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  • Static referencing error

    - by maxflow
    public class HelloWorld { public static void main(String [] args) { char[] b = {'a', 'b', 'a', 'c'}; int p = 4; deleteRepeats(b, p); } public void deleteRepeats(char[] a, int size) { int currentElement; currentElement = 0; do { for (int i = currentElement; i < size-1; i++) { if (a[currentElement] == a[i+1]) a[i+1] = ' '; } currentElement++; } while (currentElement < size-1); } } I get the error: non-static method deleteRepeats(char[],int) cannot be referenced from a static context deleteRepeats(b,p); Can someone tell me what this means? I tried removing "static" from the main method, but I get the error: Exception in thread "main" java.lang.NoSuchMethodError: main. Thanks in advance

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  • Shedule tasks question

    - by gabac
    Hi everyone I have a though question :) Let's say you get some data which is due at a certain point int the future. You get A saying my task is due in 1h and other which says his task is due in 1.5h. The information is collected on your server. In which programming language or even how would solve that? So task a will be executed in 1h, task B in 1.5h. I read something about java scheduler but I'm not yet sure if this is the right way. What are ur ideas? Cheers

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  • GregorianCalander

    - by namitjain23
    Hey guys, i know this is a very simple question but i am new to Java so please bare with me. I have create a program that can calculate the time a book is due to come back after being issed! So please help me out Here is the piece of code that i have: public void loan(int numOfDays) { if( onLoan == true) { System.out.println("Already on Loan, Return Date : "+Calendar.DATE ); } else { due.set( numOfDays, Calendar.DATE ); System.out.println("Available"); onLoan = true; } } // Mark the book as having been returned Basically i need to replace that Calendar.DATE to get me calculations right. I need to calculate the date passed by the TEST file and calulate the date it will be returned. This project needs to be submitted TOMORROW, so please please help me out!

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  • sending request to a page

    - by gklots
    hi there. I'm trying to fill-out a form automatically and press a button on that form and wait for a response. How do I go about doing this? To be more particular, I have a a --HUGE-- collection DNA strains which I need to compare to each-other. Luckily, there's a website that does exactly what I need. Basically, I type-in 2 different sequences of DNA and click the "Align Sequences" button and get a result (the calculation of the score is not relevant). Is there a way to make a Java program that will automatically insert the input, "click" the button and read the response from this website? Thanks!

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  • Android camera to take multiple photos

    - by user2975407
    problem.java public class problem extends Activity { ImageView iv; @Override protected void onCreate(Bundle savedInstanceState) { // TODO Auto-generated method stub super.onCreate(savedInstanceState); setContentView(R.layout.problem); iv=(ImageView) findViewById(R.id.imageView1); Button b=(Button) findViewById(R.id.button1); b.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { Intent intent=new Intent(android.provider.MediaStore.ACTION_IMAGE_CAPTURE); startActivityForResult(intent, 0); } }); } @Override protected void onActivityResult(int requestCode, int resultCode, Intent data) { // TODO Auto-generated method stub super.onActivityResult(requestCode, resultCode, data); Bitmap bm=(Bitmap) data.getExtras().get("data"); iv.setImageBitmap(bm); } } From this code I can only take one photo and it displayed in the screen. **But I want to take more photos nearly 5 photos and display in the screen** Further I want to add these photos to MySQL database.please help me to do that.I am new to android

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  • Is it possible to use a String as a seed for an instance Random? [duplicate]

    - by danpetruk
    This question already has an answer here: Converting String to long in Java 5 answers I have a String value and I would like to init a random class using the string as a seed? Is it possible to do this, and if so how? UPDATE 1: The string consists not only of ASCII. I can have any utf-8 symbols. UPDATE 2: Why did you close it? The questions really aren't about the same. Firstly because I've utf8 string and secondary because different strings can produce same seeds

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  • problem with pageFetcher

    - by kate
    hello i use this code for(int i=0; i < citylink.length; i++){ body=pF.fetchpage(citylink[i][1]); //it's for taking the url from the table citylink and returns the source of this url!! i have also declare it in my pagefetcher.java class like this public String fetchPage(String url) { try { url = URIUtil.encodeQuery(url); } catch (URIException e) { // TODO Auto-generated catch block e.printStackTrace(); } but when i compile it it says that The method fetchpage(String) is undefined for the type PageFetcher and i can't run my problem!!! i don't know what to do

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  • Should I create a new window or modify the old one?

    - by Roman
    I am programming a GUI application in Java. I do it for the first time. I would like to have a form (with radio buttons and so on). After the form is filled in and the "Submit" button is pressed I would like to have a new window. I see two potential ways to do it: Close the "old" window and open a "new" one. Remove "old" elements from the existing window and put there "new" elements. What is the standard way to go? If it is the first way, what is the command to close the window? If it is the second one, how can I remove elements from the existing window?

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  • What you would learn. [closed]

    - by NDeveloper
    Hi, I have a little free time and would like to learn new development language/technology. I know it can be very subective, but please share with us what you would learn and why. I have about 4 years of .NET development experience mostly distributed applications. And a little more than 2 years of c/c++. There are a lot of options to choose like Google Go/F#/Python/Scala/Java/ASP.NET/Mobile App development like for Android, BB, iPhone.../DB (MS SQL, Oracle or even MongoDB or CouchDB)/any new concepts, etc... I would like to use the time for investment, so gained knowledge will be useful.

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  • @MustOverride annotation?

    - by Harrypotter2k5
    In .NET, one can specify a "mustoverride" attribute to a method in a particular superclass to ensure that subclasses override that particular method. I was wondering whether anybody has a custom java annotation that could achieve the same effect. Essentially what i want is to push for subclasses to override a method in a superclass that itself has some logic that must be run-through. I dont want to use abstract methods or interfaces, because i want some common functionality to be run in the super method, but more-or-less produce a compiler warning/error denoting that derivative classes should override a given method.

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  • convert object to in

    - by hoora
    hello! i'm beginner and i want to write a java code in eclipse! this program take two linkedlist of integers(for exp:a & b) and make a linkedlist (for exp:d) that every elements of it are summation of elements of that linkedlist! but i can't add this two element of linkedlist because these are Object!! please help me!! exp: a=[3,4,6,7,8] b=[4,3,7,5,3,2,1] d=[7,7,13,12,11,2,1] THANK YOU VERY VERY VERY MUCH!

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  • In a JDBC ResultSet, what should happen when getLong() or getShort() is called on an int result colu

    - by Uri
    Say that I have a JDBC ResultSet, and I call the getLong() or getshort() method. For which of the following SQL types {SMALLINT, INT, BIGINT} should I get long, and for which types should I get an error? In other words, if I have an INT and I want a SMALLINT (A short), would I get it, or would I get an error? Similarly, if I have an INT and want a BIGINT (a long), would I get it, or would I get an error? The Javadocs (listed below) say nothing. public long getLong(int columnIndex) throws SQLException Retrieves the value of the designated column in the current row of this ResultSet object as a long in the Java programming language. Parameters: columnIndex - the first column is 1, the second is 2, ... Returns: the column value; if the value is SQL NULL, the value returned is 0 Throws: SQLException - if a database access error occurs

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  • Deleting the first occurrence of a target in aList [closed]

    - by Bandz Jooz
    /** Replaces each occurrence of oldItem in aList with newItem */ public static void replace(List<Student> aList, Student oldItemStudent newItem) { int index = aList.indexOf(oldItem); while(index != -1){ aList.set(index, newItem); index = aList.indexOf(oldItem); } /** Deletes the first occurrence of target in aList */ public static void delete(List<Student> aList, Student target){ Object o = //stuck here, dont know how to set up boolean stuff } } I figured out how to do the first method by looking up Java documentation, however I can't figure out how to finish my code for the second method even though I looked up the documentation which states: boolean remove(Object o) Removes the first occurrence of the specified element from this list, if it is present.

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  • What language should I write my 2D game in? [closed]

    - by jmgrosen
    I'm thinking of writing a game. It's inspired by Minecraft/Terraria (but don't worry it will be different). My main question is what language I should write it in -- it'll be relatively simple graphics, more like Terraria than Minecraft. I know Java relatively well and Minecraft is written in it, but C++ seems like the industry standard for game development. However, I know next to no C++. I'm willing to learn but am worried how it will turn out for my first real project in the language. In addition to that, I'd also like suggestions on a good game engine for the language that you suggest. I'd like it to run on: Windows for sure Linux for sure Mac for sure Android would be really nice iOS is optional Thank you in advance!

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  • Android custom ListView unable to click on items

    - by MattC
    So I have a custom ListView object. The list items have two textviews stacked on top of each other, plus a horizontal progress bar that I want to remain hidden until I actually do something. To the far right is a checkbox that I only want to display when the user needs to download updates to their database(s). When I disable the checkbox by setting the visibility to Visibility.GONE, I am able to click on the list items. When the checkbox is visible, I am unable to click on anything in the list except the checkboxes. I've done some searching but haven't found anything relevant to my current situation. I found this question but I'm using an overridden ArrayAdapter since I'm using ArrayLists to contain the list of databases internally. Do I just need to get the LinearLayout view and add an onClickListener like Tom did? I'm not sure. Here's the listview row layout XML: <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent" android:layout_height="?android:attr/listPreferredItemHeight" android:padding="6dip"> <LinearLayout android:orientation="vertical" android:layout_width="0dip" android:layout_weight="1" android:layout_height="fill_parent"> <TextView android:id="@+id/UpdateNameText" android:layout_width="wrap_content" android:layout_height="0dip" android:layout_weight="1" android:textSize="18sp" android:gravity="center_vertical" /> <TextView android:layout_width="fill_parent" android:layout_height="0dip" android:layout_weight="1" android:id="@+id/UpdateStatusText" android:singleLine="true" android:ellipsize="marquee" /> <ProgressBar android:id="@+id/UpdateProgress" android:layout_width="fill_parent" android:layout_height="wrap_content" android:indeterminateOnly="false" android:progressDrawable="@android:drawable/progress_horizontal" android:indeterminateDrawable="@android:drawable/progress_indeterminate_horizontal" android:minHeight="10dip" android:maxHeight="10dip" /> </LinearLayout> <CheckBox android:text="" android:id="@+id/UpdateCheckBox" android:layout_width="wrap_content" android:layout_height="wrap_content" /> </LinearLayout> And here's the class that extends the ListActivity. Obviously it's still in development so forgive the things that are missing or might be left laying around: import java.util.List; import android.app.ListActivity; import android.content.Context; import android.os.Bundle; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup; import android.widget.ArrayAdapter; import android.widget.Button; import android.widget.CheckBox; import android.widget.ListView; import android.widget.ProgressBar; import android.widget.TextView; import com.xxxx.android.R; import com.xxxx.android.DAO.AccountManager; import com.xxxx.android.model.UpdateItem; public class UpdateActivity extends ListActivity { AccountManager lookupDb; boolean allSelected; UpdateListAdapter list; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); lookupDb = new AccountManager(this); lookupDb.loadUpdates(); setContentView(R.layout.update); allSelected = false; list = new UpdateListAdapter(this, R.layout.update_row, lookupDb.getUpdateItems()); setListAdapter(list);

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  • JSF: Cannot catch ViewExpiredException

    - by ifischer
    I'm developing a JSF 2.0 application on Glassfish v3 and i'm trying to handle the ViewExpiredException. But whatever i do, i always get a Glassfish error report instead of my own error page. To simulate the occurrence of the VEE, i inserted the following function into my backing bean, which fires the VEE. I'm triggering this function from my JSF page through a commandLink. The Code: @Named public class PersonHome { (...) public void throwVEE() { throw new ViewExpiredException(); } } At first i tried it by simply adding an error-page to my web.xml: <error-page> <exception-type>javax.faces.application.ViewExpiredException</exception-type> <location>/error.xhtml</location> </error-page> But this doesn't work, i'm not redirected to error but i'm shown the Glassfish errorpage, which shows a HTTP Status 500 page with the following content: description:The server encountered an internal error () that prevented it from fulfilling this request. exception: javax.servlet.ServletException: javax.faces.application.ViewExpiredException root cause: javax.faces.el.EvaluationException:javax.faces.application.ViewExpiredException root cause:javax.faces.application.ViewExpiredException Next thing i tried was to write ExceptionHandlerFactory and a CustomExceptionHandler, as described in JavaServerFaces 2.0 - The Complete Reference. So i inserted the following tag into faces-config.xml: <factory> <exception-handler-factory> exceptions.ExceptionHandlerFactory </exception-handler-factory> </factory> And added these classes: The factory: package exceptions; import javax.faces.context.ExceptionHandler; public class ExceptionHandlerFactory extends javax.faces.context.ExceptionHandlerFactory { private javax.faces.context.ExceptionHandlerFactory parent; public ExceptionHandlerFactory(javax.faces.context.ExceptionHandlerFactory parent) { this.parent = parent; } @Override public ExceptionHandler getExceptionHandler() { ExceptionHandler result = parent.getExceptionHandler(); result = new CustomExceptionHandler(result); return result; } } The custom exception handler: package exceptions; import java.util.Iterator; import javax.faces.FacesException; import javax.faces.application.NavigationHandler; import javax.faces.application.ViewExpiredException; import javax.faces.context.ExceptionHandler; import javax.faces.context.ExceptionHandlerWrapper; import javax.faces.context.FacesContext; import javax.faces.event.ExceptionQueuedEvent; import javax.faces.event.ExceptionQueuedEventContext; class CustomExceptionHandler extends ExceptionHandlerWrapper { private ExceptionHandler parent; public CustomExceptionHandler(ExceptionHandler parent) { this.parent = parent; } @Override public ExceptionHandler getWrapped() { return this.parent; } @Override public void handle() throws FacesException { for (Iterator<ExceptionQueuedEvent> i = getUnhandledExceptionQueuedEvents().iterator(); i.hasNext();) { ExceptionQueuedEvent event = i.next(); System.out.println("Iterating over ExceptionQueuedEvents. Current:" + event.toString()); ExceptionQueuedEventContext context = (ExceptionQueuedEventContext) event.getSource(); Throwable t = context.getException(); if (t instanceof ViewExpiredException) { ViewExpiredException vee = (ViewExpiredException) t; FacesContext fc = FacesContext.getCurrentInstance(); NavigationHandler nav = fc.getApplication().getNavigationHandler(); try { // Push some useful stuff to the flash scope for // use in the page fc.getExternalContext().getFlash().put("expiredViewId", vee.getViewId()); nav.handleNavigation(fc, null, "/login?faces-redirect=true"); fc.renderResponse(); } finally { i.remove(); } } } // At this point, the queue will not contain any ViewExpiredEvents. // Therefore, let the parent handle them. getWrapped().handle(); } } But STILL i'm NOT redirected to my error page - i'm getting the same HTTP 500 error like above. What am i doing wrong, what could be missing in my implementation so that the exception is handled correctly?

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  • hibernate fail mapping two tables

    - by sebbalex
    Hi guys, I'd like to understand how it is possible: Until I was working with one table everything worked fine, when I have mapped another table it fails as shown below: Glassfish start: INFO: configuring from resource: /hibernate.cfg.xml INFO: Configuration resource: /hibernate.cfg.xml INFO: Reading mappings from resource : hibernate_centrale.hbm.xml //first table INFO: Mapping class: com.italtel.patchfinder.objects.centrale - centrale INFO: Reading mappings from resource : hibernate_impianti.hbm.xml //second table INFO: Mapping class: com.italtel.patchfinder.objects.Impianto - impianti INFO: Configured SessionFactory: null INFO: schema update complete INFO: Hibernate: select centrale0_.id as id0_, centrale0_.name as name0_, centrale0_.impianto as impianto0_, centrale0_.servizio as servizio0_ from centrale centrale0_ group by centrale0_.name INFO: Hibernate: select centrale0_.id as id0_, centrale0_.name as name0_, centrale0_.impianto as impianto0_, centrale0_.servizio as servizio0_ from centrale centrale0_ where centrale0_.name='ANCONA' order by centrale0_.name asc //Error org.hibernate.hql.ast.QuerySyntaxException: impianti is not mapped [from impianti where impianto='SD' order by modulo asc] at org.hibernate.hql.ast.util.SessionFactoryHelper.requireClassPersister(SessionFactoryHelper.java:181) ..... config: table1 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <hibernate-mapping> <class name="com.italtel.patchfinder.objects.Impianto" table="impianti"> <id column="id" name="id"> <generator class="increment"/> </id> <property name="impianto"/> <property name="modulo"/> </class> </hibernate-mapping> table2 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <hibernate-mapping> <class name="com.italtel.patchfinder.objects.centrale" table="centrale"> <id column="id" name="id"> <generator class="increment"/> </id> <property name="name"/> <property name="impianto"/> <property name="servizio"/> </class> </hibernate-mapping> connection stuff ... <property name="hbm2ddl.auto">update</property> <mapping resource="hibernate_centrale.hbm.xml"/> <mapping resource="hibernate_impianti.hbm.xml"/> </session-factory> </hibernate-configuration> Class: public List loadAll() { Session session = sessionFactory.getCurrentSession(); session.beginTransaction(); return session.createQuery("from centrale group by name").list(); } public List<centrale> loadImplants(String centrale) { Session session = sessionFactory.getCurrentSession(); session.beginTransaction(); return session.createQuery("from centrale where name='" + centrale + "' order by name asc").list(); } public List<Impianto> loadModules(String implant) { Session session = sessionFactory.getCurrentSession(); session.beginTransaction(); return session.createQuery("from impianti where impianto='" + implant + "' order by modulo asc").list(); } } Do you have some advice? Thanks in advance

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  • Enunciate http error 404

    - by malakan
    Hi, I tried to setup a simple project with spring and enunciate+jax-ws/jax-rs annotation, but I didn't get it work. I used some great tutorial for the enunciate integration tutorial as template: http://docs.codehaus.org/display/ENUNCIATE/A+Rich+Web+service+API+for+your+favorite+framework Enunciate create the api-page like in the tutorial, but I get this error : If I open a mount point, for example the REST one (/rest/Service/getService/1), I'll get a 404-Error: NOT_FOUND Here is sample of my code : pom.xml: <plugin> <groupId>org.codehaus.enunciate</groupId> <artifactId>maven-enunciate-spring-plugin</artifactId> <version>1.19</version> <configuration> <configFile>src/main/webapp/WEB-INF/enunciate.xml</configFile> </configuration> <executions> <execution> <goals> <goal>assemble</goal> </goals> </execution> </executions> </plugin> enunciate.xml: <api-classes> <include pattern="com.myProject.model.*"/> <include pattern="com.myProject.services.MyService"/> <include pattern="com.myProject.services.MyServiceImpl"/> </api-classes> <webapp mergeWebXML="web.xml"/> <modules> <docs docsDir="api" title="myApp API"/> <spring-app> <springImport file="spring/applicationContext-config.xml"/> </spring-app> </modules> my service : package com.myProject.services; import java.util.List; import javax.jws.WebService; import javax.ws.rs.GET; import javax.ws.rs.Path; import javax.ws.rs.PathParam; import com.myProject.model.*; @WebService public interface MyService { @GET @Path("getService/{id}") public Service getService(@PathParam(value = "id")Integer id); } MyServiceImpl: package com.myProject.services; import javax.jws.WebService; ...(all import) import javax.persistence.EntityManager; @Service @Path("/Service") @WebService (endpointInterface="com.myProjects.services.MyService") @RemotingDestination(channels={"my-amf"}) public class MyServiceImpl implements MyService { private final Log logger = LogFactory.getLog(getClass()); @Autowired private MyServiceDao myServiceDao ; /*@Inject private MyServiceDao myServiceDao ;*/ public Service getService (Integer id) { return myServiceDao.getService (id); } } and I put @XmlRootElement on the model. I have tried several configuration, I couldn't get the xml or json response...just 404. Doesn't anyone know what is wrong?

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  • How do I handle calls to AudioTrack from jni without crashing?

    - by icecream
    I was trying to write to an AudioTrack from a jni callback, and I get a signal 7 (SIGBUS), fault addr 00000000. I have looked at the Wolf3D example for odroid and they seem to use a android.os.Handler to post a Runnable that will do an update in the correct thread context. I have also tried AttachCurrentThread, but I fail in this case also. It works to play the sound when running from the constructor even if I wrap it in a thread and then post it to the handler. When I do the "same" via a callback from jni it fails. I assume I am braeaking some rules, but I haven't been able to figure out what they are. So far, I haven't found the answer here on SO. So I wonder if anyone knows how this should be done. EDIT: Answered below. The following code is to illustrate the problem. Java: package com.example.jniaudiotrack; import android.app.Activity; import android.media.AudioFormat; import android.media.AudioManager; import android.media.AudioTrack; import android.os.Bundle; import android.os.Handler; import android.util.Log; public class JniAudioTrackActivity extends Activity { AudioTrack mAudioTrack; byte[] mArr; public static final Handler mHandler = new Handler(); /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); mArr = new byte[2048]; for (int i = 0; i < 2048; i++) { mArr[i] = (byte) (Math.sin(i) * 128); } mAudioTrack = new AudioTrack(AudioManager.STREAM_MUSIC, 11025, AudioFormat.CHANNEL_CONFIGURATION_MONO, AudioFormat.ENCODING_PCM_8BIT, 2048, AudioTrack.MODE_STREAM); mAudioTrack.play(); new Thread(new Runnable() { public void run() { mHandler.post(new Runnable() { public void run() { mAudioTrack.write(mArr, 0, 2048); Log.i(TAG, "*** Handler from constructor ***"); } }); } }).start(); new Thread(new Runnable() { public void run() { audioFunc(); } }).start(); } public native void audioFunc(); @SuppressWarnings("unused") private void audioCB() { mHandler.post(new Runnable() { public void run() { mAudioTrack.write(mArr, 0, 2048); Log.i(TAG, "*** audioCB called ***"); } }); } private static final String TAG = "JniAudioTrackActivity"; static { System.loadLibrary("jni_audiotrack"); } } cpp: #include <jni.h> extern "C" { JNIEXPORT void Java_com_example_jniaudiotrack_JniAudioTrackActivity_audioFunc(JNIEnv* env, jobject obj); } JNIEXPORT void Java_com_example_jniaudiotrack_JniAudioTrackActivity_audioFunc(JNIEnv* env, jobject obj) { JNIEnv* jniEnv; JavaVM* vm; env->GetJavaVM(&vm); vm->AttachCurrentThread(&jniEnv, 0); jclass cls = env->GetObjectClass(obj); jmethodID audioCBID = env->GetMethodID(cls, "audioCB", "()V"); if (!audioCBID) { return; } env->CallVoidMethod(cls, audioCBID); } Trace snippet: I/DEBUG ( 1653): pid: 9811, tid: 9811 >>> com.example.jniaudiotrack <<< I/DEBUG ( 1653): signal 7 (SIGBUS), fault addr 00000000 I/DEBUG ( 1653): r0 00000800 r1 00000026 r2 00000001 r3 00000000 I/DEBUG ( 1653): r4 42385726 r5 41049e54 r6 bee25570 r7 ad00e540 I/DEBUG ( 1653): r8 000040f8 r9 41048200 10 41049e44 fp 00000000 I/DEBUG ( 1653): ip 000000f8 sp bee25530 lr ad02dbb5 pc ad012358 cpsr 20000010 I/DEBUG ( 1653): #00 pc 00012358 /system/lib/libdvm.so

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  • Nightmare: Upgrading Tomcat 5.5 to 6.0

    - by pavanlimo
    I'm trying to upgrade a perfectly running embedded Tomcat 5.5 to Tomcat 6.0. I understand that all I need to do is replace Tomcat 5.5 jars with 6.0. That's what I did. So I replaced the following jars: catalina-5.0.28.jar catalina-5.5.9.jar catalina-optional-5.5.9.jar commons-el.jar commons-modeler-1.1.0.jar jasper-compiler-jdt.jar jasper-compiler.jar jasper-runtime.jar jmx-5.0.28.jar jsp-api-2.0.jar naming-factory.jar naming-resources.jar servlet-api-2.4.jar servlets-default.jar tomcat-coyote.jar tomcat-http.jar tomcat-util.jar with: annotations-api.jar catalina.jar jasper.jar tomcat-dbcp.jar catalina-ant.jar el-api.jar jsp-api.jar tomcat-i18n-es.jar catalina-ha.jar jasper-el.jar servlet-api.jar tomcat-i18n-fr.jar catalina-tribes.jar jasper-jdt.jar tomcat-coyote.jar tomcat-i18n-ja.jar tomcat-juli.jar As soon as I start the server, I get the following message in the logs at INFO level: INFO: Starting Servlet Engine: Apache Tomcat/6.0.29 Dec 31, 2010 6:04:18 AM org.apache.catalina.loader.WebappClassLoader validateJarFile INFO: validateJarFile(/usr/local/blah/blue/./WEB-INF/lib/servlet-api.jar) - jar not loaded. See Servlet Spec 2.3, section 9.7.2. Offending class: javax/servlet/Servlet.class Based on the this explanation, I need to remove a jar file which has a conflicting Servlet.class. I swear to God, there is no other conflicting jar file, I grepped system wide for Servlet.class, it matched only servlet-api.jar. I also downloaded javaee.jar and replaced it by servlet-api.jar, to same avail. Having tried lot of these stuff, I did not have much to look upto, so set the tomcat logging level to ALL. In the log I could see that it is trying to check for Servlet.class in each and every jar it is loading until it finds servlet-api.jar and throws "jar not loaded" message as soon as it finds servlet-api.jar. See below: FINE: Checking for javax/servlet/Servlet.class Jan 2, 2011 7:39:33 AM org.apache.catalina.loader.WebappLoader setRepositories FINE: Deploy JAR /WEB-INF/lib/servlet-api.jar to /usr/local/blah/blue/./WEB-INF/lib/servlet-api.jar Jan 2, 2011 7:39:33 AM org.apache.catalina.loader.WebappClassLoader addJar FINE: addJar(/WEB-INF/lib/servlet-api.jar) Jan 2, 2011 7:39:33 AM org.apache.catalina.loader.WebappClassLoader validateJarFile FINE: Checking for javax/servlet/Servlet.class Jan 2, 2011 7:39:33 AM org.apache.catalina.loader.WebappClassLoader validateJarFile INFO: validateJarFile(/usr/local/blah/blue/./WEB-INF/lib/servlet-api.jar) - jar not loaded. See Servlet Spec 2.3, section 9.7.2. Offending class: javax/servlet/Servlet.class Jan 2, 2011 7:39:33 AM org.apache.catalina.loader.WebappLoader setRepositories Please note however, that Tomcat starts successfully! And as soon as I hit the URL on the browser, I get blank page(this may be in my case only, I guess 'cuz of my web.xml, sorta different from most. Other people on the internet have got Error 404 instead.) with following log statements(at finest level) Jan 2, 2011 9:40:01 AM org.apache.catalina.connector.CoyoteAdapter parseSessionCookiesId FINE: Requested cookie session id is 0FBA716E3F9B0147C3AF7ABAE3B1C27B Jan 2, 2011 9:40:01 AM org.apache.catalina.authenticator.AuthenticatorBase invoke FINE: Security checking request GET /login.jsp Jan 2, 2011 9:40:01 AM org.apache.catalina.realm.RealmBase findSecurityConstraints FINE: Checking constraint 'SecurityConstraint[protected]' against GET /login.jsp --> false Jan 2, 2011 9:40:01 AM org.apache.catalina.realm.RealmBase findSecurityConstraints FINE: Checking constraint 'SecurityConstraint[protected]' against GET /login.jsp --> false Jan 2, 2011 9:40:01 AM org.apache.catalina.realm.RealmBase findSecurityConstraints FINE: Checking constraint 'SecurityConstraint[protected]' against GET /login.jsp --> false Jan 2, 2011 9:40:01 AM org.apache.catalina.realm.RealmBase findSecurityConstraints FINE: Checking constraint 'SecurityConstraint[protected]' against GET /login.jsp --> false Jan 2, 2011 9:40:01 AM org.apache.catalina.realm.RealmBase findSecurityConstraints FINE: No applicable constraint located Jan 2, 2011 9:40:01 AM org.apache.catalina.authenticator.AuthenticatorBase invoke FINE: Not subject to any constraint Jan 2, 2011 9:40:01 AM org.apache.catalina.core.StandardWrapper allocate FINEST: Returning non-STM instance I'm not sure if the above log message is important, but I'm for all-out disclosure here. One interesting thing though, I manually created a dummy jsp file containing only "helloooo" just outside WEB-INF folder(no security constraints for this file). This file was accessible and could be displayed. But, all my jsp's and classes are inside WEB-INF(ofcourse). Sick and tired of this issue, please help me solve it. I've already spent 20-24 hours on this unsuccessfully. Any pointers directions hints leads?

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  • JavaMail SMTP credentials verification, without actually sending an email.

    - by DarK
    Hi, Is there a way to check user SMTP server credentials without sending email, or connecting to POP/IMAP. Some code I tried to write, fails at it. Can you find what is missing there. Don't worry about Email / password. I know it's there. NOTE : If you are trying out the code. The case 1 should pass when supplying the correct credentials. If it fails, then someone changed the password. You should use some other email address. import java.util.Properties; import javax.mail.Authenticator; import javax.mail.MessagingException; import javax.mail.PasswordAuthentication; import javax.mail.Session; import javax.mail.Transport; public class EmailTest { public static void main(String[] args) { EmailHelper eh = new EmailHelper(); /* GMail Setting for SMTP using STARTTLS */ String name = "AAA"; String email = "[email protected]"; String smtpHost = "smtp.gmail.com"; String serverPort = "587"; String requireAuth = "true"; String dontuseAuth = "false"; String userName = email; // same as username for GMAIL String password = "zaq12wsx"; String incorrectPassword = "someRandomPassword"; String enableSTARTTLS = "true"; String dontenableSTARTTLS = "false"; try { /* only valid case */ eh.sendMail(name, email, smtpHost, serverPort, requireAuth, userName, password, enableSTARTTLS); System.out.println("Case 1 Passed"); /* should fail since starttls is required for GMAIL. */ eh.sendMail(name, email, smtpHost, serverPort, requireAuth, userName, password, dontenableSTARTTLS); System.out.println("Case 2 Passed"); /* should fail since GMAIL requires authentication */ eh.sendMail(name, email, smtpHost, serverPort, dontuseAuth, "", "", dontenableSTARTTLS); System.out.println("Case 3 Passed"); /* should fail. password is incorrect and starttls is not enabled */ eh.sendMail(name, email, smtpHost, serverPort, requireAuth, userName, incorrectPassword, dontenableSTARTTLS); System.out.println("Case 4 Passed"); } catch (MessagingException e) { e.printStackTrace(); } } } class EmailHelper { private Properties properties = null; private Authenticator authenticator = null; private Session session = null; public void sendMail(String name, String email, String smtpHost, String serverPort, String requireAuth, String userName, String password, String enableSTARTTLS) throws MessagingException { properties = System.getProperties(); properties.put("mail.smtp.host", smtpHost); properties.put("mail.smtp.port", serverPort); properties.put("mail.smtp.starttls.enable", enableSTARTTLS); properties.put("mail.smtp.auth", requireAuth); properties.put("mail.smtp.timeout", 20000); authenticator = new SMTPAuthenticator(userName, password); session = Session.getInstance(properties, authenticator); // session.setDebug(true); Transport tr = session.getTransport("smtp"); tr.connect(); /* * do I need more than just connect? Since when i try to send email with * incorrect credentials it fails to do so. But I want to check * credentials without sending an email. Assume that POP3/IMAP username * is not same as the SMTP username, since that might be one of the * cases */ } } class SMTPAuthenticator extends Authenticator { private String userName = null; private String password = null; public SMTPAuthenticator(String userName, String password) { this.userName = userName; this.password = password; } @Override public PasswordAuthentication getPasswordAuthentication() { return new PasswordAuthentication(userName, password); } }

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  • .exe is not created when using launch4j and maven

    - by Ismail Sen
    I'm trying to create an exe file for my JAVA project using launch4j and Maven. Here is my pom.xml <build> <pluginManagement> <plugins> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-compiler-plugin</artifactId> <version>3.0</version> <configuration> <source>1.7</source> <target>1.7</target> </configuration> </plugin> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-jar-plugin</artifactId> <version>2.3.2</version> </plugin> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-assembly-plugin</artifactId> <version>2.4</version> <configuration> <descriptorRefs> <descriptortRef>jar-with-dependencies</descriptortRef> </descriptorRefs> <archive> <manifest> <mainClass>dev.main.App</mainClass> </manifest> </archive> </configuration> <executions> <execution> <id>make-assembly</id> <phase>package</phase> <goals> <goal>single</goal> </goals> </execution> </executions> </plugin> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-shade-plugin</artifactId> <version>1.7.1</version> <executions> <execution> <phase>package</phase> <goals> <goal>shade</goal> </goals> </execution> </executions> <configuration> <shadedArtifactAttached>true</shadedArtifactAttached> <shadedClassifierName>shaded</shadedClassifierName> <transformers> <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer"> <mainClass>dev.main.App</mainClass> </transformer> </transformers> </configuration> </plugin> <plugin> <groupId>com.akathist.maven.plugins.launch4j</groupId> <artifactId>launch4j-maven-plugin</artifactId> <version>1.5.1</version> <executions> <execution> <id>l4j-clui</id> <phase>package</phase> <goals> <goal>launch4j</goal> </goals> <configuration> <headerType>console</headerType> <jar>${project.build.directory}/target/App-jar-with-dependencies.jar</jar> <outfile>${project.build.directory}/target/App.exe</outfile> <downloadUrl>http://java.com/download</downloadUrl> <classPath> <mainClass>dev.main.App</mainClass> </classPath> <jre> <minVersion>1.6.0</minVersion> <jdkPreference>preferJre</jdkPreference> </jre> <versionInfo> <fileVersion>1.0.0.0</fileVersion> <txtFileVersion>${project.version}</txtFileVersion> <fileDescription>${project.name}</fileDescription> <copyright>C</copyright> <productVersion>1.0.0.0</productVersion> <txtProductVersion>1.0.0.0</txtProductVersion> <productName>${project.name}</productName> <internalName>AppName</internalName> <originalFilename>App.exe</originalFilename> </versionInfo> </configuration> </execution> </executions> </plugin> </plugins> </pluginManagement> </build> I run : mvn clean compile assembly:single to create my jar app with all Maven dependencies. To create the .exe I do : mvn package but nothing is created under target folder. Am I missing a goal or a configuration ? Ismail

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  • migrating Solaris to RH: network latency issue, tcp window size & other tcp parameters

    - by Bastien
    Hello I have a client/server app (Java) that I'm migrating from Solaris to RH Linux. since I started running it in RH, I noticed some issues related to latency. I managed to isolate the problem that looks like this: client sends 5 messages (32 bytes each) in a row (same application timestamp) to the server. server echos messages. client receives replies and prints round trip time for each msg. in Solaris, all is well: I get ALL 5 replies at the same time, roughly 80ms after having sent original messages (client & server are several thousands miles away from each other: my ping RTT is 80ms, all normal). in RH, first 3 messages are echoed normally (they arrive 80ms after they've been sent), however the following 2 arrive 80ms later (so total 160ms RTT). the pattern is always the same. clearly looked like a TCP problem. on my solaris box, I had previously configured the tcp stack with 2 specific options: disable nagle algorithm globally set tcp_deferred_acks_max to 0 on RH, it's not possible to disable nagle globally, but I disabled it on all of my apps' sockets (TCP_NODELAY). so I started playing with tcpdump (on the server machine), and compared both outputs: SOLARIS: 22 2.085645 client server TCP 56150 > 6006 [PSH, ACK] Seq=111 Ack=106 Win=66672 Len=22 "MSG_1 RCV" 23 2.085680 server client TCP 6006 > 56150 [ACK] Seq=106 Ack=133 Win=50400 Len=0 24 2.085908 client server TCP 56150 > 6006 [PSH, ACK] Seq=133 Ack=106 Win=66672 Len=22 "MSG_2 RCV" 25 2.085925 server client TCP 6006 > 56150 [ACK] Seq=106 Ack=155 Win=50400 Len=0 26 2.086175 client server TCP 56150 > 6006 [PSH, ACK] Seq=155 Ack=106 Win=66672 Len=22 "MSG_3 RCV" 27 2.086192 server client TCP 6006 > 56150 [ACK] Seq=106 Ack=177 Win=50400 Len=0 28 2.086243 server client TCP 6006 > 56150 [PSH, ACK] Seq=106 Ack=177 Win=50400 Len=21 "MSG_1 ECHO" 29 2.086440 client server TCP 56150 > 6006 [PSH, ACK] Seq=177 Ack=106 Win=66672 Len=22 "MSG_4 RCV" 30 2.086454 server client TCP 6006 > 56150 [ACK] Seq=127 Ack=199 Win=50400 Len=0 31 2.086659 server client TCP 6006 > 56150 [PSH, ACK] Seq=127 Ack=199 Win=50400 Len=21 "MSG_2 ECHO" 32 2.086708 client server TCP 56150 > 6006 [PSH, ACK] Seq=199 Ack=106 Win=66672 Len=22 "MSG_5 RCV" 33 2.086721 server client TCP 6006 > 56150 [ACK] Seq=148 Ack=221 Win=50400 Len=0 34 2.086947 server client TCP 6006 > 56150 [PSH, ACK] Seq=148 Ack=221 Win=50400 Len=21 "MSG_3 ECHO" 35 2.087196 server client TCP 6006 > 56150 [PSH, ACK] Seq=169 Ack=221 Win=50400 Len=21 "MSG_4 ECHO" 36 2.087500 server client TCP 6006 > 56150 [PSH, ACK] Seq=190 Ack=221 Win=50400 Len=21 "MSG_5 ECHO" 37 2.165390 client server TCP 56150 > 6006 [ACK] Seq=221 Ack=148 Win=66632 Len=0 38 2.166314 client server TCP 56150 > 6006 [ACK] Seq=221 Ack=190 Win=66588 Len=0 39 2.364135 client server TCP 56150 > 6006 [ACK] Seq=221 Ack=211 Win=66568 Len=0 REDHAT: 17 2.081163 client server TCP 55879 > 6006 [PSH, ACK] Seq=111 Ack=106 Win=66672 Len=22 "MSG_1 RCV" 18 2.081178 server client TCP 6006 > 55879 [ACK] Seq=106 Ack=133 Win=5888 Len=0 19 2.081297 server client TCP 6006 > 55879 [PSH, ACK] Seq=106 Ack=133 Win=5888 Len=21 "MSG_1 ECHO" 20 2.081711 client server TCP 55879 > 6006 [PSH, ACK] Seq=133 Ack=106 Win=66672 Len=22 "MSG_2 RCV" 21 2.081761 client server TCP 55879 > 6006 [PSH, ACK] Seq=155 Ack=106 Win=66672 Len=22 "MSG_3 RCV" 22 2.081846 server client TCP 6006 > 55879 [PSH, ACK] Seq=127 Ack=177 Win=5888 Len=21 "MSG_2 ECHO" 23 2.081995 server client TCP 6006 > 55879 [PSH, ACK] Seq=148 Ack=177 Win=5888 Len=21 "MSG_3 ECHO" 24 2.082011 client server TCP 55879 > 6006 [PSH, ACK] Seq=177 Ack=106 Win=66672 Len=22 "MSG_4 RCV" 25 2.082362 client server TCP 55879 > 6006 [PSH, ACK] Seq=199 Ack=106 Win=66672 Len=22 "MSG_5 RCV" 26 2.082377 server client TCP 6006 > 55879 [ACK] Seq=169 Ack=221 Win=5888 Len=0 27 2.171003 client server TCP 55879 > 6006 [ACK] Seq=221 Ack=148 Win=66632 Len=0 28 2.171019 server client TCP 6006 > 55879 [PSH, ACK] Seq=169 Ack=221 Win=5888 Len=42 "MSG_4 ECHO + MSG_5 ECHO" 29 2.257498 client server TCP 55879 > 6006 [ACK] Seq=221 Ack=211 Win=66568 Len=0 so, I got confirmation things are not working correctly for RH: packet 28 is sent TOO LATE, it looks like the server is waiting for packet 27's ACK before doing anything. seems to me it's the most likely reason... then I realized that the "Win" parameters are different on Solaris & RH dumps: 50400 on Solaris, only 5888 on RH. that's another hint... I read the doc about the slide window & buffer window, and played around with the rcvBuffer & sendBuffer in java on my sockets, but never managed to change this 5888 value to anything else (I checked each time directly with tcpdump). does anybody know how to do this ? I'm having a hard time getting definitive information, as in some cases there's "auto-negotiation" that I might need to bypass, etc... I eventually managed to get only partially rid of my initial problem by setting the "tcp_slow_start_after_idle" parameter to 0 on RH, but it did not change the "win" parameter at all. the same problem was there for the first 4 groups of 5 messages, with TCP retransmission & TCP Dup ACK in tcpdump, then the problem disappeared altogether for all following groups of 5 messages. It doesn't seem like a very clean and/or generic solution to me. I'd really like to reproduce the exact same conditions under both OSes. I'll keep researching, but any help from TCP gurus would be greatly appreciated ! thanks !

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  • Traditional IO vs memory-mapped

    - by Senne
    I'm trying to illustrate the difference in performance between traditional IO and memory mapped files in java to students. I found an example somewhere on internet but not everything is clear to me, I don't even think all steps are nececery. I read a lot about it here and there but I'm not convinced about a correct implementation of neither of them. The code I try to understand is: public class FileCopy{ public static void main(String args[]){ if (args.length < 1){ System.out.println(" Wrong usage!"); System.out.println(" Correct usage is : java FileCopy <large file with full path>"); System.exit(0); } String inFileName = args[0]; File inFile = new File(inFileName); if (inFile.exists() != true){ System.out.println(inFileName + " does not exist!"); System.exit(0); } try{ new FileCopy().memoryMappedCopy(inFileName, inFileName+".new" ); new FileCopy().customBufferedCopy(inFileName, inFileName+".new1"); }catch(FileNotFoundException fne){ fne.printStackTrace(); }catch(IOException ioe){ ioe.printStackTrace(); }catch (Exception e){ e.printStackTrace(); } } public void memoryMappedCopy(String fromFile, String toFile ) throws Exception{ long timeIn = new Date().getTime(); // read input file RandomAccessFile rafIn = new RandomAccessFile(fromFile, "rw"); FileChannel fcIn = rafIn.getChannel(); ByteBuffer byteBuffIn = fcIn.map(FileChannel.MapMode.READ_WRITE, 0,(int) fcIn.size()); fcIn.read(byteBuffIn); byteBuffIn.flip(); RandomAccessFile rafOut = new RandomAccessFile(toFile, "rw"); FileChannel fcOut = rafOut.getChannel(); ByteBuffer writeMap = fcOut.map(FileChannel.MapMode.READ_WRITE,0,(int) fcIn.size()); writeMap.put(byteBuffIn); long timeOut = new Date().getTime(); System.out.println("Memory mapped copy Time for a file of size :" + (int) fcIn.size() +" is "+(timeOut-timeIn)); fcOut.close(); fcIn.close(); } static final int CHUNK_SIZE = 100000; static final char[] inChars = new char[CHUNK_SIZE]; public static void customBufferedCopy(String fromFile, String toFile) throws IOException{ long timeIn = new Date().getTime(); Reader in = new FileReader(fromFile); Writer out = new FileWriter(toFile); while (true) { synchronized (inChars) { int amountRead = in.read(inChars); if (amountRead == -1) { break; } out.write(inChars, 0, amountRead); } } long timeOut = new Date().getTime(); System.out.println("Custom buffered copy Time for a file of size :" + (int) new File(fromFile).length() +" is "+(timeOut-timeIn)); in.close(); out.close(); } } When exactly is it nececary to use RandomAccessFile? Here it is used to read and write in the memoryMappedCopy, is it actually nececary just to copy a file at all? Or is it a part of memorry mapping? In customBufferedCopy, why is synchronized used here? I also found a different example that -should- test the performance between the 2: public class MappedIO { private static int numOfInts = 4000000; private static int numOfUbuffInts = 200000; private abstract static class Tester { private String name; public Tester(String name) { this.name = name; } public long runTest() { System.out.print(name + ": "); try { long startTime = System.currentTimeMillis(); test(); long endTime = System.currentTimeMillis(); return (endTime - startTime); } catch (IOException e) { throw new RuntimeException(e); } } public abstract void test() throws IOException; } private static Tester[] tests = { new Tester("Stream Write") { public void test() throws IOException { DataOutputStream dos = new DataOutputStream( new BufferedOutputStream( new FileOutputStream(new File("temp.tmp")))); for(int i = 0; i < numOfInts; i++) dos.writeInt(i); dos.close(); } }, new Tester("Mapped Write") { public void test() throws IOException { FileChannel fc = new RandomAccessFile("temp.tmp", "rw") .getChannel(); IntBuffer ib = fc.map( FileChannel.MapMode.READ_WRITE, 0, fc.size()) .asIntBuffer(); for(int i = 0; i < numOfInts; i++) ib.put(i); fc.close(); } }, new Tester("Stream Read") { public void test() throws IOException { DataInputStream dis = new DataInputStream( new BufferedInputStream( new FileInputStream("temp.tmp"))); for(int i = 0; i < numOfInts; i++) dis.readInt(); dis.close(); } }, new Tester("Mapped Read") { public void test() throws IOException { FileChannel fc = new FileInputStream( new File("temp.tmp")).getChannel(); IntBuffer ib = fc.map( FileChannel.MapMode.READ_ONLY, 0, fc.size()) .asIntBuffer(); while(ib.hasRemaining()) ib.get(); fc.close(); } }, new Tester("Stream Read/Write") { public void test() throws IOException { RandomAccessFile raf = new RandomAccessFile( new File("temp.tmp"), "rw"); raf.writeInt(1); for(int i = 0; i < numOfUbuffInts; i++) { raf.seek(raf.length() - 4); raf.writeInt(raf.readInt()); } raf.close(); } }, new Tester("Mapped Read/Write") { public void test() throws IOException { FileChannel fc = new RandomAccessFile( new File("temp.tmp"), "rw").getChannel(); IntBuffer ib = fc.map( FileChannel.MapMode.READ_WRITE, 0, fc.size()) .asIntBuffer(); ib.put(0); for(int i = 1; i < numOfUbuffInts; i++) ib.put(ib.get(i - 1)); fc.close(); } } }; public static void main(String[] args) { for(int i = 0; i < tests.length; i++) System.out.println(tests[i].runTest()); } } I more or less see whats going on, my output looks like this: Stream Write: 653 Mapped Write: 51 Stream Read: 651 Mapped Read: 40 Stream Read/Write: 14481 Mapped Read/Write: 6 What is makeing the Stream Read/Write so unbelievably long? And as a read/write test, to me it looks a bit pointless to read the same integer over and over (if I understand well what's going on in the Stream Read/Write) Wouldn't it be better to read int's from the previously written file and just read and write ints on the same place? Is there a better way to illustrate it? I've been breaking my head about a lot of these things for a while and I just can't get the whole picture..

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  • Null-free "maps": Is a callback solution slower than tryGet()?

    - by David Moles
    In comments to "How to implement List, Set, and Map in null free design?", Steven Sudit and I got into a discussion about using a callback, with handlers for "found" and "not found" situations, vs. a tryGet() method, taking an out parameter and returning a boolean indicating whether the out parameter had been populated. Steven maintained that the callback approach was more complex and almost certain to be slower; I maintained that the complexity was no greater and the performance at worst the same. But code speaks louder than words, so I thought I'd implement both and see what I got. The original question was fairly theoretical with regard to language ("And for argument sake, let's say this language don't even have null") -- I've used Java here because that's what I've got handy. Java doesn't have out parameters, but it doesn't have first-class functions either, so style-wise, it should suck equally for both approaches. (Digression: As far as complexity goes: I like the callback design because it inherently forces the user of the API to handle both cases, whereas the tryGet() design requires callers to perform their own boilerplate conditional check, which they could forget or get wrong. But having now implemented both, I can see why the tryGet() design looks simpler, at least in the short term.) First, the callback example: class CallbackMap<K, V> { private final Map<K, V> backingMap; public CallbackMap(Map<K, V> backingMap) { this.backingMap = backingMap; } void lookup(K key, Callback<K, V> handler) { V val = backingMap.get(key); if (val == null) { handler.handleMissing(key); } else { handler.handleFound(key, val); } } } interface Callback<K, V> { void handleFound(K key, V value); void handleMissing(K key); } class CallbackExample { private final Map<String, String> map; private final List<String> found; private final List<String> missing; private Callback<String, String> handler; public CallbackExample(Map<String, String> map) { this.map = map; found = new ArrayList<String>(map.size()); missing = new ArrayList<String>(map.size()); handler = new Callback<String, String>() { public void handleFound(String key, String value) { found.add(key + ": " + value); } public void handleMissing(String key) { missing.add(key); } }; } void test() { CallbackMap<String, String> cbMap = new CallbackMap<String, String>(map); for (int i = 0, count = map.size(); i < count; i++) { String key = "key" + i; cbMap.lookup(key, handler); } System.out.println(found.size() + " found"); System.out.println(missing.size() + " missing"); } } Now, the tryGet() example -- as best I understand the pattern (and I might well be wrong): class TryGetMap<K, V> { private final Map<K, V> backingMap; public TryGetMap(Map<K, V> backingMap) { this.backingMap = backingMap; } boolean tryGet(K key, OutParameter<V> valueParam) { V val = backingMap.get(key); if (val == null) { return false; } valueParam.value = val; return true; } } class OutParameter<V> { V value; } class TryGetExample { private final Map<String, String> map; private final List<String> found; private final List<String> missing; public TryGetExample(Map<String, String> map) { this.map = map; found = new ArrayList<String>(map.size()); missing = new ArrayList<String>(map.size()); } void test() { TryGetMap<String, String> tgMap = new TryGetMap<String, String>(map); for (int i = 0, count = map.size(); i < count; i++) { String key = "key" + i; OutParameter<String> out = new OutParameter<String>(); if (tgMap.tryGet(key, out)) { found.add(key + ": " + out.value); } else { missing.add(key); } } System.out.println(found.size() + " found"); System.out.println(missing.size() + " missing"); } } And finally, the performance test code: public static void main(String[] args) { int size = 200000; Map<String, String> map = new HashMap<String, String>(); for (int i = 0; i < size; i++) { String val = (i % 5 == 0) ? null : "value" + i; map.put("key" + i, val); } long totalCallback = 0; long totalTryGet = 0; int iterations = 20; for (int i = 0; i < iterations; i++) { { TryGetExample tryGet = new TryGetExample(map); long tryGetStart = System.currentTimeMillis(); tryGet.test(); totalTryGet += (System.currentTimeMillis() - tryGetStart); } System.gc(); { CallbackExample callback = new CallbackExample(map); long callbackStart = System.currentTimeMillis(); callback.test(); totalCallback += (System.currentTimeMillis() - callbackStart); } System.gc(); } System.out.println("Avg. callback: " + (totalCallback / iterations)); System.out.println("Avg. tryGet(): " + (totalTryGet / iterations)); } On my first attempt, I got 50% worse performance for callback than for tryGet(), which really surprised me. But, on a hunch, I added some garbage collection, and the performance penalty vanished. This fits with my instinct, which is that we're basically talking about taking the same number of method calls, conditional checks, etc. and rearranging them. But then, I wrote the code, so I might well have written a suboptimal or subconsicously penalized tryGet() implementation. Thoughts?

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