It is always set to 4.0.0 in Maven 2 and 3, because, at present, there is no other model.

&gt; Notice that `modelVersion` contains 4.0.0. That is currently the only supported POM version, and is always required. [[source](https://maven.apache.org/pom.html#quick-overview)]

But it wouldn&#39;t necessarily *need* to always be set to 4.0.0 if there was another version of the model. A POM has to comply with a model. Let&#39;s say Maven 4 comes up with model 4.1. If you write your pom to comply with 4.1, it wouldn&#39;t be compatible with Maven 3 and model 4.0.0.

It&#39;s defined as a mandatory, possibly to enforce a specific XML model in case new models are defined.

model version is the version of project descriptor  your POM conforms to.
It needs to be included and is set.
The value 4.0.0 just indicated that it is compatible Maven 3.

The Correct answer should be the combination of the answers by @Toumi and @Boj. Also have a look at https://cwiki.apache.org/confluence/display/MAVEN/POM+Model+Version+5.0.0 for more background of this.

**modelVersion** - containing the model version of the POM. 
Maven 1.x used a model which contained a &lt;modelVersion&gt;3.0.0&lt;/modelVersion&gt; element as an immediate child of the root. 
Maven 2.x / 3.x has used a &lt;modelVersion&gt;4.0.0&lt;/modelVersion&gt; element. 

**version** - containing the version of the project. If this attribute is missing then the parent element must be present and the version will be inherited from the parent project.

I know that this changes quite often, but is there a list as exhaustive as possible out there of the possible values returned by `navigator.platform`?

List so far:

 - HP-UX
 - Linux i686
 - Linux armv7l
 - Mac68K
 - MacPPC
 - MacIntel
 - SunOS
 - Win16
 - Win32
 - WinCE
 - iPhone
 - iPod
 - iPad
 - Android
 - BlackBerry
 - Opera 

What is the list of possible values for navigator.platform as of today?

I&#39;m trying to create an asynchronous console app that does a some work on a collection. I have one version which uses parallel for loop another version that uses async/await. I expected the async/await version to work similar to parallel version but it executes synchronously. What am I doing wrong?
```csharp
public class Program 
{
    public static void Main(string[] args) 
    {
        var worker = new Worker();
        worker.ParallelInit();
        var t = worker.Init();
        t.Wait();
        Console.ReadKey();
    }
}

public class Worker 
{
    public async Task&lt;bool&gt; Init() 
    {
        var series = Enumerable.Range(1, 5).ToList();
        foreach(var i in series) 
        {
          Console.WriteLine(&quot;Starting Process {0}&quot;, i);
          var result = await DoWorkAsync(i);
          
          if (result) 
          {
            Console.WriteLine(&quot;Ending Process {0}&quot;, i);
          }
        }

        return true;
    }

    public async Task&lt;bool&gt; DoWorkAsync(int i) 
    {
        Console.WriteLine(&quot;working..{0}&quot;, i);
        await Task.Delay(1000);
        
        return true;
    }

    public bool ParallelInit() 
    {
        var series = Enumerable.Range(1, 5).ToList();
        
        Parallel.ForEach(series, i =&gt; 
        {
            Console.WriteLine(&quot;Starting Process {0}&quot;, i);
            DoWorkAsync(i);
            Console.WriteLine(&quot;Ending Process {0}&quot;, i);
        });
        
        return true;
    }

}
```

How to use await in a loop

I have noticed that Maven&#39;s `&lt;modelVersion&gt;&lt;/modelVersion&gt;` of `pom.xml` is always set to `4.0.0`.

Can you please help me understand what is the importance of this tag and why it should be set to `4.0.0`?




Why modelVersion of pom.xml is necessary and always set to 4.0.0?

<p>I have noticed that Maven's <code>&#x3C;modelVersion>&#x3C;/modelVersion></code> of <code>pom.xml</code> is always set to <code>4.0.0</code>.</p>
<p>Can you please help me understand what is the importance of this tag and why it should be set to <code>4.0.0</code>?</p>


I am trying to parse JSON strings in Java and find the key-value pairs so that I can determine the approximate structure of the JSON object since object structure of JSON string is unknown.

For example, one execution may have a JSON string like this:

      {&quot;id&quot; : 12345, &quot;days&quot; : [ &quot;Monday&quot;, &quot;Wednesday&quot; ], &quot;person&quot; : { &quot;firstName&quot; : &quot;David&quot;, &quot;lastName&quot; : &quot;Menoyo&quot; } }

And another like this:

      {&quot;url&quot; : &quot;http://someurl.com&quot;, &quot;method&quot; : &quot;POST&quot;, &quot;isauth&quot; : false }

How would I cycle through the various JSON elements and determine the keys and their values? I looked at `jackson-core`&#39;s [`JsonParser`](http://fasterxml.github.io/jackson-core/javadoc/2.2.0/com/fasterxml/jackson/core/JsonParser.html). I see how I can grab the next &quot;token&quot; and determine what type of token it is (i.e., field name, value, array start, etc), but, I don&#39;t know how to grab the actual token&#39;s value.

For example:

    public void parse(String json)  {
      try {
         JsonFactory f = new JsonFactory();
         JsonParser parser = f.createParser(json);
         JsonToken token = parser.nextToken();
         while (token != null) {
            if (token.equals(JsonToken.START_ARRAY)) {
               logger.debug(&quot;Start Array : &quot; + token.toString());
            } else if (token.equals(JsonToken.END_ARRAY)) {
               logger.debug(&quot;End Array : &quot; + token.toString());
            } else if (token.equals(JsonToken.START_OBJECT)) {
               logger.debug(&quot;Start Object : &quot; + token.toString());
            } else if (token.equals(JsonToken.END_OBJECT)) {
               logger.debug(&quot;End Object : &quot; + token.toString());
            } else if (token.equals(JsonToken.FIELD_NAME)) {
               logger.debug(&quot;Field Name : &quot; + token.toString());
            } else if (token.equals(JsonToken.VALUE_FALSE)) {
               logger.debug(&quot;Value False : &quot; + token.toString());
            } else if (token.equals(JsonToken.VALUE_NULL)) {
               logger.debug(&quot;Value Null : &quot; + token.toString());
            } else if (token.equals(JsonToken.VALUE_NUMBER_FLOAT)) {
               logger.debug(&quot;Value Number Float : &quot; + token.toString());
            } else if (token.equals(JsonToken.VALUE_NUMBER_INT)) {
              logger.debug(&quot;Value Number Int : &quot; + token.toString());
            } else if (token.equals(JsonToken.VALUE_STRING)) {
               logger.debug(&quot;Value String : &quot; + token.toString());
            } else if (token.equals(JsonToken.VALUE_TRUE)) {
               logger.debug(&quot;Value True : &quot; + token.toString());
            } else {
               logger.debug(&quot;Something else : &quot; + token.toString());
            }
            token = parser.nextToken();
         }
      } catch (Exception e) {
         logger.error(&quot;&quot;, e);
      }
    }

Is there a class in `jackson` or some other library (`gson` or `simple-json`) that produces a tree, or allows one to cycle through the json elements and obtain the actual key names in addition to the values?


Parsing JSON in Java without knowing JSON format

My multithreading concepts are weak and trying to learn.

In Java what I know is, we can&#39;t call a thread more than once: 

    Thread t = new Thread; //Some Runnable
    t.start();
    
    t.start(); //Illegal and throw Exception at runtime.

As far as I know, it throws exception when you call `t.start()` again because the associated stack for the thread is destroyed once it goes out of `run()` method and you are trying to initialize things again.

In that case, what I know about thread pool is, it gives better performance &amp; saves time because there is no need to create new thread (I read in [this][1]).

If there is no need to create new thread in thread pool scenario, then how it works with same thread which just finished its run method, will that thread can be used again?


I read [this][2], and it says that &quot;**Most of the executor implementations in java.util.concurrent use thread pools, which consist of worker threads. This kind of thread exists separately from the Runnable and Callable tasks it executes and is often used to execute multiple tasks.**&quot;

So what is Worker thread here, is it something different then normal Java threads?

With [this][3] link, I got something but still confused on what kind of stuff can be eliminated when we use thread pool and why it gives better performance than using normal java threads.

So can we say like this,

Thread has three parts,

 1. Creation (Telling OS that it is new thread, create stack for it.)
 2. Execute Runnable with run() method.
 3. Destroying threads.

So, considering above 3 steps, With thread pool step 1 and step 3 can be eliminated after fixed number of thread creation. Only step 2 for each task will be executed that is why threadpool is faster? Can we say like this? Am I correct?


  [1]: http://www.javatpoint.com/thread-pooling-in-java
  [2]: http://docs.oracle.com/javase/tutorial/essential/concurrency/pools.html
  [3]: https://stackoverflow.com/questions/13699335/how-does-a-cached-thread-pool-reuse-existing-threads

How Threadpool re-use Threads and how it works

I am aware of following projects (mostly from http://www.w3.org/community/markdown/wiki/MarkdownImplementations):

implemented in Java:

 - txtmark http://github.com/rjeschke/txtmark (claims to be fastest MD processor running on the JVM)
 - Markdown4j http://code.google.com/p/markdown4j (fork of txtmark, advantages? more active dev?)
 - MarkdownPapers http://markdown.tautua.org/ (based on JavaCC parser)
 - pegdown http://github.com/sirthias/pegdown
 - MarkdownJ http://code.google.com/p/markdownj (abandoned?)

implemented in Scala:

 - Laika https://github.com/planet42
 - Actuarius http://henkelmann.eu/projects/actuarius/ (acc. to author not fully standards compliant)
 - Knockoff http://tristanhunt.com/projects/knockoff (only subset of MD?)
 - ScalaMD https://github.com/chirino/scalamd

**Q:** What are the respective performance characteristics, pitfalls, quirks? Which ones support the Github extensions? Which one would you recommend for a Play! / Scala application?


Markdown to HTML with Java/Scala

I&#39;m working on a Java EE web application with the following source code directory structure:

&lt;!-- language: lang-none --&gt;

    src/main/java                 &lt;-- multiple packages containing Java classes
    src/test/java                 &lt;-- multiple packages containing JUnit tests
    src/main/resources            &lt;-- includes properties files for textual messages
    src/main/webapp/resources     &lt;-- includes CSS, images and all Javascript files
    src/main/webapp/WEB-INF
    src/main/webapp/WEB-INF/tags
    src/main/webapp/WEB-INF/views

The folder I&#39;m interested in is `WEB-INF`: It contains `web.xml`, XML files for setting up servlets, Spring bean wiring contexts and JSP tags and views. I&#39;m trying to understand what constrains/defines this structure. E.g. do JSP files always have to be within `WEB-INF` or could they be somewhere else? And is there anything else that might go in `WEB-INF`? Wikipedia&#39;s [WAR files](http://en.wikipedia.org/wiki/WAR_file_format_%28Sun%29) entry mentions `classes` for Java classes and `lib` for JAR files - not sure I&#39;ve fully grasped when these would be needed in addition to the other source file locations.

What is WEB-INF used for in a Java EE web application?

Am I correct in thinking that the goodness of Cloud Endpoints comes with the following limitations:

 1. The REST Api cannot be deployed to a custom domain (it&#39;ll remain on appspot.com).
 2. The only authentication supported is OAuth against Google accounts.
  1. Corollary: it isn&#39;t currently possible to create a user login/session-tracking mechanism that is Google-accounts-agnostic (e.g., with email as username and a password).

Is there any plan to do away with these limitations and if so, what is the ETA?


Google Cloud Endpoints limitations... any proposed solutions?

Title says it all.

I want to run the console command `mvn clean install` on my project in question *directly* in Eclipse, not from the command line.

It would just be more convenient for me to do this, as I already have the project open in Eclipse.  It would save me time if I would not have to navigate to the folder in Windows Explorer.

Not a big deal if I can&#39;t do this... but can I?  And if so, how?

It would be great if I could just right click my project, then click &quot;mvn clean install&quot; from the context menu.

Run &quot;mvn clean install&quot; in Eclipse

I am creating a new maven project with `pom.xml` as below:-

    &lt;project xmlns=&quot;http://maven.apache.org/POM/4.0.0&quot; xmlns:xsi=&quot;http://www.w3.org/2001/XMLSchema-instance&quot;
      xsi:schemaLocation=&quot;http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd&quot;&gt;
      &lt;modelVersion&gt;4.0.0&lt;/modelVersion&gt;
    
      &lt;groupId&gt;firstRestlet&lt;/groupId&gt;
      &lt;artifactId&gt;restlet1&lt;/artifactId&gt;
      &lt;version&gt;0.0.1-SNAPSHOT&lt;/version&gt;
      &lt;packaging&gt;war&lt;/packaging&gt;
    
      &lt;name&gt;restlet1&lt;/name&gt;
      &lt;url&gt;http://maven.apache.org&lt;/url&gt;
      &lt;repositories&gt;
    &lt;repository&gt;
       &lt;id&gt;maven-restlet&lt;/id&gt;
       &lt;name&gt;Public online Restlet repository&lt;/name&gt;
       &lt;url&gt;http://maven.restlet.org&lt;/url&gt;
    &lt;/repository&gt; 
    &lt;/repositories&gt;
      &lt;properties&gt;
        &lt;project.build.sourceEncoding&gt;UTF-8&lt;/project.build.sourceEncoding&gt;
      &lt;/properties&gt;
    
      &lt;dependencies&gt;
        &lt;dependency&gt;
          &lt;groupId&gt;junit&lt;/groupId&gt;
          &lt;artifactId&gt;junit&lt;/artifactId&gt;
          &lt;version&gt;3.8.1&lt;/version&gt;
          &lt;scope&gt;test&lt;/scope&gt;
        &lt;/dependency&gt;
      &lt;/dependencies&gt;
    &lt;/project&gt;

The problem which i am facing is that target war file is not getting generated.
On eclipse console after i ran this `pom.xml` what i found was goals missing in `pom.xml`.

**ECLIPSE CONSOLE MESSAGE:** 

    No goals have been specified for this build. You must specify a valid lifecycle phase or a goal in the format &lt;plugin-prefix&gt;:&lt;goal&gt; or &lt;plugin-group-id&gt;:&lt;plugin-artifact-id&gt;[:&lt;plugin-version&gt;]:&lt;goal&gt;. Available lifecycle phases are: validate, initialize, generate-sources, process-sources, generate-resources, process-resources, compile, process-classes, generate-test-sources, process-test-sources, generate-test-resources, process-test-resources, test-compile, process-test-classes, test, prepare-package, package, pre-integration-test, integration-test, post-integration-test, verify, install, deploy, pre-clean, clean, post-clean, pre-site, site, post-site, site-deploy. -&gt; [Help 1]
    [ERROR] 

Please tell me how to specify goals in `pom.xml`.

Also tell me how to create RESTLET project using maven as build tool.

Thanks &amp; Regards,

specifying goal in pom.xml

I have seen similar questions, but haven&#39;t yet found the answer. 

Using maven compile, I get: 

    [ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.0:compile (default-compile) on project api: Fatal error compiling: invalid target release: 1.7 -&gt; [Help 1]

Here is the pom.xml:

    &lt;plugin&gt;
        &lt;groupId&gt;org.apache.maven.plugins&lt;/groupId&gt;
        &lt;artifactId&gt;maven-compiler-plugin&lt;/artifactId&gt;
        &lt;version&gt;3.0&lt;/version&gt;
        &lt;configuration&gt;
            &lt;source&gt;1.7&lt;/source&gt;
            &lt;target&gt;1.7&lt;/target&gt;
            &lt;encoding&gt;UTF-8&lt;/encoding&gt;
        &lt;/configuration&gt;
    &lt;/plugin&gt;

Javac version:

    javac 1.7.0_25

Java version:

    java version &quot;1.7.0_25&quot;
    Java(TM) SE Runtime Environment (build 1.7.0_25-b15)
    Java HotSpot(TM) 64-Bit Server VM (build 23.25-b01, mixed mode)

Any idea what it could be?

invalid target release: 1.7

I&#39;m using SVN, Maven 3.0.3 on the latest version of Jenkins and the Maven Release plugin.  I&#39;m trying to use the Maven release plugin (through Jenkins) do a dry run and so am executing the options …

	Executing Maven:  -B -f /scratch/jenkins/workspace/myproject/myproject/pom.xml -DdevelopmentVersion=53.0.0-SNAPSHOT -DreleaseVersion=52.0.0 -Dusername=***** -Dpassword=********* -DskipTests -P prod -Dresume=false -DdryRun=true release:prepare

But the dry run is dying with the error below …

	[JENKINS] Archiving /scratch/jenkins/workspace/myproject/myproject/pom.xml to /home/evotext/hudson_home/jobs/myproject/modules/org.mainco.subco$myproject/builds/2013-11-18_16-09-14/archive/org.mainco.subco/myproject/52.0.0/myproject-52.0.0.pom
	Waiting for Jenkins to finish collecting data
	mavenExecutionResult exceptions not empty
	message : Failed to execute goal org.apache.maven.plugins:maven-release-plugin:2.0:prepare (default-cli) on project myproject: You don&#39;t have a SNAPSHOT project in the reactor projects list.
	cause : You don&#39;t have a SNAPSHOT project in the reactor projects list.
		Stack trace : 
	org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal 	org.apache.maven.plugins:maven-release-plugin:2.0:prepare (default-cli) on project myproject: You don&#39;t have a SNAPSHOT project in the reactor projects list.
		at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:213)
		at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:153)
		at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:145)
		at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:84)
		at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:59)
		at org.apache.maven.lifecycle.internal.LifecycleStarter.singleThreadedBuild(LifecycleStarter.java:183)
		at org.apache.maven.lifecycle.internal.LifecycleStarter.execute(LifecycleStarter.java:161)
		at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:320)
		at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:156)
		at org.jvnet.hudson.maven3.launcher.Maven3Launcher.main(Maven3Launcher.java:117)
		at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
		at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
		at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
		at java.lang.reflect.Method.invoke(Method.java:606)
		at org.codehaus.plexus.classworlds.launcher.Launcher.launchStandard(Launcher.java:329)
		at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:239)
		at org.jvnet.hudson.maven3.agent.Maven3Main.launch(Maven3Main.java:178)
		at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
		at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
		at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
		at java.lang.reflect.Method.invoke(Method.java:606)
		at hudson.maven.Maven3Builder.call(Maven3Builder.java:129)
		at hudson.maven.Maven3Builder.call(Maven3Builder.java:67)
		at hudson.remoting.UserRequest.perform(UserRequest.java:118)
		at hudson.remoting.UserRequest.perform(UserRequest.java:48)
		at hudson.remoting.Request$2.run(Request.java:326)
		at hudson.remoting.InterceptingExecutorService$1.call(InterceptingExecutorService.java:72)
		at java.util.concurrent.FutureTask.run(FutureTask.java:262)
		at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
		at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
		at java.lang.Thread.run(Thread.java:744)
	Caused by: org.apache.maven.plugin.MojoFailureException: You don&#39;t have a SNAPSHOT project in the reactor projects list.
		at org.apache.maven.plugins.release.PrepareReleaseMojo.prepareRelease(PrepareReleaseMojo.java:219)
		at org.apache.maven.plugins.release.PrepareReleaseMojo.execute(PrepareReleaseMojo.java:181)
		at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:101)
		at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:209)
		... 30 more
	Caused by: org.apache.maven.shared.release.ReleaseFailureException: You don&#39;t have a SNAPSHOT project in the reactor projects list.
		at org.apache.maven.shared.release.phase.CheckPomPhase.execute(CheckPomPhase.java:111)
		at org.apache.maven.shared.release.phase.CheckPomPhase.simulate(CheckPomPhase.java:123)
		at org.apache.maven.shared.release.DefaultReleaseManager.prepare(DefaultReleaseManager.java:199)
		at org.apache.maven.shared.release.DefaultReleaseManager.prepare(DefaultReleaseManager.java:140)
		at org.apache.maven.shared.release.DefaultReleaseManager.prepare(DefaultReleaseManager.java:103)
		at org.apache.maven.plugins.release.PrepareReleaseMojo.prepareRelease(PrepareReleaseMojo.java:211)
		... 33 more


My SVN checkout method is set to &quot;Always checkout a fresh copy&quot; and I have a snapshot version in question in my snapshot repository, but not in my release repository.  Is there a way I can get the &quot;reactor projects list&quot; to look at my snapshot repo?

&lt;b&gt;Edit:&lt;/b&gt; I&#39;m including the snippet of my pom where the project gets its version -- it inherits it from a parent

        &lt;parent&gt;
                &lt;artifactId&gt;subco&lt;/artifactId&gt;
                &lt;groupId&gt;org.mainco.subco&lt;/groupId&gt;
                &lt;version&gt;52.0.0&lt;/version&gt;
        &lt;/parent&gt;


&quot;You don&#39;t have a SNAPSHOT project in the reactor projects list.&quot; when using Jenkins Maven release plugin

How do I add a Java library from its GitHub repo (the library uses Maven as a build system) as a dependency to my Maven project? Can I do that without downloading and compiling the library?

Content Type	Original Author	Original Content on Stackoverflow
Question	mahesh	View Question on Stackoverflow
Solution 1 - Java	Boj	View Answer on Stackoverflow
Solution 2 - Java	Toumi	View Answer on Stackoverflow
Solution 3 - Java	Asanke	View Answer on Stackoverflow
Solution 4 - Java	Nilotpal	View Answer on Stackoverflow

Why modelVersion of pom.xml is necessary and always set to 4.0.0?

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How to use await in a loop

What is the list of possible values for navigator.platform as of today?

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