[Yes, it is][1]:

&gt; DateTimeFormat is thread-safe and immutable, and the **formatters** it
&gt; returns are as well.

and so is the [Java 8 version](http://docs.oracle.com/javase/8/docs/api/java/time/format/DateTimeFormatter.html)

&gt; **Implementation Requirements:** This class is immutable and thread-safe.


  [1]: http://www.joda.org/joda-time/apidocs/org/joda/time/format/DateTimeFormat.html

A quick look at the [code](http://grepcode.com/file/repo1.maven.org/maven2/joda-time/joda-time/2.1/org/joda/time/format/DateTimeFormatter.java#DateTimeFormatter) shows there isn&#39;t any mutable shared state in `DateTimeFormatter`, which would make it thread safe.

*Found this question on top of google&#39;s answers when checking for Java&#39;s java.time.format.DateTimeFormatter thread safety*

Java&#39;s own DateTimeFormatter is also thread-safe, as [the documentation](https://docs.oracle.com/javase/8/docs/api/java/time/format/DateTimeFormatter.html) states:

&gt; This class is immutable and thread-safe



I have a simple question about tagging different versions of my project with git. If I just completed my 1.1 branch and plan to merge it into master, should I tag this branch as 1.1 before I merge it, or should I merge it to master and then tag it as 1.1? Would it make a difference either way? Maybe one way is preferred? Thanks.

Git tag before or after merge?

Is there a comprehensive list that explains all of the new features of MVC4 and what all has changed from MVC3? 

(The [release notes][1] are not much helpful)


  [1]: http://www.asp.net/whitepapers/mvc4-release-notes#_Toc303253808

Difference between ASP.NET MVC 3 and 4?

Is the [Joda-Time][1] `DateTimeFormatter` class [thread safe][2]? Once I get an instance from `DateTimeFormat.forPattern`, can its various parse methods be called by multiple threads? DateTimeFormatter&#39;s [Javadocs][3] makes no mention of thread safety.


  [1]: http://www.joda.org/joda-time/
  [2]: https://en.wikipedia.org/wiki/Thread_safety
  [3]: http://www.joda.org/joda-time/apidocs/org/joda/time/format/DateTimeFormatter.html

Is Joda-Time DateTimeFormatter class thread safe?

<p>Is the <a href="http://www.joda.org/joda-time/" target="_blank" rel="noopener noreferrer">Joda-Time</a> <code>DateTimeFormatter</code> class <a href="https://en.wikipedia.org/wiki/Thread_safety" target="_blank" rel="noopener noreferrer">thread safe</a>? Once I get an instance from <code>DateTimeFormat.forPattern</code>, can its various parse methods be called by multiple threads? DateTimeFormatter's <a href="http://www.joda.org/joda-time/apidocs/org/joda/time/format/DateTimeFormatter.html" target="_blank" rel="noopener noreferrer">Javadocs</a> makes no mention of thread safety.</p>


I am looking for the easiest and simplest way to bind and convert data in Spring MVC. If possible, without doing any xml configuration. 

So far I&#39;ve been using [PropertyEditors][1] like so :

    public class CategoryEditor extends PropertyEditorSupport {
    
        // Converts a String to a Category (when submitting form)
        @Override
        public void setAsText(String text) {
            Category c = new Category(text);
            this.setValue(c);
        }
    
        // Converts a Category to a String (when displaying form)
        @Override
        public String getAsText() {
            Category c = (Category) this.getValue();
            return c.getName();
        }
    
    }

and

    ...
    public class MyController {
    
        @InitBinder
        public void initBinder(WebDataBinder binder) {
            binder.registerCustomEditor(Category.class, new CategoryEditor());
        }
    
        ...
    
    }

It is simple : both conversion are defined in the same class, and the binding is straightforward. If I wanted to do a general binding across all my controllers, I could still add [3 lines in my xml config][2].

----------

But Spring 3.x introduced a new way to do it, using [Converters][3] :

&gt; Within a Spring container, this system can be used as an alternative
&gt; to PropertyEditors

So let&#39;s say I want to use Converters because it is &quot;the latest alternative&quot;. I would have to create **two** converters :
    
    public class StringToCategory implements Converter&lt;String, Category&gt; {
        
        @Override
        public Category convert(String source) {
            Category c = new Category(source);
            return c;
        }

    }

    public class CategoryToString implements Converter&lt;Category, String&gt; {

        @Override
        public String convert(Category source) {
            return source.getName();
        }

    }

**First drawback :** I have to make two classes. Benefit : no need to cast thanks to genericity.

Then, how do I simply data bind the converters ?  

**Second drawback :** I haven&#39;t found any simple way (annotations or other programmatic facilities) to do it in a controller : nothing like `someSpringObject.registerCustomConverter(...);`.

The only ways I&#39;ve found would be tedious, not simple, and only about general cross-controller binding :

 - [XML config][4] :

        &lt;bean id=&quot;conversionService&quot;
          class=&quot;org.springframework.context.support.ConversionServiceFactoryBean&quot;&gt;
            &lt;property name=&quot;converters&quot;&gt;
                &lt;set&gt;
                    &lt;bean class=&quot;somepackage.StringToCategory&quot;/&gt;
                    &lt;bean class=&quot;somepackage.CategoryToString&quot;/&gt;
                &lt;/set&gt;
            &lt;/property&gt;
        &lt;/bean&gt;

 - [Java config][5] (**only in Spring 3.1+**) :

        @EnableWebMvc
        @Configuration
        public class WebConfig extends WebMvcConfigurerAdapter {

            @Override
            protected void addFormatters(FormatterRegistry registry) {
                registry.addConverter(new StringToCategory());
                registry.addConverter(new CategoryToString());
            }

        }

With all these drawbacks, why using Converters ? Am I missing something ? Are there other tricks that I am not aware of ?

I am tempted to go on using PropertyEditors... Binding is much easier and quicker.


  [1]: http://static.springsource.org/spring/docs/3.0.x/spring-framework-reference/html/validation.html#beans-beans-conversion-customeditor-registration
  [2]: http://static.springsource.org/spring/docs/3.0.x/spring-framework-reference/html/mvc.html#mvc-ann-webdatabinder
  [3]: http://static.springsource.org/spring/docs/3.0.x/spring-framework-reference/html/validation.html#core-convert
  [4]: http://static.springsource.org/spring/docs/3.0.x/spring-framework-reference/html/validation.html#core-convert-Spring-config
  [5]: http://static.springsource.org/spring/docs/3.1.x/spring-framework-reference/html/mvc.html#mvc-config-customize

Spring MVC type conversion : PropertyEditor or Converter?

&gt; **Possible Duplicate:**  
&gt; [Static Initialization Blocks](https://stackoverflow.com/questions/2420389/static-initialization-blocks)  

&lt;!-- End of automatically inserted text --&gt;

Consider the following *code*:

    public class Test {
    	{
    		System.out.println(&quot;Empty block&quot;);
    	}
    	static {
    		System.out.println(&quot;Static block&quot;);
    	}
    	public static void main(String[] args) {
    		Test t = new Test();
    	}
    }

We understand that first the *static* block would be executed followed by the *empty* block. But the problem is that I have never been able to understand the real utility of an *empty* block. Can anyone show a real example in which -

 - Both *static* and *empty* blocks are being used
 - Both *static* and *empty* blocks have different utilities


Static block vs. initializer block in Java?

The Java 7 *try-with-resources* syntax (also known as ARM block (*Automatic Resource Management*)) is nice, short and straightforward when using only one `AutoCloseable` resource. However, I am not sure what is the correct idiom when I need to declare multiple resources that are dependent on each other, for example a `FileWriter` and a `BufferedWriter` that wraps it. Of course, this question concerns any case when some `AutoCloseable` resources are wrapped, not only these two specific classes.

I came up with the three following alternatives:

## 1) ##

The naive idiom I have seen is to declare only the top-level wrapper in the ARM-managed variable:

	static void printToFile1(String text, File file) {
		try (BufferedWriter bw = new BufferedWriter(new FileWriter(file))) {
			bw.write(text);
		} catch (IOException ex) {
			// handle ex
		}
	}

This is nice and short, but it is broken. Because the underlying `FileWriter` is not declared in a variable, it will never be closed directly in the generated `finally` block. It will be closed only through the `close` method of the wrapping `BufferedWriter`. The problem is, that if an exception is thrown from the `bw`&#39;s constructor, its `close` will not be called and therefore the underlying `FileWriter` **will not be closed**.

## 2) ##

	static void printToFile2(String text, File file) {
		try (FileWriter fw = new FileWriter(file);
				BufferedWriter bw = new BufferedWriter(fw)) {
			bw.write(text);
		} catch (IOException ex) {
			// handle ex
		}
	}

Here, both the underlying and the wrapping resource are declared in the ARM-managed variables, so both of them will certainly be closed, but the underlying `fw.close()` **will be called twice**: not only directly, but also through the wrapping `bw.close()`.

This should not be a problem for these two specific classes that both implement `Closeable` (which is a subtype of `AutoCloseable`), whose contract states that multiple calls to `close` are permitted:

&gt; Closes this stream and releases any system resources associated with it. If the stream is already closed then invoking this method has no effect.

However, in a general case, I can have resources that implement only `AutoCloseable` (and not `Closeable`), which doesn&#39;t guarantee that `close` can be called multiple times:

&gt; Note that unlike the close method of java.io.Closeable, this close method is not required to be idempotent. In other words, calling this close method more than once may have some visible side effect, unlike Closeable.close which is required to have no effect if called more than once. However, implementers of this interface are strongly encouraged to make their close methods idempotent.

## 3) ##

	static void printToFile3(String text, File file) {
		try (FileWriter fw = new FileWriter(file)) {
			BufferedWriter bw = new BufferedWriter(fw);
			bw.write(text);
		} catch (IOException ex) {
			// handle ex
		}
	}

This version should be theoretically correct, because only the `fw` represents a real resource that needs to be cleaned up. The `bw` doesn&#39;t itself hold any resource, it only delegates to the `fw`, so it should be sufficient to only close the underlying `fw`.

On the other hand, the syntax is a bit irregular and also, Eclipse issues a warning, which I believe is a false alarm, but it is still a warning that one has to deal with:

&gt; Resource leak: &#39;bw&#39; is never closed

----------

So, which approach to go for? Or have I missed some other idiom that is *the correct* one?

Correct idiom for managing multiple chained resources in try-with-resources block?

I need to check if a value is an integer. I found this: https://stackoverflow.com/questions/4727569/how-to-check-whether-input-value-is-integer-or-float, but if I&#39;m not mistaken, the variable there is still of type `double` even though the ***value*** itself is indeed an `integer`.

How can I check if a value is of type Integer?

I have a small piece of code that runs through some transactions for processing. Each transaction is marked with a transaction number, which is generated by an outside program and is not necessarily sequenced. When I catch an Exception in the processing code I am throwing it up to the main class and logging it for review later. I&#39;d like to add the transaction number to this thrown Exception. Is it possible to do this while still maintaining the correct stack trace?

For Example:

	public static void main(String[] args) {
		try{
			processMessage();
		}catch(Exception E){
			E.printStackTrace();
		}

	}
	
	private static void processMessage() throws Exception{
		String transNbr = &quot;&quot;;
		try{
			transNbr = &quot;2345&quot;;
			throw new Exception();
		}catch(Exception E){
			if(!transNbr.equals(&quot;&quot;)){
                //stack trace originates from here, not from actual exception
				throw new Exception(&quot;transction: &quot; + transNbr); 
			}else{
                //stack trace gets passed correctly but no custom message available
				throw E;
			}
		}
	}

Add custom message to thrown exception while maintaining stack trace in Java

I was reading multi-threading in Java and I come across this

&gt;Local variables are thread safe in Java.

Since then I have been thinking How/Why local variables are thread safe.

Can somebody please let me know.

Why are local variables thread safe in Java

What is the way to obtain a thread safe counter in C# with best possible performance?

This is as simple as it gets:

    public static long GetNextValue()
    {
        long result;
        lock (LOCK)
        {
            result = COUNTER++;
        }
        return result;
    }

But are there faster alternatives?

C# Thread safe fast(est) counter

Is there any general way or rules exits by which we can ensure the thread safety of static methods specifically used in various Utility classes of any applications. Here I want to specifically point out the thread safety of Web Applications.

It is well know that static methods with Immutable Objects as parameters are thread safe and Mutable Objects are not.

If I have a utility method for some manipulation of `java.util.Date` and that method accepts an instance of `java.util.Date`, then this method would not be thread safe. Then how to make it thread safe without changing the way of parameter passing?

    public class DateUtils {
    
    	public static Date getNormalizeDate(Date date) {
    		// some operations
    	}	
    }

Also is the class `javax.faces.context.FacesContext` mutable? Is it thread safe to pass an instance of this class to such static utility method?

This list of classes, instances of which can be or cannot be passed as parameters, could be long; so what points should we keep in mind while writing codes of such utility classes?

How to ensure thread safety of utility static method?

I hear that `const` means _thread-safe_ in _C++11_. Is that true?

Does that mean `const` is now the equivalent of _Java_&#39;s `synchronized`?

Are they running out of _keywords_?


Does const mean thread-safe in C++11?

[starting from Rails 4][1], everything would have to run in threaded environment by default. What this means is all of the code we write **AND** __ALL__ the gems we use are required to be `threadsafe`

so, I have few questions on this:

1. what is NOT thread-safe in ruby/rails? **Vs** What is thread-safe in ruby/rails?
2. Is there a list of gems that _is_ known to be threadsafe or vice-versa?
3. is there List of common patterns of code which are NOT threadsafe example `@result ||= some_method`?
4. Are the data structures in ruby lang core such as `Hash` etc threadsafe?
5. On MRI, where there a [`GVL`/`GIL`][2] which means only 1 ruby thread can run at a time except for `IO`, does the threadsafe change effect us? 


  [1]: http://edgeguides.rubyonrails.org/4_0_release_notes.html#railties-notable-changes
  [2]: http://en.wikipedia.org/wiki/Global_Interpreter_Lock

how to know what is NOT thread-safe in ruby?

Below is the method I wrote: 

    public List&lt;Map&lt;String, Object&gt;&gt; loadNotYetInEmployee(int shift, Date date,
            int transitionVal, String type, User user) {

        DateTime datetime = new DateTime(date);
        datetime = datetime
                .plus(Period.minutes(shiftTiming.getSession1InTime()));

        List&lt;Map&lt;String, Object&gt;&gt; result = new ArrayList&lt;Map&lt;String, Object&gt;&gt;();

        sql = SqlMapUtils.getSql(&quot;attendance.attendancestatus.latein&quot;,
                parameters);
        result = getJdbcTemplate().queryForList(sql);
        for (int i = 0; i &lt; result.size(); i++) {
            Date punchInTime = (Date) result.get(i).get(&quot;punchtime&quot;);
            DateTime punchTime = new DateTime(punchInTime);
        }
        return result;
    }


Now from my method you can see I have a [Joda-Time][1] [DateTime][2] object in object named `datetime` and from my result I am getting one timestamp which I am converting to jodatime `punchTime`. Now I want to find out the diff between these two dates, how do I do that?



  [1]: http://www.joda.org/joda-time/
  [2]: http://www.joda.org/joda-time/apidocs/org/joda/time/DateTime.html

How to find difference between two Joda-Time DateTimes in minutes

I&#39;m adding the Joda Time repository to SBT with

    libraryDependencies ++= Seq(
      &quot;joda-time&quot;         % &quot;joda-time&quot;           % &quot;2.1&quot;
    )

Then I merrily use it like this:

     val ymd = org.joda.time.format.DateTimeFormat.forPattern(&quot;yyyyMMdd&quot;)
      ymd.parseDateTime(&quot;20121212&quot;)

But, when I compile the project in SBT, I get a nasty:

    [warn] Class org.joda.convert.FromString not found - continuing with a stub.
    [warn] Caught: java.lang.NullPointerException while parsing annotations in /home/jack/.ivy2/cache/joda-time/joda-time/jars/joda-time-2.1.jar(org/joda/time/DateTime.class)
    [error] error while loading DateTime, class file &#39;/home/jack/.ivy2/cache/joda-time/joda-time/jars/joda-time-2.1.jar(org/joda/time/DateTime.class)&#39; is broken
    [error] (class java.lang.RuntimeException/bad constant pool tag 10 at byte 42)

I tried the 2.0 version of joda-time, but get the same error.


Class broken error with Joda Time using Scala

Is it possible to do that? If yes, then how do I do the conversion from [Joda-Time][1] to [Date][2] and vice versa?


  [1]: http://www.joda.org/joda-time/
  [2]: http://docs.oracle.com/javase/7/docs/api/java/util/Date.html

How to convert Joda-Time DateTime to java.util.Date and vice versa?

I have date `Wed May 08 00:00:00 GMT+06:30 2013`. I add one day into it by using [Joda-Time][1] [DateTime][2] like this.

    DateTime dateTime = new DateTime(date);
    dateTime.plusDays(1);


When I print dateTime, I got this date `2013-05-08T00:00:00.000+06:30`. The joda date time didn&#39;t add one day. I haven&#39;t found any error.

Thanks


  [1]: https://www.joda.org/joda-time/
  [2]: https://www.joda.org/joda-time/apidocs/org/joda/time/DateTime.html

Add one day into Joda-Time DateTime

I am getting UTC timestamp from database which is I am setting into a JodaTime `DateTime` instance

    DateTime dt = new DateTime(timestamp.getTime());

It stores the time perfectly say `10:00 AM` but with local time zone. E.g, I am in IST time zone which is +5:30 from UTC

I have tried lots of things for changing the timezone but with every thing it changes the time from `10:00 AM` to something else by using +5:30 difference

Is there any way by which I can change TimeZone without affecting current time

EDIT:
If my current time is:

    2013-09-25 11:27:34 AM	    UTC

Following is the result when I use this `new DateTime(timestamp.getTime());` 

    2013-09-25 11:27:34 AM	Asia/Kolkata

And following is the result when I use this `new DateTime(timestamp.getTime(), DateTimeZone.UTC)`;

    2013-09-25 05:57:34 AM	UTC


In joda time how to convert time zone without changing time

I need to format a date as `yyyy-MM-dd&#39;T&#39;HH:mm:ss.SSS&#39;Z&#39;` as specified by [Parse&#39;s REST API for Facebook][1]. I was wondering what the most **lightweight** solution to this would be.


  [1]: https://parse.com/docs/rest#users-login

Format Date as &quot;yyyy-MM-dd&#39;T&#39;HH:mm:ss.SSS&#39;Z&#39;&quot;

I&#39;m trying to check that dates entered by end users are in the YYYY-MM-DD. Regex has never been my strong point, I keep getting a false return value for the preg_match() I have setup.

So I&#39;m assuming I have made a mess of the regex, detailed below.

		
    $date=&quot;2012-09-12&quot;;

    if (preg_match(&quot;^[0-9]{4}-[0-1][0-9]-[0-3][0-9]$&quot;,$date))
		{
			return true;
		}else{
			return false;
		}

Any thoughts?

PHP Regex to check date is in YYYY-MM-DD format

I have a `java.util.Date` in the format `yyyy-mm-dd`. I want it to be in the format `mm-dd-yyyy`

Below is the sample util I tried out for this conversion:

	// Setting the pattern
	SimpleDateFormat sm = new SimpleDateFormat(&quot;mm-dd-yyyy&quot;);
	// myDate is the java.util.Date in yyyy-mm-dd format
	// Converting it into String using formatter
	String strDate = sm.format(myDate);
	//Converting the String back to java.util.Date
	Date dt = sm.parse(strDate);

Still the output I am getting is not in the format `mm-dd-yyyy`.

Kindly let me know how to format a `java.util.Date` from `yyyy-mm-dd` to `mm-dd-yyyy`



java.util.Date format conversion yyyy-mm-dd to mm-dd-yyyy

Currently the time displayed as **13:35 PM** 
However **I want to display as 12 hour format with AM/PM, i.e 1:35 PM instead of 13:35 PM**

The current code is as below 

    private static final int FOR_HOURS = 3600000;
    private static final int FOR_MIN = 60000;
    public String getTime(final Model model) {
        SimpleDateFormat formatDate = new SimpleDateFormat(&quot;HH:mm a&quot;);
        formatDate.setTimeZone(userContext.getUser().getTimeZone());
        model.addAttribute(&quot;userCurrentTime&quot;, formatDate.format(new Date()));
        final String offsetHours = String.format(&quot;%+03d:%02d&quot;, userContext.getUser().getTimeZone().getRawOffset()
        / FOR_HOURS, Math.abs(userContext.getUser().getTimeZone().getRawOffset() % FOR_HOURS / FOR_MIN));
        model.addAttribute(&quot;offsetHours&quot;,
                    offsetHours + &quot; &quot; + userContext.getUser().getTimeZone().getDisplayName(Locale.ROOT));
        return &quot;systemclock&quot;;
    }

Display current time in 12 hour format with AM/PM

I have SimpleDateFormat constructor as 

    SimpleDateFormat(&quot;yyyy-MM-dd&#39;T&#39;HH:mm:ss&#39;Z&#39;&quot;)

and I am parsing string `&quot;2013-09-29T18:46:19Z&quot;.` 

I have read that here Z represents the `GMT/UTC` timezone. but when I print this date on console , It prints IST timezne for the returned date.

Now my question is whether my output is right or wrong?

Content Type	Original Author	Original Content on Stackoverflow
Question	Steve Kuo	View Question on Stackoverflow
Solution 1 - Java	Erre Efe	View Answer on Stackoverflow
Solution 2 - Java	Mark Elliot	View Answer on Stackoverflow
Solution 3 - Java	Dariusz	View Answer on Stackoverflow

Is Joda-Time DateTimeFormatter class thread safe?

Java Problem Overview

Java Solutions

Solution 1 - Java

Solution 2 - Java

Solution 3 - Java

Difference between ASP.NET MVC 3 and 4?

Git tag before or after merge?

Attributions