Sometimes I'll have to run the app 3 or 4 times, then the errors will just stop, as though the query was getting "warmed up". I've run the query manually and there doesn't appear to be any performance problems. Thanks again!

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  • Override Java System.currentTimeMillis

    - by Mike Clark
    Is there a way, either in code or with JVM arguments, to override the current time, as presented via System.currentTimeMillis, other than manually changing the system clock on the host machine? A little background: We have a system that runs a number of accounting jobs that revolve much of their logic around the current date (ie 1st of the month, 1st of the year, etc) Unfortunately, a lot of the legacy code calls functions such as new Date() or Calendar.getInstance(), both of which eventually call down to System.currentTimeMillis. For testing purposes, right now, we are stuck with manually updating the system clock to manipulate what time and date the code thinks that the test is being run. So my question is: Is there a way to override what is returned by System.currentTimeMillis? For example, to tell the JVM to automatically add or subtract some offset before returning from that method? Thanks in advance!

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  • Is java.util.Scanner that slow?

    - by Cristian Vrabie
    Hi guys, In a Android application I want to use Scanner class to read a list of floats from a text file (it's a list of vertex coordinates for OpenGL). Exact code is: Scanner in = new Scanner(new BufferedInputStream(getAssets().open("vertexes.off"))); final float[] vertexes = new float[nrVertexes]; for(int i=0;i<nrVertexFloats;i++){ vertexes[i] = in.nextFloat(); } It seems however that this is incredibly slow (it took 30 minutes to read 10,000 floats!) - as tested on the 2.1 emulator. What's going on? I don't remember Scanner to be that slow when I used it on the PC (truth be told I never read more than 100 values before). Or is it something else, like reading from an asset input stream? Thanks for the help!

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  • Non-blocking MySQL updates with java?

    - by justkevin
    For a multiplayer game I'm working on I'd like to record events to the mysql database without blocking the game update thread so that if the database is busy or a table is locked the game doesn't stop running while it waits for a write. What's the best way to accomplish this? I'm using c3p0 to manage the database connection pool. My best idea so far is to add query update strings to a synchronized list with an independent thread checking the list every 100ms and executing the queries it finds there.

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  • Class unloading in java

    - by java_geek
    When a classloader is garbage collected, are the classes loaded by it unloaded? When the JVM is running is verbose mode, all the loaded classes are o/p. Similarly will the JVM log when it unloads a class? I wrote a custom class loader to test this, but could not see any verbose log for unloading of the classes. CustomClassLoader loader = new CustomClassLoader(new URL[]{}, CustomClassLoader.class.getClassLoader()); loader.addURL("D:\workspace\ClassLoaderTest\implementation.jar"); Class c = null; try { c = Class.forName("Horse",false,loader); if (c != null) { try { Animal animal = (Animal)c.newInstance(); animal.eat(); } catch(Exception ex) { ex.printStackTrace(); } } } catch(Exception e) { e.printStackTrace(); } loader = null; byte[] b = new byte[58*1024*1024]; System.gc(); ClassLoadingMXBean clBean = ManagementFactory.getClassLoadingMXBean(); System.out.println("Number of classes currently loaded " + clBean.getLoadedClassCount()); System.out.println("Number of classes loaded totally " + clBean.getTotalLoadedClassCount()); System.out.println("Number of classes unloaded " + clBean.getUnloadedClassCount()); Even the ClassLoadingMXBean gives number of unloaded classes as 0. How can i know that a class is unloaded when the class loader is GCed?

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  • JAVA Inheritance Generics and Casting.

    - by James Moore
    Hello, I have two classes which both extends Example. public class ClassA extends Example { public ClassA() { super("a", "class"); } .... } public class ClassB extends Example { public ClassB() { super("b", "class"); } .... } public class Example () { public String get(String x, String y) { return "Hello"; } } So thats all very well. So suppose we have another class called ExampleManager. With example manager I want to use a generic type and consequently return that generic type. e.g. public class ExampleManager<T extends Example> { public T getExample() { return new T("example","example"); // So what exactly goes here? } } So where I am returning my generic type how do i get this to actually work correctly and cast Example as either classA or classB? Many Thanks

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  • Java - Circular Garbage Collection

    - by aloh
    A <- B <- C <- D <- A... // A is firstNode, D is lastNode if ( length == 1 ) { firstNode = null; lastNode = null; firstNode.next = null; firstNode.prev = null; } else { Node secondNode = firstNode.next; Node secondToLast = lastNode.prev; firstNode.next = null; firstNode.prev = null; lastNode.next = null; lastNode.prev = null; secondNode.prev = null; secondToLast.next = null; firstNode = null; lastNode = null; } That should send everything in between as candidates for garbage collection, I hope?

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  • Dijkstra's Algorithm explanation java

    - by alchemey89
    Hi, I have found an implementation for dijkstras algorithm on the internet and was wondering if someone could help me understand how the code works. Many thanks private int nr_points=0; private int[][]Cost; private int []mask; private void dijkstraTSP() { if(nr_points==0)return; //algorithm=new String("Dijkstra"); nod1=new Vector(); nod2=new Vector(); weight=new Vector(); mask=new int[nr_points]; //initialise mask with zeros (mask[x]=1 means the vertex is marked as used) for(int i=0;i<nr_points;i++)mask[i]=0; //Dijkstra: int []dd=new int[nr_points]; int []pre=new int[nr_points]; int []path=new int[nr_points+1]; int init_vert=0,pos_in_path=0,new_vert=0; //initialise the vectors for(int i=0;i<nr_points;i++) { dd[i]=Cost[init_vert][i]; pre[i]=init_vert; path[i]=-1; } pre[init_vert]=0; path[0]=init_vert; pos_in_path++; mask[init_vert]=1; for(int k=0;k<nr_points-1;k++) { //find min. cost in dd for(int j=0;j<nr_points;j++) if(dd[j]!=0 && mask[j]==0){new_vert=j; break;} for(int j=0;j<nr_points;j++) if(dd[j]<dd[new_vert] && mask[j]==0 && dd[j]!=0)new_vert=j; mask[new_vert]=1; path[pos_in_path]=new_vert; pos_in_path++; for(int j=0;j<nr_points;j++) { if(mask[j]==0) { if(dd[j]>dd[new_vert]+Cost[new_vert][j]) { dd[j]=dd[new_vert]+Cost[new_vert][j]; } } } } //Close the cycle path[nr_points]=init_vert; //Save the solution in 3 vectors (for graphical purposes) for(int i=0;i<nr_points;i++) { nod1.addElement(path[i]); nod2.addElement(path[i+1]); weight.addElement(Cost[path[i]][path[i+1]]); } }

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  • PreparedStatement question in Java against Oracle.

    - by fardon57
    Hi everyone, I'm working on the modification of some code to use preparedStatement instead of normal Statement, for security and performance reason. Our application is currently storing information into an embedded derby database, but we are going to move soon to Oracle. I've found two things that I need your help guys about Oracle and Prepared Statement : 1- I've found this document saying that Oracle doesn't handle bind parameters into IN clauses, so we cannot supply a query like : Select pokemon from pokemonTable where capacity in (?,?,?,?) Is that true ? Is there any workaround ? ... Why ? 2- We have some fields which are of type TIMESTAMP. So with our actual Statement, the query looks like this : Select raichu from pokemonTable where evolution = TO_TIMESTAMP('2500-12-31 00:00:00.000', 'YYYY-MM-DD HH24:MI:SS.FF') What should be done for a prepared Statement ? Should I put into the array of parameters : 2500-12-31 or TO_TIMESTAMP('2500-12-31 00:00:00.000', 'YYYY-MM-DD HH24:MI:SS.FF') ? Thanks for your help, I hope my questions are clear ! Regards,

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  • Close resources before exiting JFrame and TCP communication in Java

    - by Oz Molaim
    1. I'm writing a chat based application on TCP communication. I'm using NetBeans and I want to add functionality to the default EXIT_ON_CLOSE when exiting JFrame. The reason of course is because I want to clean resources and end threads safely. How can I call a method that clear resources and only then close the JFrame safely and end the process. 2. I need to implement the server side. The server has List/HashMap/Queue of 'Socket' with their chat nick-names. Is there any simple design pattern to do it correctly because I don't want to re-invent the wheel. thanks.

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  • Facebook app request in java not working

    - by Arpit Solanki
    I am trying to send a facebook app request to a user through the code below.But it gives an IO Exception and HTTP status code 400 in running.I dont see a any app request being sent to a user on running this. StringBuffer buffer = new StringBuffer(); buffer.append("access_token").append('=').append(this.app_access_token); buffer.append('&').append("message=").append("sent an app request!"); String content = buffer.toString(); try{ URLConnection connection = new URL("https://graph.facebook.com/me/apprequests").openConnection(); connection.setDoOutput(true); connection.setRequestProperty("Content-Type","application/x-www-form-urlencoded"); connection.setRequestProperty("Content-Length",Integer.toString(content.length())); DataOutputStream outs = new DataOutputStream(connection.getOutputStream()); outs.writeBytes(content); outs.flush(); outs.close(); BufferedReader in = new BufferedReader(new InputStreamReader(connection.getInputStream())); String inputLine; while ((inputLine = in.readLine()) != null) { System.out.println(inputLine); } in.close(); } catch(Exception e){ System.out.println(e); }

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  • Saving part of audio file (java)

    - by m159701m
    Hi evryone, While playing an audio file (.wav) I want , if I resort to ctrl+c , to stop the playback and save part of the audio file in a file called "file2.wav". Here's the thread I'd like to add to my code. Unfortunately it doesn't work at all. Thanks in advance class myThread extends Thread{ public void run(){ try { PipedOutputStream poStream = new PipedOutputStream(); PipedInputStream piStream = new PipedInputStream(); poStream.connect(piStream); File cutaudioFile = new File ("file2.wav"); AudioInputStream ais = new AudioInputStream(piStream, AudioFileFormat.Type.WAVE , cutaudioFile); poStream.write(ais,AudioFileFormat.Type.WAVE,cutaudioFile); }catch (Exception e){ e.printStackTrace(); } } // end run } // end myThread

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  • Should I catch exceptions thrown when closing java.sql.Connection

    - by jb
    Connection.close() may throw SqlException, but I have always assumed that it is safe to ignore any such exceptions (and I have never seen code that does not ignore them). Normally I would write: try{ connection.close(); }catch(Exception e) {} Or try{ connection.close(); }catch(Exception e) { logger.log(e.getMessage(), e); } The question is: Is it bad practice (and has anyone had problems when ignoring such exeptions). When Connection.close() does throw any exception. If it is bad how should I handle the exception. Comment: I know that discarding exceptions is evil, but I'm reffering only to exceptions thrown when closing a connection (and as I've seen this is fairly common in this case). Does anyone know when Connection.close() may throw anything?

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  • Using mail servers in java

    - by sword101
    greeting all i want to use a mail server where the users send emails to it and then i parse this emails then do some action please suggest me what mail server to be used and where to start some links,tutorials,guide is very appreciated .

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  • java applet communication port

    - by udhaya
    Communication ports: Change a given class in an applet in that way, that browser-defined proxy-configuration files can be used for applet communication with serve(upload method). i.e browser communicate via port 8080 or via ssl(443) - applet should also communicate by this port automatically. In the given method port 80 is hardcoded. -- please give some code or program for this..

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  • Cast element in Java For Each statement

    - by Carl Summers
    Is it possible (or even advisable) to cast the element retrieved from a for each statement in the statement itself? I do know that each element in list will be of type . I.E.: List<BaseType> list = DAO.getList(); for(<SubType> element : list){ // Cannot convert from element type <BaseType> to <SubType> ... } rather than: List <BaseType> list = DAO.getList(); for(<BaseType> el : list){ <SubType> element = (<SubType>)el; ... }

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